Alteration of starch- sucrose transition in germinating wheat seed under sodium chloride salinity

Alterations in starch-sucrose transition during germination were studied in wheat seeds under saline conditions. NaCI significantly reduced the speed of germination and resultant seedling growth, but delayed the degradation of seed storage components. The endogenous level of ABA increased while osmotic potential decreased. NaCI also inhibited the expression of α-amylase. Increasing the concentration of NaCI induced the expression of sucrose phosphate synthase, and sugars, including sucrose, were accumulated in the seedlings. This accumulation of sugar closely correlated with an increase in ABA. However, sugar accumulation was reversible when the salt stress was removed. Overall our results strongly suggest that the germinating wheat seeds alter the starch-to-sucrose conversion to adapt for salt stress. This is probably mediated by the increase in ABA.     

Endogenous abscisic acid during the germination of chick-pea seeds

Over the past twenty years many studies have been undertaken to elucidate the regulation of seed germination. Abscisic acid (ABA) and the gibberellins (GAs) are the hormones proposed to control this process, the first by inhibiting and the second by inducing germination. It has been proposed that a high water potential increases the growth potential of the embryo, presumably permitting the production or activation by GA of the cell wall hydrolases and thus decreasing the yield threshold of the endosperm close to the radicle tip. A low water potential, e.g., imbibition in an osmoticum. imposes a stress on cell metabolism, by reducing the turgor of the radicle cells, and there is a decrease in growth potential. Exogenous ABA also causes a decline in growth potential of the radicle: however, the actions of low water potential in preventing germination are not mediated through an increase in ABA in the seeds. In the present paper an attempt is made to asses the role of ABA and polyethylene glycol (PEG) in the germination of chick-pea (Cicer arietinum L.) seeds. The endogenous ABA of chick-pea seeds was purified by reversed-phase HPLC and quantified by GC-ECD. The variations in the ABA levels in the embryonic axes and the cotyledons were studied during 120 h. of imbibition. The highest ABA level in the embryome axes was found at 18 h. coinciding with an increase in fresh weight and a high germination percentage. ABA was not detected in the cotyledons during incubation which probably indicates that the hormone is more involved in the active growth of the embryonic axes itself than in the mobilization process of the reserves. When seeds were treated with different PEG-cycles. PEG delayed germination, reduced the fresh weight of embryonic axes, and retarded the onset of ABA synthesis. It is concluded that endogenous ABA is related to the onset of germination and the growth of the embryonic axis. In addition, there is no correlation among the different PEG-cycles and the level of ABA and germination. Germination was related more to the water conditions inside the embryo's cells than to ABA levels.     

Changes in Seed Constituents During Germination and Seedling Growth of Precociously Matured Soybean Seeds(Glycine max)

During 7 d of precocious maturation of soybean seed (Glycinemax), the starch content declined and soluble sugar levels increasedin patterns similar to natural seed dehydration and maturation.Total seed protein content and total seed dry weight increasedwhereas oil content remained relatively unchanged. Overall,the proportions of the constituents in precociously maturedseeds were comparable to naturally mature seeds. Precociouslymatured soybean seeds showed much the same germination and seedlinggrowth frequency patterns as naturally matured seeds. Duringgermination and seedling growth of precociously matured seeds,starch, soluble sugar, protein and oil levels followed patternssimilar to naturally mature, germinating seeds and seedlings.Therefore, precocious maturation may be used as a model systemto investigate the control of the physiological and biochemicalevents occurring during seed maturation which lead to germinationand subsequently, seedling growth. Glycine max (L.) Merr., soybean, cotyledons, maturation, germination/seedling growth     

A Role for the Surrounding Fruit Tissues in Preventing the Germination of Tomato (Lycopersicon esculentum) Seeds : A Consideration of the Osmotic Environment and Abscisic Acid

