Anaerobic germination and metabolism ofErythrinaseeds with special reference to mitochondria and nitrate reductase

Abstract

AbstractSeeds ofErythrina caffraThunb. are able to germinate anaerobically. Cycloheximide, chloramphenicol and malonate depressed germination. N2-incubated seeds metabolised [2-14C] Na-acetate. Synthesis of ATP in embryonic axes of N2-incubated seeds occurred to the same extent as in air-germinated seeds. Cycloheximide but not chloramphenicol depressed ATP and ethanol contents and respiratory capacity of embryonic axes.Embryonic axis mitochondrial O2uptake capacity was similar for seeds incubated for 24 h in air and N2. The activities of five mitochondrial enzymes at this stage were slightly lower in N2-incubated than in air-incubated axes. However, at 12 h, i.e. prior to germination, activities in N2-incubated axes were higher for malate dehydrogenase, oxoglutarate dehydrogenase and pyruvate dehydrogenase, similar for succinate dehydrogenase and slightly lower for cytochrome oxidase than corresponding activities in axes of air-germinated seeds. Mitochondrial protein synthesis occurred in axes of N2-incubated seeds but at a slightly lower rate than in air-incubated seeds.When assayed anaerobically nitrate reductase activity was found associated with purified mitochondria. The nitrate reductase associated with mitochondria utilised NADH, succinate and to a lesser extent malate as electron donors. The activities measured were much lower than those of typical mitochondrial enzymes.It is concluded that mitochondrial activity occurs anaerobically inE. caffraembryonic seed axes and might possibly play a role in anoxic germination.