Endogenous ABA Levels Research Articles

Gibberellin-producing Serratia nematodiphila PEJ1011 ameliorates low temperature stress in Capsicum annuum L.

We studied the effects of plant growth-promoting rhizobacteria (PGPR) on the physio-hormonal attributes of pepper (Capsicum annuum L.) plants grown under low-temperature stress. After initial screening for growth promoting effect on gibberellin (GA) mutant Waito-C rice seeds, the PGPRs were analysed for gibberellins (GA) production through advanced chromatographic and spectroscopic techniques. Among 17 bacterial isolates, a novel isolate PEJ1011 produced bioactive GA4 (8.65 ng ml−1) and physiologically inactive GA20 (6.21 ng ml−1) and GA9 (1.64 ng ml−1). The isolate PEJ1011 was identified as Serratia nematodiphila PEJ1011 using molecular techniques. To further assess it growth promoting effects, S. nematodiphila PEJ1011 was inoculated to pepper plant, where it significantly improved the growth attributes of pepper plants, while mitigated the deleterious effects of low temperature on pepper exposed to low temperature stress of 5 °C. It was observed that the inoculated plants grown under normal and low temperature stress contained higher endogenous GA4 contents. To modulate cold stress, the beneficial association of PGPR up-regulated the endogenous ABA levels in pepper plants, while reduced the endogenous jasmonic acid and salicylic acid contents. This up and down regulation of stress hormones contribute to the immediate adaptation of plants exposed to low temperature stress. Current study showed the significance of S. nematodiphila PEJ1011 association to crops grown under adverse climatic conditions, and also reports the GA producing capacity of genus Serratia for the first time.

Redox proteomics and physiological responses in Cistus albidus shrubs subjected to long-term summer drought followed by recovery.

Main conclusion The interaction between enzymatic and non-enzymatic antioxidants, endogenous levels of ABA and ABA-GE, the rapid recuperation of photosynthetic proteins under re-watering as well the high level of antioxidant proteins in previously drought-stressed plants under re-watering conditions, will contribute to drought resistance in plants subjected to a long-term drought stress under Mediterranean field conditions. This work provides an overview of the mechanisms of Cistus albidus acclimation to long-term summer drought followed by re-watering in Mediterranean field conditions. To better understand the molecular mechanisms of drought resistance in these plants, a proteomic study using 2-DE and MALDI-TOF/TOF MS/MS was performed on leaves from these shrubs. The analysis identified 57 differentially expressed proteins in water-stressed plants when contrasted to well watered. Water-stressed plants showed an increase, both qualitatively and quantitatively, in HSPs, and downregulation of photosynthesis and carbon metabolism enzymes. Under drought conditions, there was considerable upregulation of enzymes related to redox homeostasis, DHA reductase, Glyoxalase, SOD and isoflavone reductase. However, upregulation of catalase was not observed until after re-watering was carried out. Drought treatment caused an enhancement in antioxidant defense responses that can be modulated by ABA, and its catabolites, ABA-GE, as well as JA. Furthermore, quantification of protein carbonylation was shown to be a useful marker of the relationship between water and oxidative stress, and showed that there was only moderate oxidative stress in C. albidus plants subjected to water stress. After re-watering plants recovered although the levels of ABA-GE and antioxidant enzymes still remain higher than in well-watered plants. We expect that our results will provide new data on summer acclimation to drought stress in Mediterranean shrubs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-014-2221-0) contains supplementary material, which is available to authorized users.

OsRACK1 is involved in abscisic acid- and H2O2-mediated signaling to regulate seed germination in rice (Oryza sativa, L.).

The receptor for activated C kinase 1 (RACK1) is one member of the most important WD repeat–containing family of proteins found in all eukaryotes and is involved in multiple signaling pathways. However, compared with the progress in the area of mammalian RACK1, our understanding of the functions and molecular mechanisms of RACK1 in the regulation of plant growth and development is still in its infancy. In the present study, we investigated the roles of rice RACK1A gene (OsRACK1A) in controlling seed germination and its molecular mechanisms by generating a series of transgenic rice lines, of which OsRACK1A was either over-expressed or under-expressed. Our results showed that OsRACK1A positively regulated seed germination and negatively regulated the responses of seed germination to both exogenous ABA and H2O2. Inhibition of ABA biosynthesis had no enhancing effect on germination, whereas inhibition of ABA catabolism significantly suppressed germination. ABA inhibition on seed germination was almost fully recovered by exogenous H2O2 treatment. Quantitative analyses showed that endogenous ABA levels were significantly higher and H2O2 levels significantly lower in OsRACK1A-down regulated transgenic lines as compared with those in wildtype or OsRACK1A-up regulated lines. Quantitative real-time PCR analyses showed that the transcript levels of OsRbohs and amylase genes, RAmy1A and RAmy3D, were significantly lower in OsRACK1A-down regulated transgenic lines. It is concluded that OsRACK1A positively regulates seed germination by controlling endogenous levels of ABA and H2O2 and their interaction.

