The alternative of ABA degradation pathways as a key process on adaptation of hygrophytes to anaerobic environments

藜属植物具有不同的旱地和水稻生态型。在水稻生态型种子中，在厌氧和有氧条件下，脱落酸(ABA)含量均下降，且与种子萌发有关。ABA通过氧化途径和/或葡萄糖结合途径降解，在这些途径中其反应不需要氧气。萌发的水稻生态型种子中ABA葡萄糖结合物增加。相反，氧化途径中的主要分解代谢物二氢相酸在旱地生态型种子中积累。综上所述，旱地生态型种子通过氧化降解减少内源ABA，水稻生态型种子通过结合降解减少内源ABA。在本研究中使用的所有湿生植物和中生植物中都观察到了类似的现象，表现在棘豆生态型中。因此，我们认为ABA降解途径的替代是湿生植物适应淹水引起的厌氧环境的关键因素。

Echinochloa plants have differentiated upland and paddy ecotypes. In paddy ecotype seeds, abscisic acid (ABA) decreased under both anaerobic and aerobic conditions, in association with their germination. ABA is degraded via an oxidation pathway and/or a glucose conjugation pathway in which oxygen is not required for its reaction. The ABA glucose conjugates increased in the germinating paddy ecotype seeds. In contrast, dihydrophaseic acid, a major catabolite in the oxidation pathway, accumulated in the upland ecotype seeds. Conclusively, it appeared that seeds of the upland ecotype decrease endogenous ABA by the oxidative degradation and those of the paddy ecotype by the conjugative degradation. Similar phenomena, shown in the Echinochloa ecotypes, were observed in all hygrophytes and mesophytes used in this study. We thus propose that the alternative of ABA degradation pathways is a key factor with which hygrophytes adapted to anaerobic environments, which resulted from flooding.