Studies on starch breakdown of cereal seeds during anoxic germination

充足的碳水化合物供应有助于种子在氧气供应有限的条件下存活。干燥谷物种子中可溶、易发酵的碳水化合物的数量通常非常有限，淀粉是主要的储存化合物。谷物种子萌发过程中淀粉的降解是水解酶作用的结果，只有在α-淀粉酶(EC3.2.1.1)、β-淀粉酶(EC3.2.1.2)、去支化酶(EC3.2.1.41)和α-葡萄糖苷酶(EC3.2.1.20)的共同作用下，淀粉才能被完全水解。本文介绍了耐厌氧的水稻和小麦(Triticum aestivum L.)三种谷物淀粉降解酶的全套数据。和大麦(Hordeum visgare L.)在缺氧条件下不能萌发。在缺氧条件下测试的谷物种子中，只有大米能够降解未煮熟的可溶性淀粉，这反映了在体内降解淀粉颗粒的能力。这是由于完全降解淀粉所需的一整套酶的存在，要么是从头合成(α-淀粉酶、β-淀粉酶)的结果，要么是先前存在的、不活跃的酶(去支化酶、α-葡萄糖苷酶)激活的结果。在厌氧条件下保存的小麦和大麦种子中，这些酶要么不存在，要么不活跃。

An adequate carbohydrate supply contributes to the survival of seeds under conditions of limited oxygen availability. The amount of soluble, readily fermentable carbohydrates in dry cereal seeds in usually very limited, with starch representing the main storage compound. Starch breakdown during the germination of cereal seeds is the result of the action of hydrolytic enzymes and only through the concerted action of alpha-amylase (EC3.2.1.1), beta-amylase (EC3.2.1.2), debranching enzyme (EC3.2.1.41), and alpha-glucosidase (EC3.2.1.20) can starch be hydrolyzed 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 anoxia. Among the cereal seeds tested under anoxia, only rice is able to degrade nonboiled, soluble starch, reflecting the ability to degrade the starch granules in vivo. This is explained by the presence of the complete set of enzymes needed to degrade starch completely either as the result of de novo synthesis (alpha-amylase, beta-amylase) or activation of preexisting, inactive form of the enzyme (debranching enzyme, alpha-glucosidase). These enzymes are either absent or inactive in wheat and barley seeds kept under anaerobic conditions.