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 in cubated at 15 degrees C and 25 degrees C. The fully oxidized form, deh ydroascorbate, was inhibitory. Ascorbate only stimulated cell elongati on if it underwent appreciable autoxidation at 25 degrees C or at 15 d egrees C in the presence of small amounts of Cu2+. When ascorbate oxid ation was inhibited, no stimulation of root growth was found at 25 deg rees C. Ascorbate oxidation rate was lower in the presence of onion ro ots, indicating that ascorbate free radical may be used as an electron acceptor for the transplasma membrane redox system regenerating ascor bate. The activation of this system could explain the reported growth stimulation.