Abscisic Acid Content In Seeds Research Articles

Rice CENTRORADIALIS 2 regulates seed germination and salt tolerance via ABA-mediated pathway.

A FT/TFL1 subfamily gene, rice CENTRORADIALIS 2, also known as RCN1, regulates seed germination and increase salt tolerance via ABA-mediated pathway. The ABA synthesis and metabolism related genes were changed relative expression levels. Seed germination is a complex biological process that is affected by many factors. Although a number of germination-related genes have been reported, the molecular mechanism of germination regulation has not yet been fully elucidated. Here, we reported that the rice OsCEN2 gene can negatively regulate seed germination. The germination speed of OsCEN2-RNAi seeds was significantly faster while that of OsCEN2-overexpression (OE) seeds was slower than that of the wild type (WT). The results of qRT-PCR showed that the OsCEN2 expression was increased in the early stage of seed germination. Exogenous application of abscisic acid (ABA) on seeds and seedlings showed that OsCEN2-OE seeds and seedlings were highly sensitive to ABA during germination and post-germination growth, respectively. The determination of endogenous ABA content in seeds also showed that the ABA content of OsCEN2-RNAi seeds was lower, while that of OsCEN2-OE seeds was higher. Moreover, the transgenic plants changed salt tolerance because of the altered ABA level. In addition, differences were also observed in the expression of genes related to ABA synthesis and metabolism in the seeds of OsCEN2-transgenic lines. This study reveals that OsCEN2 regulates the germination speed by affecting the content of ABA during seed germination and provides a theoretical basis for research on rice direct seeding.

The H3K27me3 Demethylase RELATIVE OF EARLY FLOWERING6 Suppresses Seed Dormancy by Inducing Abscisic Acid Catabolism.

Seed dormancy is an adaptive trait that is crucial to plant survival. Abscisic acid (ABA) is the primary phytohormone that induces seed dormancy. However, little is known about how the level of ABA in seeds is determined. Here we show that the Arabidopsis (Arabidopsis thaliana) H3K27me3 demethylase RELATIVE OF EARLY FLOWERING6 (REF6) suppresses seed dormancy by inducing ABA catabolism in seeds. Seeds of the ref6 loss-of-function mutants displayed enhanced dormancy that was associated with increased endogenous ABA content. We further show that the transcripts of two genes key to ABA catabolism, CYP707A1 and CYP707A3, but not genes involved in ABA biosynthesis, were significantly reduced in ref6 mutants during seed development and germination. In developing siliques, REF6 bound directly to CYP707A1 and CYP707A3, and was responsible for reducing their H3K27me3 levels. Genetic analysis demonstrated that the enhanced seed dormancy and ABA concentration in ref6 depended mainly on the reduced expression of CYP707A1 and CYP707A3 Conversely, overexpression of CYP707A1 could offset the enhanced seed dormancy of ref6 Taken together, our results revealed an epigenetic regulation mechanism that is involved in the regulation of ABA content in seeds.

Coumarin-Induced Delay of Rice Seed Germination Is Mediated by Suppression of Abscisic Acid Catabolism and Reactive Oxygen Species Production.

Abscisic acid (ABA) is a crucial phytohormone for the regulation of seed germination. The ABA content of seeds is regulated by synthesis and catabolic pathways. Coumarin, an important plant allelochemical, can inhibit seed germination effectively, although whether it is involved in the regulation of ABA content during seed germination has not been elucidated. For the study reported herein, we show that coumarin effectively inhibits rice seed germination and vivipary. We found that the ABA content gradually decreased in water-imbibed rice seeds and that the content and activity of the Oryza sativa 9-cis epoxycarotenoid dioxygenases (OsNCEDs), which are ABA synthases, decreased during seed germination. At the transcription level, the expression of OsNCED1–3 appeared to decrease, whereas the expression of the ABA 8′-hydroxylase 2 and 3 genes (OsABA8’ox2/3) first appeared to increase and then decrease. Samples of rice seeds were also imbibed in water containing coumarin, which increased their ABA content but did not significantly increase the activity or content of their OsNCEDs or OsNCED1–3 transcription. Interestingly, coumarin imbibition remarkably reduced OsABA8’ox2/3 expression in rice embryos, which partially explained how coumarin increased the ABA content of germinating rice embryos. Coumarin also inhibited the accumulation of reactive oxygen species (ROS) in rice embryos and increased the activity of superoxide dismutase and catalase, which are indispensable for seed germination. These results indicate that coumarin delays seed germination by inhibiting ABA catabolism, particularly by decreasing the expression of OsABA8’ox2/3 rather than by increasing ABA synthesis. Moreover, coumarin increases the ABA content while decreasing the ROS content in rice embryos. Our results enhance our understanding of the regulation of ABA and ROS during seed germination and provide theoretical support for application of coumarin to prevent sprouting before crop harvesting.

