Involvement of ABA and antioxidant system in brassinosteroid-induced water stress tolerance of grapevine (Vitis vinifera L.)

The objective of this study was to investigate the role of the ascorbate-glutathione (AsA-GSH) cycle and abscisic acid (ABA) in brassinosteroids (BRs)-induced water tolerance in grape seedlings. The grape seedlings were treated with half-strength Hoaglands nutrient solution, polyethylene glycol (PEG-6000) and PEG combination with 24-epibrassinolide (EBR). The results showed that water stress led to typical drought injury symptoms and significantly increased in the contents of hydrogen peroxide (H2O2), the production rate of superoxide radicals (O-2(center dot-)) and the decrease in the contents of ascorbic acid, reduced glutathione in grape seedlings. However, application of EBR alleviated the water stress injury symptoms, reduced the H2O2 content and O-2(center dot-) production rate and enhanced the contents of antioxidants and the activities of antioxidases involved in the AsA-GSH cycle. Interestingly, the ABA content, the transcriptional activation of some key genes involved in ABA biosynthesis including VviNCED1, VviNCED2 and VviZEP and ABA signaling-key genes (VviSnRK2.6, VviPP2C4, VviABF1 and VviABF2) were further enhanced with EBR treatment under water stress. Taken together, we speculate that there is a more complex mechanism in the crosstalk of BR and ABA under drought stress in grape seedlings and ABA is involved in brassinosteroids-induced antioxidant defense.