Anaerobic Metabolism in Germinating Seeds of Echinochloa crus-galli (Barnyard Grass)

Abstract

Echinochloa crus-galli, a problem weed in rice fields, has the rare ability to germinate and to grow in a totally oxygen-free environment. After 7 days growth in the light or dark under N₂, E. crus-galli var. oryzicola produces a 2- to 3-centimeter nonpigmented shoot.

Ethanol, malate, and lactate were measured in seeds germinated under N₂ and air, and compared with changes in the activities of alcohol dehydrogenase, malate dehydrogenase, NADP-malic enzyme, and phosphoenolpyruvate carboxylase. During a 7-day time course, ethanol levels increased 661 micromoles per gram dry weight under N₂, with no increase under air. Alcohol dehydrogenase activity increased 5.5 micromoles per gram dry weight per minute in N₂ compared to 1.0 in air. Corresponding increases for lactate were 7.9 micromoles per gram dry weight under N₂ and 2.7 under air, and for malate, 5.3 micromoles per gram dry weight under N₂ and 0.4 under air.

Although 85% of the ethanol produced by the seedlings was found in the external solution under N₂, the seeds still contained 90 times more ethanol under anaerobic conditions than under air. No phosphoenolpyruvate carboxykinase activity was detected and phosphoenolpyruvate carboxylase activity was 10 times less under N₂ than air. Malic enzyme activity increased 5-fold under anaerobic conditions, comparable to the change under aerobic conditions. Proposed adaptive mechanisms of flood-tolerant species to anaerobiosis are discussed.

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