Loss of organic compounds from roots. II. Effect of O2 and CO2 tension on release of sugars from peanut roots under axenic conditions

The effects of O₂ and CO₂ tensions, both individually and combined, on peanut root exudation of sugars from peanut plants grown in nutrient solutions under axenic conditions were measured. There were no effects on plant growth, but root exudation was increased under decreased aerbiosis. Sugars in peanut root exudates were separated and identified by thinlayer chromatography. Comparison of Rf's and colors of root exudate sugar spots with standard sugars indicated the presence of galactose, mannose, xylose, ribose, and dihydroxyacetone. Galactose was present in all 72 root exudate samples, dihydroxyacetone in 69, ribose in 33, mannose in 8, and xylose in 5. Galactose and dihydroxyacetone were present in peanut root exudates in sufficient quantity to be measured by densitometry but concentrations of other sugars were too low be measured. Galactose exudation increased with plant age. Young plants (2 weeks old) showed a significantly greater amount of galactose exuded under more aerobic conditions. There was no difference in the total amounts of dihydroxyacetone exuded as a result of treatment or of plant age. Young plants (2 weeks old) exuded a significantly greater amount of dihydroxyacetone under more aerobic conditions (P = 0.05). As the plants matured (4 and 6 weeks old) there was a trend toward greater amounts of dihydroxyacetone exuded under less aerobic conditions.