Higher Abscisic Acid Content Research Articles

Exogenous Abscisic Acid Alleviates Harmful Effect of Salt and Alkali Stresses on Wheat Seedlings.

Exogenous hormones play an important role in plant growth regulation and stress tolerance. However, little is known about the effect of exogenous abscisic acid (ABA) on wheat seedlings under salt and alkali stresses. Here, a pot experiment of saline and alkaline stresses (0 and 100 mmol/L) in which ABA water solution (0, 50 and 100 μmol/L) was sprayed on wheat seedlings was conducted to study the alleviative effectiveness of ABA on salt and alkali stresses. After spraying ABA (50 μmol·L−1), shoot biomass increased 19.0% and 26.7%, respectively. The Na+ content in shoots reduced from 15-fold and 61.5-fold to 10-fold and 37.3-fold in salt and alkali stresses, compared to controls. In addition, proline and organic acid synthesis in shoots also reduced significantly, but the soluble sugar content increased under alkali stress. A high concentration of ABA (100 μmol·L−1) had no significant effects on biomass and ion content in wheat seedlings under both stresses. In conclusion, foliar application of ABA with moderate concentration could effectively accelerate shoot growth of salt-induced wheat seedlings by adjusting the levels of ions and organic solutes.

Metabolomic and transcriptomic profiling of three types of litchi pericarps reveals that changes in the hormone balance constitute the molecular basis of the fruit cracking susceptibility of Litchi chinensis cv. Baitangying

Many Litchi chinensis cv. Baitangying orchards are suffering from a serious fruit cracking problem, but few studies have improved our understanding of the mechanism or the molecular basis of cracking susceptibility in 'Baitangying'. We conducted metabolome and transcriptome analyses of three types of litchi pericarps. To prevent passive progression after fruit cracking from affecting the results, we mainly focused on 11 metabolites and 101 genes that showed the same regulatory status and overlap in pairwise comparisons of cracking 'Baitangying' versus noncracking 'Baitangying' and noncracking 'Baitangying' versus noncracking 'Feizixiao'. Compared with the cracking-resistant cultivar 'Feizixiao', the 'Baitangying' pericarp has higher abscisic acid contents, and the presence of relevant metabolites and genes suggests increased biosynthesis of ethylene and jasmonic acid and decreased auxin and brassinosteroid biosynthesis. The fruit cracking-susceptible trait in 'Baitangying' might be associated with differences in the balance of these five types of hormones between the pericarp of this cultivar and that of 'Feizixiao'. Additionally, combined analyses showed a correspondence between the metabolite profiles and transcript patterns. qRT-PCR validation indicated the reliability of our high-throughput results. The acquired information might help in further studying the mechanisms that mediate fruit cracking susceptibility in 'Baitangying' and other litchi cultivars.

Salinity and ABA Seed Responses in Pepper: Expression and Interaction of ABA Core Signaling Components.

Abscisic acid (ABA) plays an important role in various aspects of plant growth and development, including adaptation to stresses, fruit development and ripening. In seeds, ABA participates through its core signaling components in dormancy instauration, longevity determination, and inhibition of germination in unfavorable environmental conditions such as high soil salinity. Here, we show that seed germination in pepper was delayed but only marginally reduced by ABA or NaCl with respect to control treatments. Through a similarity search, pepper orthologs of ABA core signaling components PYL (PYRABACTIN RESISTANCE1-LIKE), PP2C (PROTEIN PHOSPHATASE2C), and SnRK2 (SUCROSE NONFERMENTING1 (SNF1)-RELATED PROTEIN KINASE2) genes were identified. Gene expression analyses of selected members showed a low abundance of PYL and SnRK2 transcripts in dry seeds compared to other tissues, and an up-regulation at high concentrations of ABA and/or NaCl for both positive and negative regulators of ABA signaling. As expected, in hydroponically-grown seedlings exposed to NaCl, only PP2C encoding genes were up-regulated. Yeast two hybrid assays performed among putative pepper core components and with Arabidopsis thaliana orthologs confirmed the ability of the identified proteins to function in ABA signaling cascade, with the exception of a CaABI isoform cloned from seeds. BiFC assay in planta confirmed some of the interactions obtained in yeast. Altogether, our results indicate that a low expression of perception and signaling components in pepper seeds might contribute to explain the observed high percentages of seed germination in the presence of ABA. These results might have direct implications on the improvement of seed longevity and vigor, a bottleneck in pepper breeding.

