Nutrient Uptake Changes in Ascorbate Free Radical-Stimulated Onion Roots

Long-term treatments with ascorbate free radical-stimulated glucose, fucose, sucrose, and nitrate uptake in Allium cepa roots. Glucose and fucose showed saturation kinetics in untreated roots, but after treatment with the ascorbate free radical, uptake was linear with time. Although the rates of nitrate and sucrose uptake increased after treatment with ascorbate free radical, the kinetics were similar to those observed in the controls. Ascorbate and dehydroascorbate inhibited nutrient uptake. The uptake rates for all nutrients increased throughout the 48-h period of pretreatment with ascorbate free radical. During the treatment an increase in the vacuole volume and tonoplast surface area also occurred. These results show the relationship between an increase in vacuolar volume and stimulated nutrient uptake from ascorbate-free radical, resulting in enhanced root elongation. These results suggest that activation of a transplasma membrane redox system by ascorbate-free radical is involved in these responses.