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1.  Respiration, temperature regulation and energetics of thermogenic inflorescences of the dragon lily Dracunculus vulgaris (Araceae) 
Dracunculus vulgaris is a protogynous arum lily with thermogenic inflorescences consisting of male and female florets on a spadix within a floral chamber. Above the chamber, an odour-producing appendix and a carrion-coloured spathe attract flying insects. The inflorescence shows a triphasic warming pattern. The floral chamber warms weakly on the first night as the spathe opens. Then the appendix produces a large amount of heat and a powerful scent during the first day. As the appendix cools on the second night, scent production ceases and the floral chamber rewarms. Warming ceases when the pollen is shed on the second day. The heating pattern is associated with attraction of pollinating insects by the appendix on the first day, entrapment in the warm chamber at night and release after pollen shedding. The temperature in the floral chamber is regulated at around 18 °C during the second night. The oxygen consumption rate of the florets is inversely related to the ambient temperature as in other thermoregulatory flowers. Conversely, the oxygen consumption rate of the appendix is directly related to the ambient temperature, indicating that it does not thermoregulate. Thus, temperature regulation is not associated with scent production, but with some activity inside the floral chamber.
PMCID: PMC1690307
2.  Developmental changes and organelle biogenesis in the reproductive organs of thermogenic skunk cabbage (Symplocarpus renifolius) 
Journal of Experimental Botany  2009;60(13):3909-3922.
Sex-dependent thermogenesis during reproductive organ development in the inflorescence is a characteristic feature of some of the protogynous arum species. One such plant, skunk cabbage (Symplocarpus renifolius), can produce massive heat during the female stage but not during the subsequent male stage in which the stamen completes development, the anthers dehisce, and pollen is released. Unlike other thermogenic species, skunk cabbage belongs to the bisexual flower group. Although recent studies have identified the spadix as the thermogenic organ, it remains unclear how individual tissues or intracellular structures are involved in thermogenesis. In this study, reproductive organ development and organelle biogenesis were examined during the transition from the female to the male stage. During the female stage, the stamens exhibit extensive structural changes including changes in organelle structure and density. They accumulate high levels of mitochondrial proteins, including possible thermogenic factors, alternative oxidase, and uncoupling protein. By contrast, the petals and pistils do not undergo extensive changes during the female stage. However, they contain a larger number of mitochondria than during the male stage in which they develop large cytoplasmic vacuoles. Comparison between female and male spadices suggests that mitochondrial number rather than their level of activity correlates with thermogenesis. Their spadices, even in the male, contain a larger amount of mitochondria that had greater oxygen consumption, compared with non-thermogenic plants. Taken together, our data suggest that the extensive maturation process in stamens produces massive heat through increased metabolic activities. The possible mechanisms by which petal and pistil metabolism may affect thermogenesis are also discussed.
PMCID: PMC2736897  PMID: 19640927
Alternative oxidase; bisexual flower; mitochondrial density; respiration; stamen; thermogenesis; thermoregulation; ultrastructure; uncoupling protein; vacuole
3.  Function of the heater: the dead horse arum revisited. 
The dead horse arum, Helicodiceros muscivorus, is a conspicuous, foul smelling and thermogenic plant of the Araceae family. This Mediterranean arum lily copies several aspects of a carcass in order to attract carrion blowflies, which are subsequently exploited as unrewarded pollinators. We have previously shown that this plant exhibits a highly accurate olfactory carrion mimicry, which serves to attract the blowflies. In this study, we have investigated the role of thermogeny in the arum. We show that the thermogeny has a direct effect on the pollinators, altering their behaviour. By manipulating heat and odour release of the plant, we can show that the heat, produced along the appendix, is important to lure the flies to this structure, which is vital as the flies from the appendix are more prone to enter the trap chamber that houses the female and male florets. This study provides rare evidence for a direct functional role of thermogeny.
PMCID: PMC1809992  PMID: 15101405
4.  The Role of Thermogenesis in the Pollination Biology of the Amazon Waterlily Victoria amazonica 
Annals of Botany  2006;98(6):1129-1135.
• Background and Aims Several families of tropical plants have thermogenic flowers that show a 2-d protogynous sequence. Most are pollinated by large beetles that remain for the entire period in the flowers, where they compete for mates and feed. Active beetles require high body temperatures that they can achieve endogenously at great energy expense or attain passively and cheaply in a warm environment. Floral heating is therefore hypothesized to be a direct energy reward to endothermic beetles, in addition to its accepted role in enhancing scent production.
• Methods This study measures the pattern of floral heat production (as temperature in 20 flowers and respiration rates in five flowers) in Victoria amazonica at field sites in Guyana and correlates floral temperatures with body temperatures necessary for activity in visiting Cyclocephala hardyi beetles.
