Exogenous Application Of Abscisic Acid Research Articles

Use of ABA Treatment for the Activation of Drought Protective Mechanisms in Barley Under Non-stress Conditions

The present study evaluated the sensitivity of three different barley genotypes to stress simulated by the application of exogenous abscisic acid (20 µmol.l−1) at the early stage of the plant development. We used RIA method, instantaneous water use efficiency (WUE), the discrimination of 13C (Δ13C) and the expression levels of Dhn4 gene. The increase of ABA concentration in leaves after exogenous ABA application was detected in all tested genotypes; however, the lowest amount was found in the most tolerant genotype. Increased level of the instantaneous WUE after ABA treatment was found in all genotypes. The Δ13C in ABA treated plants decreased, however, relatively drought-tolerant genotype Tadmor showed lower discrimination even in control variant. The genotype-dependent differences were observed in the expression levels of Dhn4 gene in the leaves. High expression level of this gene was observed in Tadmor. Based on the exogenous ABA level, it was possible to distinguish two types of response of plants to exogenous ABA. Tadmor represented one of them as manifesting high sensitivity to exogenous ABA, leading to fast induction of Dhn4 gene relative expression. Conversely, spring genotypes of Jersey and Malz manifested slower response to exogenous ABA as well as lower WUE values and relative expression of Dhn4. The results supported the idea that ABA application may activate similar stress reactions in plants as drought conditions and additionally the intensity of this reaction is genotype dependent.

Physiological and Biochemical Processes of Magnolia wufengensis in Response to Foliar Abscisic Acid Application during Natural Cold Acclimation

The rare species Magnolia wufengensis frequently suffers from freezing injury in northern China. To investigate the influence of exogenous abscisic acid (ABA) application on the natural cold acclimation of M. wufengensis, physiological and biochemical changes in field-grown M. wufengensis seedlings subjected to foliar ABA treatments at four concentrations (0, 300, 600, and 900 mg·L−1) were evaluated from Sept. 2012 to Jan. 2013. The optimum foliar application concentrations of ABA for M. wufengensis were between 600 and 900 mg·L−1, which led to faster shoot growth cessation, leaf senescence, and development rates of bud endodormancy level and shoot freezing tolerance. The improved freezing tolerance under exogenous ABA application was associated with promoted dehydration and accumulation of proline, soluble protein, and certain soluble sugars such as glucose and fructose. Foliar ABA treatments initiated a cascade of steps for advancing the cold acclimation process of M. wufengensis. We suggest that exogenous ABA application may be used on M. wufengensis grown in northern China, where there are short growing seasons and early fall frost events.

Pulsing Treatments of Abscisic Acid and Sucrose for Improving Postharvest Quality of Cut Lily Flowers

Abscisic acid (ABA), as a senescence phytohormone, has been proved to be related to flower petal senescence in rose (Mayak and Halevy, 1972; Kumar et al., 2008) and carnation (Nowak and Veen, 1982). Higher ABA concentrations were found in short–lived cultivars compared to long–lived rose cultivars (Halevy and Mayak, 1975). Exogenous application of ABA leads to enhancement of aging–related process in daffodil petals (Hunter et al., 2004). ABA, as one of the preservation agents, was also applied in the fresh–keeping of cut roses (Kohl and Rundle, 1972), Baccara roses (Pompodakis and Joyce, 2003; Pompodakis et al., 2004) and Eustoma flowers (Shimizu–Yumoto and Ichimura, 2009). ABA prolongs the vase life of cut roses with leaves, but shortens the vase life of leafless cut roses (Halevy et al., 1974). ABA can regulate water balance of cut flower through controlling stomata opening, increase the postharvest quality, and extend the vase life of cut flowers (Kohl and Rundle, 1972; Pompodakis and Joyce, 2003; Pompodakis et al., 2004). On the other hand it has been reported that ABA regulates water balance through ways other than stomata opening regulation (Borohov et al., 1976), the application of ABA did not affect the transpiration (Ichimura and Shimizu–Yumoto, 2007). ABA treatment can alleviate the sucrose–induced leaf chlorosis and improve the quality of cut flowers (Pompodakis and Joyce, 2003; Shimizu–Yumoto and Ichimura, 2009). Lilies are the world famous cut flowers with high ornamental value. Yang et al. (1996) indicated that ABA probably is the main factor affecting senescence of cut lilies, because morphology of cut flowers showed senescence symptoms following the peak of ABA, while ethylene can accelerate the aging process only to a certain extent. But Li et al. (2012) indicated that the addition of lower concentrations of ABA with sucrose and 8–hydroxyquinoline citrate (8–HQC) induced the increase of fresh weight, and partly alleviate the sucrose–induced leaf yellowing. Based on the above researches, the preservation mechanism of ABA in cut lilies is still not clear. Lilium ‘Sorbonne’ (Oriental hybrid group) was used as an experimental material in this study to observe the preservation effect of ABA, and to confirm further the preservation mechanism of ABA by determining the physiological indices and ethylene release of cut ‘Sorbonnes’ petals during postharvest.

