Showing papers on "Germination published in 2002"

Gibberellin regulates Arabidopsis seed germination via RGL2, a GAI/RGA-like gene whose expression is up-regulated following imbibition

Abstract: The germination of Arabidopsis seeds is promoted by gibberellin (GA). Arabidopsis GAI, and RGA are genes encoding key GA signal-transduction components (GAI and RGA) that mediate GA regulation of stem elongation. The Arabidopsis genome contains two further genes, RGL1 and RGL2, that encode proteins (RGL1 and RGL2) that are closely related to GAI and RGA. Here, we show that RGL2 regulates seed germination in response to GA, and that RGL1, GAI, and RGA do not. In addition, we show that RGL2 transcript levels rise rapidly following seed imbibition, and then decline rapidly as germination proceeds. In situ GUS staining revealed that RGL2 expression in imbibed seeds is restricted to elongating regions of pre-emergent and recently emerged radicles. These observations indicate that RGL2 is a negative regulator of GA responses that acts specifically to control seed germination rather than stem elongation. Furthermore, as RGL2 expression is imbibition inducible, RGL2 may function as an integrator of environmental and endogenous cues to control seed germination.

Applications of hydrothermal time to quantifying and modeling seed germination and dormancy

Abstract: Knowledge and prediction of seasonal weed seedling emergence patterns is useful in weed management programs. Seed dormancy is a major factor influencing the timing of seedling emergence, and once dormancy is broken, environmental conditions determine the rate of germination and seedling emergence. Seed dormancy is a population-based phenomenon, because individual seeds are independently sensing their environment and responding physiologically to the signals they perceive. Mathematical models based on characterizing the variation that occurs in germination times among individual seeds in a population can describe and quantify environmental and after-ripening effects on seed dormancy. In particular, the hydrothermal time model can describe and quantify the effects of temperature and water potential on seed germination. This model states that the time to germination of a given seed fraction is inversely proportional to the amount by which a given germination factor (e.g., temperature or water potential) exceeds a threshold level for that factor. The hydrothermal time model provides a robust method for understanding how environmental factors interact to result in the germination phenotype (i.e., germination pattern over time) of a seed population. In addition, other factors that influence seed dormancy and germination act by causing the water potential thresholds of the seed population to shift to higher or lower values. This relatively simple model can describe and quantify the germination behavior of seeds across a wide array of environmental conditions and dormancy states, and can be used as an input to more general models of seed germination and seedling emergence in the field.

Effects of metals on seed germination, root elongation, and coleoptile and hypocotyl growth in triticum aestivum and cucumis sativus

Abstract: A simple, fast, and easy-to-perform method was carried out for the quantification of the inhibitory effects of metals on wheat and cucumber. The method uses seed germination, root elongation, and hypocotyl and coleoptile growth in these plants as parameters in the presence of varying concentrations of metals. Metals selected for this study were Hg, Cd, Co, Cu, Pb, and Zn. Although effective concentrations of these metals for a certain degree of inhibition were different, both plants had a reduced seed germination rate, root, and hypocotyl or coleoptile length with increasing concentrations. Mercury was determined to be the most inhibitory metal on these parameters. This metal caused a complete inhibition of germination in wheat and cucumber seeds at certain concentrations—≥1.5 mM in cucumber and at 1.7 mM in wheat. No other metal caused this kind of inhibition even at the highest concentration (8.0 mM) applied. Though this metal possessed a higher inhibition of germination in cucumber than in wheat seeds, the inhibitory effects of other metals used were the reverse, being higher in wheat. With some exceptions, all metals in selected concentrations caused a significant (p < 0.01 or p < 0.05) decrease in germination rate of both plants compared to control group seeds.

