Sugar And Abscisic Acid Signaling Are Involved In The Sex Expression Response Of Monoecious Cucumber To Low Night Temperature

The sex differentiation of cucumber has a close relationship about its yield. Research on the mechanism of sex differentiation of cucumber will provide a basis for gender regulation, which has an theoretical and practical value.it has been shown that low temperature is preferable for the formation of female flowers, In order to investigate how low temperature alters the sex expression of monoecious cucumbers (Cucumis sativus L.). Plants were grown under different day/night temperature regimes, which were design as28℃/18℃(12h/12h),18℃/12℃,28℃/12℃and28℃/(6h18℃+6h12℃). We found that plant femaleness is highest in the treatment of28℃/(6h18℃+6h12℃), and lowest in28℃/18℃. The analysis of endogenous phytohormones and sugars in shoot apex reveal that plant femaleness is positively correlated with the levels of ethylene, ABA, glucose and sucrose by HPLC.To investigate the role of sugar signaling in low-temperature-induced femaleness of cucumber, and also to check whether the induction is HXK-mediated, we analyzed the effects of exogenous sugars, such as glucose, sucrose, mannose (can be phosphorylated by HXK), mannose is useless in cucumber but is a sugar signaling;3-O-methylglucose (a poor substrate of HXK), The results suggest that the ABA and ethylene biosynthesis, as well as plant femaleness was enhanced by glucose, sucrose, and mannose, but not by3-O-methylglucose.ZEP (zeaxanthin epoxidase) is a key enzyme of ABA biosynthesis, ASC2(ACC synthase2) is a key enzyme in ethylene biosynthesis pathway. In this study, our results suggest that exogenous application of glucose, sucrose and mannose enhanced the expression of ZEP and ACS2in cucumber shoot apex. Consistent with the transcriptional increase, ABA and ethylene levels in shoot apex were also up-regulated, which led to enhanced plant femaleness. On the other hand,3-O-methylglucose did not induce either ABA and ethylene biosynthesis or plant femaleness. Exogenous ABA application promoted the endogenous ABA biosynthesis significantly, but did not alter the ACS2expression, ethylene evolution and plant sex expression.NDGA (nordihydroguaiaretic acid) is an ABA biosynthesis inhibitor, glucosamine is an HXK inhibitor. We found that both low-temperature and sugar-induced ABA or ethylene biosynthesis and plant femaleness were antagonized by lucosamine and NDGA.We conclude that the enhancement of cucumber femaleness in various temperature regimes is induced by the elevated levels of glucose and sucrose in the shoot apex through a sugar signaling pathway involving ABA and hexokinase.