No description available.

No description available.

No description available.

Examination of the imbibition characteristics of eighty chickpea genetic lines (53 Desi and 27 Kabuli types) and eleven cowpea cultivars revealed that in both species seeds with unpigmented testae imbibed more rapidly than the pigmented seeds. Rapid imbibition was associated with high solute leakage, indicative of possible imbibition damage. Further evidence of imbibition damage was revealed in cowpea where the rapidly imbibing unpigmented seeds had poor vital staining with tetrazolium chloride after 24h imbibition. In chickpea, all the genetic lines of white Kabuli seeds had similar rapid rates of imbibition. In contrast, the pigmented Desi genetic lines revealed a range of rates of water uptake although many imbibed more slowly than the Kabuli lines. The incidence of delayed imbibers, that is, seeds which failed to imbibe until after 8h in water, was the main reason for reduced rates of imbibition in Desi lines. The restriction to water uptake by the pigmented seeds was mainly influenced by the properties of the seed coat. In cowpea seeds, the permeability of the seed coat was the most important factor limiting water uptake whereas in chickpea the permeability of the seed coat as a whole and of the micropyle as well as the degree of adherence of the seed coat to the cotyledons were important in regulating the movement of water into the seed. Investigation of the rate of imbibition during the maturation of dwarf French bean, cowpea and chickpea seeds revealed that development of slow water uptake by coloured cultivars was clearly associated with the appearance of pigmentation. In chickpea, this also coincided with the development of the adherence of the seed coat to the cotyledons. In contrast, seeds from unpigmented cultivars imbibed rapidly at all stages of maturation. Examination of the seed coat anatomy of chickpea and cowpea indicated that the pigmented seeds tended to have shorter and narrower palisade cells and also shorter tracheid bars than the unpigmented seeds. Differences in water uptake by Kabuli and Desi seeds were not evident when seeds were stored at 100% relative humidity and 40<SUP>o</SUP>C for days. All seeds deteriorated at a similar rate. However, the importance of initial seed quality in influencing deterioration during storage was emphasised by the rapid loss of germination of the Kabuli seeds in which germination and vital staining revealed poor initial quality.

Niche-differentiation has been proposed to explain the coexistence of large numbers of tree species in tropical forests. Previous studies on established individuals have found little evidence for this. However, niche-differentiation may be apparent at the seed and seedling stages. This study investigated the effects of environmental variation in germination and seedling establishment for a range of Central Panamanian species. Firstly, topography has a large impact on soil water availability; slopes are wetter than nearby plateaux. The potential impact on seedling emergence and survival was studied by monitoring seedling emergence and survival over 15 months. This revealed that small-seeded species are unlikely to establish on plateaux, presumably because of the rider conditions. Secondly, the germination of four pioneer species in response to four environmental variables, related to canopy gap size, was investigated. Species exhibited consistent patterns of response suggesting adaptation for germination in particular gap sizes; Piper marginatum responded to nitrate, had a low base potential for germination and tolerated large temperature fluctuations, suggesting adaptation for germination in comparatively large gaps. Conversely, Pipe peltatum exhibited responses, which suggested adaptations for germination in small gaps. Finally, germination and seedling mortality for four pioneer species in two sizes of canopy gap was predicted using computer modelling. This indicated that large-seeded pioneers can germinate and establish in large gaps. Conversely, percentage germination and survival of small-seeded species was low in large gaps. However, small-seeded species produce greater quantities of seed than large-seeded species. Consequently they may "win by default" in large gaps, because of the absence of seeds of larger species. These results indicate that there are a number of axes of environmental variation along with nice-differentiation can occur. Furthermore, the response is variable between species. Thus niche-differentiation is important for fostering species coexistence, although density-dependent mortality and dispersal-limitation also contribute.

No description available.

