Background and Aims
Fruit set in indeterminate plant species largely depends on the balance between source and sink strength. Plants of these species show fluctuations in fruit set during the growing season. It was tested whether differences in fruit sink strength among the cultivars explained the differences in fruit-set patterns.
Capsicum was chosen as a model plant. Six cultivars with differences in fruit set, fruit size and plant growth were evaluated in a greenhouse experiment. Fruit-set patterns, generative and vegetative sink strength, source strength and the source : sink ratio at fruit set were determined. Sink strength was quantified as potential growth rate. Fruit set was related to total fruit sink strength and the source : sink ratio. The effect of differences observed in above-mentioned parameters on fruit-set patterns was examined using a simple simulation model.
Sink strengths of individual fruits differed greatly among cultivars. Week-to-week fruit set in large-fruited cultivars fluctuated due to large fluctuations in total fruit sink strength, but in small-fruited cultivars, total fruit sink strength and fruit set were relatively constant. Large variations in week-to-week fruit set were correlated with a low fruit-set percentage. The source : sink threshold for fruit set was higher in large-fruited cultivars. Simulations showed that within the range of parameter values found in the experiment, fruit sink strength and source : sink threshold for fruit set had the largest impact on fruit set: an increase in these parameters decreased the average percentage fruit set and increased variation in weekly fruit set. Both were needed to explain the fruit-set patterns observed. The differences observed in the other parameters (e.g. source strength) had a lower effect on fruit set.
Both individual fruit sink strength and the source : sink threshold for fruit set were needed to explain the differences observed between fruit-set patterns of the six cultivars.
Fruit-set patterns; fruit sink strength; source : sink ratio; threshold for fruit set; Capsicum annuum; cultivars
Background and Aims
It is widely accepted that fruit-set in plants is related to source–sink ratio. Despite its critical importance to yield, prediction of fruit-set remains an ongoing problem in crop models. Functional–structural plant models are potentially able to simulate organ-level plasticity of plants. To predict fruit-set, the quantitative link between source–sink ratio and fruit-set probability is analysed here via a functional–structural plant model, GreenLab.
Two experiments, each with four plant densities, were carried out in a solar greenhouse during two growth seasons (started in spring and autumn). Dynamic fruit-set probability was estimated by frequent observation on inflorescences. Source and sink parameter values were obtained by fitting GreenLab outputs for the biomass of plant parts (lamina, petiole, internode, fruit), at both organ and plant level, to corresponding destructive measurements at six dates from real plants. The dynamic source–sink ratio was calculated as the ratio between biomass production and plant demand (sum of all organ sink strength) per growth cycle, both being outputs of the model.
Key Results and Conclusions
Most sink parameters were stable over multiple planting densities and seasons. From planting, source–sink ratio increased in the vegetative stage and reached a peak after fruit-set commenced, followed by a decrease of leaf appearance rate. Fruit-set probability was correlated with the source–sink ratio after the appearance of flower buds. The relationship between fruit-set probability and the most correlated source–sink ratio could be quantified by a single regression line for both experiments. The current work paves the way to predicting dynamic fruit-set using a functional structure model.
Tomato; Solanum lycopersicum; fruit-set probability; time step; source–sink ratio; sink strength; functional–structural plant model; inverse modelling; plant plasticity
Background and Aims
To model plasticity of plants in their environment, a new version of the functional–structural model GREENLAB has been developed with full interactions between architecture and functioning. Emergent properties of this model were revealed by simulations, in particular the automatic generation of rhythms in plant development. Such behaviour can be observed in natural phenomena such as the appearance of fruit (cucumber or capsicum plants, for example) or branch formation in trees.
In the model, a single variable, the source–sink ratio controls different events in plant architecture. In particular, the number of fruits and branch formation are determined as increasing functions of this ratio. For some sets of well-chosen parameters of the model, the dynamical evolution of the ratio during plant growth generates rhythms.
Key Results and Conclusions
Cyclic patterns in branch formation or fruit appearance emerge without being forced by the model. The model is based on the theory of discrete dynamical systems. The mathematical formalism helps us to explain rhythm generation and to control the behaviour of the system. Rhythms can appear during both the exponential and stabilized phases of growth, but the causes are different as shown by an analytical study of the system. Simulated plant behaviours are very close to those observed on real plants. With a small number of parameters, the model gives very interesting results from a qualitative point of view. It will soon be subjected to experimental data to estimate the model parameters.
Rhythms; plasticity; plant growth model; GREENLAB; interactions; branching system; fructification; emergent properties
Background and Aims
Models based on the consideration of plant development as the result of source–sink relationships between organs suffer from an inherent lack of quantification of the effect of trophic competition on organ growth processes. The ‘common assimilate pool theory’ underlying many such models is highly debatable.
