Showing papers on "Germination published in 2005"

Plant hormone interactions during seed dormancy release and germination

Abstract: This review focuses mainly on eudicot seeds, and on the interactions between abscisic acid (ABA), gibberellins (GA), ethylene, brassinosteroids (BR), auxin and cytokinins in regulating the interconnected molecular processes that control dormancy release and germination. Signal transduction pathways, mediated by environmental and hormonal signals, regulate gene expression in seeds. Seed dormancy release and germination of species with coat dormancy is determined by the balance of forces between the growth potential of the embryo and the constraint exerted by the covering layers, e.g. testa and endosperm. Recent progress in the field of seed biology has been greatly aided by molecular approaches utilizing mutant and transgenic seeds of Arabidopsis thaliana and the Solanaceae model systems, tomato and tobacco, which are altered in hormone biology. ABA is a positive regulator of dormancy induction and most likely also maintenance, while it is a negative regulator of germination. GA releases dormancy, promotes germination and counteracts ABA effects. Ethylene and BR promote seed germination and also counteract ABA effects. We present an integrated view of the molecular genetics, physiology and biochemistry used to unravel how hormones control seed dormancy release and germination.

Effect of nano-TiO(2) on strength of naturally aged seeds and growth of spinach.

Abstract: The effects of nano-TiO2 (rutile) and non-nano-TiO2 on the germination and growth of naturally aged spinach seeds were studied by measuring the germination rate and the germination and vigor indexes of aged spinach seeds. An increase of these factors was observed at 0.25–4‰ nano-TiO2 treatment. During the growth stage, the plant dry weight was increased, as was the chlorophyll formation, the ribulosebisphosphate carboxylase/oxygenase activity, and the photosynthetic rate. The best results were found at 2.5‰ nano-TiO2. The effects of non-nano-TiO2 are not significant. It is shown that the physiological effects are related to the nanometer-size particles, but the mechanism by which nano-TiO2 improves the growth of spinach seeds still needs further study.

Pre‐Sowing Seed Treatment—A Shotgun Approach to Improve Germination, Plant Growth, and Crop Yield Under Saline and Non‐Saline Conditions

Abstract: Rapid seed germination and stand establishment are critical factors to crop production under salt‐stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to salinity stress. Salinity may delay the onset, reduce the rate, and increase the dispersion of germination events, leading to reductions in plant growth and final crop yield. The adverse effects of salt‐stress can be alleviated by various measures, including seed priming (a.k.a. pre‐sowing seed treatment). The general purpose of seed priming is to partially hydrate the seed to a point where germination processes are begun but not completed. Most priming treatments involve imbibing seed with restricted amounts of water to allow sufficient hydration and advancement of metabolic processes but preventing germination or loss of desiccation tolerance. Treated seeds are usually redried before use, but they would exhibit rapid germination when re‐imbibed under normal or stress conditions. Various seed priming techniques have been developed, including hydropriming (soaking in water), halopriming (soaking in inorganic salt solutions), osmopriming (soaking in solutions of different organic osmotica), thermopriming (treatment of seed with low or high temperatures), solid matrix priming (treatment of seed with solid matrices), and biopriming (hydration using biological compounds). Each treatment has advantages and disadvantages and may have varying effects depending upon plant species, stage of plant development, concentration/dose of priming agent, and incubation period. In this article, we review, evaluate, and compare effects of various methods of seed priming in improving germination of different plant species under saline and non‐saline conditions. We also discuss the known metabolic and ultra‐structural changes that occur during seed priming and subsequent germination. To maximize the utility of various seed priming techniques, factors affecting their efficiency must be examined and potential benefits and drawbacks determined. For example, quality of the seed before treatment, concentration/dose of priming agent, time period for priming, and storage quality of the seed following priming treatment must be carefully determined. Furthermore, such assessments must be based on large‐scale experiments if seed priming is to be used for large‐scale field planting. A better understanding of the metabolic events that take place in the seed during priming and subsequent germination will improve the effective application of this technology. The incorporation of advanced molecular biology techniques in seed research is vital to the understanding and integration of multiple metabolic processes that can lead to enhanced seed germination, and consequently to improved stand establishment and crop yield under saline and non‐saline conditions.