Specific roles of Os4BGlu10, Os6BGlu24, and Os9BGlu33 in seed germination, root elongation, and drought tolerance in rice.

Morphological, physiological, and gene expression analyses showed that Os4BGlu10, Os6BGlu24, and Os9BGlu33 played specific roles in seed germination, root elongation, and drought tolerance of rice, with various relations with indole-3-acetic acid (IAA) and abscisic acid (ABA) signaling. β-Glucosidases (BGlus) belong to glycoside hydrolase family 1 and have many functions in plants. In this study, we investigated the function of three BGlus in seed germination, drought tolerance, and root elongation using the loss-of-function mutants bglu10, bglu24, and bglu33. These mutants germinated slightly later under normal conditions and had significantly longer roots than the wild type. In the presence of ABA, bglu10 and bglu24 exhibited a higher germination inhibition percentage, whereas bglu33 had a lower germination inhibition percentage, compared to the wild type. All of the mutants exhibited less drought tolerance, with the survival rates significantly lower than that of the wild type, which was also confirmed by a decrease in relative leaf water content and Fv/Fm ratio after drought treatment. The root length of bglu10 did not respond to IAA, whereas that of bglu24 responded to a high (0.25µM) concentration of IAA, and that of bglu33 to a low (0.05µM) concentration of IAA. The root length of bglu10 and bglu24 did not respond to ABA, whereas that of bglu33 increased significantly in response to a high (0.05µM) concentration of ABA. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that expression of Os4BGlu10 was up-regulated by polyethylene glycol (PEG), whereas that of Os6BGlu24 was up-regulated by 0.25µM IAA, and Os9BGlu33 was up-regulated by PEG, IAA, and ABA. Taken together, we demonstrate that Os4BGlu10, Os6BGlu24, and Os9BGlu33 play specific roles in seed germination, root elongation, and drought tolerance with various relation with IAA and ABA signaling.

Abscisic acid stimulates the release of insulin and of GLP‐1 in the rat perfused pancreas and intestine

Previous results indicate that nanomolar concentrations of abscisic acid (ABA) stimulate insulin release from β-pancreatic cells in vitro and that oral ABA at 50mg/kg increases plasma GLP-1 in the fasted rat. The aim of this study was to test the effect of ABA on the perfused rat pancreas and intestine, to verify the insulin- and incretin-releasing actions of ABA in controlled physiological models. Rat pancreas and small intestine were perfused with solutions containing ABA at high-micromolar concentrations, or control secretagogues. Insulin and GLP-1 concentrations in the venous effluent were analysed by radioimmunoassay, and ABA levels were determined by ELISA. High micromolar concentrations of ABA induced GLP-1 secretion from the proximal half of the small intestine and insulin secretion from pancreas. GLP-1 stimulated ABA secretion from pancreas in a biphasic manner. Notably, a positive correlation was found between the ABA area under the curve (AUC) and the insulin AUC upon GLP-1 administration. Our results indicate the existence of a cross talk between GLP-1 and ABA, whereby ABA stimulates GLP-1 secretion, and vice versa. Release of ABA could be considered as a new promising molecule in the strategy of type 2 diabetes treatment and as a new endogenous hormone in the regulation of glycaemia.

