Nitric Oxide Enhances Resistance to PEG-induced Water Deficiency is Associated with the Primary Photosynthesis Reaction in Triticum aestivum L.

Photosynthesis is affected by water deficiency (WD) stress, and nitric oxide (NO) is a free radical that participates in the photosynthesis process. Previous studies have suggested that NO regulates the excitation energy distribution of photosynthesis under WD stress. Here, quantitative phosphoproteomic profiling was conducted using isobaric tags for relative and absolute quantitation. Differentially phosphorylated protein species (DEPs) were identified in leaves of NO or polyethylene glycol (PEG)-treated wheat seedlings (D) and in control seedlings, 2,257 unique phosphorylated peptides and 2,416 phosphorylation sites were identified from 1,396 unique phosphoproteins. Of these, 96 DEPs displayed significant changes (≥ 1.50-fold, p < 0.01). These DEPs are involved in photosynthesis and signal transduction, etc. Furthermore, phosphorylation of several DEPs were up-regulated by both D and NO treatments, but down-regulated only in NO treatment. These differences affected the chlorophyll A-B binding protein, chloroplast post-illumination chlorophyll fluorescence increase protein, and SNT7, implying that NO indirectly regulated the absorption and transport of light energy in photosynthesis in response to WD stress. The significant difference of chlorophyll (Chl) content, Chl a fluorescence transient, photosynthesis index, and trapping and transport of light energy further indicated that exogenous NO under D stress enhanced the primary reaction of photosynthesis compared to D treatment. A putative pathway is proposed to elucidate NO regulation of the primary reaction of photosynthesis under WD.

水分缺失（water deficiency, WD）胁迫会影响光合作用，而一氧化氮（nitric oxide, NO）作为一种自由基参与光合作用过程。既往研究表明，一氧化氮可在水分缺失胁迫下调控光合作用的激发能分配。本研究采用同位素相对与绝对定量（isobaric tags for relative and absolute quantitation）技术开展定量磷酸化蛋白质组学分析，对一氧化氮或聚乙二醇（polyethylene glycol, PEG）处理的小麦幼苗（D组）及对照幼苗的叶片进行差异磷酸化蛋白质（differentially phosphorylated protein species, DEPs）筛选，最终从1396个独特磷酸化蛋白质中鉴定出2257条独特磷酸化肽段与2416个磷酸化位点。其中，96个差异磷酸化蛋白质呈现出显著表达变化（变化倍数≥1.50，p<0.01）。这些差异磷酸化蛋白质参与光合作用、信号转导等生物学过程。此外，部分差异磷酸化蛋白质的磷酸化水平在D处理与NO处理下均被上调，但仅在NO处理组中出现下调。上述变化影响了叶绿素a/b结合蛋白、叶绿体照后叶绿素荧光增加蛋白以及SNT7，这表明一氧化氮可间接调控水分缺失胁迫下光合作用中光能的吸收与转运过程。叶绿素（chlorophyll, Chl）含量、叶绿素a荧光瞬变、光合作用参数以及光能捕获与转运的显著差异进一步表明，相较于单独D处理，外源一氧化氮在D胁迫下可增强光合作用的原初反应。本研究提出一条推定通路，以阐明一氧化氮在水分缺失胁迫下对光合作用原初反应的调控机制。