The effect of illumination and oxygen concentration on repiration metabolites content in pea leaves

Abstract

The rates of CO2 evolution during respiration of pea (P.sativum) leaves darkened for 24 hours were practically identical at both, low (1%) and atmospheric (21%) oxygen concentration. Following illumination of leaves in the atmosphere of air the respiration rate increased by about twice during the first 3-4 minutes. When O2 concentration during the period of illumination was low no enhancement in respiratory CO2 evolution was noted. The dependence of respiratory O2 uptake by mesophyll protoplasts on oxygen concentration and illumination period have shown the same pattern as noted for the respiration of the whole leaves. The ATP/ADP ratio was significantly higher in the leaves illuminated in the atmosphere of air than at low O2. Mitochondria isolated from leaves darkened for 24 hours oxidized respiratory substrates (glycine, succinate,malate) with the rates nearly the same. Mitochondria from leaves illuminated for 24 hours oxidized glycine with the twice higher rates comparing to the darkened ones. The oxidation of succinate was slightly higher (40%) and no effect of illumination of leaves on malate oxidation was noted. The content of free amino acids and malate was considerable higher in mitochondria from the illuminated leaves than from the darkened ones. The results show that the oxygen at the atmospheric concentration, during the period of illumination, affects mitochondrial respiration and, that both, the TCA cycle and the respiratory electron transport chain are capable of operation in illuminated leaves with the rate higher than in the darkened.