Exogenous melatonin accelerates seed germination in cotton (Gossypium hirsutum L.).

Seed germination is considered the beginning of the spermatophyte lifecycle, and it is a crucial stage in determining subsequent plant growth and development. Although many previous studies have found that melatonin can promote seed germination, the role of melatonin in cotton germination remains unexamined. The main objective of this study is the characterization of potential promotional effects of melatonin (at doses of 0, 10, 20, 50, 100 and 200 μM) on cotton seed germination. This experiment demonstrated that low concentrations of melatonin can promote germination, while high concentrations failed to promote germination and even inhibited germination. Together, these results indicate that a 20 μM melatonin treatment optimally promotes cotton seed germination. Compared with the control, germination potential (GP), germination rate (GR), and final fresh weight (FW) increased by 16.67%, 12.30%, and 4.81%, respectively. Although low concentrations of melatonin showed some improvement in vigor index (VI), germination index (GI), and mean germination time (MGT), these effects were not statistically significant. Antioxidant enzyme activity during seed germination was most prominent under the 20 μM melatonin treatment. Superoxide dismutase (SOD) and peroxidase (POD) activities were significantly increased by 10.37–59.73% and 17.79–47.68%, respectively, compared to the melatonin-free control. Malondialdehyde (MDA) content was reduced by 16.73–40.33%. Two important plant hormones in seed germination, abscisic acid (ABA) and gibberellins (GAs), were also studied. As melatonin concentration increased, ABA content in seeds decreased first and then increased, and GA3 content showed a diametrically opposite trend, in which the 20 μM melatonin treatment was optimal. The 20 μM melatonin treatment reduced ABA content in seeds by 42.13–51.68%, while the 20 μM melatonin treatment increased GA3 content in seeds to about 1.7–2.5 times that of seeds germinated without melatonin. This study provides new evidence suggesting that low concentrations of melatonin can promote cotton seed germination by increasing the activity of antioxidant enzymes, thereby reducing the accumulation of MDA and regulating plant hormones. This has clear applications for improving the germination rate of cotton seeds using melatonin.

The interplay of PsABAUGT1 with other abscisic acid metabolic genes in the regulation of ABA homeostasis during the development of pea seeds and germination in the presence of H2O2

Inactivation of abscisic acid (ABA) in vitro may be catalyzed either by ABA 8′-hydroxylase (ABA8′OH) or by ABA uridine diphosphate glucosyltransferase (ABAUGT), which conjugates ABA with glucose. However, the involvement of these enzymes in the control of ABA content in vivo, especially ABAUGT, has not been fully elucidated. In pea seeds, both PsABAUGT1 and PsABA8′OH1 contribute to the reduction of ABA content during seed maturation and imbibition; however, during the first hours of imbibition, a high expression of only PsABAUGT1 was observed. Imbibition of seeds with H2O2 increased the ABA content despite the oxygen availability and altered the expression of metabolic genes. The expression of the biosynthetic gene 9-cis-epoxycarotene dioxygenase (PsNCED2) was increased, while that of PsABAUGT1 was decreased in each H2O2 experiment despite O2 availability. Under hypoxia, only seeds imbibed with H2O2 germinated, while under nonlimiting oxygen conditions, the germination rate was not altered by H2O2. Under hypoxia, the germination rate of H2O2-imbibed seeds seemed to not depend on the absolute ABA content and rather on the balance between ABA and gibberellins (GA), as H2O2 increased the expression of GA synthesis genes.Overexpression of PsABAUGT1 in Arabidopsis decreases seed ABA content, accelerates germination and reduces seed sensitivity to exogenously applied ABA, confirming the ability of PsABAUGT1 to inactivate ABA. Thus, PsABAUGT1 is a new player in the regulation of ABA content in maturating and imbibed pea seeds, both under standard conditions and in response to H2O2.

