Interactions between ethylene, gibberellin and abscisic acid in regulating submergence induced petiole elongation in Nelumbo nucifera

Nelumbo nucifera (Lotus) responds to complete submergence with increasing petiole elongation which allows leaves to emerge above the water surface thereby restoring contact with the atmosphere. We carried out a detailed study of this growth response under submergence, to elucidate the role of several phytohormones. Under submergence, petiole elongation of lotus was mainly caused by cell division on the apical part of petiole. Exogenous phytohormone application studies and endogenous ethylene measurements revealed that ethylene, abscisic acid (ABA), and gibberellin (GA) were all involved in regulating petiole elongation under submergence. In response to submergence, ethylene accumulated first, which then initiated elongation growth of lotus petiole. An exogenously applied ethylene releasing compound, ethrel, and its precursor, 1-aminocyclopropane-1-carboxylate (ACC) promoted petiole elongation under submergence. An inhibitor of ethylene action (silver thiosulphate, STS) could partially block petiole elongation under submergence. Exogenous GA treatment caused a similar promotion in petiole elongation. Lotus seedlings treated with different concentrations of paclobutrazol (PAC, a GA inhibitor) induced a dose-dependent decrease of petiole elongation under submergence. In contrast, ABA treatment eliminated submergence-induced petiole elongation completely, while its biosynthesis inhibitor, Tungstate, and GA could reverse the inhibitory effect of ABA. However, the effect of ethrel was not affected by Tungstate. Meanwhile, an ABA biosynthesis inhibitor enhanced the effect of GA and ethrel. In summary, under submergence, increased ethylene altered the balance between a growth-inhibiting hormone (ABA) and a growth-promoting (GA) and contributed to the submergence-induced petiole elongation in lotus.