The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway

Abstract: The seeds of parasitic plants of the genera Striga and Orobanche will only germinate after induction by a chemical signal exuded from the roots of their host. Up to now, several of these germination stimulants have been isolated and identified in the root exudates of a series of host plants of both Orobanche and Striga spp. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones, and suggested by many authors to be sesquiterpene lactones. However, this classification was never proven; hence, the biosynthetic pathways of the germination stimulants are unknown. We have used carotenoid mutants of maize (Zea mays) and inhibitors of isoprenoid pathways on maize, cowpea (Vigna unguiculata), and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of Striga hermonthica and Orobanche crenata. Here, we show that for these three host and two parasitic plant species, the strigolactone germination stimulants are derived from the carotenoid pathway. Furthermore, we hypothesize how the germination stimulants are formed. We also discuss this finding as an explanation for some phenomena that have been observed for the host-parasitic plant interaction, such as the effect of mycorrhiza on S. hermonthica infestation.

Longevity of seeds stored in a genebank: species characteristics

Abstract: Seeds of different species are believed to have characteristic shelf lives, although data confirming this are scarce, and a mechanistic understanding of why this should be remains elusive. We have quantified storage performance of c. 42,000 seed accessions, representing 276 species, within the USDA National Plant Germplasm System (NPGS) collection, as well as a smaller experiment of 207 cultivars from 42 species. Accessions from the NPGS collection were harvested between 1934 and 1975, and had relatively high initial germination percentages that decreased at a variable rate during storage at both 5 and –18°C. Germination time courses, which represent the average performance of the species, were fitted to Avrami kinetics, to calculate the time at which germination characteristically declined to 50% (P50). These P50 values correlated with other longevity surveys reported in the literature for seeds stored under controlled conditions, but there was no correlation among these studies and seed persistence observed in the classic buried seed experiment by Duvel. Some plant families had characteristically short-lived (e.g. Apiaceae and Brassicaceae) or long-lived (e.g. Malvaceae and Chenopodiaceae) seeds. Also, seeds from species that originated from particular localities had characteristically short (e.g. Europe) or long (e.g. South Asia and Australia) shelf lives. However, there appeared to be no correlation between longevity and dry matter reserves, soluble carbohydrates and parameters relating to soil persistence or resource allocation. Although data from this survey support the hypothesis that some species tend to survive longer than others in a genebank environment, there is little information on the attributes of the seed that affect its storage performance.

Thermal Hardening: A New Seed Vigor Enhancement Tool in Rice

Abstract: In a laboratory study, indica and japonica rice (Oryza sativa L.) seeds were exposed to thermal hardening (heating followed by chilling followed by heating; chilling followed by heating followed by chilling; heating followed by chilling or chilling followed by heating). In indica rice, heating followed by chilling followed by heating resulted in decreased mean germination time, time to start germination, electrical conductivity of seed leachates, and time to 50% germination, as well as increased germination index, energy of germination, radicle and plumule length, root length, root/shoot ratio, root fresh and dry weight, radicle and plumule growth rate, and shoot fresh weight. In japonica rice, chilling followed by heating followed by chilling performed better than all other treatments, including control. ( Managing editor: Ping HE)

Nitrate, a signal relieving seed dormancy in Arabidopsis.

Abstract: Nitrate is an important nitrogen source for plants, but also a signal molecule that controls various aspects of plant development. In the present study the role of nitrate on seed dormancy in Arabidopsis was investigated. The effects of either mutations affecting the Arabidopsis nitrate reductase genes or of different nitrate regimes of mother plants on the dormancy of the seeds produced were analysed. Altogether, data show that conditions favouring nitrate accumulation in mother plants and in seeds lead to a lower dormancy of seeds with little other morphological or biochemical differences. Analysis of germination during seed development indicated that nitrate does not prevent the onset of dormancy but rather its maintenance. The effect of an exogenous supply of nitrate on seed germination was tested: nitrate in contrast to glutamine or potassium chloride clearly stimulated the germination of dormant seeds. Data show, moreover, that the Arabidopsis dual affinity nitrate transporter NRT1.1 (CHL1) may be involved in conveying the nitrate signal into seeds. Thus, nitrate provided exogenously or by mother plants to the produced seeds, acts as a signal molecule favouring germination in Arabidopsis. This signalling may involve interaction with the abscisic acid or gibberellin pathway.

