Germination Of Non-dormant Seeds Research Articles

Dormancy, germination, and associated seed ecological traits of 25 Fabaceae species from northern India.

Fabaceae produce seeds with water-impermeable seed coats, i.e., physical dormancy (PY). We hypothesized that the proportion of PY seeds will increase with the dryness of the habitat, and some key seed ecological traits will be strongly associated with different levels of PY. Fresh seed of 25 Fabaceae species collected in northern India were used for imbibition and germination experiments to determine the proportion of seeds with PY and of nondormant (ND) seeds compared to their Sri Lankan congeners. Seed coat:seed mass ratio (SCR), 1000 seed weight, seed shape index (SSI), embryo type and median germination time of ND seeds were determined. Four imbibition and germination patterns were identified among seeds of the studied species. Seeds collected from Indian populations had a higher proportion of PY seeds than those of Sri Lankan populations. We identified a type of embryo called 'spatulate axile' that had not been identified before among the studied species. Species with ND seeds had a lower SCR and a higher SSI than those with PY. Our hypothesis was confirmed since populations from drier habitats in India produce a higher proportion of PY seeds than those from Sri Lanka. A low SCR ensures minimal resistance to germinating seeds, while seeds with a high SSI have a lower tendency to incorporate into the soil seed bank. Thus, these seed traits aid the fast germination of ND seeds, often dispersed just before the rainy season.

The Influence of Environmental Factors on Germination of Burcucumber (Sicyos angulatus) Seeds: Implications for Range Expansion and Management

AbstractBurcucumber (Sicyos angulatusL.) is a highly invasive vine that has become naturalized in the humid Black Sea region of Turkey, but previous to this study there was no information on the germination biology of this weed. The germination biology of three naturalized populations ofS. angulatusfrom the Black Sea region was studied in laboratory and greenhouse experiments. The germination of nondormant seeds was observed under different photoperiods, constant temperatures, and varying levels of pH, salinity, and osmotic potential. Furthermore, seedling emergence from various soil depths was investigated. The seeds of all populations proved nonphotoblastic (82% to 90%, 55% to 66%, and 48% to 56% germination under 12-, 24-, and 0-h photoperiod, respectively) and germinated over a wide range of temperatures (5 to 40 C). Seedlings emerged from all seed burial depths (0 to 15 cm); however, germination was drastically reduced (>90% reduction) beyond 6 to 8 cm. Seed germination was 30% to 38% for seeds placed on the surface and increased to 78% to 88% for seeds buried 2 cm deep, while germination was severely reduced for seeds buried 10 and 15 cm deep (8 to 12% and 0 to 6%, respectively). Seeds of all populations were found to be sensitive to osmotic and salinity stress and to highly acidic and alkaline pH levels. All populations had similar requirements for germination that are directly related to their area of naturalization. These results indicate that the species has limited potential for range expansion to arid, semiarid (nonirrigated), and relatively saline areas. However, humid, salinity-free, and frequently irrigated areas of the country are at high risk of invasion. In arable lands, deep tillage followed by shallow tillage and effective management of emerging seedlings could deplete the soil seedbank in the long run. However, there is an urgent need for effective strategies to manage the species in other nonarable areas.

Regulation of mRNA translation controls seed germination and is critical for seedling vigor.

Regulation of mRNA translation controls seed germination and is critical for seedling vigor.

Cross-species approaches to seed dormancy and germination: conservation and biodiversity of ABA-regulated mechanisms and the Brassicaceae DOG1 genes

Seed dormancy is genetically determined with substantial environmental influence mediated, at least in part, by the plant hormone abscisic acid (ABA). The ABA-related transcription factor ABI3/VP1 (ABA INSENSITIVE3/VIVIPAROUS1) is widespread among green plants. Alternative splicing of its transcripts appears to be involved in regulating seed dormancy, but the role of ABI3/VP1 goes beyond seeds and dormancy. In contrast, DOG1 (DELAY OF GERMINATION 1), a major quantitative trait gene more specifically involved in seed dormancy, was so far only known from Arabidopsis thaliana (AtDOG1) and whether it also has roles during the germination of non-dormant seeds was not known. Seed germination of Lepidium sativum ('garden cress') is controlled by ABA and its antagonists gibberellins and ethylene and involves the production of apoplastic hydroxyl radicals. We found orthologs of AtDOG1 in the Brassicaceae relatives L. sativum (LesaDOG1) and Brassica rapa (BrDOG1) and compared their gene structure and the sequences of their transcripts expressed in seeds. Tissue-specific analysis of LesaDOG1 transcript levels in L. sativum seeds showed that they are degraded upon imbibition in the radicle and the micropylar endosperm. ABA inhibits germination in that it delays radicle protrusion and endosperm weakening and it increased LesaDOG1 transcript levels during early germination due to enhanced transcription and/or inhibited degradation. A reduced decrease in LesaDOG1 transcript levels upon ABA treatment is evident in the late germination phase in both tissues. This temporal and ABA-related transcript expression pattern suggests a role for LesaDOG1 in the control of germination timing of non-dormant L. sativum seeds. The possible involvement of the ABA-related transcription factors ABI3 and ABI5 in the regulation of DOG1 transcript expression is discussed. Other species of the monophyletic genus Lepidium showed coat or embryo dormancy and are therefore highly suited for comparative seed biology.

