棉花不同部位主茎叶对脱叶剂噻苯隆的响应及机理

Responses and Underlying Mechanisms of Different Mainstem Leaves on Cotton to Defoliant Thidiazuron

【目的】明确棉花不同部位主茎叶对脱叶剂噻苯隆响应的差异及其作用机理。【方法】在室内光照培养条件下,用4.54 mmol·L^-1噻苯隆均匀涂抹10叶期棉株的所有主茎叶或功能叶(倒4叶)和幼叶,观察不同部位叶片的离层形成及脱落时间,检测叶片中乙烯合成及信号转导相关基因的表达量。【结果】噻苯隆处理后离层形成顺序为:幼叶(倒1叶)>基部第1~2叶(倒9~10叶,叶龄35~40 d)>功能叶(倒4叶);叶片脱落顺序为:幼叶>功能叶>基部第1~2叶,且基部第1~2叶容易出现枯而不落的现象。噻苯隆涂抹后24 h内,功能叶和幼叶中的乙烯合成基因Gh ACS1均上调表达,但幼叶中上调表达的时间早于功能叶,上调幅度也大于功能叶;此外,幼叶中的乙烯合成基因GhACO1、乙烯信号转导基因Gh EIN3和GhERF23在涂抹噻苯隆24 h后显著上调数倍或数十倍,但功能叶中这几种基因的表达量变化不大。【结论】应用脱叶剂噻苯隆处理棉花叶片后,不同叶位叶片离层形成的时间不同,且脱落的顺序与离层形成的顺序不一致。幼叶离层形成及脱落较早,与其乙烯合成及信号转导相关基因的表达上调较早且幅度较高有关。

[Objective]This study elucidates the responses of different mainstem leaves on cotton to defoliant thidiazuron and reveal the underlying mechanisms.[Method]Cotton plants were raised hydroponically.At the ten-leaf stage,4.54 mmol·L^-1 thidiazuron was evenly applied to all mainstem leaves,the youngest full-expanded leaf(the fourth leaf from apex)and the youngest leaf(the first leaf from apex).Then,the progress of abscission zone formation and shedding of each leaf was observed,and the expression level of genes related to ethylene synthesis and signal transduction in the fourth and first leaf from apex was analysed.[Result]The abscission zone developed in the following sequence:the first leaf from the top,then the lowest leaves(the ninth or tenth leaf from the top,35-40 days old),and the fourth leaf from the top.However,the leaf abscission was in a different order:the earliest was the first leaf from apex,then the fourth leaf from apex,and the latest was the lowest leaves which were prone to wither and stick to the stalk.The GhACS1 expression was up regulated in both the first leaf and the fourth leaf from apex within 24 h after thidiazuron treatment.However,the expression of this gene changed more rapidly and sharply in the first leaf from the top than that in the fourth leaf from the top.In addition,the expression of GhACO1(ethylene synthesis gene),Gh EIN3 and Gh ERF23(ethylene signal transduction genes)was significantly increased up to ten times in the first leaf from the top,whereas the expression of these genes did not change in the fourth leaf from the apex.[Conclusion]After exposed to defoliant thidiazuron,the time of the abscission zone formation of different leaves on cotton main stem is different,and the order of shedding is not consistent with that of abscission zone formation.The youngest ready to expand leaf abscises earlier than the youngest fully expanded leaf after thidiazuron treatment,which is possibly associated with the rapid expression change of genes related to ethylene synthesis and signal transduction in the former.