Optimized potassium nutrition improves plant-water-relations of barley under PEG-induced osmotic stress

Water use efficiency (WUE) of crop plants is an important plant trait for maintaining high yield in water limited areas. By influencing osmoregulation of plants, potassium (K) plays a critical role in stress avoidance and adaptation. However, whole plant physiological mechanisms modulated by K supply in respect of plant drought tolerance and water use efficiency are not well understood. In the present study, growth, development and transpiration dynamics of two barley cultivars were evaluated with and without PEG-induced osmotic stress using an automated balance system and image based leaf area determination. Experiments were conducted to study the effects of varied K supply under different osmotic stress treatments on a wide range of morphological, biochemical and physiological characteristics of barley plants such as leaf area development, daily whole plant transpiration rate (DTR), stomatal conductance (gs), assimilation rate (AN), biomass and leaf water use efficiency (WUE) as well as foliar abscisic acid (ABA) concentrations. Two barley cultivars (cv. Sahin-91 and cv. Milford) were treated with two K supply levels (0.04 and 0.8 mM K) and osmotic stress induced by polyethylene glycol 6000 (PEG) for a period of 9 days (in total 48 days experiment) in the hydroponic plant culture (non-PEG and + 20% PEG ). Without PEG, low-K supply depressed dry matter (DM) by almost 60% averaged across both cultivars. Under osmotic stress (+PEG), total leaf area was reduced by almost 70% in low-K compared to adequate-K plants. Low K concentration under PEG stress was correlated with higher ABA concentration and was correlated with lower leaf- and whole plant transpiration rate. Biomass-WUE under low K supply decreased significantly in both barley cultivars, to a greater extent in cv. Milford under osmotic stress. However, leaf-WUE was not affected by K supply in the absence of osmotic stress. It was suggested that reduced biomass-WUE in low-K treated barley plants was not related to inefficient stomatal control under K deficiency, but instead due to reduced assimilation rate. It was further hypothesized that under low K supply, a number of energy consuming activities reduce biomass-WUE, which are not distinguished by measuring leaf-WUE. This study showed that low K supply under osmotic stress increases foliar ABA concentration thereby decreasing plant transpiration.

Molecular characterization and expression analysis of the gene for zeaxanthin epoxidase from ‘Yinhong’ grape (Vitis vinifera L.)

The dual-function monooxygenase zeaxanthin epoxidase (ZEP) is embedded in the thylakoid membrane and positioned on one side of the thylakoid membrane matrix. In this study, ZEP cDNA was cloned and the specific expression vector PBI121-VvZEP was constructed to study the enzymatic control of abscisic acid (ABA) synthesis. We hypothesized that the VvZEP genes can be transferred into Arabidopsis thaliana (L.) Heynh plants via the Agrobacterium-mediated impregnation method. ZEP was cloned from the ‘Yinhong’ grape (Vitis vinifera L.) cultivar and designated as VvZEP. Quantitative real-time polymerase chain reaction analyses showed that grape accumulated higher levels of VvZEP mRNA during the later stages of development than during early stages. VvZEP transcripts were detected in all parts of the analyzed grape plant, although the highest levels were found in the fruits. Gas chromatography analysis of ABA showed the highest ABA concentration in ripe fruits. Transgenic analysis revealed that VvZEP was successfully transformed into A. thaliana and showed no obvious effects on seed germination. The flowering stage and time of seed maturity were significantly increased in transgenic Arabidopsis. Our results will help elucidate the effects of overexpression of the VvZEP gene on the ripening stage of grape.

The Role of Plant Abiotic Factors on the Interactions Between Cnaphalocrocis medinalis (Lepidoptera: Crambidae) and its Host Plant.

