Respiratory Metabolism in Detached Rhododendron Leaves

Abstract

Detached leaves of R. ponticum evolved CO2 in air in the dark for long periods with the RQ falling from 1-0 to 0.8. In oxygen concentrations less than 1.6% the CO2 output was enhanced initially and ethanol accumulated; acetaldehyde and lactate accumulations were slight. The molar quotient for anaerobic ethanol accumulation/CO2 production was about 0.6. On return to air after a period in N the CO2 output was markedly enhanced; the RQ was very low for the 1st hour but rose rapidly thereafter. Changes in the concentrations of starch, soluble sugars, glycosides, ester phosphates, nonvolatile di- and tricarboxylic acids and keto acids in air, N, and in air after a period in N were measured. The leaves exhibited a Pasteur effect but the CO2 outputs were not fully accounted for by changes in carbohydrates or any of the substances measured. On transfer to N there were rapid decreases in 3-P-glycerate, P-enolpyruvate, and 6-P-gluconate, whereas the hexose phosphates all showed transient increases in concentration. In the first hours in air after a period in N the utilization of glucose-C14 was very slow. The slow changes in level of keto acids in this period suggest a slow resumption of TCA cycle reactions.