A hydrothermal time model explains the cardinal temperatures for seed germination

Abstract: Temperature ( T ) and water potential ( y ) are two primary environmental regulators of seed germination. Seeds exhibit a base or minimum T for germination ( T b ), an optimum T at which germination is most rapid ( T o ), and a maximum or ceiling T at which germination is prevented ( T c ). Germination at suboptimal T can be characterized on the basis of thermal time, or the T in excess of T b multiplied by the time to a given germination percentage ( t g ). Similarly, germination at reduced y can be characterized on a hydrotime basis, or t g multiplied by the y in excess of a base or threshold y that just prevents germination ( y b ). Within a seed population, the variation in thermal times to germination among different seed fractions ( g ) is based on a normal distribution of y b values among seeds ( y b ( g )). Germination responses across a range of suboptimal T and y can be described by a general hydrothermal time model that combines the T and y components, but this model does not account for the decrease in germination rates and percentages when T exceeds T o . We report here that supra-optimal temperatures shift the ψ b ( g ) distribution of a potato ( Solanum tuberosum L.) seed population to more positive values, explaining why both germination rates and percentages are reduced as T increases above T o . A modified hydrothermal time model incorporating changes in ψ b ( g ) at T > T o describes germination timing and percentage across all T and ψ at which germination can occur and provides physiologically relevant indices of seed behaviour.

Proteomics of Arabidopsis seed germination. A comparative study of wild-type and gibberellin-deficient seeds

Abstract: We examined the role of gibberellins (GAs) in germination of Arabidopsis seeds by a proteomic approach. For that purpose, we used two systems. The first system consisted of seeds of the GA-deficient ga1 mutant, and the second corresponded to wild-type seeds incubated in paclobutrazol, a specific GA biosynthesis inhibitor. With both systems, radicle protrusion was strictly dependent on exogenous GAs. The proteomic analysis indicated that GAs do not participate in many processes involved in germination sensu stricto (prior to radicle protrusion), as, for example, the initial mobilization of seed protein and lipid reserves. Out of 46 protein changes detected during germination sensu stricto (1 d of incubation on water), only one, corresponding to the cytoskeleton component α-2,4 tubulin, appeared to depend on the action of GAs. An increase in this protein spot was noted for the wild-type seeds but not for the ga1 seeds incubated for 1 d on water. In contrast, GAs appeared to be involved, directly or indirectly, in controlling the abundance of several proteins associated with radicle protrusion. This is the case for two isoforms of S -adenosyl-methionine (Ado-Met) synthetase, which catalyzes the formation of Ado-Met from Met and ATP. Owing to the housekeeping functions of Ado-Met, this event is presumably required for germination and seedling establishment, and might represent a major metabolic control of seedling establishment. GAs can also play a role in controlling the abundance of a β-glucosidase, which might be involved in the embryo cell wall loosening needed for cell elongation and radicle extension.

Germination ecology of neotropical pioneers: interacting effects of environmental conditions and seed size

Abstract: Germination provides many potentially unrecognized sources of variation in the regeneration niche. In this study we relate germination requirements and seed size for 16 species of pioneer trees to microclimatic conditions present in gaps in semi-deciduous rain forest in Panama. We found that, whereas increased duration of direct irradiance can be an effective indicator of the presence of a canopy gap across all scales of canopy openness, diel fluctuations in soil temperature effectively discriminate both understory sites and small gaps (25 m2) from larger gaps. Germination response was significantly related to seed size. Small-seeded species (seed mass 2 mg) germinated equally in light and darkness (wit...

Effect of Salinity Stress on Growth and Nutrient Composition of Three Soybean (Glycine max L. Merrill) Cultivars

Abstract: Soil salinity is a major limitation to legume production in many areas of the world. The salinity sensitivity of soybean was studied to determine the effect of salinity on seed germination, shoot and root dry weights, and leaf mineral contents. Three soybean cultivars, Lee, Coquitt, and Clark 63, were planted in soils of different salinity levels. The electrical conductivity (EC) of the soils used in this experiment was 0.5 dS m−1. The soil salinity treatments were 0.5, 2.5 4.5, 6.5 and 8.5 dS m−1. Saline drainage water from a drainage canal with an EC of 15 dS m−1 was used to treat the soil samples in order to obtain the desired salinity levels. Germination percentages were recorded 10 days after planting. Shoot and root dry weights of 45-day-old plants were measured. Nutrient concentrations for Na+, K+, Ca2+, Mg2+ and Cl− were determined. Germination percentages were significantly reduced with increasing salinity levels. The cultivar Lee was less affected by salinity stress than Coquitt and Clark 63. At 8.5 dS m−1 a significant reduction in plant height was found in all three cultivars. However, Lee plants were taller than plants of the other two cultivars. Salinity stress induced a significant increase in leaf sodium (Na+) and chloride (Cl−) in all cultivars. However, the cultivar Lee maintained lower Na+ and Cl+ concentrations, a higher potassium (K+) concentration and a higher K+/Na+ ratio at higher salinity levels than Coquitt and Clark 63. Saline stress reduced the accumulation of K+, calcium (Ca2+) and magnesium (Mg2+) in the leaves of the cultivars studied. This study suggests that Lee is the most tolerant cultivar, and that there is a relationship between the salt tolerance of the cultivar and macronutrient accumulation in the leaves.