How do population genetic parameters affect germination of the heterocarpic species Atriplex tatarica (Amaranthaceae)?

The heterocarpic species Atriplex tatarica produces two types of seeds. In this study, how basic population genetic parameters correlate with seed germinability under various experimental conditions was tested. Population genetic diversity was ascertained in eight populations of A. tatarica by assessing patterns of variation at nine allozyme loci. Germinability of both seed types from all sampled populations was determined by a common laboratory experiment under different salinity levels. Basic population genetic parameters, i.e. percentage of polymorphic loci, average number of alleles per locus and observed heterozygosity were correlated with observed population germination characteristics. Atriplex tatarica possesses a remarkable heterocarpy, i.e. one type of seed is non-dormant and the other shows different dormancy levels in relation to experimental conditions. Significant negative correlations have been detected between germination of both seed types and the coefficient of inbreeding, and a significant negative correlation between germination of dormant seeds and other population genetic parameters, i.e. percentage of polymorphic loci and average number of alleles per polymorphic locus. Moreover, populations from the region characterized by a shorter growing season manifested higher germinability, i.e. had lower dormancy, than those from the lower-latitude one. In general, germination of non-dormant seeds is probably not under strong genetic control. Hence, they germinate as soon as conditions are favourable, thus ensuring survival in the short term, but populations risk local extinction if conditions become adverse (i.e. a high-risk strategy). In contrast, germination of the dormant type of seeds is under stronger genetic control and is significantly correlated with basic population genetic parameters. These seeds ensure long-term reproduction and survival in the field by protracted germination, albeit in low quantities (i.e. A. tatarica also adopts a low-risk strategy).

Physical dormancy in seeds of Dodonaea viscosa (Sapindales, Sapindaceae) from Hawaii

Dormancy in seeds ofDodonaea viscosais due to a water-impermeable seed coat (physical dormancy, PY). Thus, mechanically scarified seeds imbibed water (c.95% increase in mass) and germinated to high percentages over a wide range of temperature regimes in both white light and darkness, whereas non-scarified seeds did not take up water. Dry heat at 80–160°C and dipping in boiling water for 1–60 s also broke dormancy in a high percentage of the seeds, and continuous far-red light was not inhibitory to germination. However, dry storage in the laboratory for >1 year did not overcome dormancy. Seeds made water-permeable by boiling imbibed water, and thus germinated, at a much slower rate than those made water-permeable by mechanical scarification. We suggest that boiling opened the ‘water gap’ in the seed coat (not yet described inSapindaceaebut present in other taxa with PY) and that water entered the seed only through this small opening, thereby accounting for the slow rate of imbibition and subsequent germination. Physical dormancy has now been shown to occur in seeds of this polymorphic, worldwide species from Australia, Brazil, Hawaii, Mexico and New Zealand. The low level of dormancy reported for seed lots ofD. viscosain China, India and Pakistan is probably due to collection of seeds before they dried to the critical moisture content for development of water-impermeability of the seed coat. Germination of non-dormant seeds over a wide range of temperatures and in white light, far-red (leaf-canopy shade) light and darkness are part of the germination strategy ofD. viscosaand of other taxa whose seeds have PY at maturity.