• Key Results Thermogenesis occurred in a bimodal pattern, with peaks associated with the arrival and departure of beetles near sunset. Peak CO2 production rates averaged 2·9 µmol s−1, equivalent to a heat production of 1·4 W. Heat was generated mainly in the floral chamber on the first evening and by the stamen complex on the second. Mean chamber temperature remained between 29·3 and 34·7 °C during the first night, when ambient temperature was 23·5–25·2 °C. Beetles actively competed for mates and consumed stylar processes in the floral chamber, where their mean thoracic temperature was 33·2 °C. At the lower ambient temperatures outside of the flower, beetles capable of sustained flight had a similar mean temperature of 32·0 °C.
• Conclusions Floral heating is not only associated with attraction, but continues throughout the night when beetles are active inside the flower and increases again when they leave. Floral chamber temperatures similar to activity temperatures of actively endothermic beetles imply that thermogenesis is an energy reward.
PMCID: PMC2803590  PMID: 17018568
Pollination biology; thermogenesis; respiration; beetle; endothermy; Nymphaeaceae; Guyana; Victoria amazonica; Cyclocephala hardyi
5.  Objective Display and Discrimination of Floral Odors from Amorphophallus titanum, Bloomed on Different Dates and at Different Locations, Using an Electronic Nose 
Sensors (Basel, Switzerland)  2012;12(2):2152-2161.
As olfactory perceptions vary from person to person, it is difficult to describe smells objectively. In contrast, electronic noses also detect smells with their sensors, but in addition describe those using electronic signals. Here we showed a virtual connection method between a human nose perceptions and electronic nose responses with the smell of standard gases. In this method, Amorphophallus titanum flowers, which emit a strong carrion smell, could objectively be described using an electronic nose, in a way resembling the skill of sommeliers. We could describe the flower smell to be close to that of a mixture of methyl mercaptan and propionic acid, by calculation of the dilution index from electronic resistances. In other words, the smell resembled that of “decayed cabbage, garlic and pungent sour” with possible descriptors. Additionally, we compared the smells of flowers which bloomed on different dates and at different locations and showed the similarity of odor intensities visually, in standard gas categories. We anticipate our assay to be a starting point for a perceptive connection between our noses and electronic noses.
PMCID: PMC3304159  PMID: 22438757
electronic nose; FF-2A; semiconductor; Amorphophallus titanum; titan arum; smell; objective display; smell description
6.  Pollination of Schisandra henryi (Schisandraceae) by Female, Pollen-eating Megommata Species (Cecidomyiidae, Diptera) in South-central China 
Annals of Botany  2007;99(3):451-460.
Background and Aims
The mutualistic interaction between insects and flowers is considered to be a major factor in the early evolution of flowering plants. The Schisandraceae were, until now, the only family in the ANITA group lacking information on pollination biology in natural ecosystems. Thus, the objective of this research was to document the pollination biology and breeding system of Schisandra henryi.
Field observations were conducted in three populations of S. henryi and the floral phenology, floral characters and insect activities were recorded. Floral fragrances were sampled in the field and analysed using TCT-GC-MS. Floral thermogenesis was measured with a TR-71U Thermo Recorder. Pollen loads and location of pollen grains on insect bodies (including the gut) were checked with a scanning electron microscope and under a light microscope.
Key Results
Schisandra henryi is strictly dioecious. Male flowers are similar to female flowers in colour, shape, and size, but more abundant than female flowers. The distance between tepals and the androecium or gynoecium is narrow. Neither male nor female flowers are fragrant or thermogenic. Schisandra henryi is pollinated only by adult female Megommata sp. (Cecidomyiidae, Diptera) that eat the pollen grains as extra nutrition for ovary maturation and ovipositing. Both male and female flowers attract the pollinators using similar visual cues and thus the female flowers use deceit as they offer no food.
Schisandra henryi exhibits a specialized pollination system, which differs from the generalized pollination system documented in other ANITA members. Pollen is the sole food resource for Megommata sp. and the female flowers of S. henryi attract pollinators by deceit. This is the first report of predacious gall midges utilizing pollen grains as a food source. The lack of floral thermogenesis and floral odours further enforces the visual cues by reducing attractants for other potential pollinators.
PMCID: PMC2802962  PMID: 17237212
Schisandra henryi; Schisandraceae; ANITA group; Megommata sp.; Cecidomyiidae; specialized pollination system; pollination by deceit
7.  Diversity of Flowering and Fruiting Phenology of Trees in a Tropical Deciduous Forest in India 
Annals of Botany  2006;97(2):265-276.
•Background and Aims In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species.
•Methods Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles.
•Key Results Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3–4 months) in dry-season and winter-flowering species, 6–9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized.
•Conclusions The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.
PMCID: PMC2803360  PMID: 16357055
Tropical tree phenology; flowering types; fruiting; asynchrony; leafless period; semi-evergreen species; summer flowering; summer leaf flushing
8.  Sexual Dimorphism of Staminate- and Pistillate-Phase Flowers of Saponaria officinalis (Bouncing Bet) Affects Pollinator Behavior and Seed Set 
PLoS ONE  2014;9(4):e93615.