Six experiments were carried out in a greenhouse and outdoors with two grapevine cultivars and with 12 management systems, resulting in different types of plant architecture. Ten variables were used to quantify the impact of variations in assimilate supply and topological distances between sources and sinks on organogenesis, morphogenesis and biomass growth.
A hierarchy of the responses of these processes to variations in assimilate supply was identified. Organ size seemed to be independent of assimilate supply, whereas both organogenesis and biomass growth were affected by variations in assimilate supply. Lower levels of organ biomass growth in response to the depletion of assimilate supplies seemed to be the principal mechanism underlying the plasticity of plant development in different environments. Defoliation or axis ablation resulted in changes in the relationship between growth processes and assimilate supply, highlighting the influence of non-trophic determinants. The findings cast doubt on the relevance of ‘the common assimilate pool theory’ for modelling the development of grapevine.
The results of this study suggest new formalisms for increasing the ability of models to take plant plasticity into account. The combination of an ecophysiological model for morphogenesis taking environmental signals into account and a biomass driven model for organogenesis and biomass allocation taking the topological distances between the sources and the sinks into account appears to be a promising approach. Moreover, in order to simulate the impact of agronomic practices, it will be necessary to take into account the non-trophic determinants of plant development such as hormonal signaletics.
Biomass growth; branching system; common assimilate pool; morphogenesis; organogenesis; source–sink; grapevine; Vitis vinifera
Background and Aims
In traditional crop growth models assimilate production and partitioning are described with empirical equations. In the GREENLAB functional–structural model, however, allocation of carbon to different kinds of organs depends on the number and relative sink strengths of growing organs present in the crop architecture. The aim of this study is to generate sink functions of wheat (Triticum aestivum) organs by calibrating the GREENLAB model using a dedicated data set, consisting of time series on the mass of individual organs (the ‘target data’).
An experiment was conducted on spring wheat (Triticum aestivum, ‘Minaret’), in a growth chamber from, 2004 to, 2005. Four harvests were made of six plants each to determine the size and mass of individual organs, including the root system, leaf blades, sheaths, internodes and ears of the main stem and different tillers. Leaf status (appearance, expansion, maturity and death) of these 24 plants was recorded. With the structures and mass of organs of four individual sample plants, the GREENLAB model was calibrated using a non-linear least-square-root fitting method, the aim of which was to minimize the difference in mass of the organs between measured data and model output, and to provide the parameter values of the model (the sink strengths of organs of each type, age and tiller order, and two empirical parameters linked to biomass production).
Key Results and Conclusions
The masses of all measured organs from one plant from each harvest were fitted simultaneously. With estimated parameters for sink and source functions, the model predicted the mass and size of individual organs at each position of the wheat structure in a mechanistic way. In addition, there was close agreement between experimentally observed and simulated values of leaf area index.
Wheat; Triticum aestivum ‘Minaret’; tiller; GREENLAB; organ mass; functional–structural model; model calibration; multi-fitting; source–sink
Background and Aims
The strong influence of environment and functioning on plant organogenesis has been well documented by botanists but is poorly reproduced in most functional–structural models. In this context, a model of interactions is proposed between plant organogenesis and plant functional mechanisms.
The GreenLab model derived from AMAP models was used. Organogenetic rules give the plant architecture, which defines an interconnected network of organs. The plant is considered as a collection of interacting ‘sinks’ that compete for the allocation of photosynthates coming from ‘sources’. A single variable characteristic of the balance between sources and sinks during plant growth controls different events in plant development, such as the number of branches or the fruit load.
Variations in the environmental parameters related to light and density induce changes in plant morphogenesis. Architecture appears as the dynamic result of this balance, and plant plasticity expresses itself very simply at different levels: appearance of branches and reiteration, number of organs, fructification and adaptation of ecophysiological characteristics.
The modelling framework serves as a tool for theoretical botany to explore the emergence of specific morphological and architectural patterns and can help to understand plant phenotypic plasticity and its strategy in response to environmental changes.
