Hydrogen peroxide mediates high-intensity blue light-induced hypocotyl phototropism of cotton seedlings

Phototropism is a classic adaptive growth response that helps plants to enhance light capture for photosynthesis.It was shown that hydrogen peroxide(H_(2)O_(2))participates in the regulation of blue light-induced hypocotyl phototropism;however,the underlying mechanism is unclear.In this study,we demonstrate that the unilateral high-intensity blue light(HBL)could induce asymmetric distribution of H_(2)O_(2) in cotton hypocotyls.Disruption of the HBL-induced asymmetric distribution of H_(2)O_(2) by applying either H_(2)O_(2) itself evenly on the hypocotyls or H_(2)O_(2) scavengers on the lit side of hypocotyls could efficiently inhibit hypocotyl phototropic growth.Consistently,application of H_(2)O_(2) on the shaded and lit sides of the hypocotyls led to reduced and enhanced hypocotyl phototropism,respectively.Further,we show that H_(2)O_(2) inhibits hypocotyl elongation of cotton seedlings,thus supporting the repressive role of H_(2)O_(2) in HBL-induced hypocotyl phototropism.Moreover,our results show that H_(2)O_(2) interferes with HBL-induced asymmetric distribution of auxin in the cotton hypocotyls.Taken together,our study uncovers that H_(2)O_(2) changes the asymmetric accumulation of auxin and inhibits hypocotyl cell elongation,thus mediating HBL-induced hypocotyl phototropism.

Cryptochrome-mediated hypocotyl phototropism was regulated antagonistically by gibberellic acid and sucrose in Arabidopsis

Both phototropins(phot1 and phot2)and cryptochromes(cry1 and cry2)were proven as the Arabidopsis thaliana blue light receptors.Phototropins predominately function in photomovement,and crypto-chromes play a role in photomorphogenesis.Although cryptochromes have been proposed to serve as positive modulators of phototropic responses,the underlying mechanism remains unknown.Here,we report that depleting sucrose from the medium or adding gibberellic acids(GAs)can partially restore the defects in phototropic curvature of the phot1 phot2 double mutants under high-intensity blue light;this restoration does not occur in phott phot2 cry1 cry2 quadruple mutants and nph3(nonphototropic bypocotyl 3)mu-tants which were impaired phototropic response in sucrose-containing medium.These results indicate that GAS and sucrose antgonistically regulate hypocotyl phototropism in a cryptochromes dependent manner,butit showed a crosstalk with phototropin signaling on NPH3.Furthermore,cryptochromes activation by blue light inhibit GAS synthesis,thus stabilizing DELLAS to block hypocotyl growth,which result in the higher GAs content in the shade side than the lit side of hypocotyl to support the asymmetric growth of hypocotyl.Through modulationof the abundance of DELLAS by sucrose depletion or added GAs,it revealed that cryptochromes have a function in mediating phototropic curvature.