Activities of Isolated Mitochondria and Mitochondrial Enzymes from Aerobically and Anaerobically Germinated Barnyard Grass (Echinochloa) Seedlings

Abstract

ABSTRACrActivity of mitochondria isolated from whole seedlings of Echinlochca cra-gaii (L.) Beauv. var oryzicola ge ted under aerobic and anaerobic conditions for 5 to 7 days was investigated. Mitochondria (4,14,19,24) appear to play equally important roles. Mitochondrial electron transport may so be an important metabolic consideration not only during anoxia, but also during the transition from anaerobic to aerobic conditions. Reduction of an alternate electron acceptor, such as nitrate (6) or organic acids (5, 8), could permit electron transport in the absence of 02. In support of this hypothesis, we have found that nitrate reserves are depleted in oryzicola seeds during germination (13). Once germinated, the ability to rapidly shift from an anaerobic mode to an aerobic one may be an important metabolic feature during early establishment of this flood tolerant species.In previous studies, we noticed that, unlike rice, germination of oryzicola is inhibited by cyanide and azide (13). In addition, tricarboxylic acid cycle intermediates are produced and acetate is readily metabolized under anaerobic conditions (19). Finally, unlike reports for other flood tolerant species (16,23,24,26), mitochondrial ultrastructure in seedlings germinated under N2 were indistinguishable from those grown in air (1 1

Anaerobic Carbon Metabolism by the Tricarboxylic Acid Cycle

“…The important observation is that the specific activity of glutamic acid continues to increase over the course of the experiment, suggesting continued flux of radiolabel into this compound (Fig. 3) (8,17). To our knowledge, however, the present study is the first study demonstrating oxidative TCAC carbon flow to aKG occurring in a photosynthetic tissue under anaerobic conditions.…”

Long-Term Anaerobic Metabolism in Root Tissue (Metabolic Products of Pyruvate Metabolism)

“…Under anaerobic conditions, aspartate concentration drops rapidly, whereas the concentration of malate showed a transient increase followed by a steady decrease. The final enzyme involved in the synthesis of succinate, succinate dehydrogenase, is not induced under anaerobic conditions (Kennedy et al, 1987). These data suggest a correlation between the anaerobic induction of an enzyme and an increase in the level of product for at least the first 24 h of anaerobiosis.…”

“…In addition, none of the enzymes involved in aspartate deamination and succinate production show any form of anaerobic induction ( Fig. 1; Kennedy et al, 1987). The predominant long-term anaerobic product in this system is clearly ethanol.…”

Anaerobic Metabolism in Plants

“…Although our data indicate that acetyl CoA is used for lipid synthesis, we also have evidence that it enters the TCA cycle. Mitochondrial activity, including both the TCA cycle (7) and electron transport (16) (27). In maize and pea seeds, both relatively flood-intolerant plants, death is correlated with the collapse of the vacuolar-cytoplasmic proton gradient (27).…”