24-Epibrassinolide and nitric oxide combined to improve the drought tolerance in kiwifruit seedlings by proline pathway and nitrogen metabolism

Abstract

24-Epibrassinolide (EBR) and nitric oxide (NO) are redox signaling molecules that participate in plant stress response, but their combined role in drought stress response remains unclear. In this study, potted kiwifruit seedlings grown under drought stress were treated with sodium nitroprusside, a NO donor (SNP, 100 μM), 24-epibrassinolide (EBR, 0.01 mg·L−1), and their combination (S+E), as well as well-watered (CK) and drought treatments (DCK). Results revealed that plant biomass, leaf relative water content, photosynthetic pigment content, and photosynthetic capacity of leaves decreased, whereas MDA, H2O2, relative electrolyte leakage, endogenous NO, proline, and soluble sugar content increased in response to drought stress. The application of SNP and EBR alleviated the above adverse effects caused by drought stress and improved the enzyme activities of glutamine synthetase (GS), reduced the glutamate dehydrogenase (GDH) involved in nitrogen metabolism to maintain plant growth, and regulated the expression of aquaporin genes PIP1;1 and PIP2;2–1 to maintain normal water metabolism. The up-regulation of proline synthesis gene P5CR1 expression and the down-regulation of proline degradation gene ProDH expression caused proline accumulation under drought stress. Overall, the combination of SNP and EBR was more effective than independent SNP or EBR in mitigating drought stress in kiwifruit seedlings.