Soluble Sugar Availability of Aerobically Germinated Barley, Oat and Rice Coleoptiles in Anoxia

Physiological and metabolic responses to anoxia were compared for aerobically germinated seedlings of barley (Hordeum vulgare), oat (Avena sativa) and rice (Oryza sativa). Coleoptile growth of barley, oat and rice seedlings was suppressed by a 24 h-anoxic stress, but the growth of the rice coleoptiles was much greater than that of the barley and oat coleoptiles. ATP concentration in the anoxic rice coleoptiles was greater than that in the anoxic barley and oat coleoptiles. Concentrations of ethanol and activity of alcohol dehydrogenase (ADH) in the anoxic rice coleoptiles were also greater than those of the anoxic barley and oat coleoptiles, suggesting that ethanolic fermentation may be more active in the rice coleoptiles than in the barley and oat coleoptiles, where glycolysis and ethanolic fermentation are the main source of ATP production. Soluble sugar concentration in the anoxic rice coleoptiles was greater than that of the anoxic barley and oat coleoptiles. However, α-amylase, which catabolizes reserve starch to soluble sugars, was active in anoxic barley, oat and rice endosperms, and soluble sugar concentration in the anoxic barley, oat and rice endosperms was not significantly different. Therefore, anoxia stress may inhibit soluble sugar transport from the endosperms to the coleoptiles in barley and oat more than in rice. Since the availability of soluble sugar is essential for operation of glycolysis and fermentation in plant cells, ability for sugar transport from the endosperms to the coleoptiles may be one means to distinguish the coleoptile growth of these plant species in anoxia and anoxia tolerance of these plants.