How rice germinates under water

Rice (Oryza sativa) has the rare ability to germinate and elongate a coleoptile under oxygen-deficient conditions, which include both hypoxia and anoxia. It has previously been shown that Alcohol Dehydrogenase 1 (ADH1) is required for cell division and cell elongation in the coleoptile of submerged rice seedlings by means of studies using a rice ADH1-deficient mutant, reduced adh activity (rad).

A recent paper in Annals of Botany aims to understand how low ADH1 in rice affects carbohydrate metabolism in the embryo and endosperm, and lactate and alanine synthesis in the embryo during germination and subsequent coleoptile growth in submerged seedlings.

Even in a submerged environment containing substantial amounts of dissolved oxygen, a reduction in ADH (as brought about by an ADH1 mutation) reduces seedling viability, changes the balance between the end-products of glycolysis and decreases sugar concentrations in the endosperm and embryo. Exogenous sugar did not improve the growth or survival of the ADH1 mutant, indicating that sugar processing in the embryo was probably the limiting factor. However, how low ADH activity affects the endosperm deserves further experimental attention. The endosperm is well suited for investigations of sugar production and transport because of its simple composition and metabolism.

Takahashi, H., Greenway, H., Matsumura, H., Tsutsumi, N., & Nakazono, M. (2014) Rice alcohol dehydrogenase 1 promotes survival and has a major impact on carbohydrate metabolism in the embryo and endosperm when seeds are germinated in partially oxygenated water. Annals of Botany, 113 (5): 851-859. doi: 10.1093/aob/mct305