Trophic plasticity; plant growth; functional–structural models; dynamic system; interactions; GreenLab
Municipal solid waste compost (MSWC) and/or fertigation used in greenhouse pepper (Capsicum annuum L.) cultivation with five different substrates with soil (S) and/or MSWC mixtures (0–5–10–20–40%) used with or without fertigation. Plants growth increased in 10–20% MSWC and fertigation enhanced mainly the plant height. Fruit number increased in S : MSWC 80 : 20 without fertilizer. Plant biomass increased as MSWC content increased. There were no differences regarding leaf fluoresces and plant yield. The addition of MSWC increased nutritive value (N, K, P, organic matter) of the substrate resulting in increased EC. Fruit fresh weight decreased (up to 31%) as plants grown in higher MSWC content. Fruit size fluctuated when different MSWC content used into the soil and the effects were mainly in fruit diameter rather than in fruit length. Interestingly, the scale of marketable fruits reduced as MSWC content increased into the substrate but addition of fertilizer reversed this trend and maintained the fruit marketability. MSWC affected quality parameters and reduced fruit acidity, total phenols but increased fruit lightness. No differences observed in fruit dry matter content, fruit firmness, green colour, total soluble sugars and EC of peppers and bacteria (total coliform and E. coli) units. Low content of MSWC improved plant growth and maintained fruit fresh weight for greenhouse pepper without affecting plant yield, while fertigation acted beneficially.
Background and Aims
Despite its simple architecture and small phenotypic plasticity, oil palm has complex phenology and source–sink interactions. Phytomers appear in regular succession but their development takes years, involving long lag periods between environmental influences and their effects on sinks. Plant adjustments to resulting source–sink imbalances are poorly understood. This study investigated oil palm adjustments to imbalances caused by severe fruit pruning.
An experiment with two treatments (control and complete fruit pruning) during 22 months in 2006–2008) and six replications per treatment was conducted in Indonesia. Phenology, growth of above-ground vegetative and reproductive organs, leaf morphology, inflorescence sex differentiation, dynamics of non-structural carbohydrate reserves and light-saturated net photosynthesis (Amax) were monitored.
Artificial sink limitation by complete fruit pruning accelerated development rate, resulting in higher phytomer, leaf and inflorescence numbers. Leaf size and morphology remained unchanged. Complete fruit pruning also suppressed the abortion of male inflorescences, estimated to be triggered at about 16 months before bunch maturity. The number of female inflorescences increased after an estimated lag of 24–26 months, corresponding to time from sex differentiation to bunch maturity. The most important adjustment process was increased assimilate storage in the stem, attaining nearly 50 % of dry weight in the stem top, mainly as starch, whereas glucose, which in controls was the most abundant non-structural carbohydrate stored in oil palm, decreased.
The development rate of oil palm is in part controlled by source–sink relationships. Although increased rate of development and proportion of female inflorescences constituted observed adjustments to sink limitation, the low plasticity of plant architecture (constant leaf size, absence of branching) limited compensatory growth. Non-structural carbohydrate storage was thus the main adjustment process.
Carbon allocation; non-structural carbohydrates; source–sink relationships; Elaeis guineensis; phenotypic plasticity; photosynthesis
Background and Aims
Growth imbalances between individual fruits are common in indeterminate plants such as cucumber (Cucumis sativus). In this species, these imbalances can be related to differences in two growth characteristics, fruit growth duration until reaching a given size and fruit abortion. Both are related to distribution, and environmental factors as well as canopy architecture play a key role in their differentiation. Furthermore, events leading to a fruit reaching its harvestable size before or simultaneously with a prior fruit can be observed. Functional–structural plant models (FSPMs) allow for interactions between environmental factors, canopy architecture and physiological processes. Here, we tested hypotheses which account for these interactions by introducing dominance and abortion thresholds for the partitioning of assimilates between growing fruits.
Using the L-System formalism, an FSPM was developed which combined a model for architectural development, a biochemical model of photosynthesis and a model for assimilate partitioning, the last including a fruit growth model based on a size-related potential growth rate (RP). Starting from a distribution proportional to RP, the model was extended by including abortion and dominance. Abortion was related to source strength and dominance to sink strength. Both thresholds were varied to test their influence on fruit growth characteristics. Simulations were conducted for a dense row and a sparse isometric canopy.
The simple partitioning models failed to simulate individual fruit growth realistically. The introduction of abortion and dominance thresholds gave the best results. Simulations of fruit growth durations and abortion rates were in line with measurements, and events in which a fruit was harvestable earlier than an older fruit were reproduced.
Dominance and abortion events need to be considered when simulating typical fruit growth traits. By integrating environmental factors, the FSPM can be a valuable tool to analyse and improve existing knowledge about the dynamics of assimilates partitioning.
