Seed germination of seven celery cultivars was studied after storage in liquid nitrogen for 1 or 30 d. Cryopreservation was also carried out on pelleted and primed seeds. None of the treatments applied reduced germination percentages. T50 (time for germination to reach 50%) significantly decreased in Florida, Utah and Istar cultivars when priming, alone or in combination with cryopreservation, was used.
Apium graveolens L.; celery; cryopreservation; liquid nitrogen; pellet; priming
Matriconditioning improved the performance of pepper, tomato, sweet corn, snap bean, table beet, sugar beet and watermelon seeds in early field plantings at suboptimal temperatures (averaged over 10 d after planting) ranging from 12 to 18 °C. Reduction in the time to 50% (T50) emergence in conditioned seeds ranged from 0·6 d in watermelon to 3·3 d in pepper and improvement in emergence from 10% in sugar beet to 30% in table beet. Further improvement in emergence occurred by inclusion of pesticides and/or gibberellin during conditioning. A 4 d conditioning of pepper at 25 °C was superior to 7 d conditioning at 15 °C in seeds germinated at 15 °C on filter paper, but 15 °C conditioning was superior in improving percentage emergence in early field plantings. Tomato seeds conditioned at 15 or 25 °C performed equally well in the field. A 2 d conditioning was superior to 1 d conditioning in improving the performance of supersweet sweet corn cultivars grown in a growth chamber at 10/20 °C. The water uptake rate in the presence of Micro-Cel E during matriconditioning of sweet corn seeds was slower than when the seeds were exposed to the same amount of water in absence of the carrier. Electrolyte leakage was greater in supersweet ‘Challenger’ sweet corn seeds carrying the sh2 gene compared to the sugary type sweet corn ‘More’, and in both cases matriconditioning reduced the leakage. Lettuce seeds matriconditioned for 24 h had higher 1-aminocyclopropane-l-carboxylic acid (ACC) content, developed greater ACC oxidase activity and performed better at 10 °C (germinated earlier and had higher percentage germination) than the untreated seeds. Matriconditioning appears to bring about beneficial physical, physiological and biochemical changes that seemingly improve embryo growth potential and tolerance to low temperatures.
Seed matriconditioning; seed osmoconditioning; imbibitional chilling injury; water uptake; solute leakage; vegetable seeds
Two populations of Rhytidiadelphus squarrosus, from metal-contaminated and uncontaminated habitats, differed in their intra- and extracellular Cd contents but had similar cellular levels of Cu. Moss shoots were supplied with a pulse of toxic metal by incubating in Cu or Cd nitrate solutions and effects on respiration, photosynthesis and intracellular K loss were monitored with time after initial exposure. Increasing intracellular Cu levels correlated most closely with a concurrent decline in intracellular K. Photosynthesis also declined in proportion to intracellular Cu; significant Cu-induced stimulation of respiration was observed. The most significant effect of Cd treatment was a decline in photosynthesis in proportion to the intracellular concentration of Cd. Apical segments from both populations showed similar sensitivity to Cu, whereas the metal-contaminated population showed increased resistance to Cd. Sensitivity to Cd increased in the more basal portions of moss gametophores, indicating that apparent resistance of Cd might reflect shoot vitality and age effects. After laboratory growth to eliminate differences in the physiological status of apical segments, it was confirmed that the metal-contaminated population of the moss was photosynthetically more tolerant to Cd at intracellular Cd concentrations found to cause considerable photosynthetic inhibition in the uncontaminated population. The metal-contaminated population of the moss that was tolerant to Cd was not co-tolerant to Cu.
