Abstract
Glutathione (GSH) and ascorbate (ASA) are associated with the abscisic acid (ABA)-induced abiotic tolerance in higher plant, however, its molecular mechanism remains obscure. In this study, exogenous application (10 μM) of ABA significantly increased the tolerance of seedlings of common wheat (Triticum aestivum L.) suffering from 5 days of 15% polyethylene glycol (PEG)-stimulated drought stress, as demonstrated by increased shoot lengths and shoot and root dry weights, while showing decreased content of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Under drought stress conditions, ABA markedly increased content of GSH and ASA in both leaves and roots of ABA-treated plants. Temporal and spatial expression patterns of eight genes encoding ASA and GSH synthesis-related enzymes were measured using quantitative real-time reverse transcription polymerase chain reaction (qPCR). The results showed that ABA temporally regulated the transcript levels of genes encoding ASA-GSH cycle enzymes. Moreover, these genes exhibited differential expression patterns between the root and leaf organs of ABA-treated wheat seedlings during drought stress. These results implied that exogenous ABA increased the levels of GSH and ASA in drought-stressed wheat seedlings in time- and organ-specific manners. Moreover, the transcriptional profiles of ASA-GSH synthesis-related enzyme genes in the leaf tissue were compared between ABA- and salicylic acid (SA)-treated wheat seedlings under PEG-stimulated drought stress, suggesting that they increased the content of ASA and GSH by differentially regulating expression levels of ASA-GSH synthesis enzyme genes. Our results increase our understanding of the molecular mechanism of ABA-induced drought tolerance in higher plants.
Highlights
It is known that biotic and abiotic stresses induces the generation of reactive oxygen species (ROS), such as the superoxide radical (O·2) and hydrogen peroxide (H2O2) (Liu et al, 2009; Borges et al, 2014)
Effects of Exogenous abscisic acid (ABA) on Phenotypes and Growth Parameters of Wheat Seedlings Exposed to polyethylene glycol (PEG)-stimulated Drought-stress Conditions In the present study, wheat seedlings suffering from 15% PEGstimulated drought stress showed time-dependent characteristics (Figure 1)
In root and leaf tissues of PEGtreated wheat seedlings to which ABA had been applied, the transcript profiles of ASA-GSH synthesis-related genes varied in a time-dependent manner, and the transcript levels of at least one of the genes were markedly enhanced by ABA application at each time point (Figures 3, 4, Supplementary Figures S3, S4)
Summary
It is known that biotic and abiotic stresses (including drought) induces the generation of reactive oxygen species (ROS), such as the superoxide radical (O·2) and hydrogen peroxide (H2O2) (Liu et al, 2009; Borges et al, 2014). The accumulation of ROS damages lipids and proteins, results in cell death, and inhibits plant growth (Li et al, 2011). To alleviate ROS accumulation under stress conditions, both enzymatic and non-enzymatic antioxidants are present in plants. The enzymatic antioxidants include superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX) (Asada, 1992), while the non-enzymatic antioxidants include glutathione (GSH) and ascorbate (ASA) (Li et al, 2011). ASA and GSH function as cofactors of enzymes of the antioxidant pathways, both can directly quench ROS (Hernandez et al, 2001; Hossain et al, 2012)
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