Biochemical Adaptations to Anoxia in Barnyard Grass

Although higher plants require oxygen for growth, they frequently experience low oxygen environments which occur in natural wetlands and during flooding or irrigation. Plants tolerate these conditions for only a short period of time before irreversible damage occurs. We have been studying a group of rice weeds which, like cultivated rice (Oryza sativa), can germinate and grow without oxygen. Echinochloa crus-galli var. oryzicola (hereafter oryzicola) metabolizes its seed reserves under N2 and produces a larger seedling from a smaller seed than rice (Kennedy, Rumpho and VanderZee, 1983b). In response to temperature, oryzicola and rice exhibit similar germination characteristics under aerobic conditions. Under anaerobic conditions, however, oryzicola germinates better and tolerates colder temperatures than rice. Thus, both Echinochloa and rice provide excellent opportunities to study metabolic adaptations to low oxygen stress. In addition, the Echinochloa ‘complex’ is composed of several species that differ in their ability to germinate under anoxia (Kennedy et al., 1983b), each exhibiting a full range of habitat preference and weediness in rice cultivation — an ideal natural system for comparative studies on the biochemistry of these important weed species.