The Carbohydrate Nutrition of Tomato Roots

The addition of 0.01–0.015 per cent. galactose or 0.005–0.01 per cent, mannose reduces by 50 per cent, the linear growth of excised tomato roots cultured in a I per cent, sucrose medium. An addition of 0.03–0.04 per cent, of either sugar causes not less than a 90 per cent, inhibition of growth. The survival of meriste-matic activity is higher in presence of fully inhibitory concentrations of mannose than of galactose. Roots inhibited by galactose are distinguishable from those inhibited by mannose. The inhibitory effect of concentrations of galactose up to 0.15 per cent, and of mannose up to 0.4 per cent, can be fully antagonized by the simultaneous addition to the culture medium of dextrose. The minimum ratio of dextrose: inhibitory sugar for maximum antagonism of the growth inhibition is with galactose 5: 1 and with mannose 3.5: 1. Growth of roots in a dextrose-containing medium does not protect them from subsequent inhibition by either galactose or mannose. d-xylose has significant activity as an antagonist of mannose inhibition and even more so of galactose inhibition. However, the restoration of growth achievable from the addition of xylose is not comparable with that resulting from the addition of dextrose. The inhibition of growth by xylose is not alleviated by the simultaneous addition of dextrose. Maltose has low activity as an antagonist of galactose and mannose inhibition. All other sugars tested and the sugar alcohols corresponding to galactose and mannose were quite inactive as antagonists of the growth inhibition by these two sugars. Mixtures of partially inhibitory concentrations of galactose and mannose were less inhibitory than their more inhibitory component. The concentration of dextrose required to reverse the inhibitory activity of such mixtures was not greater than the minimum concentration required to antagonize the action of the more inhibitory component. The antagonism of galactose inhibition by dextrose is not due to dextrose impeding galactose uptake.