SISOM inhibits seed germination by regulating the expression of ABA/GA metabolic genes and SIABI5 in Solanum lycopersicum

SOM encodes a nucleus-localized CCCH-type zinc finger protein and negatively regulates seed germination in Arabidopsis thaliana. We have previously demonstrated that ectopic expression of SIABI3, an important transcription factor in abscisic acid (ABA) signaling pathway, resulted in alteration of SISOM expression patterns in both leaf and seed of tomato. In this study, we aimed to elucidate the function of tomato SISOM in regarding to seed germination and seedling development. Here, we constructed SISOM over-expression vector pBI121-SOM driven by CaMV 35S promoter, and the recombinant plasmid was incorporated into wild-type tomato by the method of Agrobacterium tumefaciens-mediated transformation. The result showed that over-expression of SISOM conferred enhanced responses to exogenous ABA application during seed germination and seedling development. In addition, ectopic expression of SISOM resulted in the alteration of expression level of ABA/GA (gibberellins) metabolic genes, such as SIABA1, SlCYP707A1, SlGA3ox2, and SIGA2ox4, in both leaf and seed. The ABA anabolic gene SIABA1 and the GA catabolic gene SIGA2ox4 were up-regulated while the ABA catabolic gene SICYP707A1 and the GA anabolic gene SIGA3ox2 were down-regulated. Compared to wild type, the expression level of SIABI5 was increased by about 40–50% in transgenic seeds while adding exogenous ABA treatment. These results support the notion that SISOM inhibits seed germination by regulating ABA/GA metabolic genes and SIABI5 expression in Solanum lycopersicum.

Reduced photosynthetic dark reaction triggered by ABA application increases intercellular CO2 concentration, generates H2O2 and promotes closure of stomata in ginger leaves

Exogenous abscisic acid application decreased stomatal conductance (Gs), net photosynthetic rate (Pn), photorespiration rate (Pr), carboxylation efficiency (CE), and actual photochemical efficiency (ΦPSII) but increased the Mehler reaction, antioxidant enzyme activities and H2O2 content in ginger leaves. The observed reopening of the stomata triggered by varying concentrations of external CO2 indicates that increased intercellular CO2 concentration (caused by decreased photosynthetic dark reaction activity) promotes stomatal closure under ABA content regulation. By comparing the relationships between H2O2 content, stomatal conductance and ABA content under well-watered conditions compared to osmotic drought stress conditions, we concluded that increased H2O2 content caused by exogenous ABA application also promoted stomata closure in ginger leaves. Thus, CO2 and H2O2 signalling promote more complete stomatal closure under the influence of ABA in ginger leaves.

Exogenous abscisic acid application decreases cadmium accumulation in Arabidopsis plants, which is associated with the inhibition of IRT1-mediated cadmium uptake.

