An Investigation of the Association Between the Hydrolysis of Sucrose and Its Absorption by Grains of Wheat

Abstract

The possibility of a linkage between the hydrolysis of sucrose and its uptake by wheat grain was investigated by culturing isolated grain in solutions of sugar. The grain hydrolyses sucrose to glucose and fructose, the catalyst seems to be extracellular acid invertase (ß-fructofuranosidase), and the rate of hydrolysis is at least as fast as the deposition of starch. However, tris-HCl buffers inhibit hydrolysis but have no effect on the uptake of sucrose or on the speed of its conversion to starch.

The grains absorb invert sugar (glucose and fructose) faster than sucrose, but more sucrose accumulates and less starch is produced from invert sugar than from sucrose. Culturing grain in a mixture of non-radioactive glucose or fructose and symmetrically labelled sucrose introduces very little asymmetry into the sucrose taken up, but sucrose accumulated from [fructosyl-¹⁴C]sucrose loses half the asymmetry, while sucrose produced from a mixture of [¹²C]glucose and [¹⁴C]fructose is not completely symmetrical. Both moieties of sucrose are converted into starch.

It is concluded that absorption of sucrose is not dependent on extracellular hydrolysis, and intracellular hydrolysis of sucrose prior to conversion to starch is unlikely.