The mechanism underlying fast germination of tomato cultivar LA2711

Seed germination is important for early plant morphogenesis as well as abiotic stress tolerance, and is mainly controlled by the phytohormones abscisic acid (ABA) and gibberellic acid (GA). Our previous studies identified a salt-tolerant tomato cultivar, LA2711, which is also a fast-germinating genotype, compared to its salt-sensitive counterpart, ZS-5. In an effort to further clarify the mechanism underlying this phenomenon, we compared the dynamic levels of ABA and GA4, the transcript abundance of genes involved in their biosynthesis and catabolism as well as signal transduction between the two cultivars. In addition, we tested seed germination sensitivity to ABA and GAs. Our results revealed that insensitivity of seed germination to exogenous ABA and low ABA content in seeds are the physiological mechanisms conferring faster germination rates of LA2711 seeds. SlCYP707A2, which encodes an ABA catabolic enzyme, may play a decisive role in the fast germination rate of LA2711, as it showed a significantly higher level of expression in LA2711 than ZS-5 at most time points tested during germination. The current results will enable us to gain insight into the mechanism(s) regarding seed germination of tomato and the role of fast germination in stress tolerance.

Control of Seed Germination by Light-Induced Histone Arginine Demethylation Activity

For optimal survival, various environmental and endogenous factors should be monitored to determine the appropriate timing for seed germination. Light is a major environmental factor affecting seed germination, which is perceived by phytochromes. The light-dependent activation of phytochrome B (PHYB) modulates abscisic acid and gibberellic acid signaling and metabolism. Thus far, several negative regulators of seed germination that act when PHYB is inactive have been reported. However, neither positive regulators of seed germination downstream of PHYB nor a direct mechanism for regulation of the hormone levels has been elucidated. Here, we show that the histone arginine demethylases, JMJ20 and JMJ22, act redundantly as positive regulators of seed germination. When PHYB is inactive, JMJ20/JMJ22 are directly repressed by the zinc-finger protein SOMNUS. However, upon PHYB activation, JMJ20/JMJ22 are derepressed, resulting in increased gibberellic acid levels through the removal of repressive histone arginine methylations at GA3ox1/GA3ox2, which in turn promotes seed germination.

Shade and Plant Location Effects on Germination and Hormone Content of Palmer Amaranth (Amaranthus palmeri) Seed

Experiments were conducted to investigate the effects of shading on and location of the mother plant on germination and hormone content of Palmer amaranth seed. Increasing the shading from 0 to 87% decreased germination of fresh, viable seeds in dark from 25 to 12%. Abscisic acid (ABA) content of seeds from plants in 0% shade increased from 13.3 ng g−1dry seed to 19.1 ng g−1dry seed with 87% shade. Shading of the mother plant did not influence the 1,000-seed weight of Palmer amaranth. Seeds that matured in the top and middle third of the mother plant had 67 to 78% greater germination than those that matured in the bottom third of the mother plant. Endogenous gibberellic acid (GA) content of seeds did not differ between locations on the mother plant; however, the ABA content of seeds produced on the bottom third of the plant was 46 and 59% higher than the ABA content of seeds produced at the middle and top third of the plant, respectively. Endogenous ABA or GA content of seeds and 1,000-seed weight had no relationship with seed germination over and above the treatment effects. This research suggests that shading and plant location can influence germination of fresh, viable seeds of Palmer amaranth, which will be a dormancy strategy for seed dispersal over time.

Hormonal nature of seed responses to fluctuating temperatures in Cynara cardunculus (L.)