Cadmium (Cd) contamination of agricultural soils is an increasingly serious problem. Measures need to be developed to minimize Cd entering the human food chain from contaminated soils. We report here that, under Cd exposure condition, application with low doses of (0.1–0.5 μM) abscisic acid (ABA) clearly inhibited Cd uptake by roots and decreased Cd level in Arabidopsis wild-type plants (Col-0). Expression of IRT1 in roots was also strongly inhibited by ABA treatment. Decrease in Cd uptake and the inhibition of IRT1 expression were clearly lesser pronounced in an ABA-insensitive double mutant snrk2.2/2.3 than in the Col-0 in response to ABA application. The ABA-decreased Cd uptake was found to correlate with the ABA-inhibited IRT1 expression in the roots of Col-0 plants fed two different levels of iron. Furthermore, the Cd uptake of irt1 mutants was barely affected by ABA application. These results indicated that inhibition of IRT1 expression is involved in the decrease of Cd uptake in response to exogenous ABA application. Interestingly, ABA application increased the iron level in both Col-0 plants and irt1 mutants, suggesting that ABA-increased Fe acquisition does not depend on the IRT1 function, but on the contrary, the ABA-mediated inhibition of IRT1 expression may be due to the elevation of iron level in plants. From our results, we concluded that ABA application might increase iron acquisition, followed by the decrease in Cd uptake by inhibition of IRT1 activity. Thus, for crop production in Cd contaminated soils, developing techniques based on ABA application potentially is a promising approach for reducing Cd accumulation in edible organs in plants.

A NAP-AAO3 regulatory module promotes chlorophyll degradation via ABA biosynthesis in Arabidopsis leaves.

Chlorophyll degradation is an important part of leaf senescence, but the underlying regulatory mechanisms are largely unknown. Excised leaves of an Arabidopsis thaliana NAC-LIKE, ACTIVATED BY AP3/PI (NAP) transcription factor mutant (nap) exhibited lower transcript levels of known chlorophyll degradation genes, STAY-GREEN1 (SGR1), NON-YELLOW COLORING1 (NYC1), PHEOPHYTINASE (PPH), and PHEIDE a OXYGENASE (PaO), and higher chlorophyll retention than the wild type during dark-induced senescence. Transcriptome coexpression analysis revealed that abscisic acid (ABA) metabolism/signaling genes were disproportionately represented among those positively correlated with NAP expression. ABA levels were abnormally low in nap leaves during extended darkness. The ABA biosynthetic genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE2, ABA DEFICIENT3, and ABSCISIC ALDEHYDE OXIDASE3 (AAO3) exhibited abnormally low transcript levels in dark-treated nap leaves. NAP transactivated the promoter of AAO3 in mesophyll cell protoplasts, and electrophoretic mobility shift assays showed that NAP can bind directly to a segment (-196 to -162 relative to the ATG start codon) of the AAO3 promoter. Exogenous application of ABA increased the transcript levels of SGR1, NYC1, PPH, and PaO and suppressed the stay-green phenotype of nap leaves during extended darkness. Overexpression of AAO3 in nap leaves also suppressed the stay-green phenotype under extended darkness. Collectively, the results show that NAP promotes chlorophyll degradation by enhancing transcription of AAO3, which leads to increased levels of the senescence-inducing hormone ABA.

Hg-responsive proteins identified in wheat seedlings using iTRAQ analysis and the role of ABA in Hg stress.

Wheat seedlings exposed to 100 μM HgCl2 for 3 days exhibited high-level mercury (Hg) accumulation, which led to inhibited growth, increased lipid peroxidation, and disrupted cellular ultrastructures. And root growth and ultrastructural changes of wheat seedlings were inhibited more severely than those of leaves. To identify the wheat protein response to Hg stress, the iTRAQ method was used to determine the proteome profiles of the roots and leaves of wheat seedlings exposed to high-Hg conditions. 249 proteins were identified with significantly altered abundance. 117 were found in roots and 132 in leaves. These proteins were classified into signal transduction, stress defense, carbohydrate metabolism, protein metabolism, energy production, and transport functional groups. The majority of proteins identified in Hg-stressed roots and leaves displayed differently altered abundance, revealing organ-specific differences in adaption to Hg stress. Pathway Studio software was used to identify the Hg-responsive protein interaction network that included 49 putative key proteins, and they were potentially regulated by abscisic acid (ABA). Exogenous ABA application conferred protection against Hg stress and increased activities of peroxidase enzyme, suggesting that it may be an important factor in the Hg signaling pathway. These findings can provide useful insights into the molecular mechanisms of Hg responses in higher plants.