Regulatory function of AMP1 in ABA biosynthesis and drought resistance in arabidopsis

In this study we reported the isolation of a mutant in which the reporter pVP14-LUC was highly expressed in Arabidopsis. The gene expression of maize VP14 is closely correlated with the endogenous ABA levels, and the Arabidopsis homolog of VP14, AtNCED1, encoding an enzyme of ABA biosynthesis, was up-regulated, and high ABA level was detected in the mutant. Map-based cloning revealed that the mutated gene is a novel allele of the AMP1 (Altered Meristem Program 1) which encodes a glutamate carboxypeptidase that plays an important role in shoot apical meristem development and phytohormone homeostasis. We found that the mutant displayed obvious drought tolerance, being with more lateral roots, high seed germination under mannitol, increased ABA accumulation, and highly induced gene expression of RD29A. Using the approaches of artificial microRNA gene silencing in transgenic plants, three AMP1 down-regulated lines were obtained. The AMP1 down-regulated plants exhibited a low rate of water loss, decreased stomatal aperture, and enhanced drought tolerance. These results provide evidence demonstrating the regulatory function of AMP1 in plant drought tolerance and stress responsive gene expression.

Endogenous abscisic acid signaling towards storage reserve filling in developing seed tissues of castor bean (Ricinus communis L.)

Abscisic acid (ABA; free form) is a naturally occurring physiological growth hormone of higher plants. A detailed study involving the time course growth of developing seed tissues associated with endogenous levels of free ABA were investigated using a novel enzyme-linked immunosorbent assay. Seed filling in castor (Ricinuc communis L.) endosperm, embryo, and pod is marked with a rapid increase in fresh weight during the mid-developmental stages [21–42 days after pollination (DAP)], followed by a steady decline at the maturation stages (42–63 DAP) accompanied with a rapid lipid synthesis (in endosperm and embryo) during the same period, except for in pod. Endogenous ABA levels in endosperm (0.001–0.32 μg/g) and embryo (0.003–0.13 μg/g) followed a concurrent pattern with seed reserve filling, showing a rapid increase during the mid-developmental stages 21–42 DAP, whereas ABA levels in seed pod (0.2–22.9 μg/g) showed a different accumulation pattern with rapid increase and decline during the early-mid developmental stages, preceded by the maximal increase during the maturation stage (63 DAP). Together, our results provide evidence for the association of endogenous ABA in seed filling as well as in reserve deposition and provides clue for the effective usage of exogenous ABA concentrations in developing seeds with a focus, on improving seed reserve complex in castor.

Effects of abscisic acid on the contents of polyamines and proline in common bean plants under salt stress

The effects of ABA treatment on the contents of polyamines (PAs) and proline (Pro) in the glycophyte Phaseolus vulgaris L. during plant adaptation to salt stress were studied. Two-week-old common bean seedlings grown in the phytotron chamber on the Jonson nutrient medium were subjected to salinity for 6 days by one-time NaCl addition to medium up to final concentrations of 50 and 100 mM. During first three days of salinity, the root system was daily treated with ABA (1, 5, 10, or 50 μM) for 30 min. Salt stress (100 mM NaCl) elevated the level of endogenous ABA, increased the content of Pro 14-fold, reduced sharply the content of free PAs (putrescine, spermidine, spermine, and cadaverine), and the accumulation of 1,3-diaminopropan, a product of oxidation of high-molecular PAs. Common bean plant treatment with 1 μM ABA weakened the adverse effects of salt stress (100 mM NaCl), which was manifested in the maintenance of plant growth, stimulation of chlorophyll (a and b) and carotenoid accumulation, a stabilization of water and Na+ balance. Seedling treatment with ABA suppressed NaCl-induced Pro and intracellular ABA accumulation and restored the levels of putrescine and spermidine. The content of spermine in the leaves of plants subjected to salt stress and treated with ABA was approximately threefold higher than in control plants, whereas the content of cadaverine increased under similar conditions more than fivefold. Simultaneously, the contents of 1,3-diaminopropan and malondialdehyde as well as activity of superoxide dismutase were reduced, which indicates a weakening of oxidative stress, one of the possible causes of defensive ABA effects against salt stress. In addition, the suppression by exogenous ABA of Pro accumulation and stimulation of PA content under salt stress confirm indirectly our hypothesis that ABA is involved in the coordinated regulation of two biosynthetic pathways, Pro and PA formation, which use a common precursor, glutamate, and play an important protective role during stress in plants.