Ecological consequences and ontogeny of seed heteromorphism

Abstract: Seed heteromorphism represents the production of different kinds of seeds by a single individual. The morphological differentiation affects either the fruit — heterocarpy — or the seed sensu stricto — heterospermy. In this study the phylogenetic distribution of seed heteromorphism among different families and habitats is investigated for 218 plant species based on existing literature. The ecological consequences of seed heteromorphism are explored as well. Seed heteromorphism is most common in the Asteraceae and Chenopodiaceae, suggesting that these families have morphological characteristics favouring the appearance of seed heteromorphism and ecological features that maintain it. Using the distribution of seed heteromorphism within the genus Crepis, the relationship between seed heteromorphism and life cycle and habitats is examined. From this analysis it appears that heterocarpic species are often monocarpic. In contrast, the relationship between heterocarpy and habitats is not obvious. Finally, a synthesis is presented about the ontogeny of heteromorphism and some guidelines are proposed for future research on this topic.

Comparative Effects of NaCl and Polyethylene Glycol on Germination, Emergence and Seedling Growth of Cowpea

Abstract: Seeds of Paceno and Cuarenteno cultivars of cowpea (Vigna unguiculata L. Walp.) were tested for salt and drought tolerance at germination, seedling emergence and early seedling growth in NaCl and PEG-8000 solutions of different osmotic potentials (0, −0.2, −0.4, −0.6, and −0.8 MPa). Daily and final germination and emergence percentage, as well as germination and seedling emergence rate, and seedling growth were recorded under controlled conditions. Results showed that germination and emergence rate were delayed by both solutions in both cultivars, with differences between cultivars among growth stages, given that cultivar Cuarenteno, showed a higher germination rate than Paceno in NaCl, but Paceno was less affected by NaCl and PEG solutions at the emergence stage. Sodium chloride had a lesser effect on both cultivars in terms of germination rate, emergence rate and the final germination and emergence percentage than did PEG-8000. This conclusively proves that the adverse effect of PEG-8000 on germination, emergence and early seedling growth was due to the osmotic effect rather than the specific ion. Seedling growth was reduced by both stresses, but NaCl usually caused less damage than PEG to cowpea seedlings, suggesting that NaCl and PEG acted through different mechanisms.

A meta-analysis of the effect of gut treatment on seed germination.

Abstract: The dispersal of seeds by vertebrate frugivores is a process that usually implies the consumption of fruit pulp and the regurgitation or defecation of viable seeds (Ridley, 1930). An important advantage of seed ingestion by frugivores is a presumed increase in germination percentage (germinability) and rate (speed) (Krefting and Roe, 1949; van der Pijl, 1982). Recent analyses show, however, that such enhancement is far from universal and that several variables intrinsic to the plant or to the frugivore can influence the response of seeds to gut treatment (Traveset, 1998). Three mechanisms determine how frugivores can directly affect seed germination: (i) possible mechanical and/or chemical scarification of the seed-coat, which may depend upon gut retention time and on the type of food ingested with seeds (e.g. Agami and Waisel, 1988; Barnea et al., 1990, 1991; Izhaki and Safriel, 1990; Yagihashi et al., 1998); (ii) separation of seeds from pulp because germination is reduced or precluded if seeds remain associated with pulp (e.g. Rick and Bowman, 1961; Temple, 1977; Izhaki and Safriel, 1990; Barnea et al., 1991; Engel, 2000; Traveset et al., 2001); and (iii) the effect that results from faecal material surrounding the seeds, which may influence germination and/or future seedling growth. For example, seedlings emerging from ingested seeds tend to be more vigorous than those emerging from uningested ones because remaining faecal material fertilizes the seedlings, especially in the case of large-mammalian faeces, which often take a long time to decompose (e.g. Dinerstein and Wemmer, 1988; Quinn et al., 1994; Ocumpaugh et al., 1996; Paulsen, 1998; Traveset et al., 2001; T.R. Paulsen, unpublished). The importance of the first mechanism – the modification of seed-coat traits (e.g. permeability of the coat to water and gases) after gut treatment, which changes the capacity of germination and/or the speed at which seeds germinate – is the focus of this study. A review of this effect has recently been published (Traveset, 1998). In this review, Traveset analysed the results of studies on nearly 200 plant species in 68 families, using a slight variation of the ‘vote-counting’ method (Light and Pillemer, 1971; Hedges and Olkin, 1980). This method is conservative and has the advantage of being simple, but it has the disadvantage of

