Dehydroascorbate and glucose are taken up into Arabidopsis thaliana cell cultures by two distinct mechanisms.

The possible involvement of glucose (Glc) carriers in the uptake of vitamin C in plant cells is still a matter of debate. For the first time, it was shown here that plant cells exclusively take up the oxidised dehydroascorbate (DHA) form. DHA uptake is not affected by 6-bromo-6-deoxy-ascorbate, an ascorbate (ASC) analogue, specifically demonstrating ASC uptake in animal cells. There is no competition between Glc and DHA uptake. Moreover, DHA and Glc carriers respond in the opposite manner to different inhibitors (cytochalasin B, phloretin and genistein). In conclusion, the plant plasma membrane DHA carrier is distinct from the plant Glc transporters.

Copper-mediated oxidative burst in Nicotiana tabacum L. cv. Bright Yellow 2 cell suspension cultures.

In cell suspension cultures of Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) a rapid and concentration-dependent accumulation of H(2)O(2) is induced by excess concentrations of copper (up to 100 microM). This specific and early response towards copper stress was shown to be extracellular. Addition of 300 U of catalase per ml decreased the level of H(2)O(2). Superoxide dismutase (5 U/ml) induced an increase in H(2)O(2) production by 22.2%. This indicates that at least part of the H(2)O(2) is produced by dismutation of superoxide. Pretreatment of the cell cultures with the NAD(P)H oxidase inhibitors diphenylene iodonium (2 and 10 microM) and quinacrine (1 and 5 mM) prevented the generation of H(2)O(2) under copper stress for 90%. The influence of the pH on the H(2)O(2) production revealed the possible involvement of cell-wall-dependent peroxidases in the generation of reactive oxygen species after copper stress.