AbstractCynara cardunculus (L.) seeds require incubation at fluctuating temperatures to terminate dormancy. In this study, we analysed the physiological mechanisms underlying such a requirement, focusing on the role of abscisic acid (ABA) and gibberellin (GA). As a conceptual framework, we considered the possibility that fluctuating temperatures and light trigger a similar set of hormonal processes after stimulus perception. To test this possibility, we (1) carried out hydrotime analysis of germination in seeds exposed to fluctuating temperatures (25/15°C) and constant temperature (20°C) with or without gibberellin (GA3) or red light; (2) determined the responses of seeds incubated at fluctuating or constant temperature to ABA, GA3, fluridone, an inhibitor of ABA biosynthesis, and paclobutrazol, an inhibitor of GA biosynthesis; and (3) determined the ABA content of seeds incubated at fluctuating or constant temperature. Incubation at 25/15°C or 20°C in the presence of GA3 reduced the mean base water potential [ψb(50)] of the population to a similar extent, compared to that observed with seeds incubated at 20°C without GA3. Irradiation with red light also reduced ψb(50) to a lesser extent than incubation in the presence of GA3. At all concentrations tested, exogenously applied GA3 did not promote germination of seeds incubated at 25/15°C. However, paclobutrazol inhibited germination, suggesting that fluctuating temperatures terminate dormancy through de novo GA biosynthesis. Fluctuating temperatures enhanced seed germination in the presence of ABA, but ABA content did not differ between seeds incubated at fluctuating and constant temperatures. This study provides clear evidence for the involvement of hormonal regulation in dormancy termination by fluctuating temperatures.

Influence of seed coat removal and chilling on abscisic acid content and germination in ornamental peach (Prunus persica Batsch) seeds

SummaryThe effects of seed coat removal and chilling on the germination of seeds of ten cultivars of ornamental peach (Prunus persica Batsch) were investigated. Seeds were rinsed in running tap water for 48 h in order to facilitate seed coat removal. Only a few non-chilled, intact seeds germinated (e.g., 6% of ‘Hito’ seeds). Seed coat removal and no chilling resulted in some seed germination in eight of the ten cultivars, ranging from 6% to 83%. Chilling intact seeds at 5°C for up to 10 weeks resulted in greater frequencies of germination (average = 85% germination) than seed coat removal before (average = 80%) or after chilling (average = 73%). There was a linear decrease in the germination percentage with an increase in abscisic acid (ABA) content for ‘Yaguchi’,‘Kanpaku’, and ‘Kikumomo’ seeds (R = –0.66; P <0.001). The most consistent decrease in total seed ABA content (average of 64%) occurred during the 48 h rinsing period. In ‘Kanpaku’, dry seeds had an intermediate ABA content (13 ng per seed); but, in the embryonic axes, this increased from 0.03 ng to 1.2 ng per seed with an increase in the duration of the chilling period. The lowest germination percentages were found in this cultivar. These results suggest that ABA synthesis in the embryonic axes during chilling may affect the varietal characteristic of seed dormancy, and that rinsing seeds for >48 h could remove sufficient ABA to allow seed germination with minimum chilling.

Storage behavior and changes in concentrations of abscisic acid and gibberellins during dormancy break and germination in seeds of Phellodendron amurense var. wilsonii (Rutaceae)

The medicinal Asian plant genus Phellodendron is known to contain several very important compounds that have biological action. The main purpose of this study was to determine whether seeds of Phellodendron amurense var. wilsonii can be stored and to characterize their dormancy. Seeds of this taxon stored at -20 and -80 degrees C and in liquid nitrogen retained their high germinability, indicating that they have orthodox storage behavior. Intact seeds from freshly collected fruits were dormant and required 12 weeks of cold stratification at 4 degrees C for complete germination. Scarifying the seed coat was partially effective in breaking seed dormancy. Exogenous gibberellins (GA(3), GA(4) and GA(4+7)) promoted germination of scarified seeds, GA(4) and GA(4+7) being more effective than GA(3). Fluridone, an abscisic acid (ABA) biosynthesis inhibitor, was efficient in breaking dormancy, but it was less effective than GA(4) or GA(4+7) alone. Paclobutrazol, a GA biosynthesis inhibitor, inhibited seed germination, and the inhibitory effect was reversed completely by GA(4) and by GA(4+7). ABA content of seeds subjected to cold stratification or to incubation at 35/10 degrees C, which enhanced seed germination, was reduced about four- to sixfold compared to that of fresh seeds. Higher concentrations of GA(3), GA(4) and GA(7) were detected in nondormant seeds and in seeds with an emerged radicle than in fresh seeds. Present results seem to indicate that dormancy in P. amurense var. wilsonii seeds is imposed partially by the seed coat and partially by high ABA content. ABA content decreased and GA(3), GA(4) and GA(7) content increased during germination.

