Proteomics analysis reveals that nitric oxide regulates photosynthesis of maize seedlings under water deficiency

Nitric oxide (NO) is an important bioactive molecule that functions in regulating diverse abiotic stresses in plants, whereas its molecular mechanism remains obscure. In this study, treatment with 0.1 mM NO donor (sodium nitroprusside, SNP) significantly alleviated the inhibited growth induced by 15% polyethyleneglycol (PEG)-stimulated water deficiency (WD) for 3 days in maize seedlings, manifested by less decreased plant total fresh weight and dry weight. Comprehensive proteome analysis was further used to measure the expression profiles of leaf proteins of SNP-pretreated maize seedlings under WD conditions to explore the molecular mechanisms of NO-induced WD tolerance. Using 2-DE method, 135 protein spots showed significantly enhanced or reduced abundance, of which 102 spots were successfully identified MALDI-TOF/TOF MS. The identified protein species were associated with diverse functions, and most (52/83, 62.7%) of known protein species were related to photosynthetic processes. Compared to alone PEG treatment, the abundance of 25 identified protein species in SNP + PEG treatment were enhanced among the identified photosynthesis-related protein species. In addition, exogenous SNP application dramatically regulated chlorophyll α fluorescence kinetics e.g. the increase of maximum quantum yield of PSII (F_v/F_m), photosynthetic performance index (PI), and IP phase, whereas it remarkably reduced the polyphasic OJIP fluorescence transient, the accumulation of reactive oxygen species (H₂O₂ and O₂^•) and malondialdehyde (MDA). These findings suggest that the NO-induced WD tolerance could be associated with improved photosynthetic capability in higher plants.