Atmospheric temperature increases along with increasing atmospheric CO2 concentration. This is a major concern for agroecosystems. Although the impact of an elevated temperature or increased CO2 has been widely reported, there are few studies investigating the combined effect of these two environmental factors on plant-insect interactions. In this study, plant responses (phenological traits, defensive enzyme activity, secondary compounds, defense-related gene expression and phytohormone) of Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae) -susceptible and resistant rice under various conditions (environment, soil type, variety, C. medinalis infestation) were used to examine the rice-C. medinalis interaction. The results showed that leaf chlorophyll content and trichome density in rice were variety-dependent. Plant defensive enzyme activities were affected environment, variety, or C. medinalis infestation. In addition, total phenolic content of rice leaves was decreased by elevated CO2 and temperature and C. medinalis infestation. Defense-related gene expression patterns were affected by environment, soil type, or C. medinalis infestation. Abscisic acid and salicylic acid content were decreased by C. medinalis infestation. However, jasmonic acid content was increased by C. medinalis infestation. Furthermore, under elevated CO2 and temperature, rice plants had higher abscisic acid content than plants under ambient conditions. The adult morphological traits of C. medinalis also were affected by environment. Under elevated CO2 and temperature, C. medinalis adults had greater body length in the second and third generations. Taken together these results indicated that elevated CO2 and temperature not only affects plants but also the specialized insects that feed on them.

INFLUENCE OF EXOGENOUS APPLICATION OF ABSCISIC ACID IN GAS EXCHANGES OF Hymenaea courbaril L. (FABACEAE) SEEDLINGS SUBJECTED TO WATER DEFICIT

This study was carried out in the greenhouse of the Federal University of Grande Dourados (UFGD), in the municipality of Dourados, state of Mato Grosso do Sul, Brazil, from April to May of 2015. The aim of this study was to assess the effect of different concentrations of abscisic acid (ABA) on the responses under water stress and recovery of Hymenaea courbaril L. seedlings after reirrigation. The following six treatments were assessed: 1) Irrigation with no ABA; 2) Irrigation + 10 µM ABA; 3) Irrigation + 100 µM ABA; 4) No irrigation nor ABA; 5) No irrigation + 10 µM ABA; and 6) No irrigation + 100 µM ABA. No irrigation treatment consisted on water suspension until the photosynthetic rate was close to zero. The plants were then irrigated daily to maintain 70% of the water holding capacity of the soil for a 12-days recovery period. ABA doses applied exogenously during the no irrigation period neither prevented the reduction of photosynthetic activity nor optimized the recovery of gas exchanges and carboxylation efficiency of Rubisco after water and seedling quality restoration. The concentration of 100 µM ABA promoted the degradation of chlorophylls independently of irrigation, which shows that high concentrations of ABA may cause a residual effect on this species. The seedlings exhibited normal metabolic recovery after about 12 days of reirrigation of the soil due to the characteristics of the species and not the tested treatments.

The varied ability of grains to synthesize and catabolize ABA is one of the factors affecting dormancy and its release by after-ripening in imbibed triticale grains of cultivars with different pre-harvest sprouting susceptibilities

Abscisic acid (ABA) is a phytohormone involved in the acquisition of primary dormancy during seeds maturation as well as dormancy maintenance in imbibed seeds. After imbibition, the ABA content decreased to a much lower level in embryos of freshly harvested triticale grains of the Leontino cultivar, which is more susceptible to pre-harvest sprouting (PHS) than embryos of the Fredro cultivar. Lower ABA content in the Leontino cultivar resulted from increased expression of TsABA8′OH1 and TsABA8′OH2, which encode ABA 8′-hydroxylase and are involved in ABA catabolism. Higher ABA content and maintenance of dormancy in Fredro grains were correlated with intensified ABA biosynthesis, which resulted from higher expression of TsNCED1, which encodes 9-cis-epoxycarotenoid dioxygenase. These results suggest that grains of triticale cultivars with different resistance to PHS vary in their ability to metabolize ABA after imbibition.After-ripening did not affect the ABA content in embryos of dry grains of either triticale cultivar. However, after-ripening caused dormancy release in Fredro grains and significantly affected the ABA content and the rate of its metabolism after imbibition. A more rapid decline in ABA content in imbibed Fredro grains was accompanied by decreased transcript levels of TsNCED1 as well as increased expression of TsABA8′OH1 and TsABA8′OH2. Thus, after-ripening may affect dormancy of grains through reduction of the ABA biosynthesis rate and intensified ABA catabolism.Overexpression of TsNCED1 in tobacco increases ABA content and delays germination, while overexpression of TsABA8′OH2 decreases ABA content, accelerates germination, and reduces the sensitivity to ABA of transgenic seeds compared to seeds of wild-type plants. Therefore, these genes might play an important role in the regulation of triticale grain dormancy, thus affecting susceptibility to PHS.