Rhytidiadelphus squarrosus; cadmium; copper; potassium leakage; photosynthesis; respiration; intracellular metals; moss; heavy-metal tolerance
Adventitious root development in lamina and midrib-petiole junction expiants of sugar beet cv. Primo was investigated using scanning electron microscopy and light microscopy. Primordia developed close to the vascular strands and areas of newly dividing cells (meristematic centres) were seen adjacent to the intrafascicular cambium after 2 d incubation on medium containing 30 mg 1−11-naphthalene acetic acid. Clearly defined primordia were visible at 4 d and the first roots had emerged by 6 d. A minimum of 24 h exposure to NAA was necessary for root induction. Four days on NAA caused twice as many roots to be initiated but more prolonged exposure (5 and 10 d) inhibited root development. Root initiation continued after transfer to medium containing no plant growth regulators, new primordia appearing as the older ones extended as roots. Attempts were made to modify the development of primordia by sequential culture on cytokinin after induction by auxin. Incubation on N6-benzylaminopurine within 48 h of exposure to NAA disrupted the development of primordia and roots but did not induce shoot formation.
Beta vulgaris; sugar beet; in vitro culture; leaf explants; rhizogenesis; morphogenetic plasticity
Stomatal behaviour in cucumber (Cucumis sativus L.) was analysed and modelled as a function of different greenhouse environmental parameters, under variable summer conditions. Solar radiation was the main regulating factor. During the day, large atmospheric vapour pressure deficit increased transpiration which was followed by a reduction in stomatal aperture, suggesting the presence of a feedback response to water stress. However, stomatal behaviour was more sensitive to high atmospheric vapour pressure deficit when this was accompanied by a rapid decrease of solar radiation. The response to the difference between leaf and air temperature was also influenced by air vapour pressure deficit and duration of plant exposure to high evaporative demand. Calculation of the crop water stress index showed that the air vapour pressure deficit of 1 kPa used in the control treatment probably caused water stress and induced some hardening, a necessary condition for adaptation to summer climate in southern Europe. The importance of the interaction between climatic parameters and plant response in greenhouse environmental management is analysed. Classical models of stomatal resistance are also discussed.
Cucumis sativus L.; stomata; transpiration; leaf temperature; modelling; greenhouse environment; vapour pressure deficit; solar radiation
A combination of physiological and structural measurements made on nodulated cowpea and soybean plants cultured with roots in different pO2 permitted the expression of data in various ways. Values of leghemoglobin concentration and nitrogenase activity from the two legumes were expressed conventionally either on a per plant or per gram nodule fresh weight basis, and where microscopy was done, on the basis of nitrogenase-containing, N2-fixing units (i.e. per bacteroid, per infected cell, or per gram infected tissue). In both legumes, acetylene reduction, N fixed and ureide content expressed on the basis of whole plants or per nitrogenase-containing units were very significantly correlated with values of leghaemoglobin concentrations expressed in a similar manner. The use of mathematical correlations in this study involving leghaemoglobin concentrations and various indices of N2 fixation indicated a strong functional relationship between the two proteins in symbiotic legumes. These findings confirm previous suggestions that leghaemoglobin and the nitrogenase complex are two proteins closely associated with N2-fixing efficiency in legume root nodules.
A study on five naturally growing epiphytic orchids viz., Bulbophyllum affine Lindl., Coelogyne ochracea Lindl., Otochilus porrecta Lindl., Cirrhopetalum cornutum Lindl. and C. cornutum (var.) was carried out in the subtropical belt of Sikkim Himalaya. Stemflow leachates formed the main source of ammonium-N and nitrate-N for uptake by these orchids. Phosphorus concentration in the tissues of these orchids was high. Phosphate-P from stemflow does not seem to be a regular source of phosphorus for these orchids. Absorption/desorption results indicate that organic-N from stemflow leachates is not utilized by these orchids.
Epiphytic orchids; stemflow; nutrients; enrichment ratio; absorption/desorption
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
The inbred maize lines Poljl7 and F-2 have previously been shown to differ by up to three-fold in leaf abscisic acid (ABA) concentration in the field. Lines from the cross Poljl7 × F-2 differing in leaf ABA concentrations, and the parents, were studied in the field to characterize the differences amongst the lines in ABA concentrations during the season, during the day and in different parts of the plants. The water status of the plants was measured and leaves were heat girdled to get information on possible causes for the genetic variation amongst the lines in ABA concentration.