Modelling; individual fruit growth; functional–structural plant model; L-System; Cucumis sativus; cucumber; plant architecture; assimilate distribution
Carotenoid accumulation confers distinct colouration to plant tissues, with effects on plant response to light and as well as health benefits for consumers of plant products. The carotenoid pathway is controlled by flux of metabolites, rate-limiting enzyme steps, feed-back inhibition, and the strength of sink organelles, the plastids, in the cell. In apple (Malus × domestica Borkh), fruit carotenoid concentrations are low in comparison with those in other fruit species. The apple fruit flesh, in particular, begins development with high amounts of chlorophylls and carotenoids, but in all commercial cultivars a large proportion of this is lost by fruit maturity. To understand the control of carotenoid concentrations in apple fruit, metabolic and gene expression analysis of the carotenoid pathway were measured in genotypes with varying flesh and skin colour. Considerable variation in both carotenoid concentrations and compound profile was observed between tissues and genotypes, with carotenes and xanthophylls being found only in fruit accumulating high carotenoid concentrations. The study identified potential rate-limiting steps in carotenogenesis, which suggested that the expression of ZISO, CRTISO,and LCY-ε, in particular, were significant in predicting final carotenoid accumulation in mature apple fruit.
Apple; carotenoid isomerase; carotenoids; gene expression; Malus × domestica; Apple
Background and Aims
Ovary swelling, and resultant fruit malformation, in bell pepper flowers is favoured by low night temperature or a high source–sink ratio. However, the interaction between night temperature and source–sink ratio on ovary swelling and the contribution of cell size and cell number to ovary swelling are unknown. The present research examined the interactive effects of night temperature and source–sink ratio on ovary size, cell number and cell size at anthesis in bell pepper flowers.
Bell pepper plants were grown in growth chambers at night temperatures of either 20 °C (HNT) or 12 °C (LNT). Within each temperature treatment, plants bore either 0 (non-fruiting) or two developing fruits per plant. Ovary fresh weight, cell size and cell number were measured.
Ovary fresh weights in non-fruiting plants grown at LNT were the largest, while fresh weights were smallest in plants grown at HNT with fruits. In general, mesocarp cell size in ovaries was largest in non-fruiting plants grown at either LNT or HNT and smallest in fruiting plants at HNT. Mesocarp cell number was greater in non-fruiting plants under LNT than in the rest of the night temperature/fruiting treatments. These responses were more marked in ovaries sampled after 18 d of treatment compared with those sampled after 40 d of treatment.
Ovary fresh weight of flowers at anthesis increased 65 % in non-fruiting plants grown under LNT compared with fruiting plants grown under HNT. This increase was due primarily to increases in mesocarp cell number and size. These results indicate that the combined effects of LNT and high source–sink ratio on ovary swelling are additive. Furthermore, the combined effects of LNT and low source–sink ratio or HNT and high source–sink ratio can partially overcome the detrimental effects of LNT and high source–sink ratio.
Capsicum annuum; fruit quality; pepper ovary swelling; source–sink effects
Localization and characterization of fruit set in winter tomato crops was investigated to determine the main internal and external controlling factors and to establish a quantitative relationship between fruit set and competition for assimilates. Individual fruit growth and development was assessed on a beef tomato cultivar during the reproductive period (first nine inflorescences). A non-destructive photograph technique was used to measure fruit growth from very early stages of their development and then calliper measurements were made on big fruits. From these measurements we determined the precise developmental stage at which fruit growth stopped. Fruit potential growth, which is defined as the growth achieved in non-limiting conditions for assimilate supply, was also assessed by this method on plants thinned to one flower per inflorescence. The latter was used to calculate the ratio between actual and potential growth, which was found to be a good index of the competition for assimilates.
Time lags of fruit set were observed mainly on distal organs. When more than three flowers were left on each inflorescence, distal organs developed at the same time as proximal organs of the following inflorescence. Consequently they were submitted to a double competition within one inflorescence and among inflorescences. It was shown that, what is commonly named ‘fruit set failure’, is not an irreversible death of the organ and that a small fruit could resume growth after a delay of several weeks as soon as the first fruits ripened and thus ceased to compete for assimilates. In that case proximal fruits resumed growth before distal ones. The delayed fruits contained only few seeds but a germination test confirmed that fertilization took place before fruit set failed.
Competition for assimilates was calculated during plant development by the ratio between actual and potential fruit growth. Potential growth of proximal fruits was strongly dependent on the position of the inflorescence on the stem, whereas potential growth of distal fruits was lower than or equal to that of proximal fruits of the same inflorescence and it was independent on the inflorescence position. We took into account both inflorescence and fruit positions to establish a quantitative relationship between fruit set of individual inflorescences and the ratio between actual and potential fruit growth.
