Vitamin C (Ascorbic acid): Uptake and Metabolism by Soybean

Abstract

The uptake of ascorbic acid by soybean roots and leaves, as well as the re-translocation of absorbed ascorbic acid into the newly formed tissues, using both 14C-labelled and unlabelled ascorbic acid was studied. Ascorbic acid was found to be absorbed by both roots and leaves. Its uptake by roots showed a saturation-type kinetics and was sensitive to root temperature, oxygen supply and presence of the metabolic inhibitor (DNP) in the rooting media. These findings indicate that the uptake of ascorbic acid by plants, similar to its uptake by some animal tissues, is an active process that requires metabolic energy. In plants loaded with 14C-labelled ascorbic acid via roots or leaves, 14C-radioactivity was quickly distributed among all plant parts. No increase in the ascorbic acid concentration of the plant parts, in comparison with the control plants, could be measured 7 days after loading. Even 24 h after loading, roots loaded with 14C-ascorbic acid contained high amounts of radioactivity, but the roots of parallel plants loaded with the same concentration of unlabelled ascorbic acid contained no (zero) ascorbic acid. Also in the roots of control plants no ascorbic acid could be measured. This points to some very efficient mechanism in the soybean roots that metabolizes the endogenous or externally applied ascorbic acid. Since the externally applied ascorbic acid is very unstable within the plants, any effect of ascorbic acid spray for their protection against air pollution may be of a very short lifetime.