Seed vigor, although not well understood, is a key critical component for yield and is in part due to a well establishment and vigorous stand of canola (<i>Brassica napus</i>) seedling under less than ideal conditions in Western Canada. My objective was to determine what constitutes vigor by studying the response of a black seed line and a yellow seed line imbibed at 8 ºC in either water, saline or osmotic solutions, abscisic acid (ABA), ABA biosynthesis inhibitor, gibberellin (GA4+7), inhibitor of GA biosynthesis and a germination promoter, fusicoccin. Also tested was the effect of seed coat (testa) on seed germination rate and percent germination. Previous studies have established that seed vigor is in part hormonal controlled and genetically controlled. In our study, gene expression was investigated by using transcriptome analysis and hormonal analysis was used to quantitate the changes in hormones and their metabolites during germination. <p> Both the black and the yellow canola seed lines were very sensitive to increasing concentrations of saline and osmotic solutions; however, at the same osmotic potential, osmotic solutions were more inhibitory. The yellow seed line was more sensitive to these conditions than the black seed line. As expected, ABA delayed seed germination, whereas GA4+7 enhanced seed germination and GA4+7 partially overcame the inhibitory effect of ABA. The seed coat was a major factor affecting the germination rate of the yellow seed line; however, GA4+7 overcame the inhibitory effect of the seed coat, whereas ABA exacerbated it. Fusicoccin was more stimulatory to germination than GA4+7; however, unlike GA4+7, it was unable to overcome the inhibitory effect of paclobutrazol, a GA biosynthesis inhibitor. Fluridone, an ABA biosynthesis inhibitor, was unable to overcome the inhibitory effects of a saline solution suggesting that the inhibitory effect was not due to elevated ABA levels. Ethylene, a stimulator of germination, did not appear to be involved in the germination of these two lines. Controlled deterioration at 35 ºC, 85% RH was either partially or completely overcome by exogenous GA4+7. This study demonstrates that the role of hormones, salinity and seed coat on the germination of canola seed under low temperature environmental conditions. <p>During germination, ABA declined while GA4 increased. Higher ABA was found in un-germinated seeds compared to germinated seeds. GA4+7 was lower in seeds imbibed in the saline solution compared to seeds imbibed in water. Un-germinated seeds imbibed in ABA had lower GA4+7 compared to un-germinated seeds imbibed in water; however, the contents of GA4+7 were similar for germinated seeds imbibed in either water or ABA. Phaseic acid (PA) and dihydrophaseic acid (DPA) increased in seeds imbibed in either water, the saline solution or ABA, while they decreased in seeds imbibed in GA4+7. In addition, we found that ABA inhibited GA4 biosynthesis, whereas, GA had no effect on ABA biosynthesis, but altered the ABA catabolic pathway. <p> Gene expression profiles revealed that there are significant differences between un-germinated and germinated seeds. Seeds imbibed in water, GA4+7, a saline solution or ABA had different gene profiles. LEA genes, hormone-related genes, hydrolase-related genes and specific seed germination-related genes were identified and their expression profiles were finely associated with seed germination performance.