During tomato seed development the endogenous abscisic acid (ABA) concentration peaks at about 50 d after pollination (DAP) and then declines at later stages (60-70 DAP) of maturation. The ABA concentration in the sheath tissue immediately surrounding the seed increases with time of development, whereas that of the locule declines. The water contents of the seed and fruit tissues are similar during early development (20-30 DAP), but decline in the seed tissues between 30 and 40 DAP. The water potential and the osmotic potential of the embryo are lower than that of the locular tissue after 35 DAP also. Seeds removed from the fruit at 30, 35, and 60 DAP and placed ex situ on 35 and 60 DAP sheath and locular tissue are prevented from germinating. Development of 30 DAP seeds is maintained or promoted by the ex situ fruit tissue with which they are in contact. Their germination is inhibited until subsequent transfer to water, and germination is normal, i.e. by radicle protrusion, and viable seedlings are produced, compared with 30 DAP seeds transferred directly to water; more of these seeds germinate, but by hypocotyl extension, and seedling viability is very poor. Isolated seeds at 35 and 60 DAP re-placed in contact with fruit tissues only germinate when transferred to water after 7 d. At 30 DAP, isolated seeds are insensitive to ABA at physiological concentrations in that they germinate as if on water, albeit by hypocotyl extension. At higher concentrations germination occurs by radicle protrusion. Osmoticum prevents germination, but there is some recovery upon subsequent transfer to water. Seeds at 35 DAP are very sensitive to ABA and exhibit little or no germination, even upon transfer to water. The response of the isolated seeds to osmoticum more closely approximates that to incubation on the ex situ fruit tissues than does their response to ABA. This is also the case for isolated 60 DAP seeds, whose germination is not prevented by ABA, but only by the osmoticum; these seeds are inhibited when in contact with ex situ fruit tissues also. It is proposed that the osmotic environment within the tissues of the tomato fruit plays a greater role than endogenous ABA in preventing precocious germination of the developing seeds.     

The regulator of G-protein signaling proteins involved in sugar and abscisic acid signaling in Arabidopsis seed germination

The regulator of G-protein signaling (RGS) proteins, recently identified in Arabidopsis (Arabidopsis thaliana; named as AtRGS1), has a predicted seven-transmembrane structure as well as an RGS box with GTPase-accelerating activity and thus desensitizes the G-protein-mediated signaling. The roles of AtRGS1 proteins in Arabidopsis seed germination and their possible interactions with sugars and abscisic acid (ABA) were investigated in this study. Using seeds that carry a null mutation in the genes encoding RGS protein (AtRGS1) and the alpha-subunit (AtGPA1) of the G protein in Arabidopsis (named rgs1-2 and gpa1-3, respectively), our genetic evidence proved the involvement of the AtRGS1 protein in the modulation of seed germination. In contrast to wild-type Columbia-0 and gpa1-3, stratification was found not to be required and the after-ripening process had no effect on the rgs1-2 seed germination. In addition, rgs1-2 seed germination was insensitive to glucose (Glc) and sucrose. The insensitivities of rgs1-2 to Glc and sucrose were not due to a possible osmotic stress because the germination of rgs1-2 mutant seeds showed the same response as those of gpa1-3 mutants and wild type when treated with the same concentrations of mannitol and sorbitol. The gpa1-3 seed germination was hypersensitive while rgs1-2 was less sensitive to exogenous ABA. The different responses to ABA largely diminished and the inhibitory effects on seed germination by exogenous ABA and Glc were markedly alleviated when endogenous ABA biosynthesis was inhibited. Hypersensitive responses of seed germination to both Glc and ABA were also observed in the overexpressor of AtRGS1. Analysis of the active endogenous ABA levels and the expression of NCED3 and ABA2 genes showed that Glc significantly stimulated the ABA biosynthesis and increased the expression of NCED3 and ABA2 genes in germinating Columbia seeds, but not in rgs1-2 mutant seeds. These data suggest that AtRGS1 proteins are involved in the regulation of seed germination. The hyposensitivity of rgs1-2 mutant seed germination to Glc might be the result of the impairment of ABA biosynthesis during seed germination.     

Nitric oxide is involved in light-specific responses of tomato during germination under normal and osmotic stress conditions