Predicting germination response of four cool-season range grasses to field-variable temperature regimes

Germination of non-dormant seeds under variable-temperature conditions can be predicted from constant-temperature germination data if it is assumed that instantaneous germination rate is independent of thermal history. Thermal-response models of this type have not been validated under simulated field-variable temperature conditions that vary in diurnal pattern, diurnal range and longer-term trends in mean–daily temperature. The purpose of this experiment was to evaluate germination response of thickspike wheatgrass ( Elymus lanceolatus), bluebunch wheatgrass ( Pseudoroegneria spicata), Sandberg bluegrass ( Poa sandbergii) and bottlebrush squirreltail ( Elymus elymoides) under both constant and field-variable temperature regimes in the laboratory. It was hypothesized that the thermal history assumption was valid and that constant-temperature data could be used to accurately estimate field-variable temperature response. Seeds were germinated at seven constant temperatures between 5 and 35°C, and under 18 variable-temperature regimes simulating six planting dates at three field sites. Predictions of germination time under variable-temperature conditions were accurate to within a fraction of 1 day up to a cumulative germination percentage of 70% for thickspike wheatgrass, 60% for bluebunch wheatgrass, 55% for Sandberg bluegrass and 70% for bottlebrush squirreltail. It was concluded that, for the variable-temperature regimes tested in this experiment, the thermal-history assumption was valid for earlier-germinating subpopulations.

Physiological dormancy and germination requirements of seeds of several North American Rhus species (Anacardiaceae)

AbstractFourteen seedlots of five species of Rhus were surveyed for presence/absence of physiological dormancy and/or for germination requirements of non-dormant seeds. Physiological dormancy was present in the four seedlots of R. aromatica studied, but not in either of the two seedlots of its close relative R. trilobata, which is in contrast to previous reports. Neither were seeds of R. glabra, R. typhina, nor R. virens physiologically dormant. Stratification at 5oC for 1 week or incubation in 500 or 1000 mg/l solutions of gibberellic acid broke physiological dormancy in > 90% of the R. aromaticaseeds. Maturation desiccation acted as a switch from a developmental to a germinative mode in R. aromatica embryos, whereas it was not required for germination of R. glabra or R. virens (R. trilobata and R. typhinanot tested). Seeds of all five species incubated on a moist substrate became fully imbibed in 2 d, at which time moisture content was approx. 70–80%of their initial weight. In general, germination of non-dormant seeds was rather insensitive to temperature and light. Seeds germinated equally well in light and in darkness over a daily (12 h/12 h) temperature range of 15/6–35/20oC. Over a 4 week period, the best germination percentages were obtained at 25/15 and 20/10oC, whereas 35/20oC appeared to be supraoptimal, though not always significantly so. If the incubation period was extended to 30 weeks, germination percentages were as high at 15/6oC as at 25/15 and 20/10oC.

Dormancy-breakage in seeds of Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco). Support for the hypothesis that LEA gene expression is essential for this process

Summary In Douglas fir seeds ( Pseudotsuga menziesii (Mirb.) Franco), dormancy-breakage is associated with quantitative and qualitative changes in gene expression. Specific examples of genes that are up-regulated during dormancy-breakage include those encoding LEA proteins (DF6, DF65 and DF77) (Jarvis et al., J. Plant Physiol. 147: 559–566, 1996). In particular, DF65, a dehydrin, was specifically expressed during stratification and DF6 and DF77 were significantly up-regulated. On examination of the tissue distribution of the LEA gene transcripts during chilling (which breaks dormancy) and warm-incubation, LEA transcripts were detected in both embryo and megagametophyte tissues. Expression of DF65 was lower, and the transcript appeared later, in the embryo than in the megagametophyte. With DF6 and DF77, transcripts reached maximal levels in the megagametophyte earlier than in the embryo. While de novo synthesis of ABA was important for the expression of dormancy, four weeks of chilling, only led to a 36% reduction in endogenous ABA and did not change its distribution between the embryo and megagametophyte, compared with warm-incubated seeds. However, following chilling, seeds showed a reduced sensitivity to applied ABA. To determine if there was a link between the expression pattern of LEA genes and the dormancy status of the seeds and/or abiotic stresses, seeds were treated with the plant growth regulators ABA and Me-JA, or subjected to osmotic, salt, and heat stresses. ABA treatment prevented germination of non dormant seeds, and did not induce expression of LEA genes. Me-JA stimulated dormant seeds to germinate and induced low level expression of all three LEA genes after 24 hours, but not after one week. Expression of all three LEA genes was detected in seeds which had been subjected to osmotic and salt stresses expression. However, under heat stress only DF6 and DF77 were expressed. The degree of induction by these treatments was much less than that induced by chilling. We conclude that the primary role of these gene products is connected with changes that occur during the cold, moist treatment that leads to dormancy-breakage in seeds.

