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NO accumulation alleviates H2O2‐dependent oxidative damage induced by Ca(NO3)2 stress in the leaves of pumpkin‐grafted cucumber seedlings

Author:
Li, Lin, Shu, Sheng, Xu, Qing, An, Ya‐hong, Sun, Jin, Guo, Shi‐rong
Source:
Physiologia plantarum 2017 v.160 no.1 pp. 33-45
ISSN:
0031-9317
Subject:
Cucurbita maxima, NAD(P)H oxidase (H2O2-forming), NADP (coenzyme), calcium nitrate, chemical elements, cucumbers, hydrogen peroxide, leaves, nitrate reductase, nitric oxide, nitric oxide synthase, photosystem II, rootstocks, salt stress, salt tolerance, seedlings
Abstract:
Nitric oxide (NO) and hydrogen peroxide (H₂O₂), two important signaling molecules, are stimulated in plants by abiotic stresses. In this study, we investigated the role of NO and its interplay with H₂O₂ in the response of self‐grafted (S‐G) and salt‐tolerant pumpkin‐grafted (Cucurbita maxima × C. moschata) cucumber seedlings to 80 mM Ca(NO₃)₂ stress. Endogenous NO and H₂O₂ production in S‐G seedlings increased in a time‐dependent manner, reaching maximum levels after 24 h of Ca(NO₃)₂ stress. In contrast, a transient increase in NO production, accompanied by H₂O₂ accumulation, was observed at 2 h in rootstock‐grafted plants. Nʷ‐Nitro‐l‐Arg methyl ester hydrochloride (l‐NAME), an inhibitor of nitric oxide synthase (NOS), tungstate, an inhibitor of nitrate reductase (NR), and 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethy‐limidazoline‐1‐oxyl‐3‐oxide (cPTIO), a scavenger of NO, were found to significantly inhibit NO accumulation induced by salt stress in rootstock‐grafted seedlings. H₂O₂ production was unaffected by these stress conditions. Ca(NO₃)₂ stress‐induced NO accumulation was blocked by pretreatment with an H₂O₂ scavenger (dimethylthiourea, DMTU) and an inhibitor of NADPH oxidase (diphenyleneiodonium, DPI). In addition, maximum quantum yield of PSII (Fv/Fm), as well as the activities and transcript levels of antioxidant enzymes, were significantly decreased by salt stress in rootstock grafted seedlings after pretreatment with these above inhibitors; antioxidant enzyme transcript levels and activities were higher in rootstock‐grafted seedlings compared with S‐G seedlings. These results suggest that rootstock grafting could alleviate the oxidative damage induced by Ca(NO₃)₂ stress in cucumber seedlings, an effect that may be attributable to the involvement of NO in H₂O₂‐dependent antioxidative metabolism.
Agid:
5714875