Malus tissue cultures. II. Sorbitol metabolism and carbon nutrition

Growth of callus cultures from stem explants of Malus pumila, cultivars McIntosh and Cortland, and of M. robusta No. 5, and from cotyledon explants of McIntosh was compared on standard medium with sorbitol, sucrose, glucose, and fructose, each at concentrations of 3 and 6%, and on nine other carbon sources, each at 3% concentration. Fructose was generally the most effective of the 13 carbon sources tested, although depending on concentration and callus type, sorbitol, glucose, and sucrose were as effective as fructose. Sucrose, accumulating in quantities ranging between 40 and 87% of total carbohydrate, was the predominant carbohydrate constituent found in all cultures grown on both concentrations (3 and 6%) of sorbitol, sucrose, glucose, and fructose except those grown on 6% sorbitol, which accumulated between 68 and 75% sorbitol. Cultures grown on sugars at the higher concentration accumulated between 6 and 34% sorbitol, whereas in corresponding cultures grown at the lower concentration no sorbitol was detected.