Physiology of ribohexulose (D-allulose) and allitol in Itea plants

Abstract

The contents of soluble carbohydrates and of starch in barks and leaves of Itea virginica were investigated during the course of a year. The predominant sugar is always ribohexulose (= D-allulose). In the barks its maximum content is in winter and in summer. The amount of the polyol allitol is high during the summer in barks and leaves. The content of starch shows only minor variations. In a starvation experiment, after six days of permanent darkness, the amount of ribohexulose is not considerably lowered whereas all other soluble carbohydrates including allitol have almost disappeared. From the labelling of the soluble carbohydrates after short periods of photosynthesis in 14CO2 a rapid synthesis and turnover of ribohexulose can be seen in the light. Ribohexulose has probably taken over storage functions which in other plant species are performed by starch. The same may be true in diverse species for other soluble carbohydrates, the amounts of which show a maximum in the summer together with the usual winter-maximum. Ribohexulose is a partially inert storage compound and to some extent behaves similarly to the polyol dulcitol in Evonymus. However, allitol in Itea is metabolically active and is rapidly synthesized in the light and converted in the dark.