Localization of ascorbic acid,ascorbic acid oxidase,and glutathione in roots of Cucurbita maxima L

To understand the function of ascorbic acid (ASC) inroot development, the distribution of ASC, ASC oxidase,and glutathione (GSH) were investigated in cellsand tissues of the root apex of Cucubita maxima. ASCwas regularly distributed in the cytosol of almost allroot cells, with the exception of quiescent centre (QC)cells. ASC also occurred at the surface of the nuclearmembrane and correspondingly in the nucleoli. NoASC could be observed in vacuoles. ASC oxidase wasdetected by immunolocalization mainly in cell wallsand vacuoles. This enzyme was particularly abundantin the QC and in differentiating vascular tissues andwas absent in lateral root primordia. Administration ofthe ASC precursor L-galactono-c-lactone markedly increasedASC content in all root cells, including the QC.Root treatment with the ASC oxidized product, dehydroascorbicacid (DHA), also increased ASC content,but caused ASC accumulation only in peripheral tissues,where DHA was apparently reduced at the expenseof GSH. The different pattern of distribution ofASC in different tissues and cell compartments reflectsits possible role in cell metabolism and root morphogenesis.