Ectopic expression of rice OsNCED3 in Arabidopsis increases ABA level and alters leaf morphology

In higher plants, many genes are involved in the abscisic acid (ABA) biosynthetic pathway. Of these, 9- cis-epoxycarotenoid dioxygenase ( NCED) encodes what is considered to be the key enzyme. In the present study, we investigated the effects of ectopically expressing a monocot rice NCED gene, OsNCED3, in dicot Arabidopsis ( Arabidopsis thaliana) plants. We showed that OsNCED3 is functionally active in dicot Arabidopsis plants since the ectopic expression of OsNCED3 successfully complements the 129B08/ nced3 mutant phenotype. Furthermore, overexpression of OsNCED3 in wild-type Arabidopsis plants results in increased accumulation of ABA, reduced relative water loss, delayed seed germination, and greater drought tolerance relative to that of wild-type. Additionally, we observed that seed ABA content and germination patterns are similar between wild-type and the 129B08/ nced3 mutant, suggesting functional redundancy or differential spatial expression of other NCED gene family members. Transgenic Arabidopsis lines overexpressing the monocot OsNCED3 gene in a wild-type background result in a smaller and rounder leaf shape and midvein. The data suggest that, in addition to ABA biosynthesis, the monocot OsNCED3 gene may have additional functions in shaping leaf morphology and vascular bundle development in Arabidopsis.

Mapping a diploid wheat abscisic acid 8′-hydroxylase homologue in the seed dormancy QTL region on chromosome 5Am

In Arabidopsis, two genes of abscisic acid (ABA) 8′-hydroxylase (cytochrome P450 (CYP) 707A1 and A2) have been found to play important roles in seed dormancy through the regulation of ABA content in seeds. In order to examine the role of wheat ABA 8′-hydroxylase gene in seed dormancy, a diploid wheat ABA 8′-hydroxylase gene was cloned that showed high similarity to a barley ABA8′-hydroxylase gene (HvABA8′OH-2), and the cloned gene was designated as TmABA8′OH-2. Using recombinant inbred lines derived from a cross between diploid wheat Triticum boeoticum L. (Tb) and Triticum monococcum L. (Tm), TmABA8′OH-2 has been mapped to near the centromeric region of the long arm of chromosome 5Am, where the major seed dormancy QTL has been previously found. Comparison of the deduced amino acid sequences of TmABA8′OH-2 between Tb and Tm revealed five amino acid residue substitutions. These amino acid residues have distinctly different characteristics, and one of the substitutions occurs in the highly conserved amino acid residues in CYP707A family, indicating that these substitutions may have effects on the enzyme activities. Moreover, hexaploid wheat TmABA8′OH-2 homologue revealed that the level of its expression during seed development peaks at mid-maturation stage. This resembles the expression pattern of the Arabidopsis CYP707A1, which was shown to control seed dormancy. These results imply a possibility that TmABA8′OH-2 might be involved in seed dormancy, and associated with the QTL on chromosome 5Am.

Seed development, dormancy and germination. Annual Plant Reviews, Volume 27.

Seed development, dormancy and germination. Annual Plant Reviews, Volume 27.

