Supply of Sucrose and Its Metabolism in Developing Grains of Wheat

Abstract

Sucrose and other soluble carbohydrates were measured in the grain and other parts of ears of wheat growing in the field. Amounts of sucrose in the cells of the endosperm fluctuated conspicuously from time to time, but there was no marked reduction in sucrose as the grain ripened, and in the final stages of ripening, as the grain lost water, the apparent concentration of sucrose increased. Amounts of sucrose and other soluble carbohydrate in the rachis were more or less steady throughout the grain's growth with, perhaps, an upward trend as the grain ripened. In the peduncle, sucrose remained steady throughout, but amounts of other soluble carbohydrate fell progressively with time.

At frequent intervals throughout development, isolated endosperm was cultured for 5 h in solutions of [¹⁴C]sucrose to evaluate changes in its capacity to absorb and metabolize the sugar. Amounts of [¹⁴C]sucrose absorbed increased progressively with the age of the grain. No marked changes associated with development were observed in the incorporation of radioactivity into the fraction (excluding sucrose) extracted from cultured endosperm with boiling ethanol, even after the grains had ceased growing. However, amounts of [¹⁴C]starch produced in the cultured endosperm rose to a maximum at about the mid-point of the grain's development, and then fell progressively to near zero in endosperm in which the deposition of starch had ceased. Although the trends for other insoluble radioactive material resembled trends for starch, radioactivity was incorporated into this fraction in endosperm no longer able to synthesize radioactive starch.

These results are taken as evidence that the normal developmental pattern of accumulation of dry matter in the endosperm is determined within the endosperm itself, rather than through the provision of precursors from the rest of the plant.