Seed removal, seed predation, and secondary dispersal

Abstract: Many studies of postdispersal seed fate use seed removal as an index of seed predation. However, following primary seed dispersal, some seeds are transported intact by ants, dung beetles, scatter-hoarding animals, or abiotic processes to new microsites (secondary dispersal) where germination is possible. Despite a growing realization that secondary seed dispersal can play an important role in plant recruitment, many researchers continue to use seed removal as a proxy for seed predation and are focused too intently on only the initial step of seed fate. We describe, using examples from the recent literature, how the results of some seed removal studies may have been misinterpreted, present plausible, alternative explanations for the fate of seeds in those studies, and discuss the importance of detailed studies of seed fates. Following the fates of seeds can be difficult, but such studies contribute much more to our understanding of seed dynamics and plant fitness.

Effects of Salt and Drought Stresses on Germination and Seedling Growth of Pea (Pisum sativum L.)

Abstract: The effects of salt and drought stresses at the water potentials of -2, -4, -6 and -8 bars induced by NaCl and PEG 6000 (polyethylene glycol 6000) each, on germination and early seedling growth, were investigated for 3 pea cultivars (Bolero, Sprinter and Utrillo). Electrical conductivity (EC) values of the NaCl solutions were 4.5, 8.8, 12.7 and 16.3 dS m-1. Germination percentage, mean germination time, root and shoot length, and seedling fresh and dry weight were measured in the study. The objective was to determine genotypic differences among pea cultivars in terms of salt and drought stress and to determine factors (salt toxicity or osmotic stress due to PEG) inhibiting seed germination. The germination results revealed that the genotypes significantly differed for salt and drought stress. Bolero appeared to be more tolerant to salt stress, but Sprinter cv. gave higher values under drought stress. Both NaCl and PEG inhibited germination and seedling growth in all cultivars, but the effects of NaCl compared to PEG were less on germination and seedling growth. All cultivars were able to germinate at all NaCl levels without a significant decrease in germination, while a drastic decrease in germination was recorded at -6 bars of PEG. It was concluded that inhibition in germination at equivalent water potentials of NaCl and PEG was mainly due to an osmotic effect rather than salt toxicity.

The etr1-2 mutation in Arabidopsis thaliana affects the abscisic acid, auxin, cytokinin and gibberellin metabolic pathways during maintenance of seed dormancy, moist-chilling and germination

Abstract: In Arabidopsis thaliana, the etr1-2 mutation confers dominant ethylene insensitivity and results in a greater proportion of mature seeds that exhibit dormancy compared with mature seeds of the wild-type. We investigated the impact of the etr1-2 mutation on other plant hormones by analyzing the profiles of four classes of plant hormones and their metabolites by HPLC-ESI/MS/MS in mature seeds of wild-type and etr1-2 plants. Hormone metabolites were analyzed in seeds imbibed immediately under germination conditions, in seeds subjected to a 7-day moist-chilling (stratification) period, and during germination/early post-germinative growth. Higher than wild-type levels of abscisic acid (ABA) appeared to contribute, at least in part, to the greater incidence of dormancy in mature seeds of etr1-2. The lower levels of abscisic acid glucose ester (ABA-GE) in etr1-2 seeds compared with wild-type seeds under germination conditions (with and without moist-chilling treatments) suggest that reduced metabolism of ABA to ABA-GE likely contributed to the accumulation of ABA during germination in the mutant. The mutant seeds exhibited generally higher auxin levels and a large build-up of indole-3-aspartate when placed in germination conditions following moist-chilling. The mutant manifested increased levels of cytokinin glucosides through zeatin-O-glucosylation (Z-O-Glu). The resulting increase in Z-O-Glu was the largest and most consistent change associated with the ETR1 gene mutation. There were more gibberellins (GA) and at higher concentrations in the mutant than in wild-type. Our results suggest that ethylene signaling modulates the metabolism of all the other plant hormone pathways in seeds. Additionally, the hormone profiles of etr1-2 seed during germination suggest a requirement for higher than wild-type levels of GA to promote germination in the absence of a functional ethylene signaling pathway.

