Respiration and NADH-Oxidation of the Roots of Flood-Tolerant and Flood-Intolerant Senecio Species as Affected by Anaerobiosis

Respiration was measured under anaerobiosis in the roots of two Senecio species: S. aquaticus Hill, which is flood-tolerant, and S. jacobaea L., which is flood-intolerant. NADH-oxidation under anaerobiosis was measured in roots of S. aquaticus, S. jacobaea and S. vulgaris L., which is also flood-intolerant. Protein content of S. aquaticus was about 15% higher under anaerobiosis. At 20°C respiration of the roots of S. aquaticus was 50% inhibited under anaerobiosis, while an almost complete inhibition occurred in the roots of S. jacobaea. The activities of nitrate reductase, glutamate dehydrogenase and lactate dehydrogenase were considerably higher in the roots of S. aquaticus grown under anaerobic conditions than in roots grown under aerobic conditions. In S. jacobaea glutamate dehydrogenase activity was lower and in S. vulgaris nitrate reductase was lower and glutamate dehydrogenase activity was higher in roots grown under anaerobic conditions. The possible role of these enzymes for metabolism under anaerobic conditions by oxidizing a surplus of NADH is discussed. Since oxidative phosphorylation is 50% inhibited under anaerobiosis, ATP has to be generated in a different way. It is argued that maintenance of the ATP-level may be compensated by way of the enzymes mentioned above, in combination with a modified glucose utilization.