A bHLH transcription factor regulates iron intake under Fe deficiency in chrysanthemum.

Iron (Fe) deficiency can represent a serious constraint on crop growth and productivity. A number of members of the bHLH transcription factor family are known to be involved in the plant Fe deficiency response. Plants have evolved two distinct uptake strategies when challenged by Fe deficiency: dicotyledonous and non-graminaceous species rely mostly on a reduction strategy regulated by bHLH transcription factors, whereas rice relies on a chelation strategy, also regulated by bHLH transcription factors. CmbHLH1, a bHLH transcription factor which is localized within the nucleus, was isolated from chrysanthemum. Its transcription was up-regulated both by Fe deficiency and by the exogenous application of abscisic acid. The roots of transgenic chrysanthemum plants in which CmbHLH1 was up-regulated were better able than those of the wild type chrysanthemum cultivar to acidify their immediate external environment by enhancing the transcription of the H+-ATPase encoding gene CmHA. However, there was no effect of the transgene on the efficiency of uptake of either manganese or zinc. Here, Chrysanthemum CmbHLH1 contributed to Fe uptake via H+-ATPase mediated acidification of the rhizosphere. ABA may be positively involved in the process.

Thylakoid membrane oxidoreductase LTO1/AtVKOR is involved in ABA-mediated response to osmotic stress in Arabidopsis.

Arabidopsis lumen thiol oxidoreductase 1 (LTO1)-the At4g35760 gene product-was previously found to be related to reactive oxygen species (ROS) accumulation. Here, we show that ROS accumulated in a mutant Arabidopsis line (lto1-2, mutant of LTO1/AtVKOR) under osmotic stress at a higher level than that observed in wild-type and transgenic complemented plants of the lto1-2 mutant (lto1-2C, transgenic complemented plants of lto1-2). Because ROS accumulation in osmotic stress is triggered by abscisic acid (ABA), an ABA-responsive gene, Annexin 1 (AnnAt1), was selected to study the response. Osmotic stress or exogenous ABA can significantly upregulate the transcription of AnnAt1 in wild-type and lto1-2C plants. Only a slight change in the transcriptional abundance of AnnAt1 was observed under osmotic stress in the lto1-2 mutant, but exogenous ABA application could increase the expression of AnnAt1, which suggested that exogenous ABA had a partial complementation role. Because the transcription of AnnAt1 is regulated by ABRE (ABA-responsive elements) binding proteins (AREBs)/ABRE binding factors (ABFs), the expression of AREBs/ABFs was also analyzed. The transcription of AREBs/ABFs in the lto1-2 mutant was not induced by osmotic stress but was significantly upregulated by exogenous ABA, which significantly differs from the wild-type and lto1-2C plant responses. Similarly, the expression of another ABA-responsive gene, RD29B (responsive to desiccation stress gene 29B), in the lto1-2 mutant was also upregulated by exogenous ABA. The partial complementation of mutants by ABA indicated that the ABA signal transduction pathway was not significantly affected in the lto1-2 mutant. Taken together, these results suggest that LTO1 is involved in ABA-mediated response to osmotic stress, possibly by affecting the biosynthesis of endogenous ABA.

Exogenous abscisic acid alleviates zinc uptake and accumulation in Populus × canescens exposed to excess zinc.

