Abstract
Systemic wound response (SWR), a well-characterized systemic signaling response, plays crucial roles in plant defense responses. Progress in understanding of the SWR in abiotic stress has also been aided by the researchers. However, the function of SWR in freezing stress remains elusive. In this study, we showed that local mild mechanical wounding enhanced freezing tolerance in newly occurred systemic leaves of wheat plants (Triticum aestivum L.). Wounding significantly increased the maximal photochemical efficiency of photosystem II, net photosynthetic rate, and the activities of the antioxidant enzymes under freezing stress. Wounding also alleviated freezing-induced chlorophyll decomposition, electrolyte leakage, water lose, and membrane peroxidation. In addition, wounding-induced freezing stress mitigation was closely associated with the ratio between reduced glutathione (GSH) and oxidized glutathione (GSSG), and the ratio between ascorbate (AsA) and dehydroascorbate (DHA), as well as the contents of total soluble sugars and free amino acids. Importantly, pharmacological study showed that wounding-induced freezing tolerance was substantially arrested by pretreatment of wheat leaves with the scavenger of hydrogen peroxide (H2O2) or the inhibitor of NADPH oxidase (RBOH). These results support the hypothesis that local mechanical wounding-induced SWR in newly occurred leaves is largely attributed to RBOH-dependent H2O2 production, which may subsequently induce freezing tolerance in wheat plants. This mechanism may have a potential application to reduce the yield losses of wheat under late spring freezing conditions.Highlights:In our previous research, we found that local mechanical wounding could induce freezing tolerance in the upper systemic leaves of wheat plants. Surprisingly, in this paper, we further demonstrated that local mechanical wounding could also increase freezing resistance in newly occurred leaves of wheat plants. RBOH mediated H2O2 and ascorbate–glutathione cycle participate in this systemic wound response.
Highlights
Plants are constantly exposed to various unfavorable environmental stresses in their natural habitat
Plants treated with freezing alone showed higher relative electrolytic conductivity (REC) (Figure 1A) and lower relative water content (RWC) (Figure 1B) in both local and systemic leaves compared with the control seedlings
The REC was significantly increased while RWC was decreased in plants pretreated with DMTU or DPI prior to wounding compared with control plants in response to freezing stress (Figure 1)
Summary
Plants are constantly exposed to various unfavorable environmental stresses in their natural habitat. Freezing stress (below 0◦C) adversely affects the physiological and metabolic processes and significantly decreases grain yield and grain quality of temperate crop plants (Xin and Browse, 2000; Shinozaki et al, 2003; Puhakainen et al, 2004; Mittler, 2006). Cold acclimation is a complex process in plants that involves extensive physiological, biochemical, and metabolic changes (Thomashow, 1999; Chinnusamy et al, 2007; Zhao et al, 2017). Abiotic stress (e.g., UV-B radiation, chilling, and drought) priming and exogenous application of plant growth hormones (e.g., salicylic acid, jasmonic acid, and abscisic acid) have been widely adopted in cold acclimation to the acquisition of plant freezing tolerance (Yang et al, 2007; Kosová et al, 2012; Zhou et al, 2012; ̇Iseri et al, 2013; Li et al, 2015b). More effective strategies to alleviate the freezing stress on crops are still unveiled
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