Composition and content of glucosinolates in developing Arabidopsis thaliana

Abstract: The glucosinolate composition and content in various tissues of Arabidopsis thaliana (L) Heynh ecotype Columbia during development from seeds to bolting plants were determined in detail by high-performance liquid chromatography Comparison of the glucosinolate profiles of leaves, roots and stems from mature plants with those of green siliques and mature seeds indicated that a majority of the seed glucosinolates were synthesized de novo in the silique A comparison of the glucosinolate profile of mature seeds with that of cotyledons indicated that a major part of seed glucosinolates was retained in the cotyledons Turnover of glucosinolates was studied by germination of seeds containing radiolabelled p-hydroxybenzylglucosinolate (p-OHBG) Approximately 70% of the content of [14C]p-OHBG in the seeds was detected in seedlings at the cotyledon stage and [14C]p-OHBG was barely detectable in young plants with rosettes of six to eight leaves The turn-over of p-OHBG was found to coincide with the expression of the glucosinolate-degrading enzyme myrosinase, which was detectable at very low levels in seedlings at the cotyledon stage, but which dramatically increased in leaves from plants at later developmental stages This indicates that there is a continuous turnover of glucosinolates during development and not only upon tissue disruption

Role of a Heterotrimeric G Protein in Regulation of Arabidopsis Seed Germination

Abstract: Seed germination is regulated by many signals. We investigated the possible involvement of a heterotrimeric G protein complex in this signal regulation. Seeds that carry a protein null mutation in the gene encoding the alpha subunit of the G protein in Arabidopsis (GPA1) are 100-fold less responsive to gibberellic acid (GA), have increased sensitivity to high levels of Glc, and have a near-wild-type germination response to abscisic acid and ethylene, indicating that GPA1 does not directly couple these signals in germination control. Seeds ectopically expressing GPA1 are at least a million-fold more responsive to GA, yet still require GA for germination. We conclude that the GPA1 indirectly operates on the GA pathway to control germination by potentiation. We propose that this potentiation is directly mediated by brassinosteroids (BR) because the BR response and synthesis mutants, bri1-5 and det2-1, respectively, share the same GA sensitivity as gpa1 seeds. Furthermore, gpa1 seeds are completely insensitive to brassinolide rescue of germination when the level of GA in seeds is reduced. A lack of BR responsiveness is also apparent in gpa1 roots and hypocotyls suggesting that BR signal transduction is likely coupled by a heterotrimeric G protein at various points in plant development.

Abscisic acid, phaseic acid and gibberellin contents associated with dormancy and germination in barley