Role of Abscisic Acid in Seed Dormancy

Abstract: Seed dormancy is an adaptive trait that improves survival of the next generation by optimizing the distribution of germination over time. The agricultural and forest industries rely on seeds that exhibit high rates of germination and vigorous, synchronous growth after germination; hence dormancy is sometimes considered an undesirable trait. The forest industry encounters problems with the pronounced dormancy of some conifer seeds, a feature that can lead to non-uniform germination and poor seedling vigor. In cereal crops, an optimum balance is most sought after; some dormancy at harvest is favored because it prevents germination of the physiologically mature grain in the head prior to harvest (that is, preharvest sprouting), a phenomenon that leads to considerable damage to grain quality and is especially prominent in cool moist environments. The sesquiterpene abscisic acid (ABA) regulates key events during seed formation, such as the deposition of storage reserves, prevention of precocious germination, acquisition of desiccation tolerance, and induction of primary dormancy. Its regulatory role is achieved in part by cross-talk with other hormones and their associated signaling networks, via mechanisms that are largely unknown. Quantitative genetics and functional genomics approaches will contribute to the elucidation of genes and proteins that control seed dormancy and germination, including components of the ABA signal transduction pathway. Dynamic changes in ABA biosynthesis and catabolism elicit hormone-signaling changes that affect downstream gene expression and thereby regulate critical checkpoints at the transitions from dormancy to germination and from germination to growth. Some of the recent developments in these areas are discussed.

The evolutionary ecology of seed germination of arabidopsis thaliana: variable natural selection on germination timing

Abstract: Germination timing of Arabidopsis thaliana displays strong plasticity to geographic location and seasonal conditions experienced by seeds. We identified which plastic responses were adaptive using recombinant inbred lines in a field manipulation of geographic location (Kentucky, KY; Rhode Island, RI), maternal photoperiod (14-h and 10- h days), and season of dispersal (June and November). Transgressive segregation created novel genotypes that had either higher fitness or lower fitness in certain environments than either parent. Natural selection on germination timing and its variation explained 72% of the variance in fitness among genotypes in KY, 30% in June-dispersed seeds in RI, but only 4% in November-dispersed seeds in RI. Therefore, natural selection on germination timing is an extremely efficient sieve that can determine which genotypes can persist in some locations, and its efficiency is geographically variable and depends on other aspects of life history. We found no evidence for adaptive responses to maternal photoperiod during seed maturation. We did find adaptive plasticity to season of seed dispersal in RI. Seeds dispersed in June postponed germination, which was adaptive, while seeds dispersed in November accelerated germination, which was also adaptive. We also found maladaptive plasticity to geographic location for seeds dispersed in June, such that seeds dispersed in KY germinated much sooner than the optimum time. Consequently, bet hedging in germination timing was favorable in KY; genotypes with more variation in germination timing had higher fitness because greater variation was associated with postponed germination. Selection on germination timing varied across geographic location, indicating that germination timing can be a critical stage in the establishment of genotypes in new locations. The rate of evolution of germination timing may therefore strongly influence the rate at which species can expand their range.

Gene Expression Programs during Brassica oleracea Seed Maturation, Osmopriming, and Germination Are Indicators of Progression of the Germination Process and the Stress Tolerance Level

Abstract: During seed maturation and germination, major changes in physiological status, gene expression, and metabolic events take place. Using chlorophyll sorting, osmopriming, and different drying regimes, Brassica oleracea seed lots of different maturity, stress tolerance, and germination behavior were created. Through careful physiological analysis of these seed lots combined with gene expression analysis using a dedicated cDNA microarray, gene expression could be correlated to physiological processes that occurred within the seeds. In addition, gene expression was studied during early stages of seed germination, prior to radicle emergence, since very little detailed information of gene expression during this process is available. During seed maturation expression of many known seed maturation genes, such as late-embryogenesis abundant or storage-compound genes, was high. Notably, a small but distinct subgroup of the maturation genes was found to correlate to seed stress tolerance in osmoprimed and dried seeds. Expression of these genes rapidly declined during priming and/or germination in water. The majority of the genes on the microarray were up-regulated during osmopriming and during germination on water, confirming the hypothesis that during osmopriming, germination-related processes are initiated. Finally, a large group of genes was up-regulated during germination on water, but not during osmopriming. These represent genes that are specific to germination in water. Germination-related gene expression was found to be partially reversible by physiological treatments such as slow drying of osmoprimed seeds. This correlated to the ability of seeds to withstand stress.