Abscisic acid and its metabolites are involved in drought tolerance in four native species of Patagonian semiarid shrublands (Argentina)

Drought is the main stress that affects growth of native species of Patagonian Monte. Physiological and biochemical traits with functional roles in adaptation to drought are still scarce in native species. The aim of this study was to evaluate changes in dry matter content and abscisic acid (ABA) and its metabolites (phaseic acid-PA, dihydrophaseic acid-DPA, ABA conjugated with glucose-ABA-GE) level in green leaves and fine roots of four native species during contrasting seasons regarding water availability. Results show that grasses had higher leaf dry matter content (LDMC) and root dry matter content (RDMC) than Lycium chilense shrub and LDMC decreased during autumn in Larrea divaricata. In green leaves, there was an interaction between species and seasons for ABA and PA contents. L. divaricata had high ABA content during spring and low ABA content during autumn; while L. chilense showed the opposite pattern. During spring, drought tolerant species had high PA content while drought avoidant species had low PA content, and during autumn these species showed the opposite pattern. ABA-GE content was highest in L. chilense green leaves. In fine roots, ABA content was highest in L. divaricata and during spring PA was higher in L. divaricata than P. ligularis and L. chilense. PA was the only metabolite that decreased in L. divaricata during autumn. Results showed that ABA homeostasis maintains the functioning of different life forms with different drought resistance strategies in Patagonia semiarid shrublands. In green leaves of the drought avoidant L. chilense shrub, the ABA conjugation pathway was active in both seasons. During spring, the most drought tolerant L. divaricata showed highest activation of ABA synthesis and ABA oxidation pathways. During autumn L. chilense showed highest activation of ABA synthesis and together with P. ligularis showed active the ABA oxidation pathway.

Differences in seed dormancy associated with the domestication ofCucurbita maxima: elucidation of some mechanisms behind this response

AbstractThis work presents the results of physiological studies developed to understand modifications linked to the reduction of seed dormancy provoked by domestication processes. The experiments performed compared wild and domesticatedCucurbitasubspecies and their hybrids developed by reciprocal crossings. Seeds of two accessions of the wild subspecies presented dormancy, but it was largely reduced in seeds from the domesticated genotype, and partially reverted in hybrids, especially in those obtained when the domesticated genotype was used as the mother plant. In addition, naked embryos of all subspecies did not display dormancy when incubation was performed at 28°C, but embryo germination was progressively reduced only in the wild genotype under decreasing incubation temperatures (22 and 16°C). In the embryos, abscisic acid (ABA) concentrations were similar in both domesticated and wild subspecies, whereas in the seed coat, it was threefold higher in the wild subspecies. The naked embryos from the wild subspecies were far more responsive to ABA than those from the domesticated subspecies. These results indicate that dormancy in the wild subspecies is imposed by the seed coat tissues and that this effect is mediated by their high ABA content and the sensitivity of the embryos to ABA. These physiological aspects were apparently removed by domestication along with the temperature-dependent response for germination.

Ectopic Expression of Pumpkin NAC Transcription Factor CmNAC1 Improves Multiple Abiotic Stress Tolerance in Arabidopsis.

