Morphogenic Responses of in vitro Grown Tobacco Plants Subjected to Ascorbic Acid vs Cadmium: Does the Redox Signal Have a Role?

The effects of different Cd concentrations (1, 32 and 64 mu M) in absence or presence of exogenously applied ascorbic acid (6x10(-4) M) in addition to the control on morphogenic response, the antioxidant and nutritional status as well as RAPD-PCR and protein pattern were studied using in vitro cultured nodal segments of tobacco plant. Concentration of Cd within the tissues increased in a concentration dependent manner. Under the highest Cd concentration, no rooting, reduced growth, chlorosis, an antagonistic relation between Fe and Mn and significant reduction in redox state were observed. Translocation of Mn and Zn was facilitated, while that of Fe and Cu was depressed due to Cd. Low Cd+Asc stimulated growth and reduced juvenility. Cd altered hormone homeostasis, meanwhile Asc may regulate auxin action and increased GSH/GSSG ratio. RAPD-banding for 32 pM Cd+Asc treatment manifested the highest number of bands with 14 unique ones accompanied by the highest activity for GR, DHAR and AO; gene up regulation and significant increase in redox state. Addition of Asc initiated rooting under the highest Cd level. Asc/DHA ratio of control plants shifted to sever oxidized state, meanwhile the redox poise of the cell was maintained by high GSH/GSSG ratio. This indicates that DHAR was upregulated upon Cd induction. It was observed that Asc supplemented medium induced direct and indirect organogenesis. Both Cd and Asc altered morphogenic responses of tobacco plants. Therefore, it can be concluded that both Cd and Asc may alter gene expression, via redox controlling, according to the cell milieu.