The sequential separation of male and female function in flowers of dichogamous species allows for the evolution of differing morphologies that maximize fitness through seed siring and seed set. We examined staminate- and pistillate-phase flowers of protandrous Saponaria officinalis for dimorphism in floral traits and their effects on pollinator attraction and seed set. Pistillate-phase flowers have larger petals, greater mass, and are pinker in color, but due to a shape change, pistillate-phase flowers have smaller corolla diameters than staminate-phase flowers. There was no difference in nectar volume or sugar content one day after anthesis, and minimal evidence for UV nectar guide patterns in staminate- and pistillate-phase flowers. When presented with choice arrays, pollinators discriminated against pistillate-phase flowers based on their pink color. Finally, in an experimental garden, in 2012 there was a negative correlation between seed set of an open-pollinated, emasculated flower and pinkness (as measured by reflectance spectrometry) of a pistillate-phase flower on the same plant in plots covered with shade cloth. In 2013, clones of genotypes chosen from the 2012 plants that produced pinker flowers had lower seed set than those from genotypes with paler flowers. Lower seed set of pink genotypes was found in open-pollinated and hand-pollinated flowers, indicating the lower seed set might be due to other differences between pink and pale genotypes in addition to pollinator discrimination against pink flowers. In conclusion, staminate- and pistillate-phase flowers of S. officinalis are dimorphic in shape and color. Pollinators discriminate among flowers based on these differences, and individuals whose pistillate-phase flowers are most different in color from their staminate-phase flowers make fewer seeds. We suggest morphological studies of the two sex phases in dichogamous, hermaphroditic species can contribute to understanding the evolution of sexual dimorphism in plants without the confounding effects of genetic differences between separate male and female individuals.
PMCID: PMC3972141  PMID: 24690875
9.  Effects of Population Size on Synchronous Display of Female and Male Flowers and Reproductive Output in Two Monoecious Sagittaria Species 
PLoS ONE  2012;7(10):e48731.
Flowering synchrony and floral sex ratio have the potential to influence the mating opportunities and reproductive success through female function. Here, we examine the variances in synchronous display of female and male function, ratio of male to female flowers per day and subsequently reproductive output in small populations of two monoecious plants, Sagittaria trifolia and Sagittaria graminea.
Methodology/Principal Finding
We created plant populations of size 2, 4, 10 and 20 and recorded the daily number of blooming male and female flowers per plant to determine daily floral display, flowering synchrony index and ratio of male to female flowers per day. We also harvested the fruits, counted the seeds and calculated the number of fruits and seeds per flower to measure reproductive success through female function. There is less overlap in flowering time of female and male function in smaller populations than in larger populations. Most importantly, we found that male-biased floral sex ratio and imbalanced display period of female and male function for individual plant can lead to a population-size-dependent ratio of male to female flowers per day. Increasing ratio of male to female flowers per day was generally associated with a greater percentage of fruit production.
Our results highlight the importance of flowering synchrony of female and male function and population-size-dependent ratio of male to female flowers per day for female reproductive success. This finding improves our understanding of a mechanism that reduces reproductive success in small populations.
PMCID: PMC3485334  PMID: 23119094
10.  Physical Constraints on Temperature Difference in Some Thermogenic Aroid Inflorescences 
Annals of Botany  2005;96(1):117-125.
• Backgrounds and Aims Thermogenesis in reproductive organs is known from several plant families, including the Araceae. A study was made of the relationship between temperature increase and spadix size in the subfamily Aroideae in order to determine whether the quantitative variation of heat production among species and inflorescences of different sizes follows a physical law of heat transfer.
• Methods Spadix temperature was measured in 18 species from eight genera of tropical Araceae from the basal clade of Aroideae, both in French Guiana and in the glasshouses of the Montreal Botanical Garden.
• Key Results A significant logarithmic relationship was found between the volume of the thermogenic spadix zone and the maximum temperature difference between the spadix and ambient air. Four heat transfer models were applied to the data (conductive heat transfer alone, convective heat transfer alone, radiative heat transfer alone, and convective and radiative heat transfers) to test if physical (geometric and thermic) constraints apply. Which heat transfer model was the most probable was determined by using the criterion of a classical minimization process represented by the least-squares method. Two heat transfer models appeared to fit the data well and were equivalent: conductive heat transfer alone, and convective plus radiative heat transfers.
• Conclusions The increase in the temperature difference between the spadix and ambient air appears to be physically constrained and corresponds to the value of a thermal model of heat conduction in an insulated cylinder with an internal heat source. In the models, a heat metabolic rate of 29.5 mW g−1 was used, which was an acceptable value for an overall metabolic heat rate in aroid inflorescences.
PMCID: PMC4246816  PMID: 15883130
Aglaonema; Anubias; Araceae; Cercestis; Culcasia; Dieffenbachia; heat transfer model; Montrichardia; Philodendron; thermogenesis
11.  Gender Variation of Sequential Inflorescences in a Monoecious Plant Sagittaria trifolia (Alismataceae) 
Annals of Botany  2002;90(5):613-622.