Background and Aims Nitric oxide (NO) is involved in the signalling and regulation of plant growth and development and responses to biotic and abiotic stresses. The photoperiod-sensitive mutant 7B-1 in tomato (Solanum lycopersicum) showing abscisic acid (ABA) overproduction and blue light (BL)-specific tolerance to osmotic stress represents a valuable model to study the interaction between light, hormones and stress signalling. The role of NO as a regulator of seed germination and ABA-dependent responses to osmotic stress was explored in wild-type and 7B-1 tomato under white light (WL) and BL. Methods Germination data were obtained from the incubation of seeds on germinating media of different composition. Histochemical analysis of NO production in germinating seeds was performed by fluorescence microscopy using a cell-permeable NO probe, and endogenous ABA was analysed by mass spectrometry. Key Results The NO donor S-nitrosoglutathione stimulated seed germination, whereas the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) had an inhibitory effect. Under WL in both genotypes, PTIO strongly suppressed germination stimulated by fluridone, an ABA inhibitor. The stimulatory effect of the NO donor was also observed under osmotic stress for 7B-1 seeds under WL and BL. Seed germination inhibited by osmotic stress was restored by fluridone under WL, but less so under BL, in both genotypes. This effect of fluridone was further modulated by the NO donor and NO scavenger, but only to a minor extent. Fluorescence microscopy using the cell-permeable NO probe DAF-FM DA (4-amino-5-methylamino-2',7'-difluorofluorescein diacetate) revealed a higher level of NO in stressed 7B-1 compared with wild-type seeds. Conclusions As well as defective BL signalling, the differential NO-dependent responses of the 7B-1 mutant are probably associated with its high endogenous ABA concentration and related impact on hormonal cross-talk in germinating seeds. These data confirm that light-controlled seed germination and stress responses include NO-dependent signalling.     

Expression of a GALACTINOL SYNTHASE gene in tomato seeds is up-regulated before maturation desiccation and again after imbibition whenever radicle protrusion is prevented

Raffinose family oligosaccharides (RFOs) have been implicated in mitigating the effects of environmental stresses on plants. In seeds, proposed roles for RFOs include protecting cellular integrity during desiccation and/or imbibition, extending longevity in the dehydrated state, and providing substrates for energy generation during germination. A gene encoding galactinol synthase (GOLS), the first committed enzyme in the biosynthesis of RFOs, was cloned from tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds, and its expression was characterized in tomato seeds and seedlings. GOLS (LeGOLS-1) mRNA accumulated in developing tomato seeds concomitant with maximum dry weight deposition and the acquisition of desiccation tolerance. LeGOLS-1 mRNA was present in mature, desiccated seeds but declined within 8 h of imbibition in wild-type seeds. However, LeGOLS-1 mRNA accumulated again in imbibed seeds prevented from completing germination by dormancy or water deficit. Gibberellin-deficient (gib-1) seeds maintained LeGOLS-1 mRNA amounts after imbibition unless supplied with gibberellin, whereas abscisic acid (ABA) did not prevent the loss of LeGOLS-1 mRNA from wild-type seeds. The presence of LeGOLS-1 mRNA in ABA-deficient (sitiens) tomato seeds indicated that wild-type amounts of ABA are not necessary for its accumulation during seed development. In all cases, LeGOLS-1 mRNA was most prevalent in the radicle tip. LeGOLS-1 mRNA accumulation was induced by dehydration but not by cold in germinating seeds, whereas both stresses induced LeGOLS-1 mRNA accumulation in seedling leaves. The physiological implications of LeGOLS-1 expression patterns in seeds and leaves are discussed in light of the hypothesized role of RFOs in plant stress tolerance.     

Structural and expression analysis of prolamin genes in <Emphasis Type="Italic">Oryza sativa</Emphasis> L.

Rice is a staple crop with a small genome of 389 Mb. Rice grain is a source of carbohydrates and proteins and has a relatively low protein content compared to other legume seeds. Glutelin and prolamin are the major storage proteins in rice. Prolamins are characterized by high glutamine and proline content and are generally soluble only in strong alcohol solutions. In this study, we obtained a total of 51,383 expressed sequence tags (ESTs) from Ilpumbyeo (Oryza sativa L.), of which 33,201 and 18,182 clones were obtained from immature and germinating seeds, respectively. From the EST clones, 15,148 unigenes were identified, and 2,590 genes were expressed in both immature and germinating seeds. Gene expression profiling of rice prolamins indicated that prolamin gene expression increased 5 days after heading and reached maximal expression after 30 days, suggesting a high demand for prolamins during seed development and germination. Phylogenetic analysis grouped 33 prolamin genes based on the abundance of sulfur-containing amino acids methionine and cysteine according to the deduced amino acid sequences. Our results enhance the understanding of the regulation of seed maturation and germination, which can result in improved agricultural traits for the seed industry.     