Drought, cold and salinity are the major environmental stresses that limit agricultural productivity. NAC transcription factors regulate the stress response in plants. Pumpkin (Cucurbita moschata) is an important cucurbit vegetable crop and it has strong resistance to abiotic stress; however, the biological functions of stress-related NAC genes in this crop are largely unknown. This study reports the function of CmNAC1, a stress-responsive pumpkin NAC domain protein. The CmNAC1-GFP fusion protein was transiently expressed in tobacco leaves for subcellular localization analysis, and we found that CmNAC1 is localized in the nucleus. Transactivation assay in yeast cells revealed that CmNAC1 functions as a transcription activator, and its transactivation domain is located in the C-terminus. CmNAC1 was ubiquitously expressed in different organs, and its transcript was induced by salinity, cold, dehydration, H2O2, and abscisic acid (ABA) treatment. Furthermore, the ectopic expression (EE) of CmNAC1 in Arabidopsis led to ABA hypersensitivity and enhanced tolerance to salinity, drought and cold stress. In addition, five ABA-responsive elements were enriched in CmNAC1 promoter. The CmNAC1-EE plants exhibited different root architecture, leaf morphology, and significantly high concentration of ABA compared with WT Arabidopsis under normal conditions. Our results indicated that CmNAC1 is a critical factor in ABA signaling pathways and it can be utilized in transgenic breeding to improve the abiotic stress tolerance of crops.

Abscisic acid treatment to avoid late spring frosts damage during ‘Chardonnay’ vines budbreak

The production of early budbreak Vitis vinifera L. cultivars in southern Brazilian highlands has been limited by the occurrence of late spring frosts. This study aimed to evaluate the abscisic acid (ABA) application on different dates to delay 'Chardonnay' vines budbreak, avoiding periods of greatest probability of frost occurrence. Experiments were carried out in a commercial vineyard, in Sao Joaquim, Santa Catarina, Brazil, at 1,270 m a.s.l., 1,270 m altitude, 28°14'51”S, 49°57'42”W, in two cycles. Five ABA concentrations were adopted on each cycle, ranging from 0 to 2000 mg L-1 and applications were made on the traditional date of pruning, which in this area represents the time when budbreak starts on shoots' apical buds, and two anticipated dates up to thirty days from this last. ABA was incorporated into lanolin and the resulting ointment was applied on the top of pruned shoots. On 2012/2013 cycle, vines treated 22 days before traditional date of pruning (DBP) sprouted in 29 days after treatment (DAT), while those treated on traditional pruning date sprouted in 18 DAT. The maximum delay observed with ABA comparing to control was four days. Treatments applied 30 DBP on 2013/2014 cycle resulted in sprouting in 37 DAT, while treatments applied on traditional pruning date, in 15 DAT. Control vines sprouted in 25 DAT and those treated with 2000 mg L-1 ABA in 28 DAT, delaying budbreak by three days. The latest pruning date and the highest ABA concentration (2000 mg L-1) presented better effect on vine budbreak delay. Changes were in general more expressively caused by the change in application dates. There were no problems with non-broken buds and the production was only slightly changed by ABA treatments. ABA application through this methodology was little effective on delaying grapevines budbreak and is not recommended for commercial use.

Cytokinins and Abscisic Acid Act Antagonistically in the Regulation of the Bud Outgrowth Pattern by Light Intensity.

Bud outgrowth is a key process in the elaboration of yield and visual quality in rose crops. Although light intensity is well known to affect bud outgrowth, little is known on the mechanisms involved in this regulation. The objective of this work was to test if the control of bud outgrowth pattern along the stem by photosynthetic photon flux density (PPFD) is mediated by sugars, cytokinins and/or abscisic acid in intact rose plants. Rooted cuttings of Rosa hybrida ‘Radrazz’ were grown in growth chambers under high PPFD (530 μmol m-2 s-1) until the floral bud visible stage. Plants were then either placed under low PPFD (90 μmol m-2 s-1) or maintained under high PPFD. Bud outgrowth inhibition by low PPFD was associated with lower cytokinin and sugar contents and a higher abscisic acid content in the stem. Interestingly, cytokinin supply to the stem restored bud outgrowth under low PPFD. On the other hand, abscisic acid supply inhibited outgrowth under high PPFD and antagonized bud outgrowth stimulation by cytokinins under low PPFD. In contrast, application of sugars did not restore bud outgrowth under low PPFD. These results suggest that PPFD regulation of bud outgrowth in rose involves a signaling pathway in which cytokinins and abscisic acid play antagonistic roles. Sugars can act as nutritional and signaling compounds and may be involved too, but do not appear as the main regulator of the response to PPFD.