In protogynous plants, female flowers of early blooming plants are at a reproductive disadvantage because they cannot set fruit due to the lack of available pollen. To study this phenomenon, gender expression of the monoecious herb Sagittaria trifolia was investigated over the entire flowering season in two field and two cultivated populations in Hubei and Hunan Provinces, China. In racemes of S. trifolia, flowers open sequentially from bottom to top, with female flowers opening first followed by male flowers. This creates a temporal separation of sexes in the species. Under field conditions small plants are often male, with production of both male and female flowers increasing with plant size. Femaleness increased among sequential inflorescences since female flower production increased whereas male flower production did not. Seed production was greater in large inflorescences because they contain more female flowers, and the number of ovules increased in female flowers at basal positions within the raceme. A consistent pattern of high seed set was observed in flowers from both field and cultivated populations. About 1 % of unfertilized ovules resulted from no pollination and 2 % of the seeds produced were only partly developed due to resource limitation. In the first inflorescence of the six experimental populations, 6·7–40·0 % of individuals produced only male flowers, and female flowers of 1·9–6·5 % individuals were aborted. The occurrence of male flowers in early blooming inflorescences could be an adaptive strategy to conserve resources and enhance pollination of female flowers in protogynous S. trifolia.
PMCID: PMC4240452  PMID: 12466102
Sagittaria trifolia; gender variation; sequential inflorescences; pollination; seed production; monoecy; dioecy; dichogamy
12.  Thermogenesis, Flowering and the Association with Variation in Floral Odour Attractants in Magnolia sprengeri (Magnoliaceae) 
PLoS ONE  2014;9(6):e99356.
Magnolia sprengeri Pamp. is an ornamentally and ecologically important tree that blooms at cold temperatures in early spring. In this study, thermogenesis and variation in the chemical compounds of floral odours and insect visitation in relation to flowering cycles were studied to increase our understanding of the role of floral thermogenesis in the pollination biology of M. sprengeri. There were five distinct floral stages across the floral cycle of this species: pre-pistillate, pistillate, pre-staminate, staminate and post-staminate. Floral thermogenesis during anthesis and consisted of two distinct peaks: one at the pistillate stage and the other at the staminate stage. Insects of five families visited M. sprengeri during the floral cycle, and sap beetles (Epuraea sp., Nitidulidae) were determined to be the most effective pollinators, whereas bees (Apis cerana, Apidae) were considered to be occasional pollinators. A strong fragrance was released during thermogenesis, consisting of 18 chemical compounds. Although the relative proportions of these compounds varied at different floral stages across anthesis, linalool, 1-iodo-2-methylundecane and 2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol were dominant. Importantly, we found that the floral blends released during the pistillate and staminate stages were very similar, and coincided with flower visitation by sap beetles and the two thermogenic episodes. Based on these results, we propose that odour acts as a signal for a reward (pollen) and that an odour mimicry of staminate-stage flowers occurs during the pistillate stage.
PMCID: PMC4055676  PMID: 24922537
13.  Resource partitioning to male and female flowers of Spinacia oleracea L. in relation to whole-plant monocarpic senescence 
Journal of Experimental Botany  2011;62(12):4323-4336.
Male plants of spinach (Spinacea oleracea L.) senesce following flowering. It has been suggested that nutrient drain by male flowers is insufficient to trigger senescence. The partitioning of radiolabelled photosynthate between vegetative and reproductive tissue was compared in male (staminate) versus female (pistillate) plants. After the start of flowering staminate plants senesce 3 weeks earlier than pistillate plants. Soon after the start of flowering, staminate plants allocated several times as much photosynthate to flowering structures as did pistillate plants. The buds of staminate flowers with developing pollen had the greatest draw of photosynthate. When the staminate plants begin to show senescence 68% of fixed C was allocated to the staminate reproductive structures. In the pistillate plants, export to the developing fruits and young flowers remained near 10% until mid-reproductive development, when it increased to 40%, declining to 27% as the plants started to senesce. These differences were also present on a sink-mass corrected basis. Flowers on staminate spinach plants develop faster than pistillate flowers and have a greater draw of photosynthate than do pistillate flowers and fruits, although for a shorter period. Pistillate plants also produce more leaf area within the inflorescence to sustain the developing fruits. The 14C in the staminate flowers declined due to respiration, especially during pollen maturation; no such loss occurred in pistillate reproductive structures. The partitioning to the reproductive structures correlates with the greater production of floral versus vegetative tissue in staminate plants and their more rapid senescence. As at senescence the leaves still had adequate carbohydrate, the resources are clearly phloem-transported compounds other than carbohydrates. The extent of the resource redistribution to reproductive structures and away from the development of new vegetative sinks, starting very early in the reproductive phase, is sufficient to account for the triggering of senescence in the rest of the plant.