Abstract: Analyses of abscisic acid (ABA), ent-kaurenoids and gibberellins (GAs) showed that there were major changes in the contents of these compounds associated with germination of after-ripened barley (Hordeum vulgare cv. Schooner and cv. Proctor) grain but not in hydrated dormant grain. Embryos from dormant and after-ripened dry grain contained similar amounts of ABA, of ent-kaurenoids and of GAs, determined by gas chromatography-mass spectrometry-selected ion monitoring. In embryos of after-ripened grain, ABA content decreased rapidly after hydration and ABA appeared to be metabolized (inactivated) to phaseic acid (PA) rather than diffusing into the endosperm or the surrounding medium as previously thought. Similar changes in ABA occurred in hydrated dormant grain during germination in darkness. Accumulation of ent-kaurenoids and GAs, including GA1, the first biologically active GA in the early 13-hydroxylation biosynthetic pathway, occurred to a much greater extent in after-ripened than in dormant grain and these changes occurred mainly after 18 h of hydration when ABA had already decreased and germination was occurring. The block in ent-kaurenoid and GA synthesis in dormant grain appeared to occur prior to ent-kaurene in the biosynthetic pathway. These results are consistent with the view that ABA is the primary effector of dormancy and that after-ripening involves the development of the ability to reduce the amount of ABA quickly following hydration. Accumulation of GAs does not appear to be causally related to loss of dormancy but it does appear to be related to germination.

New functional legume foods by germination: effect on the nutritive value of beans, lentils and peas

Abstract: The effect of different conditions of germination at a semi-pilot scale on the content of available soluble sugars, alpha-galactosides, vitamins B1 and B2, and inositol phosphates of beans, lentils and peas have been studied. Results obtained indicated that germination modified the nutritional composition of legumes depending on the type of legume and germination conditions. The storage compounds present in dry seeds (alpha-galactosides and higher forms of inositol phosphates) decreased because they were hydrolysed to glucose, fructose, IP4 and IP3, compounds that can serve as a source of energy for the new plant. Vitamin B2 suffered an important increase after germination whereas vitamin B1 did not change significantly. To achieve legume flours with enhanced nutritive value, 6 days of germination in the presence of light for beans and lentils, and in darkness for peas can be suggested.

Relative toxicity of arsenite and arsenate on germination and early seedling growth of rice (oryza sativa l.)

Abstract: Elevated soil arsenic levels resulting from long-term use of arsenic contaminated ground for irrigation in Bangladesh may inhibit seed germination and seedling establishment of rice, the country's main food crop A germination study on rice seeds and a short-term toxicity experiment with different concentrations of arsenite and arsenate on rice seedlings were conducted Percent germination over control decreased significantly with increasing concentrations of arsenite and arsenate Arsenite was found to be more toxic than arsenate for rice seed germination There were varietal differences among the test varieties in response to arsenite and arsenate exposure The performance of the dry season variety Purbachi was the best among the varieties Germination of Purbachi was not inhibited at all up to 4 mg l−1 arsenite and 8 mg l−1 arsenate treatment Root tolerance index (RTI) and relative shoot height (RSH) for rice seedlings decreased with increasing concentrations of arsenite and arsenate Reduction of RTI caused by arsenate was higher than that of arsenite In general, dry season varieties have more tolerance to arsenite or arsenate than the wet season varieties

Salinity Tolerance of Phaseolus Species during Germination and Early Seedling Growth

Abstract: Salinity tolerance during germination and early seedling growth was evaluated for 24 accessions representing four wild Phaseolus species (P. angustissimus A. Gray, P. filiformis Bentham, P. leptostachyus Bentham, and P. microcarpus Mart.) and four accessions of cultivated common bean (P. vulgaris L.) at 0, 60, 120, and 180 mM NaCl. Salinity stress delayed germination in all accessions to varying degrees. Eight accessions of P. filiformis germinated fastest under high salinity (120 mM NaCl). Additional wild accessions exhibiting rapid germination at 120 mM NaCl were P. angustissimus, PI535272, P. leptostachyus, PI535336, and P. microcarpus, PI430196. Among accessions, median germination time (days to 50% germination, T50) at 120 mM NaCl was correlated positively (r2 = 0.55, P less than or equal to 0.01) with germination in the control treatments. Seeds that germinated rapidly at 60 mM NaCl also germinated rapidly at 120 mM NaCl. At 180 mM NaCl, several accessions reached 50% germination by 6 d, demonstrating high genetic potential within Phaseolus for salinity tolerance during germination. The biomass of radicles plus hypocotyls decreased with increasing salinity. Cluster analysis separated the accessions into three groups. Group I included salt sensitive accessions with late germination, high sensitivity index (ratio of median germination time at 120 mM NaCl versus control), and reduced seedling growth. Group II included salt tolerant accessions with rapid germination, high sensitivity index, and enhanced seedling growth. Group III included cultivated accessions corresponding to the Mesoamerican and Andean gene pool with rapid germination, low sensitivity index, and intermediate seedling growth. The results confirm that wild Phaseolus species, and in particular P. filiformis, represent a genetic resource for improvement of salinity tolerance in common bean.

