Exogenous nitric oxide enhances waterlogging tolerance in Boehmeria nivea L. through modulating BnCAT3 expression

Waterlogging was one of the primarily factors affecting growth and yield of crops. As a gaseous signaling molecule, nitric oxide (NO) pays important roles in stress response and has been successfully applied in various plants to improve the tolerance under waterlogging, while there was little research in ramie. To investigate the function of exogenous NO application in ramie under waterlogging, pot experiments were carried out using ramie cultivar Zhongzhu NO.2 in this study. Three treatments, waterlogging stress (W), waterlogging stress with exogenous sodium nitroprusside (SNP) application (W+SNP), and control group with normal irrigation (CK), were established with both 1-year-old ramie (1 R) and 2-year-old ramie (2 R) plants. The results showed that NO application alleviated waterlogging stress in ramie significantly by decreasing the losses in plant height, leaf area, relative water content in leaf, SPAD value and net photosynthetic rate by 2.31 ∼ 3.17 %, 4.99 ∼ 5.77 %, 1.69 ∼ 2.93 %, 4.48 ∼ 9.93 % and 7.15 ∼ 9.33 %, respectively. Accumulation of NO under waterlogging with SNP spraying was observed by 1.7 ∼ 2.9 times, enhancing antioxidant enzyme activities by 6.75∼37.93 % and modulating osmoregulatory substances (decrease in soluble sugar and malondialdehyde but increase in proline), which resulted in the better performance of plant growth. Catalase (CAT) activity was highly positively correlated with NO, while molecular analysis identified three members of BnCATs in ramie which was up-regulated obviously with exogenous NO application under waterlogging. BnCAT3 was detected to be a candidate gene for further study, which was significantly regulated by NO content, highly expressed in all the tissues and responding positively to waterlogging, NaCl, PEG and ABA stresses. These results provided new insight for genetic breeding and application of resistance in ramie under waterlogging.