PMCID: PMC3153683  PMID: 21565983
Carbohydrates; dioecious; female; flowering; flowers; fruits; male; monocarpic; photosynthate partitioning; pistillate; nitrogen; reproduction; respiration; resource allocation; senescence; sink strength; Spinacea oleracea; spinach; staminate; whole plant
14.  Floral thermogenesis of three species of Hydnora (Hydnoraceae) in Africa 
Annals of Botany  2009;104(5):823-832.
Background and Aims
Floral thermogenesis occurs in at least 12 families of ancient seed plants. Some species show very high rates of respiration through the alternative pathway, and some are thermoregulatory, with increasing respiration at decreasing ambient temperature. This study assesses the intensity and regulation of respiration in three species of African Hydnora that represent the Hydnoraceae, an unusual family of holoparasitic plants from arid environments.
Long-term respirometry (CO2 production) and thermometry were carried out on intact flowers of H. africana, H. abyssinica and H. esculenta in the field, and short-term measurements were made on floral parts during the protogynous flowering sequence.
Key Results
For H. africana, there was no temperature elevation in either the osmophores or the gynoecial chamber in any phase, and mass-specific respiration rates of the flower parts were low (maximum 8·3 nmol CO2 g−1 s−1 in osmophore tissue). Respiration tracked ambient and floral temperatures, eliminating the possibility of the inverse relationship expected in thermoregulatory flowers. Hydnora abyssinica flowers had higher respiration (maximum 27·5 nmol g−1 s−1 in the osmophores) and a slight elevation of osmophore temperature (maximum 2·8 °C) in the female stage. Respiration by gynoecial tissue was similar to that of osmophores in both species, but there was no measurable elevation of gynoecial chamber temperature. Gynoecial chamber temperature of H. esculenta could reach 3·8 °C above ambient, but there are no respiration data available. Antheral tissue respiration was maximal in the male phase (4·8 nmol g−1 s−1 in H. africana and 10·3 nmol g−1 s−1 in H. abyssinica), but it did not raise the antheral ring temperature, which showed that thermogenesis is not a by-product of pollen maturation or release.
The exceptionally low thermogenesis in Hydnora appears to be associated with scent production and possibly gynoecial development, but has little direct benefit to beetle pollinators.
PMCID: PMC2749535  PMID: 19584128
Pollination biology; Hydnora; thermogenesis; respiration rate; temperature; flowers; insects
15.  Different molecular bases underlie the mitochondrial respiratory activity in the homoeothermic spadices of Symplocarpus renifolius and the transiently thermogenic appendices of Arum maculatum 
Biochemical Journal  2012;445(Pt 2):237-246.
Symplocarpus renifolius and Arum maculatum are known to produce significant heat during the course of their floral development, but they use different regulatory mechanisms, i.e. homoeothermic compared with transient thermogenesis. To further clarify the molecular basis of species-specific thermogenesis in plants, in the present study we have analysed the native structures and expression patterns of the mitochondrial respiratory components in S. renifolius and A. maculatum. Our comparative analysis using Blue native PAGE combined with nano LC (liquid chromatography)-MS/MS (tandem MS) has revealed that the constituents of the respiratory complexes in both plants were basically similar, but that several mitochondrial components appeared to be differently expressed in their thermogenic organs. Namely, complex II in S. renifolius was detected as a 340 kDa product, suggesting an oligomeric or supramolecular structure in vivo. Moreover, the expression of an external NAD(P)H dehydrogenase was found to be higher in A. maculatum than in S. renifolius, whereas an internal NAD(P)H dehydrogenase was expressed at a similar level in both species. Alternative oxidase was detected as smear-like signals that were elongated on the first dimension with a peak at around 200 kDa in both species. The significance and implication of these data are discussed in terms of thermoregulation in plants.
PMCID: PMC3385843  PMID: 22512685
alternative oxidase (AOX); Blue native PAGE; mitochondrial respiratory chain; thermogenic plants; type II NAD(P)H dehydrogenase; 1D, one-dimensional; 2D, two-dimensional; AOX, alternative oxidase; BCA, bicinchoninic acid; BN-PAGE, Blue native PAGE; COX, cytochrome c oxidase; Fp, flavoprotein; MS/MS, tandem MS; RACE, rapid amplification of cDNA ends; RT, reverse transcription; TCA, tricarboxylic acid; UTR, untranslated region
16.  Effects of floral display size on male and female reproductive success in Mimulus ringens 
Annals of Botany  2011;109(3):563-570.
Background and Aims
The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.
To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.
Key Results
Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.
Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.
PMCID: PMC3278290  PMID: 21880660
Bumble-bee; floral display size; functional gender; geitonogamy; male selfing rate; mating system; Mimulus ringens; paternity analysis; pollen discounting; pollination; self-fertilization; siring success
17.  A Sexually Dimorphic Corolla Appendage Affects Pollen Removal and Floral Longevity in Gynodioecious Cyananthus delavayi (Campanulaceae) 
PLoS ONE  2015;10(1):e0117149.