A greenhouse experiment was conducted to study whether exogenous abscisic acid (ABA) mediates the responses of poplars to excess zinc (Zn). Populus × canescens seedlings were treated with either basal or excess Zn levels and either 0 or 10 μm ABA. Excess Zn led to reduced photosynthetic rates, increased Zn accumulation, induced foliar ABA and salicylic acid (SA), decreased foliar gibberellin (GA3 ) and auxin (IAA), elevated root H2 O2 levels, and increased root ratios of glutathione (GSH) to GSSG and foliar ratios of ascorbate (ASC) to dehydroascorbate (DHA) in poplars. While exogenous ABA decreased foliar Zn concentrations with 7 d treatments, it increased levels of endogenous ABA, GA3 and SA in roots, and resulted in highly increased foliar ASC accumulation and ratios of ASC to DHA. The transcript levels of several genes involved in Zn uptake and detoxification, such as yellow stripe-like family protein 2 (YSL2) and plant cadmium resistance protein 2 (PCR2), were enhanced in poplar roots by excess Zn but repressed by exogenous ABA application. These results suggest that exogenous ABA can decrease Zn concentrations in P. × canescens under excess Zn for 7 d, likely by modulating the transcript levels of key genes involved in Zn uptake and detoxification.

Role of Abscisic Acid and Water Stress on the Activities of Antioxidant Enzymes in Wheat

Eight wheat varieties (Chinese Spring, Pavon, Gabo, Saleem-2000, Zamindar-04, Siren, NR-264 and Marvi) were compared for their response to exogenous application of abscisic acid (ABA), Water Stress (WS) and Control (C) during <em>invitro</em> condition. Their responses were studied in the form of seedlings growth and antioxidant enzymes. Exogenous application of ABA reflected ameliorating effect on catalase activity. Water stress treatment led to increase in levels of catalase except Pavon. Increased activity of antioxidant enzymes showed tolerance capacity under water stress. Correlation coefficient analysis reflected negative and significant relationship between total protein contents and peroxidase and catalase. Further, investigations are needed to enhance the understanding on the effect of different abiotic stresses and growth hormones during early seed development.

Transcriptional regulation of genes encoding ABA metabolism enzymes during the fruit development and dehydration stress of pear 'Gold Nijisseiki'

To investigate the contribution of abscisic acid (ABA) in pear 'Gold Nijisseiki' during fruit ripening and under dehydration stress, two cDNAs (PpNCED1 and PpNCED2) which encode 9-cis-epoxycarotenoid dioxygenase (NCED) (a key enzyme in ABA biosynthesis), two cDNAs (PpCYP707A1 and PpCYP707A2) which encode 8'-hydroxylase (a key enzyme in the oxidative catabolism of ABA), one cDNA (PpACS3) which encodes 1-aminocyclopropane-1-carboxylic acid (ACC), and one cDNA (PpACO1) which encodes ACC oxidase involved in ethylene biosynthesis were cloned from 'Gold Nijisseiki' fruit. In the pulp, peel and seed, expressions of PpNCED1 and PpNCED2 rose in two stages which corresponded with the increase of ABA levels. The expression of PpCYP707A1 dramatically declined after 60–90 days after full bloom (DAFB) in contrast to the changes of ABA levels during this period, while PpCYP707A2 stayed low during the whole development of fruit. Application of exogenous ABA at 100 DAFB increased the soluble sugar content and the ethylene release but significantly decreased the titratable acid and chlorophyll contents in fruits. When fruits harvested at 100 DAFB were stored in the laboratory (25 °C, 50% relative humidity), the ABA content and the expressions of PpNCED1/2 and PpCYP707A1 in the pulp, peel and seed increased significantly, while ethylene reached its highest value after the maximum peak of ABA accompanied with the expressions of PpACS3 and PpACO1. In sum the endogenous ABA may play an important role in the fruit ripening and dehydration of pear 'Gold Nijisseiki' and the ABA level was regulated mainly by the dynamics of PpNCED1, PpNCED2 and PpCYP707A1 at the transcriptional level.