Effects of heavy metals on seed germination and early seedling growth of Arabidopsis thaliana

Abstract: Seed is a developmental stage that is highly protective against external stresses in the plant life cycle. In this study, we analyzed toxicity of essential (Cu2+ and Zn2+) and non-essential heavy metals (Hg2+, Pb2+ and Cd2+) on seed germination and seedling growth in the model species Arabidopsis. Our results show that seedling growth is more sensitive to heavy metals (Hg2+, Pb2+, Cu2+ and Zn2+) in comparison to seed germination, while Cd2+ is the exception that inhibited both of these processes at similar concentrations. To examine if toxicity of heavy metals is altered developmentally during germination, we incubated seeds with Hg2+ or Cd2+ only for a restricted period during germination. Hg2+ displayed relatively strong toxicity at period II (12–24 h after imbibition), while Cd2+ was more effective to inhibit germination at period I (0–12 h after imbibition) rather than at period II. The observed differences are likely to be due in part to selective uptake of different ions by the intact seed, because isolated embryos (without seed coat and endosperm) are more sensitive to both Hg2+ and Cd2+ at period I. We assessed interactive toxicity between heavy metals and non-toxic cations, and found that Ca2+ was able to partially restore the inhibition of seedling growth by Pb2+ and Zn2+.

Loss of function of four DELLA genes leads to light- and gibberellin-independent seed germination in Arabidopsis

Abstract: The Arabidopsis severe gibberellin-deficient mutant ga1-3 does not germinate even when the optimal light and temperature conditions are provided. This fact suggests that (1) gibberellin (GA) is absolutely necessary for the germination of an intact seed and (2) the ga1-3 mutant can be used as a good system to identify factors that repress seed germination. In this report, using ga1-3 mutation as the genetic background, we confirm that RGL2, one member of the DELLA family, encodes the predominant repressor of seed germination in Arabidopsis and show that the other DELLA genes GAI,RGA and RGL1 enhance the function of RGL2. More importantly, we show that ga1-3 seeds lacking RGA, RGL1 and RGL2 or GAI, RGL1 and RGL2, confer GA-independent germination in the light but not in the darkness whilst ga1-3 seeds lacking GAI, RGA and RGL2 germinate both in the light and darkness. This suggests that the destabilization or inactivation of RGA and GAI is not only triggered by GA but also possibly by light. In addition, ga1-3 seeds lacking in all the aforementioned four DELLA genes have elongated epidermal cells and confer light-, cold- and GA-independent seed germination. Therefore, DELLA proteins likely act as integrators of environmental and endogenous cues to regulate seed germination.

Effects of gut passage on seed germination: do experiments answer the questions they ask?

Abstract: Summary 1Frugivorous vertebrates may affect plant fitness by dispersing seeds to sites favourable for establishment and by passing seeds through their gut, thereby altering germination patterns. Although gut passage can inhibit germination, most studies have found that it improves germination rate and/or success. 2However, studies that compare seeds passed through a gut to seeds directly removed from a fruit cannot quantify the overall effect of gut passage on seed germination. They address the ecologically narrow question of whether mechanical and/or chemical action in the gut affects germination. They do not address the germination potential of seeds in unconsumed fruits and therefore ignore a common seed fate, deposition in a fruit. 3We surveyed 99 studies that included the effect of vertebrate gut passage on germination and found that only 22 included germination from intact fruits. We suggest that the strongest experimental design to evaluate the impact of gut passage should include intact fruits, since release from germination inhibitors and high osmotic pressure are mechanisms that can alter germination.

Differences in seed biology of annual plants in arid lands: a key ingredient of the storage effect

Abstract: We used a combination of field studies and laboratory experiments to characterize key ecological aspects of the seed biology and soil seed bank dynamics of annual plant communities in chenopod shrublands of South Australia. A sequential study of the soil seed bank demonstrated seasonal and between-year variability in numbers and composition of the soil seed bank. Soil samples incubated under different temperature and watering regimes produced different communities, indicating that species respond differentially to various environmental combinations. Emergence was extremely low at low water availability and at high temperatures, even in trays with ample water. A high percentage of seeds of four out of five species buried in the field remained viable for two years, while the fifth, Carrichtera annua, showed a sharp decline in seed viability, reaching nearly zero survivorship. Our results indicate that, in this system, annual plant communities result from germination of a fraction of seeds present in the soil seed bank, when autumn or winter rainfalls occur. Because different species have different responses to various combinations of environmental conditions, the community composition varies from year to year. This variability is likely to be a component of coexistence through the storage effect.

