Relationship of Solute Leakage to Solution Tonicity in Fruits and Other Plant Tissues

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Abstract
During incubation in water, sections from potato tubers, apples, pears, bananas and the 3rd internode of etiolated pea seedlings leak sugar with a basically similar pattern; a rapid initial outflow (I) with a half time of approximately 80 seconds, followed by a slower 2nd phase (II). Based on the similarity between the kinetics of I in apples, and the entry of F into this tissue''s free space (F. S.) it is concluded that the initial loss of sugar is from F. S. Compartment II is identified as the vacuole. High external tonicities of glycerol and other organic and inorganic osmotic agents are equally effective in preventing n, but do not alter I in apple slices, whereas both I and II are tonicity-dependent in pea and potato sections. Water loss, tissue browning, and reduction in the rate of ethylene formation are secondary results of leakage from fruit sections suspended in water, and consequently are tonicity-sensitive processes. The propensity to leak sugars was constant throughout the climacteric of bananas, and auxins, ethylene, anaesthetics and metabolic inhibitors did not alter the leakage pattern of apples. However, below pH 2, glycerol became progressively less effective, and above 55[degree] its action was irreversibly negated. These observations, and the fact that the Q10 for exosmosis is 1.5 in water and 2.8 in glycerol, suggests that tonicity alters a non-lipoidal component of the membrane structure. Leakage in pea sections was unresponsive to auxin and ethylene (although both altered growth), occurred solely through the cut ends, and was enhanced by metabolic inhibitors.