The Biphasic Root Growth Response to Abscisic Acid in Arabidopsis Involves Interaction with Ethylene and Auxin Signalling Pathways.

Exogenous abscisic acid (ABA) is known to either stimulate or inhibit root growth, depending on its concentration. In this study, the roles of ethylene and auxin in this biphasic effect of ABA on root elongation were investigated using chemical inhibitors and mutants. Inhibitors of ethylene perception and biosynthesis and an auxin influx inhibitor were all found to block the inhibitory effect of high ABA concentrations, but not the stimulatory effect of low ABA concentrations. In addition, three ethylene-insensitive mutants (etr1-1, ein2-1, and ein3-1), two auxin influx mutants (aux1-7, aux1-T) and an auxin-insensitive mutant (iaa7/axr2-1) were all insensitive to the inhibitory effect of high ABA concentrations. In the case of the stimulatory effect of low ABA concentrations, it was blocked by two different auxin efflux inhibitors and was less pronounced in an auxin efflux mutant (pin2/eir1-1) and in the iaa7/axr2-1 auxin-insensitive mutant. Thus it appears that the stimulatory effect seen at low ABA concentrations is via an ethylene-independent pathway requiring auxin signalling and auxin efflux through PIN2/EIR1, while the inhibitory effect at high ABA concentrations is via an ethylene-dependent pathway requiring auxin signalling and auxin influx through AUX1.

Regulation of maize kernel weight and carbohydrate metabolism by abscisic acid applied at the early and middle post-pollination stages in vitro

Abscisic acid (ABA) accumulates in plants under drought stress, but views on the role of ABA in kernel formation and abortion are not unified. The response of the developing maize kernel to exogenous ABA was investigated by excising kernels from cob sections at four days after pollination and culturing in vitro with different concentrations of ABA (0, 5, 10, 100μM). When ABA was applied at the early post-pollination stage (EPPS), significant weight loss was observed at high ABA concentration (100μM), which could be attributed to jointly affected sink capacity and activity. Endosperm cells and starch granules were decreased significantly with high concentration, and ABA inhibited the activities of soluble acid invertase and acid cell wall invertase, together with earlier attainment of peak values. When ABA was applied at the middle post-pollination stage (MPPS), kernel weight was observably reduced with high concentration and mildly increased with low concentration, which was regulated due to sink activity. The inhibitory effect of high concentration and the mild stimulatory effect of low concentration on sucrose synthase and starch synthase activities were noted, but a peak level of ADP-glucose pyrophosphorylase (AGPase) was stimulated in all ABA treatments. Interestingly, AGPase peak values were advanced by low concentration and postponed by high concentration. In addition, compared with the control, the weight of low ABA concentration treatments were not statistically significant at the two stages, whereas weight loss from high concentration applied at EPPS was considerably obvious compared with that of the MPPS, but neither led to kernel abortion. The temporal- and dose-dependent impacts of ABA reveal a complex process of maize kernel growth and development.

