RELATIONSHIP BETWEEN APOPLASTIC ASCORBATE REGENERATION AND THE STIMULATION OF ROOT-GROWTH IN ALLIUM-CEPA L

Ascorbate free radical stimulated onion root growth when bulbs were incubated at 15 degrees C and 25 degrees C. The fully oxidized form, dehydroascorbate, was inhibitory. Ascorbate only stimulated cell elongation if it underwent appreciable autoxidation at 25 degrees C or at 15 degrees C in the presence of small amounts of Cu2+. When ascorbate oxidation was inhibited, no stimulation of root growth was found at 25 degrees C. Ascorbate oxidation rate was lower in the presence of onion roots, indicating that ascorbate free radical may be used as an electron acceptor for the transplasma membrane redox system regenerating ascorbate. The activation of this system could explain the reported growth stimulation.