Tomato; Lycopersicon esculentum Mill.; fruit set; competition for assimilates; potential growth; fruit sink strength
Next-generation sequencing was exploited to gain deeper insight into the response to infection by Candidatus liberibacter asiaticus (CaLas), especially the immune disregulation and metabolic dysfunction caused by source-sink disruption. Previous fruit transcriptome data were compared with additional RNA-Seq data in three tissues: immature fruit, and young and mature leaves. Four categories of orchard trees were studied: symptomatic, asymptomatic, apparently healthy, and healthy. Principal component analysis found distinct expression patterns between immature and mature fruits and leaf samples for all four categories of trees. A predicted protein – protein interaction network identified HLB-regulated genes for sugar transporters playing key roles in the overall plant responses. Gene set and pathway enrichment analyses highlight the role of sucrose and starch metabolism in disease symptom development in all tissues. HLB-regulated genes (glucose-phosphate-transporter, invertase, starch-related genes) would likely determine the source-sink relationship disruption. In infected leaves, transcriptomic changes were observed for light reactions genes (downregulation), sucrose metabolism (upregulation), and starch biosynthesis (upregulation). In parallel, symptomatic fruits over-expressed genes involved in photosynthesis, sucrose and raffinose metabolism, and downregulated starch biosynthesis. We visualized gene networks between tissues inducing a source-sink shift. CaLas alters the hormone crosstalk, resulting in weak and ineffective tissue-specific plant immune responses necessary for bacterial clearance. Accordingly, expression of WRKYs (including WRKY70) was higher in fruits than in leaves. Systemic acquired responses were inadequately activated in young leaves, generally considered the sites where most new infections occur.
Quantifying temporal patterns of ephemeral plant structures such as leaves, flowers, and fruits gives insight into both plant and animal ecology. Different scales of temporal changes in fruits, for example within- versus across-year variability, are driven by different processes, but are not always easy to disentangle. We apply generalized additive mixed models (GAMMs) to study a long-term fruit presence–absence data set of individual trees collected from a high-altitude Afromontane tropical rain forest site within Bwindi Impenetrable National Park (BINP), Uganda. Our primary aim was to highlight and evaluate GAMM methodology, and quantify both intra- and interannual changes in fruit production. First, we conduct several simulation experiments to study the practical utility of model selection and smooth term estimation relevant for disentangling intra- and interannual variability. These simulations indicate that estimation of nonlinearity and seasonality is generally accurately identified using asymptotic theory. Applied to the empirical data set, we found that the forest-level fruiting variability arises from both regular seasonality and significant interannual variability, with the years 2009–2010 in particular showing a significant increase in the presence of fruits-driven by increased productivity of most species, and a regular annual peak associated occurring at the end of one of the two dry seasons. Our analyses illustrate a statistical framework for disentangling short-term increases/decreases in fruiting effort while pinpointing specific times in which fruiting is atypical, providing a first step for assessing the impacts of regular and irregular (e.g., climate change) abiotic covariates on fruiting phenology. Some consequences of the rich diversity of fruiting patterns observed here for the population biology of frugivores in BINP are also discussed.
Bwindi Impenetrable National Park; climate change; nonparametric models; phenology; plant reproductive ecology; tropical forest ecology
Understanding how green sink strength is regulated in planta poses a difficult problem because non-structural carbohydrate (NSC) levels can have integrated, simultaneous feedback effects on photosynthesis, sugar uptake, and respiration that depend on specific NSC moieties. Photosynthetic gametophytes of the fern Ceratopteris richardii provide a simple land plant model to assess how different NSCs imported from the apoplast of intact plants affect green sink strength. Sink strength was quantified as the amount of exogenous sugar that plants grown in low light depleted from their liquid media, and the relative contributions of carbon assimilation by photosynthesis and sugar uptake was estimated from stable isotope analysis of plant dry mass. Gametophytes absorbed fructose and glucose with equal affinity when cultured on either hexose alone, or in the presence of an equimolar blend of both sugars. Plants also depleted sucrose from the surrounding media, although a portion of this disaccharide that was hydrolysed into fructose and glucose by putative cell wall invertase activity remained in the media. The δ13C in plant dry masses harvested from sugar treatments were all close to –18‰, indicating that 25–39% of total plant carbon was from C3 photosynthesis (δ13C=–29‰) and 61–75% was from uptake of exogenous sugars (δ13C=–11‰). Carbon-use efficiency (i.e. carbon accumulated/carbon depleted) was significantly improved when plants had a blend of exogenous sugars available compared with plants grown in a single hexose alone. Plants avoided complete down-regulation of photosynthesis even though a large excess of exogenous carbon fluxed through their cells.
disaccharide; fern gametophyte; hexose; mixotrophy; monosaccharide transporter
Background and Aims
Plant population density (PPD) influences plant growth greatly. Functional–structural plant models such as GREENLAB can be used to simulate plant development and growth and PPD effects on plant functioning and architectural behaviour can be investigated. This study aims to evaluate the ability of GREENLAB to predict maize growth and development at different PPDs.
