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Ascorbate free radical (AFR) induced cell elongation in r-r-reristems of Allium cepa roots by promoting a high vacuolization as shown by the increased vacuole volur-rie, vacuole volume density, tonoplast surface and tonoplast surface density. Accordingly, both plasma n-rembrane-and tonoplastassociated ATPases and vacuole soluble acid phosphatase of n-ieristematic cells were also increased. Neither the other subcellular organelles nor cell proliferation appeared to be significantly affected. It is suggested that AFR may be involved in some plasma membrane events related to the initiation of plant cell elongation.

Long-term treatments with ascorbate free radical-stimulated glucose, fucose, sucrose, and nitrate uptake in Allium cepa roots.Clucose 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. l h e 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 ascorbatefree radical is involved in these responses.

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