Roles of gibberellins and abscisic acid in dormancy and germination of red bayberry (Myrica rubra) seeds

Intact seeds from freshly harvested fruits of Myrica rubra (Sieb et Zucc.) were dormant and required 8 weeks of warm stratification followed by 12 weeks of cold stratification for germination. Exogenous application of gibberellic acid (GA(3)) to intact fresh seeds was effective in breaking dormancy, with > 70% of seeds germinating when treated with 5.2 mM GA(3) and incubated at a day/night temperature of 30/20 degrees C for 20 weeks. Removing the hard endocarp or endocarp plus seed coat of fresh seeds promoted germination, and addition of GA(3) to the embryo accelerated germination. The gibberellins GA(1) and GA(4) were more effective than GA(3) in promoting germination of seeds with the endocarp removed. Endogenous contents of GA(1), GA(3), GA(4), GA(7) and GA(20) were quantified by gas chromatography-mass spectrometry-selected ion monitoring in the endocarps, seed coats and embryos of fresh seeds treated with 5.2 mM GA(3). The content of GA(3) decreased in the endocarp during incubation, whereas GA(1) contents increased in the endocarp and seed coat. A high GA(1) content was detected in the endocarps and embryos of newly germinated seeds. We speculate that GA(3) was converted to GA(1) during incubation and that GA(1) is involved in seed germination. Endogenous abscisic acid (ABA) contents were measured in fresh seeds and in warm and cold stratified seeds. The ABA content in fresh seeds was distributed in the order endocarp > seed coat > embryo, with the content in the endocarp being about 132-fold higher than in the seed coat and embryo. Total ABA content of seeds subjected to warm or cold stratification, or both, was 8.7- to 14.0-fold lower than that of fresh seeds. Low contents of endogenous GA(1), GA(3), GA(7) and GA(20), but elevated contents of GA(4), were found in the seed coats and endocarps of warm plus cold stratified seeds and in the seed coats and embryos of newly germinated seeds. These observations, coupled with the finding that GA stimulated germination of dormant Myrica seeds, provide evidence that endogenous ABA inhibited release of dormancy and that endogenous gibberellins, especially GA(4) or GA(1), or both, are involved in germination.

1-Aminocyclopropane-1-carboxylic acid and abscisic acid during the germination of sugar beet (Beta vulgaris L.): a comparative study of fruits and seeds

The control of sugar beet (Beta vulgaris L.) germination by plant hormones was studied by comparing fruits and seeds. Treatment of sugar beet fruits and seeds with gibberellins, brassinosteroids, auxins, cytokinins, and jasmonates or corresponding hormone biosynthesis inhibitors did not appreciably affect radicle emergence of fruits or seeds. By contrast, treatment with ethylene or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) promoted radicle emergence of fruits and seeds. Abscisic acid (ABA) acted as an antagonist of ethylene and inhibited radicle emergence of seeds, but not appreciably of fruits. High endogenous contents of ACC and of ABA were evident in seeds and pericarps of dry mature fruits, but declined early during imbibition. ABA-treatment of seeds and fruits induced seed ACC accumulation while ACC-treatment did not affect the seed ABA content. Transcripts of ACC oxidase (ACO, ethylene-forming enzyme) and ABA 8'-hydroxylase (CYP707A, ABA-degrading enzyme) accumulate in fruits and seeds upon imbibition. ABA and ACC and the pericarp did not affect the seed CYP707A transcript levels. By contrast, seed ACO transcript accumulation was promoted by ABA and by pericarp removal, but not by ACC. Quantification of the endogenous ABA and ACC contents, ABA and ACC leaching, and ethylene evolution, demonstrate that an embryo-mediated active ABA extrusion system is involved in keeping the endogenous seed ABA content low by 'active ABA leaching', while the pericarp restricts ACC leaching during imbibition. Sugar beet radicle emergence appears to be controlled by the pericarp, by ABA and ACC leaching, and by an ABA-ethylene antagonism that affects ACC biosynthesis and ACO gene expression.

