The Mechanisms Of Hypocotyl Different Curvature In Gossypium Arboreum And Gossypium Raimondii Under High Blue Light

Light is a very important environmental factor in plant growth.Light is not only a source of energy for plant growth,but also a key regulator of plant growth and development.In order to maximize the capture of light energy,plant growth usually exhibits a characteristic of growing towards the light,which is particularly evident under unilateral irradiation.Studies have shown that blue light in natural light is the main monochromatic light that causes plants to move to light,and blue light plays an important role in plant photomorphogenesis,inhibition of hypocotyl elongation,regulation of photoperiod,and chloroplast movement.Studies have shown that blue light receptors play a major role in phototropism of plants,PHOT1(phototropin 1)and PHOT2(phototropin 2),ATPHOT1 and ATPHOT2 have obvious difference in phototropism regulation in Arabidopsis.ATPHOT1 and ATPHOT2 can mediate the phototropism,but ATPHOT1 also has the function of inhibiting hypocotyl bending under strong blue light.ATPHOTs can regulates the functions of downstream auxin transporters,AUX1,ABCB families,and PIN families transporter through the interaction of bridge proteins with RPT2(Root phototropism 2),NPH3(Nonphototropic hypocotyl 3),and PKSs(Phytochrome kinase substrates),And then regulate the content and distribution of auxin,and ultimately regulate the hypocotyl bending.The study found the two diploid cotton species,Gossypium arboreum L.,(AA)and Gossypium raimondii L.(DD).had different hypocotyl curvature under high blue light of 100 ?mol·m-2·s-1(HBL)for 12 h.The hypocotyl curvature of Gossypium raimondii is larger than that of Gossypium arboretum.According to existing studies,plant hormones play an important role in the growth and development of plants,especially the growth and bending of plant hypocotyls.For example,the asymmetric distribution of auxin in the hypocotyl determines the tropism growth.Gibberellin and brassinolide synergistically promote the growth of plant hypocotyls,and the abscisic acid inhibits growth.That may be caused by the asymmetric distribution of related hormones in Gossypium arboretum and Gossypium raimondii after blue light irradiation.For this purpose,we isolated and sampled the yellowing seedlings of Gossypium arboretum and Gossypium raimondii,and the lit and shade side of Gossypium arboretum and Gossypium raimondii hypocotyls treated with unilateral blue light,then measured the related hormones content.The results showed,under high blue light treatment,the Gossypium raimondii auxin and gibberellin content on the shade side of hypocotyl was significantly higher than lit side,while the Gossypium arboretum is not significant.Through ABA content analysis,it was found that the ABA content of the etiolated seedlings of Gossypium arboretum was significantly higher than that of Gossypium raimondii before and after the high blue light treatment.It was found,after exogenous hormone GA3 treatment,GA3 can effectively promote auxin content in hypocotyls,promote the content and asymmetric distribution of GAs in hypocotyls,overcome the inhibitory effect of high content of ABA on phototropism,and promote hypocotyl curvature.At the same time,it was found that ABA could also partially inhibit the asymmetric distribution of auxin on the hypocotyls of Gossypium raimondii and hypocotyl curvature,but,at the same time,exogenous ABA treatment promoted the increase of active GAs concentration and inhibited GAs asymmetric distribution.According to above,ABA,GA3,and IAA may be in a mutual dynamic equilibrium.ABA inhibits the IAA content and polar distribution,but also inhibits the polarity distribution of GAs.However,ABA can promotes the increase of active GAs content,which reduce ABA inhibition of hypocotyl growth.GA3 does not reduce ABA content,but high GA3 can promote phototropism by increasing IAA content and GAS asymmetric distribution.The above results suggest that Gossypium arboretum hypocotyl curvature is not obvious under high blue light,which mainly due to its high ABA accumulation inhibiting the synthesis and transportation of auxin and gibberellin.Gene expression analysis showed that the ABA content of the two cottons was regulated by two key enzymes,alcohol dehydrogenase(ABA2)and aldehyde dehydrogenase(AAO3)in the ABA synthesis pathway.The expression levels of ABA2 and AAO3 in Gossypium arboretum were significantly higher than Gossypium raimondii,so ABA has greater inhibition of Gossypium arboretum hypocotyls curvature.The polar distribution of IAA is regulated by PIN1,PIN3,ABCB19,PIF4,PIF5 and ARF7.These proteins are important for IAA synthesis and transport.The high expression of these proteins is the cause of high hypocotyl curvature in Gossypium raimondii.In summary,we found the phototropism difference between the two diploid cottons are mainly regulated by hormones signaling.The regulation include GA3 can alleviate the antagonism of ABA on phototropism,elongation of the hypocotyls curveture length,and promotion of phototropism;ABA antagonizes phototropism by inhibiting the polarity distribution of auxin.And these physiological effects of IAA,GAs,ABA are regulated by their respective synthesis or transport pathways.The greater phototropism of Gossypium raimondii after unilateral high blue light is adjusted by the greater polar distribution of IAA and GA3 and lower ABA concentration.