Two field experiments were conducted on irrigated fields in the North China Plain with a block design of four replications. Each experiment included three PPDs: 2·8, 5·6 and 11·1 plants m−2. Detailed observations were made on the dimensions and fresh biomass of above-ground plant organs for each phytomer throughout the seasons. Growth stage-specific target files (a description of plant organ weight and dimension according to plant topological structure) were established from the measured data required for GREENLAB parameterization. Parameter optimization was conducted using a generalized least square method for the entire growth cycles for all PPDs and years. Data from in situ plant digitization were used to establish geometrical symbol files for organs that were then applied to translate model output directly into 3-D representation for each time step of the model execution.
The analysis indicated that the parameter values of organ sink variation function, and the values of most of the relative sink strength parameters varied little among years and PPDs, but the biomass production parameter, computed plant projection surface and internode relative sink strength varied with PPD. Simulations of maize plant growth based on the fitted parameters were reasonably good as indicated by the linearity and slopes similar to unity for the comparison of simulated and observed values. Based on the parameter values fitted from different PPDs, shoot (including vegetative and reproductive parts of the plant) and cob fresh biomass for other PPDs were simulated. Three-dimensional representation of individual plant and plant stand from the model output with two contrasting PPDs were presented with which the PPD effect on plant growth can be easily recognized.
This study showed that GREENLAB model has the ability to capture plant plasticity induced by PPD. The relatively stable parameter values strengthened the hypothesis that one set of equations can govern dynamic organ growth. With further validation, this model can be used for agronomic applications such as yield optimization.
Functional–structural plant model; GREENLAB; plant architecture; source–sink relationship; plant population density; maize (Zea mays); model parameterization
Response of tomato (Lycopersicon esculentum) cultivars to a range of conductivity levels was tested in the presence and absence of Meloidogyne incognita. The conductivity levels were produced by appropriate adjustment of a 1:1 solution of sodium chloride and calcium chloride. The growth of M. incognita resistant ('Beefmaster' and 'Atkinson') and susceptible ('Hunts 2580' and 'Ronita') tomato plants was inversely related to soil salinity between ECe 0 and 5 mmhos/cm. Nematode inoculation of salt-stressed plants significantly reduced plant height, fresh and dry weight, number of flowers, and fruit weight in most cultivars. In Hunts 2580, flower number and fruit weight increased; apparently flower production shifted from determinate to indeterminate, with negative implications for mechanical harvesting. Nematode reproduction on susceptible varieties also decreased with increase in salinity.
Lycopersicon esculentum; salt stress; root-knot
Background and Aims
Rubus chamaemorus (cloudberry) is a herbaceous clonal peatland plant that produces an extensive underground rhizome system with distant ramets. Most of these ramets are non-floral. The main objectives of this study were to determine: (a) if plant growth was source limited in cloudberry; (b) if the non-floral ramets translocated carbon (C) to the fruit; and (c) if there was competition between fruit, leaves and rhizomes for C during fruit development.
Floral and non-floral ramet activities were monitored during the period of flower and fruit development using three approaches: gas exchange measurements, 14CO2 labelling and dry mass accumulation in the different organs. Source and sink activity were manipulated by eliminating leaves or flowers or by reducing rhizome length.
Photosynthetic rates were lower in floral than in deflowered ramets. Autoradiographs and 14C labelling data clearly indicated that fruit is a very strong sink for the floral ramet, whereas non-floral ramets translocated C toward the rhizome but not toward floral ramets. Nevertheless, rhizomes received some C from the floral ramet throughout the fruiting period. Ramets with shorter rhizomes produced smaller leaves and smaller fruits, and defoliated ramets produced very small fruits.
Plant growth appears to be source-limited in cloudberry since a reduction in sink strength did not induce a reduction in photosynthetic activity. Non-floral ramets did not participate directly to fruit development. Developing leaves appear to compete with the developing fruit but the intensity of this competition could vary with the specific timing of the two organs. The rhizome appears to act both as a source but also potentially as a sink during fruit development. Further studies are needed to characterize better the complex role played by the rhizome in fruit C nutrition.