Seed vigor, although not well understood, is a key critical component for yield and is in part due to a well establishment and vigorous stand of canola (<i>Brassica napus</i>) seedling under less than ideal conditions in Western Canada. My objective was to determine what constitutes vigor by studying the response of a black seed line and a yellow seed line imbibed at 8 ºC in either water, saline or osmotic solutions, abscisic acid (ABA), ABA biosynthesis inhibitor, gibberellin (GA4+7), inhibitor of GA biosynthesis and a germination promoter, fusicoccin. Also tested was the effect of seed coat (testa) on seed germination rate and percent germination. Previous studies have established that seed vigor is in part hormonal controlled and genetically controlled. In our study, gene expression was investigated by using transcriptome analysis and hormonal analysis was used to quantitate the changes in hormones and their metabolites during germination. <p> Both the black and the yellow canola seed lines were very sensitive to increasing concentrations of saline and osmotic solutions; however, at the same osmotic potential, osmotic solutions were more inhibitory. The yellow seed line was more sensitive to these conditions than the black seed line. As expected, ABA delayed seed germination, whereas GA4+7 enhanced seed germination and GA4+7 partially overcame the inhibitory effect of ABA. The seed coat was a major factor affecting the germination rate of the yellow seed line; however, GA4+7 overcame the inhibitory effect of the seed coat, whereas ABA exacerbated it. Fusicoccin was more stimulatory to germination than GA4+7; however, unlike GA4+7, it was unable to overcome the inhibitory effect of paclobutrazol, a GA biosynthesis inhibitor. Fluridone, an ABA biosynthesis inhibitor, was unable to overcome the inhibitory effects of a saline solution suggesting that the inhibitory effect was not due to elevated ABA levels. Ethylene, a stimulator of germination, did not appear to be involved in the germination of these two lines. Controlled deterioration at 35 ºC, 85% RH was either partially or completely overcome by exogenous GA4+7. This study demonstrates that the role of hormones, salinity and seed coat on the germination of canola seed under low temperature environmental conditions. <p>During germination, ABA declined while GA4 increased. Higher ABA was found in un-germinated seeds compared to germinated seeds. GA4+7 was lower in seeds imbibed in the saline solution compared to seeds imbibed in water. Un-germinated seeds imbibed in ABA had lower GA4+7 compared to un-germinated seeds imbibed in water; however, the contents of GA4+7 were similar for germinated seeds imbibed in either water or ABA. Phaseic acid (PA) and dihydrophaseic acid (DPA) increased in seeds imbibed in either water, the saline solution or ABA, while they decreased in seeds imbibed in GA4+7. In addition, we found that ABA inhibited GA4 biosynthesis, whereas, GA had no effect on ABA biosynthesis, but altered the ABA catabolic pathway. <p> Gene expression profiles revealed that there are significant differences between un-germinated and germinated seeds. Seeds imbibed in water, GA4+7, a saline solution or ABA had different gene profiles. LEA genes, hormone-related genes, hydrolase-related genes and specific seed germination-related genes were identified and their expression profiles were finely associated with seed germination performance.

This study has examined the rate at which the seeds of certain species disappear from woodland soils, and whether the composition of the seed banks beneath stands of known age can be used to reveal management history. Associated with this is an investigation of the spatial distribution of the stored propagules. A question arises as to whether species with long lived seeds can survive as buried seed long enough to take advantage of the opening of the canopy and soil disturbance resulting from the falling of old trees. Given the great life span of most trees, this is a strategy open only to species with exceptionally long lived seed banks. One such species is Hypericum pulchrum, which, as the seed bank surveys carried out in this study show, can exist as viable seeds beneath woodlands of great age in the Tavistock Woodland Estate in Devon. Is this germination and reproduction on tree falls sufficient to maintain Hypericum in the seed bank indefinitely ? To answer this question, a computer model was developed to examine the effect of various parameters on the survival time of a Hypericum seed bank beneath a simulated woodland. The model allowed prediction of both the mean density of buried seeds in a unit area, and the development of pattern within the seed bank. Analysis of the simulation results established that the dispersal of Hypericum was insufficient to maintain a seed bank by a &quot;chain reaction&quot; of windthrown reinforcement. The implications of this are discussed with respect to pioneer species within both temperate and tropical forests.

Seeds are very complex and diverse plant organs. Seed germination is the most sensitive stage of plant life and is influenced by various environmental signals including phytohormones, salt, light, temperature and water potential. Seeds have an innate mechanism called dormancy that blocks germination, and plants have developed several dormancy-inducing strategies to optimise the timing of germination. Seed germination vigour is an important factor in crop yield. Seedling vigour is defined as the sum of the seed properties which determine the level of activity and performance during germination and seedling emergence. A poor seed lot can be improved by post-harvest treatment such as hydro-priming as it is used in the seed industry, but the biological mechanism is unknown. The aim of this study is to understand the mechanism(s) of hydro-priming in order to improve seed vigour and seed germination. I set seeds at different temperatures to produce variation in seed vigour and it showed that germination of seeds with low vigour can be improved by hydro-priming. Using LC-IT-ToF/MS I characterised compounds that leach from seeds during hydro-priming, and showed that some of these are putative germination inhibitors. Adding these compounds to the water during hydro-priming showed that the inhibitory effect of these compounds is not the main mechanism that regulates germination. Also, transcriptomic analysis showed that genes involved in OPDA pathway are expressed during hydro-priming as well as during endosperm weakening cap associated genes. I concluded that hydro-priming improves the speed of germination of low temperature set and its efficiency is dependent of activation of metabolic activity.