Seed Ecology of Hypericum gramineum, an Australian Forb

Aspects of the seed ecology of Hypericum gramineum Forster, a perennial forb that is native to Australia, were examined in several germination and seed predation experiments. Fresh seeds were innately dormant. Highest germination of non-dormant seeds occurred in the light at a temperature regime of approximately 35/25˚C. The results of field experiments indicated that there was no strongly seasonal effect on germination. Predators, such as ants, removed < 20% seeds, thereby suggesting that post-dispersal seed predation is relatively unimportant in the dynamics of H. gramineum populations. Seeds that escape predation and that fail to germinate after dispersal may be incorporated into a persistent soil seed bank.

Physiological Basis of Seed Dormancy in Woolly Cupgrass (Eriochloa villosa[Thunb.] Kunth.)

Laboratory studies were conducted to determine the effect of seed coat on woolly cupgrass seed moisture and oxygen uptake, and to determine if water-soluble growth inhibitors are present in the seed. Intact dormant seeds did not respond to any temperature regime or to oxygen concentrations above atmospheric level. Dehulling increased germination of dormant seed to about 85%. Oxygen concentrations above atmospheric level increased germination of partially dehulled (1/4 distal end of the seed dehulled) seeds an additional 10%. Oxygen uptake by dehulled dormant and intact nondormant seeds was greater than intact dormant seeds. Leaching intact dormant seeds did not promote germination, nor did the leachate inhibit germination of nondormant seeds. Embryos excised from dormant seeds germinated under laboratory conditions. Results from this study suggest that the woolly cupgrass seed coat may inhibit germination by controlling oxygen availability to the embryo.

Patterns of change in seed dormancy and persistence of Bromus diandrus Roth. (great brome) in the field

Mature seeds of great brome (Bromus diandrus Roth;.) from Western Australia were dormant when freshly harvested. This dormancy was lost progressively over summer. The rate of loss of dormancy was more rapid in the northern than in the southern accessions. Compared with bare soil, a wheat stubble microenvironment favoured the relief of dormancy during the initial period of dormancy breakdown. Shallow burial of newly shed dormant seeds also accelerated the after-ripening process. Germination of non-dormant seeds during summer was minimised by high temperatures and low soil moisture content. By autumn/winter, almost all the seeds became germinable. At 20/10�C, the temperature regime corresponding to late autumn, 95-99% germination occurred under constant darkness, but in the light germination varied from 55 to 95%. In the field, complete mass germination did not occur but germination was a well-defined event. There was little germination following this pulse until the succeeding autumn/winter. The seed bank of great brome appears to be essentially a transient one, but this is the subject of further work. The concentration of germination at a single time of year, and the very small carryover of seeds to successive years, suggest that good control should be achieved by a single, timely cultivation or spraying.

Role of Endogenous Growth Regulators in Seed Dormancy of Avena fatua

The hypothesis that endogenous short chain fatty acids (C 6-C 10) are important in maintaining seeds of wild oat (Avena fatua L.) in the dormant state by acting as natural germination inhibitors (Berrie, Buller, Don, Parker, 1979 Plant Physiol 63: 758-764) was investigated. When germination of nondormant seeds was inhibited by treatment with short chain fatty acids, the seeds did not revert to a similar biochemical and physiological state as exhibited by dormant seeds. First, nonanoic acid-induced inhibition of seed germination was not reversed by hormone treatments which normally break dormancy in wild oat seeds. Second, nondormant seeds treated with short chain fatty acids maintained similar relative proportions of the pentose phosphate pathway and the Embden-Meyerhoff-Parnas pathway for respiratory glucose metabolism as that found in the nondormant controls. Seeds imbibed in the presence of nonanoic acid lost more amino acids and proteins into the imbibition solution than did the untreated controls, suggesting membrane damage had occurred. Inasmuch as increasing concentrations of nonanoic acid also progressively reduced the growth of the coleoptile and roots of intact seedlings until all growth ceased and no germination occurred, the inhibition of seed germination could be due to a nonspecific inhibition of growth of the embryo, perhaps because of disruption of membrane structure and function. Finally, no correlation between endogenous levels of short chain fatty acids in seeds or isolated embryonic axes and seed dormancy could be demonstrated.