Allocation pattern; 14C labelling; carbon translocation; carbon reserves; cloudberry; defoliation; fruit production; gas exchange; Rubus chamaemorus; source–sink relationship; flowering
Of the Capsicum peppers (Capsicum spp.), cultivated C. annuum is the most commercially important, but has lacked an intraspecific linkage map based on sequence-specific PCR markers in accord with haploid chromosome numbers. We constructed a linkage map of pepper using a doubled haploid (DH) population derived from a cross between two C. annuum genotypes, a bell-type cultivar ‘California Wonder’ and a Malaysian small-fruited cultivar ‘LS2341 (JP187992)’, which is used as a source of resistance to bacterial wilt (Ralstonia solanacearum). A set of 253 markers (151 SSRs, 90 AFLPs, 10 CAPSs and 2 sequence-tagged sites) was on the map which we constructed, spanning 1,336 cM. This is the first SSR-based map to consist of 12 linkage groups, corresponding to the haploid chromosome number in an intraspecific cross of C. annuum. As this map has a lot of PCR-based anchor markers, it is easy to compare it to other pepper genetic maps. Therefore, this map and the newly developed markers will be useful for cultivated C. annuum breeding.
pepper (Capsicum annuum L.); SSR markers; genetic map; 12 linkage groups
This study addresses the hypothesis that stagnation of soybean yield on the farm can be improved by selection of a physiological trait favoring carbon assimilate partitioning to terminally placed pods versus genotypes having axillary pods at close plant spacing. 13C was fed to source-sink units comprising a leaf, axillary/terminal pods, and petioles at upper and lower positions of the stem axis in two soybean cultivars, namely Shakujo and Enrei, at different densities of populations. The cultivars differ significantly in architecture, Shakujo bearing a few hundreds of pods in close succession to one another in a terminally placed raceme, in contrast to Enrei having axillary racemes. Pod yield per plant was higher in Enrei than in Shakujo at low density, but Shakujo out-yielded Enrei at close spacing. Population density decreased yield per plant and altered the pattern of assimilate partitioning significantly within the plants for both varieties. At high density more assimilates moved to the upper parts at the cost of the lower parts. The terminally placed pods of Shakujo were advantaged to receive assimilates under density stress. No benefit was accrued to pod filling of Enrei, however, under this condition.
Fasciated stem; Grain yield; Photosynthesis; Photosynthate partitioning; Population density; Soybean; Source-sink unit
Parthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several C. annuum genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the Arabidopsis bel1 mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in C. annuum and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set.
We identified several additional C. annuum genotypes with a certain level of parthenocarpy, and confirmed a positive correlation between parthenocarpic potential and the development of carpelloid structures. Investigations into the source of these carpel-like structures showed that while the majority of the ovules in C. annuum gynoecia are unitegmic and anatropous, several abnormal ovules were observed, abundant at the top and base of the placenta, with altered integument growth. Abnormal ovule primordia arose from the placenta and most likely transformed into carpelloid structures in analogy to the Arabidopsis bel1 mutant. When pollination was present fruit weight was positively correlated with seed number, but in the absence of seeds, fruit weight proportionally increased with the carpelloid mass and number. Capsicum genotypes with high parthenocarpic potential always showed stronger carpelloid development. The parthenocarpic potential appeared to be controlled by a single recessive gene, but no variation in coding sequence was observed in a candidate gene CaARF8.
Our results suggest that in the absence of fertilization most C. annuum genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.
Background and Aims
Secondary growth is a main physiological sink. However, the hierarchy between the processes which compete with secondary growth is still a matter of debate, especially on fruit trees where fruit weight dramatically increases with time. It was hypothesized that tree architecture, here mediated by branch age, is likely to have a major effect on the dynamics of secondary growth within a growing season.
Three variables were monitored on 6-year-old ‘Golden Delicious’ apple trees from flowering time to harvest: primary shoot growth, fruit volume, and cross-section area of branch portions of consecutive ages. Analyses were done through an ANOVA-type analysis in a linear mixed model framework.
Secondary growth exhibited three consecutive phases characterized by unequal relative area increment over the season. The age of the branch had the strongest effect, with the highest and lowest relative area increment for the current-year shoots and the trunk, respectively. The growth phase had a lower effect, with a shift of secondary growth through the season from leafy shoots towards older branch portions. Eventually, fruit load had an effect on secondary growth mainly after primary growth had ceased.
The results support the idea that relationships between production of photosynthates and allocation depend on both primary growth and branch architectural position. Fruit load mainly interacted with secondary growth later in the season, especially on old branch portions.