Effect of abscisic acid applications on cold tolerance in chickpea (Cicer arietinum L.)

A series of field experiments were undertaken at three locations in Khyber PukhtunKhwa (KPK) Province, Pakistan to assess the effects of low temperatures and phytohormone applications on chickpea (Cicer arietinum L.) growth and yield. These trials showed that ABA application (10−4M) to 40-day-old plants (before the first seasonal frost) offset low temperature-induced growth and yield depression at harvest (200-day-old plants) by up to 17%. These yield improvements were mainly due to an increase in the number of seeds pod−1. Growth room experiments were carried out under controlled environmental conditions to establish how foliar application of 10−4M ABA to 40-day-old plants might improve seed production at harvest. The foliar application of 10−4M ABA had no detectable effect on endogenous shoot or root ABA levels four-days after spraying or on biomass when plants were maintained in warm conditions. When exposed to night temperatures of −2°C, however, the endogenous ABA levels increased dramatically in both control and ABA-treated plants, but this rise was more rapid after ABA application (p<0.01); after 14 days, these plants had gained significantly more biomass than the unsprayed controls (p<0.05). No evidence was found to suggest ABA affected the osmotic or water balance of plants, but parallel experiments have shown ABA reduced low temperature-induced cell damage. Analysis of the proteome of the shoot tissues of ABA treated and untreated plants by 2-Dimensional Gel Electrophoresis identified several proteins that are induced by low temperatures and/or by ABA application in chickpea and which may be involved in conferring cold tolerance. Attempts were made to establish the identity of these proteins using mass spectrometry but in all cases the results were ambiguous; a more complete protein data base for legumes is required before the function of these proteins can be inferred.

Carrizo citrange plants do not require the presence of roots to modulate the response to osmotic stress.

The study of the effects of a specific stress condition on the performance of plants grown under field conditions is difficult due to interactions among multiple abiotic and biotic factors affecting the system. In vitro tissue-culture-based techniques allow the study of each adverse condition independently and also make possible to investigate the performance of genotypes of interest under stress conditions avoiding the effect of the root. In this paper, the response of Carrizo citrange, a commercial citrus rootstock, to osmotic stress was evaluated by culturing in vitro intact plants and micropropagated shoots. The osmotic stress was generated by adding two different concentrations of polyethyleneglycol to the culture media. Different parameters such as plant performance, organ length, antioxidant activities, and endogenous contents of proline, malondialdehyde, and hormones were determined. Differently to that observed under high salinity, when subjected to osmotic stress conditions, Carrizo citrange showed increased endogenous levels of MDA, proline, and ABA. These results evidence that the mechanisms of response of Carrizo citrange to saline or osmotic stress are different. The presence of roots was not necessary to activate any of the plant responses which indicates that the organs involved in the stress perception and signaling depends on the type of adverse condition to which plants are subjected.

ヤマノイモのGA-誘導休眠：ABA代謝遺伝子の発現とABAおよびその異化物質の内生レベル

ヤマノイモのGA-誘導休眠：ABA代謝遺伝子の発現とABAおよびその異化物質の内生レベル

シロイヌナズナナチュラルバリエーションを用いた種子休眠性およびアブシジン酸（ABA）内生量制御機構に関する研究

シロイヌナズナナチュラルバリエーションを用いた種子休眠性およびアブシジン酸（ABA）内生量制御機構に関する研究

Overexpression of the soybean GmWNK1 altered the sensitivity to salt and osmotic stress in Arabidopsis

The WNK (With No Lysine K) serine-threonine kinases have been shown to be osmosensitive regulators and are critical for cell volume homeostasis in humans. We previously identified a soybean root-specific WNK homolog, GmWNK1, which is important for normal late root development by fine-tuning regulation of ABA levels. However, the functions of WNKs in plant osmotic stress response remains uncertain. In this study, we generated transgenic Arabidopsis plants with constitutive expression of GmWNK1. We found that these transgenic plants had increased endogenous ABA levels and altered expression of ABA-responsive genes, and exhibited a significantly enhanced tolerance to NaCl and osmotic stresses during seed germination and seedling development. These findings suggest that, in addition to regulating root development, GmWNK1 also regulates ABA-responsive gene expression and/or interacts with other stress related signals, thereby modulating osmotic stress responses. Thus, these results suggest that WNKs are members of an evolutionarily conserved kinase family that modulates cellular response to osmotic stresses in both animal and plants.

