Sucrose leakage from excised maize scutella

Abstract

Sucrose leaked from the maize scutellum into water upon removal of the seedling axis. A greater amount of sucrose leakage occurred when the seedlings were incubated with their scutella in fructose solutions for a number of hr before removal of the axis. Leakage into water was more rapid than into mannitol, and as the mannitol concentration was increased the leakage rate decreased. Ca 2+ inhibited leakage when present in the bathing solution during the leakage period, but had little or no effect when it was added to the solution bathing the scutellum before the seedling axis was removed. At 30°, the leakage rate, initially high, declined rapidly; and leakage stopped within 90 min. At 1°, leakage was slower but the rate was maintained for at least 4 hr so that the total leakage was greater at 1° than at 30°. If scutella were kept at 30° until leakage stopped and then were placed at 1°, leakage resumed but at a rate lower than that from scutella excised directly into 1° water. The Q 10 of the sucrose leakage process was well below 2·0, and leakage was not inhibited by DNP or by anoxia. It is concluded that sucrose leakage in the scutellum occurs by a pressure flow of solution which exits from the tissue through the cut ends of the phloem. Moreover, evidence is presented that indicates the flow is not restricted to the phloem but extends in an uninterrupted stream through the cytoplasm of most or all living cells of the scutellum.