Effects of exogenous abscisic acid on cadmium accumulation in two ecotypes of hyperaccumulator Bidens pilosa

Abscisic acid (ABA) is an important plant hormone that enhances plants’ tolerance to heavy metal stress. In this study, we applied ABA to two ecotypes (mining and farmland) of the cadmium (Cd) hyperaccumulator Bidens pilosa which grown under Cd‐contaminated conditions. The effects of ABA on Cd accumulation in the two ecotypes of B. pilosa were evaluated. Exogenous ABA decreased the biomass and plant height of the two ecotypes of B. pilosa compared with their respective controls. The plants treated with 10 μmol L−1 ABA showed the minimum biomass and plant height. Exogenous ABA also decreased the chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents of two ecotypes of B. pilosa compared with their controls, but increased the chlorophyll a/b ratio. For both two ecotypes of B. pilosa, application of ABA increased the Cd contents in the roots, stems, leaves, and shoots, compared with the controls, but only 40 μmol L−1 ABA increased the amount of Cd extracted by the two ecotypes (an increase of 30.26% in shoots of the farmland ecotype and 16.36% in shoots of the mining ecotype) of B. pilosa. These results show that ABA inhibits the growth of two ecotypes of B. pilosa, and the high concentration (40 μmol L−1) of ABA can enhance Cd extraction from Cd‐contaminated soil. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1643–1649, 2017

Manipulation of ABA Content in Arabidopsis thaliana Modifies Sensitivity and Oxidative Stress Response to Dickeya dadantii and Influences Peroxidase Activity.

The production of reactive oxygen species (ROS) is one of the first defense reactions induced in Arabidopsis in response to infection by the pectinolytic enterobacterium Dickeya dadantii. Previous results also suggest that abscisic acid (ABA) favors D. dadantii multiplication and spread into its hosts. Here, we confirm this hypothesis using ABA-deficient and ABA-overproducer Arabidopsis plants. We investigated the relationships between ABA status and ROS production in Arabidopsis after D. dadantii infection and showed that ABA status modulates the capacity of the plant to produce ROS in response to infection by decreasing the production of class III peroxidases. This mechanism takes place independently of the well-described oxidative stress related to the RBOHD NADPH oxidase. In addition to this weakening of plant defense, ABA content in the plant correlates positively with the production of some bacterial virulence factors during the first stages of infection. Both processes should enhance disease progression in presence of high ABA content. Given that infection increases transcript abundance for the ABA biosynthesis genes AAO3 and ABA3 and triggers ABA accumulation in leaves, we propose that D. dadantii manipulates ABA homeostasis as part of its virulence strategy.

The content of endogenous hormones and sugars in the process of early somatic embryogenesis in the tree fern Cyathea delgadii Sternb.

Somatic embryogenesis (SE) of Cyathea delgadii presents a model system for investigating the mechanisms associated with the acquisition of embryogenic competence by single epidermal cells of stipe explants cultured on plant growth regulator-free medium. The present work reveals relationship between endogenous hormone and sugar content in the process of early SE in C. delgadii. By comparing two types of initial explants, i.e. incapable (non-etiolated) and capable (etiolated) of SE, it was established that in etiolated explants, the glucose, fructose, sucrose, and abscisic acid (ABA) contents diminished, but indole-3-acetic acid (IAA) and cytokinins (CKs; i.e. cis/trans zeatin, cis/trans-zeatin riboside, kinetin, kinetin riboside, isopentenyladenosine) contents increased. The ratios between phytohormones revealed that a high concentration of ABA is the main factor inhibiting SE induction. Because of explant excision, a dramatic reduction in concentration of all phytohormones studied was observed, but hormonal balance and sugar content remained almost unchanged. During the 14-day-long culture, the ABA/CKs and ABA/IAA ratios remained constant, whereas the greatest differences were detected for the IAA/CKs and Z-type/iPA cytokinin ratios. Excluding day 6 of culture, cytokinins were found to be the predominant phytohormones over IAA. An almost 12-fold increase in soluble sucrose concentration at day 6 of culture might be the switch to the SE expression phase. Frequent cell divisions leading to somatic embryo formation are clearly associated with increase in trans-zeatin riboside content.