Environmental regulation of stomatal response in the Arabidopsis Cvi-0 ecotype

The Arabidopsis Cape Verde Islands (Cvi-0) ecotype is known to differ from other ecotypes with respect to environmental stress responses. We analyzed the stomatal behavior of Cvi-0 plants, in response to environmental signals. We investigated the responses of stomatal conductance and aperture to high [CO₂] in the Cvi-0 and Col-0 ecotypes. Cvi-0 showed constitutively higher stomatal conductance and more stomatal opening than Col-0. Cvi-0 stomata opened in response to light, but the response was slow. Under low humidity, stomatal opening was increased in Cvi-0 compared to Col-0. We then assessed whether low humidity affects endogenous ABA levels in Cvi-0. In response to low humidity, Cvi-0 had much higher ABA levels than Col-0. However, epidermal peels experiments showed that Cvi-0 stomata were insensitive to ABA. Measurements of organic and inorganic ions in Cvi-0 guard cell protoplasts indicated an over-accumulation of osmoregulatory anions (malate and Cl⁻). This irregular anion homeostasis in the guard cells may explain the constitutive stomatal opening phenotypes of the Cvi-0 ecotype, which lacks high [CO₂]-induced and low humidity-induced stomatal closure.

Volatile Emissions from the Invasive Weed Eupatorium adenophorum Induced by Aphis gossypii Feeding and Methyl Jasmonate Treatment

The volatile compounds of crofton weed infested by cotton aphids and sprayed with MeJA were collected and analyzed by the TCT-GC/MS technique. The healthy weeds were controls. Seventeen volatiles identified from crofton weed included green leaf odors, monoterpenes and sequiterpenes, and oxo-compounds. Camphene, 2-carene, α-phellandrene, ρ-cymene, and caryophyllene were the major volatiles and constituted about 77% of the total volatile emissions from the control. In the aphid-infested weeds, no new induced component was found. Among the terpenes, ρ-cymene increased markedly in the infested weeds compared with the control, whereas all sesquiterpenes decreased markedly. Levels of endogenous JA in leaves and young stems of the aphid-infested weeds were markedly higher than in the control, whereas both endogenous SA level and ABA level were not significantly different. MeJA sprayed on crofton weed with the aphid infestation had a similar effect on volatile emissions. It is suggested that JA was one of the most important signals in crofton weed and could regulate the emission of volatile compounds.

OsCIPK31, a CBL-interacting protein kinase is involved in germination and seedling growth under abiotic stress conditions in rice plants.

Calcineurin B-like protein-interacting protein kinases (CIPKs) are a group of typical Ser/Thr protein kinases that mediate calcium signals. Extensive studies using Arabidopsis plants have demonstrated that many calcium signatures that activate CIPKs originate from abiotic stresses. However, there are few reports on the functional demonstration of CIPKs in other plants, especially in grasses. In this study, we used a loss-of-function mutation to characterize the function of the rice CIPK gene OsCIPK31. Exposure to high concentrations of NaCl or mannitol effected a rapid and transient enhancement of OsCIPK31 expression. These findings were observed only in the light. However, longer exposure to most stresses resulted in downregulation of OsCIPK31 expression in both the presence and absence of light. To determine the physiological roles of OsCIPK31 in rice plants, the sensitivity of oscipk31::Ds, which is a transposon Ds insertion mutant, to abiotic stresses was examined during germination and seedling stages. oscipk31::Ds mutants exhibited hypersensitive phenotypes to ABA, salt, mannitol, and glucose. Compared with wild-type rice plants, mutants exhibited retarded germination and slow seedling growth. In addition, oscipk31::Ds seedlings exhibited enhanced expression of several stress-responsive genes after exposure to these abiotic stresses. However, the expression of ABA metabolic genes and the endogenous levels of ABA were not altered significantly in the oscipk31::Ds mutant. This study demonstrated that rice plants use OsCIPK31 to modulate responses to abiotic stresses during the seed germination and seedling stages and to modulate the expression of stress-responsive genes.

