Nitrate reductase is required for salicylic acid‐induced water stress tolerance of pepper by upraising the AsA‐GSH pathway and glyoxalase system

A trial was conducted to evaluate whether nitrate reductase (NR) participates in salicylic acid (SA)‐improved water stress (WS) tolerance in pepper ( Capsicum annuum L.) plants. Before starting WS treatment, 0.5 mM SA was applied to half of the well‐watered (WW) plants as well as to WS‐plants as a foliar spray once a day for a week. The soil water holding capacity was maintained at 40 and 80% of the full water storing capacity for WS and and well‐watered (WW) plants, respectively. Water stress caused substantial decreases in total plant dry weight, F v /F m , chlorophyll a and b , relative water content, leaf water potential (ΨI) by 53, 37, 49, 21, 36 and 33%, respectively relative to control, but significant increases in malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ), electrolyte leakage (EL), methylglyoxal (MG), proline, key antioxidant enzymes' activities, NO and NR activity. The SA reduced oxidative stress, but improved antioxidant defence system, ascorbate‐glutathione (AsA‐GSH) cycle enzymes, glyoxalase system‐related enzymes, glyoxalase I (Gly I) and glyoxalase II (Gly II), plant growth, photosynthetic traits, NO, NR and proline. SA‐induced WS tolerance was further improved by supplementation of sodium nitroprusside (SNP), a donor of NO. NR inhibitor, sodium tungstate (ST) was applied in conjunction with SA and SA + SNP to the WW and WS‐plants to assess whether NR contributes to SA‐improved WS tolerance. ST abolished the beneficial effects of SA by reducing NO and NR activity in WS‐pepper, but the application of SNP along with SA + ST reversed negative effects of ST, showing that NO and NR are jointly needed for SA‐induced WS tolerance of pepper plants.