Symbiotic germination and development of the myco‐heterotrophic orchid Neottia nidus‐avis in nature and its requirement for locally distributed Sebacina spp.

Abstract: Summary • Symbiotic germination and development of the fully myco-heterotrophic orchid Neottia nidus-avis were studied in ‘packets’ of seed placed adjacent to, or at varying distances from, adult plants in a Fagus sylvatica woodland. • The distribution and identity of the fungal partner(s) of N. nidus-avis were investigated by internal transcribed spacer (ITS)-restriction fragment length polymorphism (RFLP) and sequence analysis of part of the 28S gene in fungal DNA extracted from adult plants from the UK and Germany, and from seedlings germinated in situ. • Germination commenced in the spring, but only in the presence of a specific fungus, and occurred most frequently in plots containing adults of N. nidus-avis. Seedlings grew best in packets in which a large number of seeds germinated. Adults and seedlings of UK origin contained the same fungal partner whose 28S sequence most closely matched Sebacina dimitica. Plants of German origin contained a closely related, but distinct, fungus. • The results provide the first definitive chronology of the development of N. nidus-avis and establish its critical dependence upon, and specificity for, the locally distributed Sebacina-like fungus that is required for germination and growth.

Effect of shrubs on tree seedling establishment in an abandoned tropical pasture

Abstract: Summary 1 The objective of this study was to evaluate whether early successional shrubs facilitate, tolerate or inhibit different stages of tree establishment in abandoned tropical pasture. 2 Seed rain, seed predation, seed germination and seedling survival of tropical forest trees in pasture grass, below small ( 40 m 2 ) shrub patches, were compared in one abandoned pasture in Costa Rica over 2 years. 3 Seed rain of animal-dispersed trees was higher below both large and small shrub patches than below grass. Seed rain of wind-dispersed trees did not differ in the three patch types. 4 Predation of all animal-dispersed seeds combined and of three individual species was significantly higher below large and small shrub patches compared with below grass; predation of five species did not differ significantly in the three patch types. 5 Germination did not differ significantly in the three patch types for any of the species. 6 Seedling survival was highest below large shrub patches for three of four species. 7 Computer simulations of probabilities of seeds arriving in the pasture and surviving to the seedling stage suggest that early successional shrubs have a net facilitative effect on the early stages of forest tree seedling establishment compared with areas without shrubs in the pasture studied, although variance was high. Shrubs may facilitate, inhibit and tolerate different stages of tree seedling establishment.

Mechanisms of Induction of Germination of Bacillus subtilis Spores by High Pressure

Abstract: Spores of Bacillus subtilis lacking all germinant receptors germinate >500-fold slower than wild-type spores in nutrients and were not induced to germinate by a pressure of 100 MPa. However, a pressure of 550 MPa induced germination of spores lacking all germinant receptors as well as of receptorless spores lacking either of the two lytic enzymes essential for cortex hydrolysis during germination. Complete germination of spores either lacking both cortex-lytic enzymes or with a cortex not attacked by these enzymes was not induced by a pressure of 550 MPa, but treatment of these mutant spores with this pressure caused the release of dipicolinic acid. These data suggest the following conclusions: (i) a pressure of 100 MPa induces spore germination by activating the germinant receptors; and (ii) a pressure of 550 MPa opens channels for release of dipicolinic acid from the spore core, which leads to the later steps in spore germination.

Study of the influence of magnetic field on some biological characteristics of zea mais

Abstract: The effect of the static magnetic field of 0,15 Т induction on the maize seeds was studied. The germinating energy and seed germination were detected. The fresh weight and the shoot length were measured. The absorption spectra and the specific electroconductivity of the water extract from seeds were registered. It was detected that the magnetic field stimulated the shoot development and led to the increase of the germinating energy, germination, fresh weight and shoot length. The extinction of the samples treated with a magnetic field increased by about 20 %. The highest values of the treated sample parameters were obtained after 10-min exposure in the magnetic field.

Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature

Abstract: Air temperatures of greater than 35 °C are frequently encountered in groundnut-growing regions, especially in the semi-arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly-tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (Tmin, Topt and Tmax) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55-437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and Tmax for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance-based on pollen response were poorly related (R2 = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.

The influence of priming on germination of rice (Oryza sativa L.) seeds and seedling emergence and performance in flooded soil

Abstract: The effects of priming treatments (CaCl 2 , CaCl 2 + + NaCl (1:1.4 mol/mol), CaCl 2 + NaCl (1:1.4 mol/mol)+10, 100, or 1000 ppm GA 3 , at -1.25 MPa for 2 d and polyethylene glycol (PEG 8000) at -1.25 MPa for 3 d at 20°C) were investigated on rice seeds (Oryza sativa L. cv 'Zhenongda 454') in germination tests in the laboratory. Priming did not improve rice seed germination, but significantly increased germination energy and germination index and slightly reduced mean germination time (MGT). Seeds primed with salt solutions had a significantly higher germination index and lower MGT than those primed with PEG8000. There were no significant differences in energy of germination and germination percentage among seeds primed with salt solutions and those primed with PEG8000. The addition of GA 3 to CaCl 2 + NaCl solution did not significantly improve the rate of germination or germination percentage as compared with CaCl 2 + NaCl priming solution. In a greenhouse trial, priming improved the seedling vigour index and seedling and stand establishment in flooded soil. The addition of GA 3 to CaCl 2 + NaCl did not significantly increase either the speed of emergence or stand establishment as compared with CaCl 2 + NaCl priming solution. It is suggested that priming of rice seeds may contribute to improved seedling establishment in anaerobic soil.

The effect of salinity on some physiological parameters in two maize cultivars

Abstract: Summary. In this study, effect of salinity with different osmotic potential on shoot length, total fresh and dry weight, amounts of organic (proline) and inorganic (K + and Na + ) substance of leaf tissue, the Na + /K + ratio, and leaf area, relative water content (RWC) and leaf osmolality in two maize (Zea mays L., var. intendata, C.6127 and DK.623) cultivars which are grown as a second yield in the Southeastern Anatolia Region (SAR) of Turkey, were investigated. Plants were grown for 30 days in the controlled growth room. Salinized culture solutions at different osmotic potential (0, -0.1, -0.3 and -0.5 MPa) prepared by adding varying amounts of NaCl and CaCl 2 to the main culture solution were applied to plants from the beginning of the germination. As a result the shoot length, total fresh and dry weight and the leaf area decreased, amounts of proline Na + , Na + /K + ratio and the leaf osmolality increased, but amounts of K + did not change significantly with increasing stress, and salt stress caused a similar decrease in leaf relative water content in both maize cultivars.

Mapping quantitative trait loci controlling seed longevity in rice ( Oryza sativa L.)

Abstract: Quantitative trait loci (QTLs) controlling seed longevity in rice were identified using 98 backcross inbred lines (BILs) derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. Seeds of each BIL were kept for 12 months at 30 °C in dry conditions to promote loss of viability. To measure seed longevity, we performed an additional aging-processing treatment for 2 months at 30 °C maintaining seeds at 15% moisture content. We measured the germination percent of these treated seeds at 25 °C for 7 days as the degree of seed longevity. The germination of BILs ranged from 0 to 100% with continuous variation. Three putative QTLs for seed longevity, qLG-2, qLG-4 and qLG-9, were detected on chromosome 2, 4 and 9, respectively. Kasalath alleles increased the seed longevity at these QTLs. The QTL with the largest effect, qLG-9, explained 59.5% of total phenotypic variation in BILs. The other two QTLs, qLG-2 and qLG-4, explained 13.4 and 11.6% of the total phenotypic variation, respectively. We also verified the effect of the Kasalath allele of qLG-9 using chromosome segment substitution lines. Furthermore, QTLs for seed dormancy were identified on chromosomes 1, 3, 5, 7 and 11. Based on the comparison of the chromosomal location of QTLs for seed longevity and seed dormancy, these traits seem to be controlled by different genetic factors.