The involvement of hydrogen peroxide in the differentiation secondary walls in cotton fibers

摘要

H inferior 2O inferior 2 is a widespread molecule in many biological systems. It is created enzymatically in living cells during various oxidation reactions and by leakage of electrons from the electron transport chains. Depending on the concentration H inferior 2O inferior 2 can induce cell protective responses, programmed cell death, or necrosis. Here we provide evidence that H inferior 2O inferior 2 may function as a developmental signal in the differentiation of secondary walls in cotton (Gossypium hirsutum) fibers. Three lines of evidence support this conclusion: (a) the period of H inferior 2O inferior 2 generation coincided with the onset of secondary wall deposition, (b) inhibition of H inferior 2O inferior 2 production or scavenging the available H inferior 2O inferior 2 from the system prevented the wall differentiation process, and (c) exogenous addition of H inferior 2O inferior 2 prematurely promoted secondary wall formation in young fibers. Furthermore, we provide support for the concept that H inferior 2O inferior 2 generation could be mediated by the expression of the small GTPase Rac, the accumulation of which was shown previously to be strongly induced during the onset of secondary wall differentiation. In support of Rac's role in the activation of NADPH oxidase and the generation of reactive oxygen species, we transformed soybean (Glycine max) and Arabidopsis cells with mutated Rac genes. Transformation with a dominantly activated cotton Rac13 gene resulted in constitutively higher levels of H inferior 2O inferior 2, whereas transformation with the antisense and especially with dominant-negative Rac constructs decreased the levels of H inferior 2O inferior 2.