Permeability Characteristics and Amino Acid Incorporation during Senescence (Ripening) of Banana Tissue

Abstract

For banana tissue free space increased significantly about 44 hours before the onset of, and rose exponentially during the respiratory climacteric. The increase in free space indicates a progressive increase in the proportion of cells which became completely permeable to solutes in the ambient solution by simple diffusion. At the respiratory peak the tissue was essentially 100% free space to Cl4-labeled solutes. Active uptake of solutes declined markedly about 1 day before the onset of the climacteric and fell to a very low level by the respiratory peak. There was no change in the level of protein or amino acids during ripening, but the rate of leakage of amino acids increased greatly. Studies of incorporation of 3 concentrations of C14-labeled leucine and phenylalanine indicated marked changes in the size and specific activity of the amino-acid pool at the site of protein synthesis just prior to and during the climacteric rise, due to a diffusive mixing of the labeled substrate with the previously sequestered endogenous, unlabeled pool of substrate. Data from these studies indicated a decline in amino-acid incorporation during the climacteric. It was concluded that the initiation of permeability changes marked the onset of senescence in banana. The causative relations between alterations in permeability and other changes attending fruit ripening are discussed.