Analysis of Gene Expression and Source-sink Dynamics in Transportation Regulation of ABA Signal Accumulation

Subcellular localization of AtNCED3,AtAAO3 and AtSDR1 proteins,and dynamic changes of ABA levels in root and leaf were investigated in the present study. Results showed that the guard cells were not the main site of ABA biosynthesis,and SDR might play an important role in ABA precursor processing and transportation. The transcription level of ABA synthase gene in roots was significantly higher than that in leaves under dehydration condition,while the ABA concentration in leaf tissues were 10 times higher than root. Detection of ABA concentration in both detached leaves and attached leaves suggested that ABA accumulation in leaves was mainly derived from root-sourced ABA,it was confirmed that ABA synthesis in roots was affected by the supply of precursor carotenoids with the fluridone treatment and shading experiments. These data revealed that ABA levels in leaves were regulated by root-sourced ABA transportation and leaf-sourced carotenoids supply. Our present results showed that vascular system might be involved in the coordination and integration of this complex regulatory mechanism for ABA signal accumulation. The conclusion provided relevant information for exploring molecular mechanism of stress signal transduction,manipulating endogenous ABA levels,and enhancing plants resistance against environmental stresses.

Antagonism between salicylic and abscisic acid reflects early host–pathogen conflict and moulds plant defence responses

The importance of phytohormone balance is increasingly recognized as central to the outcome of plant-pathogen interactions. Recently it has been demonstrated that abscisic acid signalling pathways are utilized by the bacterial phytopathogen Pseudomonas syringae to promote pathogenesis. In this study, we examined the dynamics, inter-relationship and impact of three key acidic phytohormones, salicylic acid, abscisic acid and jasmonic acid, and the bacterial virulence factor, coronatine, during progression of P. syringae infection of Arabidopsis thaliana. We show that levels of SA and ABA, but not JA, appear to play important early roles in determining the outcome of the infection process. SA is required in order to mount a full innate immune responses, while bacterial effectors act rapidly to activate ABA biosynthesis. ABA suppresses inducible innate immune responses by down-regulating SA biosynthesis and SA-mediated defences. Mutant analyses indicated that endogenous ABA levels represent an important reservoir that is necessary for effector suppression of plant-inducible innate defence responses and SA synthesis prior to subsequent pathogen-induced increases in ABA. Enhanced susceptibility due to loss of SA-mediated basal resistance is epistatically dominant over acquired resistance due to ABA deficiency, although ABA also contributes to symptom development. We conclude that pathogen-modulated ABA signalling rapidly antagonizes SA-mediated defences. We predict that hormonal perturbations, either induced or as a result of environmental stress, have a marked impact on pathological outcomes, and we provide a mechanistic basis for understanding priming events in plant defence.

Glucose-Induced Delay of Seed Germination in Rice is Mediated by the Suppression of ABA Catabolism Rather Than an Enhancement of ABA Biosynthesis

Both glucose and ABA play crucial roles in the regulation of seed germination and post-germination development. In Arabidopsis thaliana, up-regulation of ABA biosynthesis is suggested as one of the possible mechanisms mediating the glucose-induced delay in seed germination. Since the endogenous ABA level is controlled by the equilibrium between ABA biosynthesis and catabolism, we investigated how this equilibrium is related to the regulation of seed germination by glucose in rice. When ABA biosynthesis was inhibited by nordihydroguaiaretic acid (NDGA), an inhibitor of the ABA anabolic enzyme 9-cis-epoxycarotenoid dioxygenase (NCED), rice seed germination showed no response. In contrast, inhibition of ABA catabolism by diniconazole significantly arrested seed germination, suggesting that the regulation of ABA catabolism plays a major role. Further experiments indicated that the expression of OsABA8ox3, a key gene in ABA catabolism and encoding ABA 8'-hydroxylase in rice, was significantly increased during the first 6 h of imbibition, which was consistent with the decline of ABA content in the imbibed seeds. Expression of OsABA8ox genes, especially OsABA8ox2 and OsABA8ox3, was sensitively suppressed in the presence of exogenously supplied glucose. In contrast, the expression profiles of OsNCED genes that control the limiting step of ABA biosynthesis showed no significant changes in response to low levels of glucose. Our results demonstrated that the glucose-induced delay of seed germination is a result of the suppression of ABA catabolism rather than any enhancement of ABA biosynthesis during rice seed germination.

