Ethanol sensitivity of rice and oat coleoptiles

The ability to avoid the ethanol-induced injury was evaluated in rice (Oryza sativa L.) and oat (Avena sativa L.) coleoptiles. The growth of the rice and oat coleoptiles was inhibited by ethanol exogenously applied at concentrations greater than 200 and 30 mM, respectively. At 300 mM ethanol, oat coleoptiles were brown and flaccid but rice coleoptiles did not show any visible symptoms of toxicity. The acetaldehyde level in rice and oat coleoptiles was increased by exogenously applied ethanol and the increases were greater in oat than in rice coleoptiles under aerobic and anaerobic conditions. At 300 mM ethanol, the acetaldehyde concentrations in the rice and oat coleoptiles were 46 and 87 nmol g-1 FW under aerobic conditions, respectively, and 52 and 124 nmol g-1 FW under anaerobic conditions, respectively. The activity of alcohol dehydrogenase (ADH; EC 1.1.1.1) in the direction of ethanol to acetaldehyde was greater in oat than in rice coleoptiles and ADH protein in oat coleoptiles was more induced by exogenously applied ethanol than that in rice coleoptiles. These results suggest that in vivo conversion rate of ethanol to acetaldehyde by ADH is lower in rice than oat coleoptiles, which may be one of the reasons that ethanol sensitivity of rice is much lower than that of oat coleoptiles. The great ability of rice to avoid the ethanol-induced injuries may contribute its anoxia tolerance when glycolysis and ethanolic fermentation replace the Krebs cycle as the main source of energy under anaerobic conditions.