The floral traits of bisexual flowers may evolve in response to selection on both male and female functions, but the relative importance of selection associated with each of these two aspects is poorly resolved. Sexually dimorphic traits in plants with unisexual flowers may reflect gender-specific selection, providing opportunities for gaining an increased understanding of the evolution of specific floral traits. We examined sexually dimorphic patterns of floral traits in perfect and female flowers of the gynodioecious species Cyananthus delavayi. A special corolla appendage, the throat hair, was investigated experimentally to examine its influences on male and female function. We found that perfect flowers have larger corollas and much longer throat hairs than female flowers, while female ones have much exerted stigmas. The presence of throat hairs prolonged the duration of pollen presentation by restricting the amount of pollen removed by pollen-collecting bees during each visit. Floral longevity was negatively related to the rate of pollen removal. When pollen removal rate was limited in perfect flowers, the duration of the female phases diminished with the increased male phase duration. There was a weak negative correlation between throat hair length and seed number per fruit in female flowers, but this correlation was not significant in perfect flowers. These results suggest that throat hairs may enhance male function in terms of prolonged pollen presentation. However, throat hairs have no obvious effect on female function in terms of seed number per fruit. The marked sexual dimorphism of this corolla appendage in C. delavayi is likely to have evolved and been maintained by gender-specific selection.
PMCID: PMC4300179  PMID: 25603479
18.  Wheat TILLING Mutants Show That the Vernalization Gene VRN1 Down-Regulates the Flowering Repressor VRN2 in Leaves but Is Not Essential for Flowering 
PLoS Genetics  2012;8(12):e1003134.
Most of the natural variation in wheat vernalization response is determined by allelic differences in the MADS-box transcription factor VERNALIZATION1 (VRN1). Extended exposures to low temperatures during the winter (vernalization) induce VRN1 expression and promote the transition of the apical meristem to the reproductive phase. In contrast to its Arabidopsis homolog (APETALA1), which is mainly expressed in the apical meristem, VRN1 is also expressed at high levels in the leaves, but its function in this tissue is not well understood. Using tetraploid wheat lines with truncation mutations in the two homoeologous copies of VRN1 (henceforth vrn1-null mutants), we demonstrate that a central role of VRN1 in the leaves is to maintain low transcript levels of the VRN2 flowering repressor after vernalization. Transcript levels of VRN2 were gradually down-regulated during vernalization in both mutant and wild-type genotypes, but were up-regulated after vernalization only in the vrn1-null mutants. The up-regulation of VRN2 delayed flowering by repressing the transcription of FT, a flowering-integrator gene that encodes a mobile protein that is transported from the leaves to the apical meristem to induce flowering. The role of VRN2 in the delayed flowering of the vrn1-null mutant was confirmed using double vrn1-vrn2-null mutants, which flowered two months earlier than the vrn1-null mutants. Both mutants produced normal flowers and seeds demonstrating that VRN1 is not essential for wheat flowering, which contradicts current flowering models. This result does not diminish the importance of VRN1 in the seasonal regulation of wheat flowering. The up-regulation of VRN1 during winter is required to maintain low transcript levels of VRN2, accelerate the induction of FT in the leaves, and regulate a timely flowering in the spring. Our results also demonstrate the existence of redundant wheat flowering genes that may provide new targets for engineering wheat varieties better adapted to changing environments.
Author Summary
Crop yields are strongly associated with flowering time, therefore a precise understanding of the mechanisms involved in the regulation of flowering is required to engineer varieties adapted to new or changing environments. In wheat, most of the natural variation in flowering time is determined by VERNALIZATION1 (VRN1), a gene responsible for the transition of the apical meristem from the vegetative to the reproductive phase. Extended exposures to low temperatures during winter (vernalization) induce VRN1 expression, which promotes flowering in the spring. VRN1 is expressed in the apices and in the leaves, but its role in the leaves is not well understood. Using two sets of VRN1 knock-out mutants, we demonstrate that a central role of VRN1 in the leaves is to maintain low transcript levels of the VRN2 flowering repressor, which allows the production of the mobile FT protein (florigen) required to initiate flowering. Both sets of VRN1 knock-out mutants flowered very late but, eventually, produced normal flowers and seeds, which demonstrates that VRN1 is not essential for wheat flowering. This last result also demonstrates the existence of redundant flowering genes that could provide new targets for engineering flowering time in wheat.
PMCID: PMC3521655  PMID: 23271982
19.  Visual discrimination between two sexually deceptive Ophrys species by a bee pollinator 
Arthropod-Plant Interactions  2010;4(3):141-148.
Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.
PMCID: PMC3080657  PMID: 21516265
Ophrys heldreichii; Colour vision; Sexual deception; Signal evolution; Object detection; Pollination
20.  Visual discrimination between two sexually deceptive Ophrys species by a bee pollinator 
Arthropod-plant interactions  2010;4(3):141-148.
Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.
PMCID: PMC3080657  PMID: 21516265
Ophrys heldreichii; Colour vision; Sexual deception; Signal evolution; Object detection; Pollination
21.  Comparative Analysis of Flower Volatiles from Nine Citrus at Three Blooming Stages 
Volatiles from flowers at three blooming stages of nine citrus cultivars were analyzed by headspace-solid phase microextraction (HS-SPME)-GC-MS. Up to 110 volatiles were detected, with 42 tentatively identified from citrus flowers for the first time. Highest amounts of volatiles were present in fully opened flowers of most citrus, except for pomelos. All cultivars were characterized by a high percentage of either oxygenated monoterpenes or monoterpene hydrocarbons, and the presence of a high percentage of nitrogen containing compounds was also observed. Flower volatiles varied qualitatively and quantitatively among citrus types during blooming. Limonene was the most abundant flower volatile only in citrons; α-citral and β-citral ranked 2nd and 3rd only for Bergamot, and unopened flowers of Ponkan had a higher amount of linalool and β-pinene while much lower amount of γ-terpinene and p-cymene than Satsuma. Taking the average of all cultivars, linalool and limonene were the top two volatiles for all blooming stages; β-pinene ranked 3rd in unopened flowers, while indole ranked 3rd for half opened and fully opened flower volatiles. As flowers bloomed, methyl anthranilate increased while 2-hexenal and p-cymene decreased. In some cases, a volatile could be high in both unopened and fully opened flowers but low in half opened ones. Through multivariate analysis, the nine citrus cultivars were clustered into three groups, consistent with the three true citrus types. Furthermore, an influence of blooming stages on clustering was observed, especially with hybrids Satsuma and Huyou. Altogether, it was suggested that flower volatiles can be suitable markers for revealing the genetic relationships between citrus cultivars but the same blooming stage needs to be strictly controlled.
PMCID: PMC3856067  PMID: 24232454
citrus types; volatiles; unopened flower; half opened flower; fully opened flower; HS-SPME; GC-MS
22.  Function and evolution of sterile sex organs in cryptically dioecious Petasites tricholobus (Asteraceae) 
Annals of Botany  2011;108(1):65-71.
Background and Aims
Why are sterile anthers and carpels retained in some flowering plants, given their likely costs? To address this question, a cryptically dioecious species, Petasites tricholobus, in which male and female plants each have two floret types that appear pistillate and hermaphroditic, was studied. The aim was to understand the function of sterile hermaphroditic florets in females. In addition, the first examination of functions of sterile female structures in male plants was conducted in the hermaphroditic florets on males of this species. These female structures are exceptionally large in this species despite being sterile.
Differences in floret morphology between the sex morphs were documented and the possible functions of sterile sex organs investigated using manipulative experiments. Tests were carried out to find out if sterile female structures in male florets attract pollinators and if they aid in pollen dispersal, also to find out if the presence and quantity of sterile hermaphroditic florets in females increase pollinator attraction and reproductive success. To investigate what floret types provide nectar, all types of florets were examined under a scanning electron microscope to search for nectaries.
Key Results
The sterile female structures in male florets did not increase pollinator visits but were essential to secondary pollen presentation, which significantly enhanced pollen dispersal. Sterile pistillate florets on male plants did not contribute to floral display and disappeared in nearly half of the male plants. The sterile hermaphroditic florets on female plants attracted pollinators by producing nectar and enhanced seed production.
The presence of female structures in male florets and hermaphroditic florets on female plants is adaptive despite being sterile, and may be evolutionarily stable. However, the pistillate florets on male plants appear non-adaptive and are presumably in decline. Differential fates of the sterile sex organs in the species are determined by both the historical constraints and the ecological functions.
PMCID: PMC3119616  PMID: 21546429
Cryptic dioecy; sterile sex organ; secondary pollen presentation; pollinator attraction; breeding system evolution; ecological function; Petasites tricholobus
23.  Phenology and Phenotypic Natural Selection on the Flowering Time of a Deceit-pollinated Tropical Orchid, Myrmecophila christinae 
Annals of Botany  2004;94(2):243-250.
• Background and aims. Flowering phenology is described and the effect of flowering time on pollination success is evaluated in the deceit-pollinated tropical orchid, Myrmecophila christinae. It was expected that, due to this species' deceit pollination strategy and low observed pollinator visit rate, there would be a higher probability of natural selection events favouring individuals flowering away from the population flowering peak.
• Methods. The study covers two consecutive years and four populations of M. christinae located along the north coast of the Yucatán Peninsula. For phenological and pollination success data, a total of 110 individuals were monitored weekly in 1998, and 83 individuals in 1999, during all the flowering and fruiting season.