Exogenous ABA induces drought tolerance in upland rice: the role of chloroplast and ABA biosynthesis-related gene expression on photosystem II during PEG stress

Abscisic acid (ABA) plays an important role in regulating photosynthesis under stress. To understand the differential function of exogenous ABA in the regulation of drought tolerance between two rice (Oryza sativa L.) genotypes, upland rice (UR, resistant to drought stress) and lowland rice (LR, susceptible to drought stress), photosynthetic parameters, chlorophyll fluorescence parameters, and the expression of chloroplast and ABA biosynthesis-related genes were investigated under 15 % polyethylene glycol (PEG) and exogenous ABA (60 µM) treatments. In both rice lines, most of the photosynthetic parameters, chlorophyll fluorescence parameters, and chloroplast and ABA biosynthesis-related gene transcript levels were rapidly reduced by PEG stress, with the exception of up-regulated levels of OsPsbA, OsNCED3, OsNCED4, and OsZEP in LR and OsNCED3, OsNCED4, and OsZEP in UR. Moreover, a rapid stress-responsive regulation mechanism was found in UR according to the more rapid and strong up-regulation of three ABA biosynthesis-related genes in UR than in LR. Under PEG stress, exogenous ABA application significantly enhanced the recovery of the net photosynthetic rate (P n), stomatal conductance (G s), and transpiration rate (T r) in UR, with increased expression of OsPsbD1, OsPsbD2, OsNCED2, OsNCED3, OsNCED4, and OsNCED5. These data suggest a role for chloroplast and ABA biosynthesis-related genes in photosystem II (PSII) induction by exogenous ABA in the UR genetic background.

Preharvest application of abscisic acid promotes anthocyanins accumulation in pericarp of litchi fruit without adversely affecting postharvest quality

Pericarp colour of litchi fruit is an important quality attribute that determines its market value and consumer acceptance. Plant growth regulators (PGR) such as abscisic acid (ABA) and ethephon are known to play important roles in peel colour development during maturation and ripening of non-climacteric fruits (e.g. grape and litchi). Our aim was to investigate the effects of preharvest application of ABA, ethephon and their combination on pericarp colour and fruit quality of litchi (cv. Calcuttia) and also to assess the potential effects on postharvest performance of fruit. Exogenous application of ABA (150 or 300mgL−1) at the colour-break stage significantly increased the concentration of total anthocyanins and cyanidin-3-O-rutinoside, the major anthocyanin contributing ∼71–96% of the total anthocyanins, in litchi pericarp compared to ethephon (500μLL−1). Among different anthocyanins quantified, the relative contribution of cyanidin-3,5-diglucoside to the total anthocyanins was significantly higher in all PGR-treated fruit compared to the control, but the concentration of cyanidin-3-O-glucoside was specifically enhanced by ABA. No significant effect on the concentrations of epicatechin, and quercetin-3-O-rutinoside was observed in response to PGR treatments. Ethephon (500μLL−1) treatment did not significantly increase the anthocyanin levels in pericarp, but it caused more degradation of chlorophyll pigments than control. Aril quality with regard to firmness, soluble solids and acidity was not significantly affected by PGR treatments, except that ethephon-treated fruit showed significant softening and lower acidity. Postharvest changes in fruit quality attributes including pericarp browning during cold storage at 5°C for 14 d were mainly related to the storage duration effect, rather than PGR treatment. In conclusion, ABA treatment (150 or 300mgL−1) at the colour-break stage enhanced anthocyanins accumulation in litchi pericarp without adversely affecting postharvest quality and storage stability for 14 d.

