Abstract:Oxygen consumption of mitochondria isolated from mung bean seeds and leaves was determined with an oxygen electrode in the dark or light. In mitochondria isolated from mung bean leaves, strong light (40 000 Ix) suppressed the NADH oxidation by 11. 8% through cytochrome pathway, and the capacity of the alternative pathway was increased by 71. 5 %. This suggested that illumination caused part of the electrons diverting from the cytochrome pathway to the alternative pathway. It was postulated that one of the physiological functions of the alternative pathway was to regulate the balance between levels of NADH and high-energy phosphate in green cells. The mechanism of this light effect on the change in respiratory pathway still remains unknown. The mitochondria from germinated seeds of mung bean, however, were different to that from leaves of mung bean, it showed no response to light.