AMYLOLYTIC ACTIVITIES IN CEREAL SEEDS UNDER AEROBIC AND ANAEROBIC CONDITIONS

An adequate carbohydrate supply contributes to the survival of seeds u nder conditions of limited oxygen availability. The amount of soluble, readily fermentable carbohydrates in dry cereal seeds is usually very limited, with starch representing the main storage compound. Starch b reakdown during the germination of cereal seeds is the result of the a ction of hydrolytic enzymes and only through the concerted action of a lpha-amylase (EC 3.2.1.1), beta-amylase (EC 3.2.1.2), debranching enzy me (EC 3.2.1.41), and alpha-glucosidase (EC 3.2.1.20) can starch be hy drolyzed completely. We present here data concerning the complete set of starch-degrading enzymes in three cereals, rice (Oryza sativa L.), which is tolerant to anaerobiosis, and wheat(Triticum aestivum L.) and barley (Hordeum vulgare L.), which are unable to germinate under anox ia. Among the cereal seeds tested under anoxia, only rice is able to d egrade nonboiled, soluble starch, reflecting the ability to degrade th e starch granules in vivo. This is explained by the presence of the co mplete set of enzymes needed to degrade starch completely either as th e result of de novo synthesis (alpha-amylase, beta-amylase) or activat ion of preexisting, inactive forms of the enzyme (debranching enzyme, alpha-glucosidase). These enzymes are either absent or inactive in whe at and barley seeds kept under anaerobic conditions.