Environmental and genetic influences on the germination of Arabidopsis thaliana in the field

Abstract: Seasonal germination timing strongly influences lifetime fitness and can affect the ability of plant populations to colonize and persist in new environments. To quantify the influence of seasonal environmental factors on germination and to test whether pleiotropy or close linkage are significant constraints on the evolution of germination in different seasonal conditions, we dispersed novel recombinant genotypes of Arabidopsis thaliana into two geographic locations. To decouple the photoperiod during seed maturation from the postdispersal season that maternal photoperiod predicts, replicates of recombinant inbred lines were grown under short days and long days under controlled conditions, and their seeds were dispersed during June in Kentucky (KY) and during June and November in Rhode Island (RI). We found that postdispersal seasonal conditions influenced germination more strongly than did the photoperiod during seed maturation. Genetic variation was detected for germination responses to all environmental factors. Transgressive segregation created novel germination phenotypes, revealing a potential contribution of hybridization of ecotypes to the evolution of germination. A genetic trade-off in germination percentage across sites indicated that determinants of fitness at or before the germination stage may constrain the geographic range that a given genotype can inhabit. However, germination timing exhibited only weak pleiotropy across treatments, suggesting that different sets of genes contribute to variation in germination behavior in different seasonal conditions and geographic locations. Thus, the genetic potential exists for rapid evolution of appropriate germination responses in novel environments, facilitating colonization across a broad geographic range.

Induction of Heat Stress Tolerance in Barley Seedlings by Pre-Sowing Seed Treatment with Glycinebetaine

Abstract: Heat stress adversely affects plant growth and development, while glycinebetaine (GB) plays a protective role under stressful conditions. The objective of this study was to assess the optimum level of GB for use as a presowing seed treatment and the subsequent effect on the heat tolerance of barley (Hordeum vulgare L. cv. Haider-93) seedlings. Among a range of GB levels, the 20 mM concentration emerged as the most effective in enhancing seed germination, shoot fresh and dry weight and shoot water content under heat stress, and this level was selected for further studies. Time course changes revealed that the seedlings developing from 20 mM GB treated seeds had greater shoot dry weight, net photosynthetic rate (PN), leaf water potential (ψw) and reduced relative membrane permeability (RMP), compared to no-GB treated plants under heat stress. Correlations between dry weight and high PN (r = 0.881), low ψw (r = −0.938) and RMP (r = −0.860) of shoots suggested the involvement of GB in heat stress tolerance. Leakage of Ca2+ and NO3− was the greatest followed by K+ and PO43− under no-GB seed treatment, and GB application under heat stress appreciably reduced the leakage of all these ions, particularly Ca2+, K+ and NO3−. In conclusion GB absorbed by seeds, after translocation to the seedlings, enhanced their capacity to maintain greater water content, and higher seedling vigor by virtue of increased PN, reduced RMP and leakage of important ions under heat stress. These results have implications for final field stand under the conditions where the ambient temperature is supra-optimal for barley growth.

Seed Source Variation in Morphology, Germination and Seedling Growth of Jatropha curcas Linn. in Central India

Abstract: The aim of the study was to determine source variation in Jatropha curcas seeds collected from ten locations in Central India. A significant seed source variation was observed in seed morphology (colour, size and weight), seed germination (viability, germination percent, germination energy, germination value) and seedling growth parameters (survival percentage, seedling height, collar diameter, leave/plant, and seedling biomass). The seed source of Chhindwara (M.P.) was found as the best source in comparison to others. The phenotypic and genotypic variance, their coefficient of variability and broad sense heritability also showed a sizeable variability. This offers a breeder ample scope to undertake screening and selection of seed sources for the desired traits. Further, high percentage of heritability coupled with moderate intensity of genetic gain, was observed for seed germination traits, which signifies that germination is under strong genetic control and good amount of heritable additive genetic component can be exploited for improvement of this species.

