FIGURE 9.

The working model illustrating the induction of freezing tolerance by mechanical wounding in wheat plant. Perception of wounding signal in local leaf results in the accumulation of H₂O₂ systemically (resulted from the plasma membrane-bound NADPH oxidase). Elevated levels of H₂O₂ triggers and amplifies the signaling pathway of wounding and then induces NO in a NR-dependent manner in systemic leaf. NO further functions as a signal molecule to up-regulate the photosystem and antioxidant system in response to freezing stress.