• Key results. The results showed significant differences in the probability of donating and receiving pollen throughout the flowering season. The probability of receiving or donating pollen increased the further an individual flowering was from the flowering peak. Regression analysis showed directional and disruptive phenotypic natural selection gradients, suggesting the presence of selection events unfavourable to flowering during flowering peak, for both male success (pollen removal) and female success (fruit production). However, the intensity and significance of the natural selection events varied between populations from year to year. The variation between seasons and populations was apparently due to variations in the density of reproductive individuals in each population and each season.
• Conclusions. As in other deceit-pollinated orchids, natural selection in M. christinae favours individuals flowering early or late in relation to population peak flowering. However, results also suggested a fluctuating regime of selective events act on flowering time of M. christinae.
PMCID: PMC4242159  PMID: 15205176
Deceit pollination; flowering time; fluctuating natural selection; negative frequency-dependent selection; México; Myrmecophila christinae; Orchidaceae; tropical perennial plant; phenology; phenotypic natural selection
24.  Seasonal change in a pollinator community and the maintenance of style length variation in Mertensia fusiformis (Boraginaceae) 
Annals of Botany  2011;108(1):1-12.
Background and Aims
In sub-alpine habitats, patchiness in snowpack produces marked, small-scale variation in flowering phenology. Plants in early- and late-melting patches are therefore likely to experience very different conditions during their flowering periods. Mertensia fusiformis is an early-flowering perennial that varies conspicuously in style length within and among populations. The hypothesis that style length represents an adaptation to local flowering time was tested. Specifically, it was hypothesized that lower air temperatures and higher frost risk would favour short-styled plants (with stigmas more shielded by corollas) in early-flowering patches, but that the pollen-collecting behaviour of flower visitors in late-flowering patches would favour long-styled plants.
Floral morphology was measured, temperatures were monitored and pollinators were observed in several matched pairs of early and late populations. To evaluate effects of cold temperatures on plants of different style lengths, experimental pollinations were conducted during mornings (warm) and evenings (cool), and on flowers that either had or had not experienced a prior frost. The effectiveness of different pollinators was quantified as seed set following single visits to plants with relatively short or long styles.
Key Results
Late-flowering populations experienced warmer temperatures than early-flowering populations and a different suite of pollinators. Nectar-foraging bumble-bee queens and male solitary bees predominated in early populations, whereas pollen-collecting female solitary bees were more numerous in later sites. Pollinators differed significantly in their abilities to transfer pollen to stigmas at different heights, in accordance with our prediction. However, temperature and frost sensitivity did not differ between long- and short-styled plants. Although plants in late-flowering patches tended to have longer styles than those in early patches, this difference was not consistent.
Seasonal change in pollinator-mediated selection on style length may help maintain variation in this trait in M. fusiformis, but adaptation to local flowering time is not apparent. The prevalence of short styles in these populations requires further explanation.
PMCID: PMC3119607  PMID: 21515606
Boraginaceae; floral morphology; frost; herkogamy; local adaptation; Mertensia fusiformis Greene; Osmia; phenology; pollination; Rocky Mountain Biological Laboratory; temperature
25.  Pollinator-mediated competition between two co-flowering Neotropical mangrove species, Avicennia germinans (Avicenniaceae) and Laguncularia racemosa (Combretaceae) 
Annals of Botany  2012;111(2):207-214.
Background and Aims
Three ecological relationships are possible between co-flowering plant species; they may have no effect on one another, compete for pollination services, or facilitate one another by attracting more pollinators to the area. In this study, the pollinator-mediated relationship between two mangrove species with overlapping flowering phenologies was investigated in one south Florida community.
Pollinator observations were recorded between 0900 h and 1700 h during June and July, 2008–2010. Insect visitation rates to Avicennia germinans and Laguncularia racemosa were estimated from 522 observation intervals of 10 min during three phenological time periods, when each species flowered alone and when they co-flowered. The number of timed intervals varied between years due to differences in flowering phenology, from four to 42 for A. germinans and from nine to 94 for L. racemosa.
Key Results
Avicennia germinans began flowering first in all years, and insect visitation rates were significantly greater to A. germinans than to L. racemosa (P<0·001). Flowers of both species received visits from bees, wasps, flies and butterflies; Apis mellifera was the most common floral visitor to both species. Visitation rates to L. racemosa increased significantly when A. germinans stopped flowering (P<0·001). However, there was no significant change in visitation rates to A. germinans after L. racemosa began flowering (P=0·628).
When they co-flowered, A. germinans outcompeted L. racemosa for pollinators. Laguncularia racemosa hermaphrodites self-pollinate autogamously when not visited by insects, so reduced visitation to L. racemosa flowers reduced the frequency of outcrossing and increased the frequency of selfing. Reduced outcrossing limits male reproductive success in this androdioecious species, which could lead to changes in the breeding system. The degree of overlap in flowering phenologies varied between years, so the effect on the mating and breeding system may differ between years.
PMCID: PMC3555529  PMID: 23235696
Androdioecy; Apis mellifera; Avicennia germinans; Florida; flowering phenology; insect visitation rate; Laguncularia racemosa; mixed mating system; pollinator-mediated interaction

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