Branch age; fruit load; growth phase; Malus domestica (apple); primary growth; secondary growth; tree architecture
NAD+-dependent sorbitol dehydrogenase (NAD-SDH, EC 126.96.36.199), a key enzyme in sorbitol metabolism, plays an important role in regulating sink strength and determining the quality of apple fruit. Understanding the tissue and subcellular localization of NAD-SDH is helpful for understanding sorbitol metabolism in the apple. In this study, two NAD-SDH cDNA sequences were isolated from apple fruits (Malus domestica Borkh cv. Starkrimson) and named MdSDH5 and MdSDH6. Immunohistochemical analysis revealed that NAD-SDH is distributed in both the flesh and the vascular tissue of the fruit, and the vascular tissue and mesophyll tissue in the young and old leaves, indicating that it is a ubiquitous protein expressed in both sink and source organs. Immunogold electron microscopy analysis demonstrated that NAD-SDH is localized mainly in the cytoplasm and chloroplast of the fruit and leaves. The chloroplast localization of NAD-SDH was confirmed by the transient expression of MdSDH5-GFP and MdSDH6-GFP in the mesophyll protoplast of Arabidopsis. NAD-SDH was also found in electron opaque deposits of vacuoles in young and mature leaves. These data show that NAD-SDH has different subcellular localizations in fruit and leaves, indicating that it might play a different role in sorbitol metabolism in different tissues of apple.
Apple; chloroplast; fruit; leaf; localization; sorbitol dehydrogenase
Background and Aims
Plant architecture and its interaction with agronomic practices and environmental constraints are determinants of the structure of the canopy, which is involved in carbon acquisition and fruit quality development. A framework for the quantitative analysis of grapevine (Vitis vinifera) shoot architecture, based on a set of topological and geometrical parameters, was developed for the identification of differences between cultivars and the origins of phenotypic variability.
Two commercial cultivars (‘Grenache N’, ‘Syrah’) with different shoot architectures were grown in pots, in well-irrigated conditions. Shoot topology was analysed, using a hidden semi-Markov chain and variable-order Markov chains to identify deviations from the normal pattern of succession of phytomer types (P0–P1–P2), together with kinematic analysis of shoot axis development. Shoot geometry was characterized by final internode and individual leaf area measurements.
Shoot architecture differed significantly between cultivars. Secondary leaf area and axis length were greater for ‘Syrah’. Secondary leaf area distribution along the main axis also differed between cultivars, with secondary leaves preferentially located towards the basal part of the shoot in ‘Syrah’. The main factors leading to differences in leaf area between the cultivars were: (a) slight differences in main shoot structure, with the supplementary P0 phytomer on the lower part of the shoot in ‘Grenache N’, which bears a short branch; and (b) an higher rate and duration of development of branches bearing by P1–P2 phytomers related to P0 ones at the bottom of the shoot in ‘Syrah’. Differences in axis length were accounted for principally by differences in individual internode morphology, with ‘Syrah’ having significantly longer internodes. This trait, together with a smaller shoot diameter, may account for the characteristic ‘droopy’ habit of ‘Syrah’ shoots.
This study highlights the architectural parameters involved in the phenotypic variability of shoot architecture in two grapevine cultivars. Differences in primary shoot structure and in branch development potential accounted for the main differences in leaf area distribution between the two cultivars. By contrast, shoot shape seemed to be controlled by differences in axis length due principally to differences in internode length.
Architecture; shoot; organogenesis; morphogenesis; branching; leaf area; genotypic variability; Vitis vinifera
The pericarp of Capsicum fruit is a rich dietary source of carotenoids. Accumulation of these compounds may be controlled, in part, by gene transcription of biosynthetic enzymes. The carotenoid composition in a number of orange-coloured C. annuum cultivars was determined using HPLC and compared with transcript abundances for four carotenogenic enzymes, Psy, LcyB, CrtZ-2, and Ccs determined by qRT-PCR. There were unique carotenoid profiles as well as distinct patterns of transcription of carotenogenic enzymes within the seven orange-coloured cultivars. In one cultivar, ‘Fogo’, carrying the mutant ccs-3 allele, transcripts were detected for this gene, but no CCS protein accumulated. The premature stop termination in ccs-3 prevented expression of the biosynthetic activity to synthesize the capsanthin and capsorubin forms of carotenoids. In two other orange-coloured cultivars, ‘Orange Grande’ and ‘Oriole’, both with wild-type versions of all four carotenogenic enzymes, no transcripts for Ccs were detected and no red pigments accumulated. Finally, in a third case, the orange-coloured cultivar, Canary, transcripts for all four of the wild-type carotenogenic enzymes were readily detected yet no CCS protein appeared to accumulate and no red carotenoids were synthesized. In the past, mutations in Psy and Ccs have been identified as the loci controlling colour in the fruit. Now there is evidence that a non-structural gene may control colour development in Capsicum.
Capsanthin; β-carotene; carotenoid biosynthesis; chromoplast; peppers; pericarp; qRT-PCR; xanthophylls