The Mechanism Of Auxin And Gibberellin Synergistically Regulating The Stalk Elongation Of Flowering Chinese Cabbage

Stalk vegetables with young fleshy stalks as product organs and its formation is directly related to the final yield and quality of vegetable crops.Environmental conditions such as temperature,light,moisture,etc.can affect the formation of stalk by means of hormones or sugar metabolism.Flowering Chinese cabbage（Brassica campestris L.ssp.chinesis var.utilis Tsen et Lee）is a typical stalk vegetable,with a large cultivation scale in South China.It was often caused by the adversity of the condition such as low tampeture,leading to early flowering and bolting,which reduces the yield and quality in the cultivation process.Studies have shown that low temperature promotes the and flowering of flowering Chinese cabbage by inducing the synthesis of gibberellins（GA）and auxin（IAA）.As we know,plant hormone signaling was involved in the stalk development.Both IAA and GA can promote the elongation of stems,but the effects on the elongation and growth of flowering Chinese cabbage stalk are still unclear.In the present study,we used appropriate concentrations of Indol-3-acetic acid（IAA）and Gibberellin3（GA₃）and auxin transport inhibitor（1-N-naphthylphthalamic acid,NPA）and gibberellin synthesis inhibitor Uniconazole to investigate IAA and GA regulation mechanisms and their relationship during the stalk elongation,by measuring the cell size of the area of pith,the content of endogenous GA and IAA at the top of stalk and the expression of the synthesis and signal transduction,cell expansion genes.The main results are as follows:1.The decapitation inhibited the elongation of the stalk,and down-regulated the expression of GA and IAA synthesis and IAA signal transduction related genes.Both IAA and GA content decreased in the tip of stalk.These results suggest the tip of stalk can regulate the elongation growth by synthesizing higher levels of IAA and GA.2.The application of exogenous IAA up-regulated expression of auxin signal transduction and GA synthesis related genes,and recovered the GA content to the level of intact plants,but the endogenous IAA levels did not change significantly.Further study showed that NPA treatment down-regulated the expression of IAA synthesis and signal transduction-related genes,and decreased the content of endogenous IAA and GA,thereby inhibiting the growth of flowering Chinese cabbage.These result indicate that IAA derived from the stalk tip can promote the elongation of the stalk.3.Exogenous GA₃ treatment can up-regulate the expression of GA synthesis and IAA signaling genes,increase the content of endogenous GA,and induce the elongation of stalk.The synergistic effect of IAA and GA₃ on the elongation of stalk was the most significant.In summary,these results showed that both IAA and GA are important factors that promote the growth of flowering Chinese cabbage stalk and the effect of GA was greater than that of IAA.IAA and GA interact with each other and synergistically promoted the elongation of flowering Chinese cabbage stalk.4.Under the simultaneous treatment of decapitation and uniconazole,IAA can promote the expression of GA synthesis and part of IAA response genes,and partially restore the growth of flowering Chinese cabbage finaly.It was further proved that IAA and GA interact with each other to jointly regulate the elongation of flowering Chinese cabbage stalk.5.GA promotes the growth of flowering Chinese cabbage by promoting cell elongation and cell expansion.IAA promotes the elongation of stalk by promoting cell division and cell expansion.In summary,IAA and GA derived from the apex of stalk were important factors regulating the growth of flowering Chinese cabbage,and IAA can promote cell division and expansion through its own signal transduction and transport pathways.GA can regulate the elongation of stalk by regulating its own synthesis and IAA signaling pathway,and GA3 has a stronger effect on promoting the elongation of stalk than IAA.