PROTEIN METABOLISM AND RESPIRATION IN ATTACHED AND DETACHED PRIMARY WHEAT LEAVES

Abstract

Attached and detached wheat leaves were supplied with C14O2 for a short period in light. They were then kept for 20 hours in the dark followed by 20 hours in light in air. Samples were taken at the beginning and end of each period and analyzed for protein nitrogen; and for amounts and total activities of respired carbon, soluble sugars, and amino acids and of protein amino acids.Similar patterns of protein metabolism were found in the two sets of leaves. The estimated protein amino acid turnover rates were somewhat higher in the detached than in the attached leaves but this may have been due to greater participation of soluble compounds which could not be translocated in detached leaves. There was a rapid synthesis of amides in the detached leaves during the light period, but this occurred at the expense of soluble sugars and supplied nitrogen salts rather than from protein breakdown products.Some contribution was made to respired CO2 by proteins during a period when protein turnover as well as a net decrease in proteins took place. During senescence, protein degradation contributed a considerable amount of carbon to respiration, but no protein turnover took place.