The effect of plant growth regulators, nitric oxide, nitrate, nitrite and light on the germination of dimorphic seeds of Suaeda salsa under saline conditions

Abstract: Suaeda salsa, a leaf succulent shrub in the family Chenopodiaceae, is one of the most important halophytes in China. Suaeda salsa produces dimorphic seeds (soft brown seeds and hard black seeds). Seeds of S. salsa were collected from the coastal salt flats near Huanghua City, China. Experiments were conducted to determine the salinity-alleviating effect of plant growth regulators, nitric oxide, nitrate, nitrite and light on the germination of dimorphic seeds of S. salsa. Brown seeds had a higher germination rate than black seeds in all experiments. Black seeds were more sensitive to salt in the absence of light in comparison to brown seeds. Brown seeds absorbed water more quickly in comparison to black seeds and were found to be more tolerant of salt stress. Our results showed that 1-aminocyclopropane-1-carboxylate (ACC, the immediate precursor of ethylene), nitrite, GA4 and BA improved seed germination in the presence of salt. However, nitrate, GA1, GA3 failed to alleviate salt stress. ABA inhibited seed germination and seedling growth. Possible mechanisms involved in the alleviation of salt stress in S. salsa seeds and the ecological adaptation of the seeds to the environment are discussed.

Seed germination of high mountain Mediterranean species: altitudinal, interpopulation and interannual variability

Abstract: The germination response of 20 species from high altitude Mediterranean climates, most of them rare endemics, was studied. Our main goal was to model the germination response of a complete set of Iberian high mountain species. The effect of temperature and other parameters, such as spatial and temporal short gradients, on germination were also evaluated. Some seed features (mass and size) were also related to the germination response. Finally, we tested the effect of cold-wet stratification pretreatment when germination was low under natural conditions. Seeds were collected at four locations from 1,900 to 2,400 m a.s.l. in the Sierra de Guadarrama (Spanish Central Range) over two consecutive growing seasons (2001–2002) and submitted to different temperatures and a constant photoperiod of 16 h light/8 h darkness. Most plants readily germinate without treatment, reaching an optimum at relatively high temperatures in contrast to lowland Mediterranean species. Seeds seem to be physiologically prepared for rapid germination even though these plants usually face very intense summer droughts after ripening and dispersal. Germination was also highly variable among altitudes, populations and years, but results were inconsistent among species. Such flexibility could be interpreted as an efficient survival strategy for species growing under unpredictable environments, such as the Mediterranean climate. Finally cold-wet stratification increased germination capacity in five of nine dormant species, as widely reported for many arctic, boreal and alpine species. In conclusion, high mountain Mediterranean species do not differ from alpine species except that a relatively high number of species are ready to germinate without any treatment.

Seed mass, seedling size and neotropical tree seedling establishment

Abstract: 1- We examined among- and within-species effects of seed mass for seedling establishment from seed to 5 years of age in a field experiment at Paracou, French Guiana. 2- Six seeds of each of eight species were weighed and planted into each of 120 plots (1 m2) throughout closed-canopy forest along 12 100-m transects in 1998. 3- We described the microhabitat of each planting site using principal components derived from measurements of light availability, soil moisture, carbon and nitrogen content, and soil phosphorus availability. Although both survival and relative growth rate (RGR) increased with increasing light availability, no other microhabitat variable significantly affected seedling performance. Nor did the magnitude of microhabitat effects on survival or RGR differ among species. 4- Larger-seeded species were more likely to survive from germination to 1 year as well as from 1 to 5 years of age. RGR for seedling height during the first year post-germination was not related to seed mass, but smaller-seeded species did grow slightly faster thereafter. Path analyses revealed that correlations between seed mass and performance were explained in part because larger seeds produced larger initial seedlings, which tended to survive better but grow more slowly. 5- We also analysed within-species effects of seed mass for the larger-seeded Eperua grandiflora and Vouacapoua americana (both Caesalpiniaceae). Larger seeds produced larger seedlings in both species, but larger seeds survived better only for Eperua. Larger seedlings grew more slowly in both species, but did not offset the early (Eperua) and later (Vouacapoua) positive direct effects of seed mass on RGR that may represent contrasting strategies for reserve deployment. 6- Our results demonstrate that seed size influences performance within and among species in part because of indirect effects of initial seedling size. However, we suggest that traits tightly correlated with seed mass at the species level, such as specific leaf area, leaf longevity and photosynthetic capacity, may also contribute to interspecific performance differences.