Effect of anoxia on starch breakdown in rice and wheat seeds

The capabilities of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) seeds (caryopses) to degrade starchy reserves present in the endosperm tissue were compared under anaerobic conditions. The results showed that rice, a species highly tolerant to anoxia, can readily break down starch under anaerobiosis concomitant with germination, while wheat does not germinate and fails to degrade starch present in the endosperm. This clearly distinct behavior is likely the consequence of the successful inducible formation of α-amylase (EC 3.2.1.1.) in rice under anoxia, whereas the enzyme is not produced in wheat seeds. We found that rice seeds possess a set of enzymes allowing starch and its degradative products to be utilized under anoxic conditions. Wheat seeds were shown to germinate even under anoxia if fed glucose or sucrose exogenously. The overall results indicate that induction of α-amylase appears to be one of the factors permiting rice seeds to germinate in totally anaerobic environments.