ASCORBATE FREE-RADICAL STIMULATES ONION ROOT-GROWTH BY INCREASING CELL ELONGATION

Ascorbate free radical increased the growth of Allium cepa roots by 20%. The nature of this stimulation was not related to cell proliferation, for neither cell cycle nor mitotic index was affected. However, an ascorbate free radical-mediated cell-size increase was observed in both meristematic and elongating cells. Further, both plasma membrane- and tonoplast-associated ATPases were increased by ascorbate free radical, as were uptake of oxygen, nitrate, and sugars. The increase in plasma-membrane ATPase was in proportion to cell enlargement, while the effect on tonoplast was disproportionately greater. The results show an activation of the elongation component of root growth by ascorbate free radical without affecting the production of new meristematic cells.