Ectopic expression of a tomato 9‐cis‐epoxycarotenoid dioxygenase gene causes over‐production of abscisic acid

The tomato mutant notabilis has a wilty phenotype as a result of abscisic acid (ABA) deficiency. The wild-type allele of notabilis, LeNCED1, encodes a putative 9-cis-epoxycarotenoid dioxygenase (NCED) with a potential regulatory role in ABA biosynthesis. We have created transgenic tobacco plants in which expression of the LeNCED1 coding region is under tetracycline-inducible control. When leaf explants from these plants were treated with tetracycline, NCED mRNA was induced and bulk leaf ABA content increased by up to 10-fold. Transgenic tomato plants were also produced containing the LeNCED1 coding region under the control of one of two strong constitutive promoters, either the doubly enhanced CaMV 35S promoter or the chimaeric 'Super-Promoter'. Many of these plants were wilty, suggesting co-suppression of endogenous gene activity; however three transformants displayed a common, heritable phenotype that could be due to enhanced ABA biosynthesis, showing increased guttation and seed dormancy. Progeny from two of these transformants were further characterized, and it was shown that they also exhibited reduced stomatal conductance, increased NCED mRNA and elevated seed ABA content. Progeny of one transformant had significantly higher bulk leaf ABA content compared to the wild type. The increased seed dormancy was reversed by addition of the carotenoid biosynthesis inhibitor norflurazon. These data provide strong evidence that NCED is indeed a key regulatory enzyme in ABA biosynthesis in leaves, and demonstrate for the first time that plant ABA content can be increased through manipulating NCED.

Effect of Potassium Nutrition during Bell Pepper Seed Development on Vivipary and Endogenous Levels of Abscisic Acid (ABA)

Seeds in fruit of bell pepper (Capsicum annuum `California Wonder') plants grown in nutrient solutions deficient in potassium (&lt;3 mmol·L-1) showed a higher incidence of sprouting (i.e., vivipary) than seeds in fruit from plants grown at adequate potassium levels (6 mmol·L-1). Tissue analysis showed a progressive drop in the leaf content of potassium with increasing plant maturation for all levels of potassium nutrition. However, potassium in fruit and seeds increased at later stages of maturity. ABA was extracted, isolated and identified from bell pepper seeds obtained from fruit grown under the potassium treatments (0.0, 0.6, 1.5, 3.0, and 6.0 mmol·L-1) at five fruit maturity stages (mature-green to overripe). At early fruit maturity stages, there were no significant differences in seed ABA content in the fruit from the different potassium treatments. However, differences in ABA content and vivipary among the potassium treatments became highly significant as the fruit matured. The concentration of ABA in seeds of potassium-deficient treatments was ≈14% of the control (0.4 versus 2.8 μg·g-1 dry mass). High concentrations of ABA in bell pepper seeds were associated with low incidence of vivipary and high potassium content in the leaves, fruit and nutrient solution.

834 PB 346 DEVELOPMENT OF SEED QUALITY IN RED CABBAGE

Brassica crops have an extended flowering period due to both progressive development within a given raceme and variability among multiple racemes. Early harvest can result in poor seed quality due to immaturity, while delayed harvest may sacrifice yield due to shattering. To characterize the development of seed quality, we measured maturity indices and conducted vigor tests on hybrid red cabbage (Brassica oleracea var capitata) seed harvested weekly starting 33 days after full bloom (DAF). Viability and germination rate increased from the top to the bottom of the raceme, and were maximal by 40 and 48 DAF, respectively. After 48 DAF, there was little difference in seed quality due to position on the raceme. Seed dry weight also reached a plateau by 48 DAF, when rapid dehydration began. Sensitivity of germination to inhibition by reduced water potential or abscisic acid (ABA) was assessed using a threshold model based upon germination rates. Germination became less sensitive to both factors and more uniform during maturation, with -1.0 MPa or 50 μM ABA being required to inhibit germination by 50% after about 48 DAF Seed ABA content reached a peak of 10 μg/g dry wt. by 40 DAF, then declined linearly to 1.5 μg/g dry wt. by 68 DAF Overall, optimal seed quality was attained at 54 DAF

Abscisic-acid in triazine-resistant and susceptible poa annua

Abscisic-acid (ABA) content in leaves and seeds were determined in two reciprocal hydbrids of cross between a triazine-resistant and a susceptible Poa annua. ABA in leaves appeared to be regulated by at least one major nuclear allele whilst ABA content in seeds appeared to maternally segregate with the cytoplasm. The lower ABA content found in seeds of the resistant parent and the resistant hybrid could be a secondary effect of the mutation that confers the resistance to the triazines.