Interaction of jasmonic acid and blue light in the regulation of arabidopsis morphogenesis

The effects of blue light (BL) and jasmonic acid (JA) on morphogenesis of Arabidopsis thaliana (L.) Heynh seedlings of genotypes Col and Ler and their mutants, namely, axr1-3 and jar1-1 mutants resistant to IAA and JA, respectively, and a CRY1 photoreceptor-deficient mutant hy4 were studied. Both 1 μM JA and BL exposure retarded hypocotyl growth of Ler, Col, and jar1-1 seedlings, whereas JA had no effect on hypocotyl growth of axr1-3, but the suppression of hypocotyl growth of this mutant by BL was even more noticeable than that of Ler, Col, and jar1-1. JA and BL applied simultaneously inhibited hypocotyl growth of axr1-3 and especially of Ler, Col, and jar1-1 more than either of factors applied separately. The hy4 mutant did not respond to BL, whereas JA stimulated its hypocotyl growth. JA did not change the cotyledon size of Col, axr1-3, and jar1-1 and reduced the cotyledon size of Ler and hy4. BL enhanced the cotyledon growth of all wild-type and mutant plants used in the study. The cotyledon sizes of all plants except Ler were also increased when JA and BL were applied together. Some of the growth responses correlated with the endogenous IAA and ABA contents. Thus, for example, the hypocotyl and cotyledon growth retardation of Ler seedlings in the presence of JA correlated with a reduced level of free IAA and a considerable increase in the free ABA level in plants grown both in darkness and in BL. Under other growth conditions, no correlation between the endogenous IAA and ABA levels and A. thaliana seedling growth was noted. The interaction between the signal transduction pathways triggered by BL and JA at the early stages of arabidopsis morphogenesis is discussed on the basis of Col, Ler, axr1-3, and jar1-1 hypocotyl growth responses.

Correlation Between Endogenous Hormones of Stem Apices and Fruit Locule Numbers in Tomatoes During Floral Bud Differentiation Stages

The study was designed to elucidate the changes in the endogenous hormones of stem apices in tomatoes and the function of correlative endogenous hormones in tomatoes during floral bud differentiation stages. The tomato parents were crossed and reverse crossed by using two inbred lines of multi-locule (MLK1) and few-locule (FL1) with significant difference, and the relationship between endogenous hormones GA3, IAA, and ABA levels and ovary locule numbers of parents and progeny during floral bud differentiation initial stage, floral bud differentiation stage, sepal petal formation stage, carpel formation initial stage, and ovary locule complete formation stage was studied. GA3 levels in P1, P2, F1, and RF1 were consistent with locule numbers, and IAA and ABA levels were reverse to ovary locule numbers during the key stage. The correlation showed that, during sepal petal formation stage, the ovary locule numbers were positively correlated with GA3, GA3/IAA, and GA3/ABA, and were negatively correlated with IAA and ABA. It was speculated that increasing GA3 levels or decreasing IAA and ABA levels of stem apices in tomato might be able to enhance ovary locule numbers. The sepal petal formation stage was an important stage which regulated endogenous hormones in the ovary locule formation.

ABA Regulates Apoplastic Sugar Transport and is a Potential Signal for Cold-Induced Pollen Sterility in Rice

Cold temperatures cause pollen sterility and large reductions in grain yield in temperate rice growing regions of the world. Induction of pollen sterility by cold involves a disruption of sugar transport in anthers, caused by the cold-induced repression of the apoplastic sugar transport pathway in the tapetum. Here we demonstrate that the phytohormone ABA is a potential signal for cold-induced pollen sterility (CIPS). Cold treatment of the cold-sensitive cultivar Doongara resulted in increased anther ABA levels. Exogenous ABA treatment at the young microspore stage induced pollen sterility and affected cell wall invertase and monosaccharide transporter gene expression in a way similar to cold treatment. In the cold-tolerant cultivar R31, ABA levels were significantly lower under normal circumstances and remained low after cold treatment. The differences in endogenous ABA levels in Doongara and R31 correlated with differences in expression of the ABA biosynthetic genes encoding zeaxanthin epoxidase (OSZEP1) and 9-cis-epoxycarotenoid dioxygenase (OSNCED2, OSNCED3) in anthers. The expression of three ABA-8-hydroxylase genes (ABA8OX1, 2 and 3) in R31 anthers was higher under control conditions and was regulated differently by cold compared with Doongara. Our results indicate that the cold tolerance phenotype of R31 is correlated with lower endogenous ABA levels and a different regulation of ABA metabolism.