A quantitative trait locus,qSE3, promotes seed germination and seedling establishment under salinity stress in rice

Seed germination is a complex trait determined by both quantitative trait loci (QTLs) and environmental factors and also their interactions. In this study, we mapped one major QTLqSE3 for seed germination and seedling establishment under salinity stress in rice. To understand the molecular basis of this QTL, we isolated qSE3 by map‐based cloning and found that it encodes a K⁺ transporter gene, OsHAK21. The expression of qSE3 was significantly upregulated by salinity stress in germinating seeds. Physiological analysis suggested that qSE3 significantly increased K⁺ and Na⁺ uptake in germinating seeds under salinity stress, resulting in increased abscisic acid (ABA) biosynthesis and activated ABA signaling responses. Furthermore, qSE3 significantly decreased the H₂O₂ level in germinating seeds under salinity stress. All of these seed physiological changes modulated by qSE3 might contribute to seed germination and seedling establishment under salinity stress. Based on analysis of single‐nucleotide polymorphism data of rice accessions, we identified a HAP3 haplotype of qSE3 that was positively correlated with seed germination under salinity stress. This study provides important insights into the roles of qSE3 in seed germination and seedling establishment under salinity stress and facilitates the practical use of qSE3 in rice breeding.     

Gene expression programs during Brassica oleracea seed maturation, osmopriming, and germination are indicators of progression of the germination process and the stress tolerance level

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.     

Role of Abscisic Acid in the Induction of Desiccation Tolerance in Developing Seeds of Arabidopsis thaliana

In contrast to wild-type seeds of Arabidopsis thaliana and to seeds deficient in (aba) or insensitive to (abi3) abscisic acid (ABA), maturing seeds of recombinant (aba,abi3) plants fail to desiccate, remain green, and lose viability upon drying. These double-mutant seeds acquire only low levels of the major storage proteins and are deficient in several low mol wt polypeptides, both soluble and bound, and some of which are heat stable. A major heat-stable glycoprotein of more than 100 kilodaltons behaves similarly; during seed development, it shows a decrease in size associated with the abi3 mutation. In seeds of the double mutant from 14 to 20 days after pollination, the low amounts of various maturation-specific proteins disappear and many higher mol wt proteins similar to those occurring during germination are induced, but no visible germination is apparent. It appears that in the aba,abi3 double mutant seed development is not completed and the program for seed germination is initiated prematurely in the absence of substances protective against dehydration. Seeds may be made desiccation tolerant by watering the plants with the ABA analog LAB 173711 or by imbibition of isolated immature seeds, 11 to 15 days after pollination, with ABA and sucrose. Whereas sucrose stimulates germination and may protect dehydration-sensitive structures from desiccation damage, ABA inhibits precocious germination and is required to complete the program for seed maturation and the associated development of desiccation tolerance.     

The effect of abscisic acid on the growth and storage of germinating rape (Brassica napus L.) seed dried following selection on the basis of a newly-emerged radicle

Abscisic acid at 1 × 10^–4M concentration controlled the progress of the emerging radicle from germinating rape seeds and apparently restricted it to the dehydration tolerant phase. ABA treatment during germination followed by washing reduced the deleterious effects of drying the seeds following selection based on a newly-emerged radicle. Furthermore, the longevity of these low-moisture-content germinating seeds at a range of temperatures was improved by the ABA treatment. The viability of the treated seeds stored at –20°C was maintained for up to 100 days.     

The influence of abscisic acid on different polysomal populations in embryonal tissue during pea seeds germination

The influence of abscisic acid (ABA) on the processes of formation of different polysomal populations, their structures and stability in embryonal tissue during pea seeds germination was studied. The contents of total ribosomal fraction increased in all samples up to 72 h of germination and then decreased. The contents of polysomal population (FP, MBP, CBP and CMBP) extracted from the embryonal tissue after 72 hrs of germination of pea seeds were then quantified. It turned out that in examined tissue of control sample, fraction of free polysomes (FP) was the most abounded. This population of polysomes in sprouts decreased after ABA treatment. FP content decreased even more when the higher ABA concentration was applied during germination. Similar changes were observed in the fraction of membrane-bound polysomes (MBP). Quite different tendencies were found, however, in forming population of the cytoskeleton-membrane-bound polysomes (CMBP). The CMBP population content in embryonal tissue increased in a dosage dependent manner with increasing concentration of ABA applied during seed germination. This indicates the important role of CMBP fraction in synthesis of specific proteins in embryos in the time when processes of seeds germination are retarded by ABA. In the final part we examined the stability of polysomes isolated from sprouts of germinating seeds in water and sprouts isolated from seeds treated with ABA (100 μM) during germination. Total polysomes isolated from embryonal tissue of germinating seeds treated with ABA showed much higher resistance to exogenous ribonuclease digestion than total polysomes of control sample. The obtained results suggest that ABA influence on different polysomal population formation also controls their stability.