Seed Dormancy in Red Rice (Oryza sativa). II. Response to Cytokinins

Dormant, dehulled red rice (Oryza sativa L. ‘Louisiana strawhulled′) germinated 80 to 90% at 30 C upon exposure to 10-3 M kinetin (6-furfurylaminopurine), benzyladenine (6-benzylaminopurine), or isopentenyladenine [6-(3-methylbut-2-enylamino)purine] at pH 3.5. Zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine] was also active, eliciting 45% germination at 10-3 M. Adenine was inactive at concentrations as high as 10-2 M. There was little influence of light and no effect of initial pH of the medium upon cytokinin-stimulated germination. At 20 C the response to cytokinins was reduced, but germination of non-dormant seeds was not prevented. At 30 C, the germination of dehulled red rice with 10-3 M kinetin occurred rapidly, with almost 70% germination after 2 days. When dehulled seeds were incubated in water and then transferred to kinetin, percent germination decreased as the duration of water incubation increased. The loss of cytokinin response did not parallel the timecourse of imbibition. Cytokinins did not break dormancy of intact seeds. The hull appeared to limit kinetin uptake and inhibited germination even when kinetin was forced into intact seeds by vacuum infiltration. Dry-after-ripening of intact seeds at 30 C did not increase the kinetin-sensitivity of intact red rice.

GERMINATION ECOLOGY OF SEDUM PULCHELLUM MICHX. (CRASSULACEAE)

Factors controlling the timing of seed germination were investigated in the small succulent winter annual Sedum pulchellum Michx. (Crassulaceae) in its natural habitat on unshaded limestone outcrops in northcentral Kentucky. At maturity in early July the dormant seeds are not dispersed but are retained in the fruits on the standing dead plants until September and October. Many, but not all, of the seeds afterripen in the fruits during summer, and at the time of dispersal some of them are dormant and some are nondormant. Germination and annual population establishment occur in September and October from seed reserves that have been in the soil for one or more years and from seeds produced in the current year. Germination of nondormant seeds may be prevented in autumn by lack of the appropriate combination of environmental factors including light, temperature and soil moisture in the seed's microsite. The effect of low winter temperatures on ungerminated seeds in the population is to induce nondormant seeds into secondary dormancy and to prevent afterripening of dormant seeds. Thus, in spring all the seeds in the population's seed reserve are dormant. During spring and summer some of these seeds afterripen, and they germinate in autumn when, and if, germination requirements are fulfilled.

Germination Ecology of Sedum pulchellum Michx. (Crassulaceae)

Factors controlling the timing of seed germination were investigated in the small succulent winter annual Sedum pulchellum Michx. (Crassulaceae) in its natural habitat on unshaded limestone outcrops in northcentral Kentucky. At maturity in early July the dormant seeds are not dispersed but are retained in the fruits on the standing dead plants until September and October. Many, but not all, of the seeds afterripen in the fruits during summer, and at the time of dispersal some of them are dormant and some are nondormant. Germination and annual population establishment occur in September and October from seed reserves that have been in the soil for one or more years and from seeds produced in the current year. Germination of nondormant seeds may be prevented in autumn by lack of the appropriate combination of environmental factors including light, temperature and soil moisture in the seed's microsite. The effect of low winter temperatures on ungerminated seeds in the population is to induce nondormant seeds into secondary dormancy and to prevent afterripening of dormant seeds. Thus, in spring all the seeds in the population's seed reserve are dormant. During spring and summer some of these seeds afterripen, and they germinate in autumn when, and if, germination requirements are fulfilled.

MECHANISM OF SEED DORMANCY IN AMBROSIA ARTEMISIIFOLIA

Dormancy in Ambrosia artemisiifolia seeds was broken by 8 weeks of stratification. Germination of nondormant seeds was greater in light than in continuous darkness. Embryos of freshly harvested seeds were nondormant. Leaching and scarification did not stimulate germination of the dormant seeds. Exogenous gibberellin (GA3) slightly increased germination of intact dormant seeds, and the effect was greatly increased by scarification. Germination was greater in the light in both tests. Exogenous indoleacetic acid did not stimulate germination of dormant seeds. Endogenous gibberellin and auxin content increased during stratification, and there was also a significant increase in GA during post‐stratification at a favorable germination temperature. Inhibitors in the dormant seeds decreased during stratification and post‐stratification. The high concentration of chlorogenic acid present in dormant seeds increased slightly during stratification. An unknown phenol very similar to chlorogenic acid in fluorescence and U.V. absorption significantly increased after 2 weeks of stratification. A significant decrease in the concentration of a second unidentified phenol occurred after 2 weeks of stratification. It is proposed that dormancy in Ambrosia artemisiifolia may be controlled by an inhibitor‐promoter complex. The dormant seed is characterized by high inhibitor and low promoter levels. In the nondormant seed the balance was shifted to favor the promoter. Evidence suggests that the inhibitor involved may be abscisic acid and the promoters may be gibberellin and auxin. The content of auxin may be partially controlled by the concentration of phenols.