Abscisic Acid Increases Carotenoid and Chlorophyll Concentrations in Leaves and Fruit of Two Tomato Genotypes

One important regulator that coordinates response to environmental stress is the hormone abscisic acid (ABA), which is synthesized from xanthophyll pigments. Despite the fact that there is strong evidence of increases in ABA concentrations under various environmental stresses, information concerning the effects of exogenous ABA applications on leaf pigments and fruit carotenoids in tomato (Solanum lycopersicum) is lacking. This study investigated the impacts of root tissue ABA applications on tomato leaf and fruit pigmentation concentrations of ‘MicroTina’ and ‘MicroGold’ tomato plants. Tomato plants were treated with increasing concentrations of ABA in the nutrient solution. Therefore, the purpose of this study was to determine dose–response effects of ABA treatment in solution culture for maximum leaf pigmentation and fruit carotenoids in two distinct genotypes of dwarf tomato. Because ABA is a product of the carotenoid biosynthetic pathway, we hypothesized that applications of ABA treatments would have a positive impact on leaf chlorophylls and carotenoids. Applications of ABA treatments may also have a positive impact on tomato fruit carotenoids. The results indicated that ‘MicroTina’ plants treated with ABA (0.5, 5.0, and 10.0 mg·L−1) had a significant increase in β-carotene [BC (P ≤ 0.001)], lutein [LUT (P ≤ 0.001)], zeaxanthin [ZEA (P ≤ 0.05)], and neoxanthin [NEO (P ≤ 0.001)] in the leaf tissue. In ‘MicroGold’ tomato plants, carotenoids responded similarly. For example, there were significant increases in BC (P ≤ 0.01), LUT (P ≤ 0.001), ZEA (P ≤ 0.05), and NEO (P ≤ 0.001). In ‘MicroTina’ tomato leaves, there were significant increases in chlorophyll a [Chl a (P ≤ 0.001)] and chlorophyll b [Chl b (P ≤ 0.001)] concentrations. Furthermore, there were significant increases in Chl a (P ≤ 0.001) and Chl b (P ≤ 0.001) in ‘MicroGold’ leaf tissue. In ‘MicroTina’ tomato fruit tissue, the concentration increased significantly for lycopene [LYCO (P ≤ 0.01)]. However, in ‘MicroGold’, there were no significant changes in BC and LUT concentrations. In addition, LYCO was found to be below detection limits in ‘MicroGold’ tomato fruit. Therefore, ABA has been shown to positively change tomato leaf pigments in both genotypes and fruit tissue carotenoid concentrations in ‘MicroTina’ tomato.

Exogenous Abscisic Acid Application During Grain Filling in Winter Wheat Improves Cold Tolerance of Offspring's Seedlings

AbstractLow temperature seriously depresses seed germination and seedling growth in winter wheat (Triticum aestivum L.). In this study, wheat plants were sprayed with abscisic acid (ABA) and fluridone (inhibitor of ABA biosynthesis) at 19 days after anthesis (DAA) and repeated at 26 DAA. The seeds of those plants were harvested, and seed germination and offspring's seedling growth under low temperature were evaluated. The results showed that exogenous ABA application decreased seed weight and slightly reduced seed set and seed number per spike. Under low temperature, seeds from ABA‐treated plants showed reduced germination rate, germination index, growth of radicle and coleoptile, amylase activity and depressed starch degradation as compared with seeds from non‐ABA‐treated plants; however, activities of the antioxidant enzymes in both germinating seeds and seedling were enhanced from those exposed to exogenous ABA, resulting in much lowered malondialdehyde (MDA) and H2O2 concentrations and production rate. In addition, the maximum quantum efficiency of photosystem II was also enhanced in ABA‐treated offspring's seedlings. It is concluded that exogenous ABA treatment at later grain‐filling stage could be an effective approach to improve cold tolerance of the offspring during seed germinating and seedlings establishment in winter wheat.