Leaf ABA concentrations of the high-AB A lines increased markedly and consistently from flowering time onwards, whereas leaf ABA concentrations of the low-ABA lines gradually fell after flowering. Leaf water potentials of high-ABA and low-ABA lines were similar during this time. Leaf ABA concentrations varied little during the day, and heat girdling caused a rise in ABA concentrations, which was similar in both high-ABA and low-ABA lines, only after girdling for at least 4 h. ABA concentrations were highest in the leaves and it was only in the leaves and developing kernels that substantial differences in ABA concentrations were found between the high-ABA and low-ABA classes. Although aerial brace roots also had high ABA concentrations, other roots and stem internodes had ABA concentrations which were consistently low and the same for both ABA classes.
Differences between the ABA classes were unlikely to be due to differences in leaf water status or in ABA export from the leaves. Other possible explanations for the genotypic differences in leaf ABA concentrations are discussed.
Maize; Zea mays L.; abscisic acid (ABA); seasonal and diurnal variation; tissue distribution; genetic variation
Many vascular plant species are unable to colonize calcareous sites. Thus, the floristic composition of adjacent limestone and acid silicate soils differs greatly. The inability of calcifuge plants to establish in limestone sites seems related to a low capacity of such plants to solubilize and absorb Fe or phosphate from these soils. Until now, mechanisms regulating this differing ability of plants to colonize limestone sites have not been elucidated. We propose that contrasting exudation of low-molecular organic acids is a major mechanism involved and show that germinating seeds and young seedlings of limestone plants exude considerably more di- and tricarboxylic acids than calcifuges, which mainly exude monocarboxylic acids. The tricarboxylic citric acid is a powerful extractor of Fe, and the dicarboxylic oxalic acid a very effective extractor of phosphate from limestone soils. Monocarboxylic acids are very weak in these respects. The study is based on ten species from limestone soils and ten species from acid silicate soils.
Calcifuge; calcicole; acidifuge; plant; organic acid; citrate; oxalate; exudation; germination
A physiologically based model of a grass-legume pasture is used to study the dynamics of these competing species. In our model, we consider carbon and nitrogen pools and fluxes, incorporating competition for light and soil mineral nitrogen, and including the processes of nitrogen fixation, nitrogen losses and dry matter allocation. First, the steadystate responses of each species to nitrogen deposition, to leaching rate, and to other nitrogen losses are examined. We then consider the dynamic behaviour of these species when there is no time delay for nitrogen cycled through the soil organic matter pool. Next, the effects of various time delays associated with the soil organic matter nitrogen pool on the system dynamics are examined: the behaviour becomes complex, non-linear and exhibits lightly or heavily damped oscillations at two frequencies. The high sensitivity of the system both to the initial value of the soil organic matter nitrogen pool, and to any photosynthetic competitive advantage, is investigated. The implications of these results in relation to observations and experiments on grass-legume pastures are discussed.
Model; grass; legume; competition; co-existence; carbon; nitrogen; fixation; instability; chaos
Five populations of tetraploid Acacia heterophylla, endemic from La Réunion island, were compared together and with their Australian diploid relative A. melanoxylon for cytogenetic and DNA characteristics. A. melanoxylon (2n = 26) had 1·59 pg nuclear DNA; A. heterophylla (2n = 4x = 52) had double this value (3·19 pg), and there was no difference between populations within species. Both species had 39 % GC. Interchromosome connections were evident at metaphase and mitotic irregularities at anaphase were twice as frequent in A. heterophylla as in A. melanoxylon, again with no difference between populations within species. These results argue for a recent autotetraploid origin of A. heterophylla from A. melanoxylon. Yet, fluorochrome banding showed that in some A. heterophylla populations, GC-rich bands had slightly changed from the supposed ancestral pattern, probably by means of translocations involving parts of nuclear organizer areas. No clear relation was found between banding patterns and ecological factors.
Acacia heterophylla Willd.; Acacia melanoxylon R. Br. (Blackwood); interpopulation variation; autotetraploidy; insular evolution; flow cytometry; DNA content; base ratio; cytogenetics; fluorochrome banding