Translation initiation factor 5A in Picrorhiza is up-regulated during leaf senescence and in response to abscisic acid

Translation initiation, the first step of protein synthesis process is the principal regulatory step controlling translation and involves a pool of translation initiation factors. In plants, from recent studies it is becoming evident that these translation initiation factors impact various aspects of plant growth and development in addition to their role in protein synthesis. Eukaryotic translation initiation factor eIF5A is one such factor which functions in start site selection for the eIF2-GTP-tRNAi ternary complex within the ribosomal-bound preinitiation complex and also stabilizes the binding of GDP to eIF2. In the present study we have cloned and analysed a gene (eIF5a) encoding eIF5A from Picrorhiza (Picrorhiza kurrooa Royle ex Benth.) a medicinal plant of the western Himalayan region. The full length eIF5a cDNA consisted of 838 bp with an open reading frame of 480 bp, 88 bp 5' untranslated region and 270 bp 3' untranslated region. The deduced eIF5A protein contained 159 amino acids with a molecular weight of 17.359 kDa and an isoelectric point of 5.59. Secondary structure analysis revealed eIF5A having 24.53% α-helices, 8.81% β-turns, 23.27% extended strands and 43.40% random coils. pk-eIF5a transcript was found to be expressing during the active growth phase as well as during leaf senescence stage, however, highest expression was observed during leaf senescence stage. Further, its expression was up-regulated in response to exogenous application of abscisic acid. Both high intensity as well as low intensity light decreased the expression of pk-eIF5a. The findings suggest eIF5a to be an important candidate to develop genetic engineering based strategies for delaying leaf senescence.

Abscisic Acid Regulates Early Seed Development in Arabidopsis by ABI5-Mediated Transcription of SHORT HYPOCOTYL UNDER BLUE1

Seed development includes an early stage of endosperm proliferation and a late stage of embryo growth at the expense of the endosperm in Arabidopsis thaliana. Abscisic acid (ABA) has known functions during late seed development, but its roles in early seed development remain elusive. In this study, we report that ABA-deficient mutants produced seeds with increased size, mass, and embryo cell number but delayed endosperm cellularization. ABSCISIC ACID DEFICIENT2 (ABA2) encodes a unique short-chain dehydrogenase/reductase that functions in ABA biosynthesis, and its expression pattern overlaps that of SHORT HYPOCOTYL UNDER BLUE1 (SHB1) during seed development. SHB1 RNA accumulation was significantly upregulated in the aba2-1 mutant and was downregulated by the application of exogenous ABA. Furthermore, RNA accumulation of the basic/region leucine zipper transcription factor ABSCISIC ACID-INSENSITIVE5 (ABI5), involved in ABA signaling, was decreased in aba2-1. Consistent with this, seed size was also increased in abi5. We further show that ABI5 directly binds to two discrete regions in the SHB1 promoter. Our results suggest that ABA negatively regulates SHB1 expression, at least in part, through the action of its downstream signaling component ABI5. Our findings provide insights into the molecular mechanisms by which ABA regulates early seed development.

Effects of exogenous ABA application on post-anthesis dry matter redistribution and grain starch accumulation of winter wheat with different staygreen characteristics

The objective of this study was to investigate whether and how exogenous abscisic acid (ABA) is involved in mediating starch accumulation in the grain and redistribution of carbohydrates during grain filling of two wheat cultivars with different staygreen characteristics. At blooming stage, plants of Wennong 6 (a staygreen cultivar) and Jimai 20 (control) were sprayed with 10mgL−1 abscisic acid (ABA) for 3days. The application of ABA significantly (P<0.05) increased grain filling rate, starch accumulation rate and content, remobilization of dry matters to kernels, and 1000-grain weight of the two cultivars. Exogenous ABA markedly (P<0.05) increased grain yield at maturity, and Wennong 6 and Jiami 20 showed 14.14% and 4.86% higher compared yield than the control. Dry matter accumulation after anthesis of Wennong 6 was also significantly (P<0.05) influenced by exogenous ABA, whereas that of Jimai 20 was unchanged. Application of ABA increased endogenous zeatin riboside (ZR) content 7days after anthesis (DAA), and spraying ABA significantly increased endogenous indole-3-acetic acid (IAA) and ABA contents from 7 to 21 DAA and decreased gibberellin (GA3) content at 14 DAA, but increased GA3 content from 21 to 35 DAA. The results suggested that increased yield of staygreen was due to greater starch assimilation owing to a higher filling rate and longer grain-filling duration.