UV‐B and UV‐C induction of NADP‐malic enzyme in tissues of different cultivars of Phaseolus vulgaris (bean)

The effects of the treatment of different tissues of three bean cultivars (Pinto, Vilmorin and Arroz) with ultra-violet (UV) UV-B and UV-C radiation and red light on the activity, quantity and RNA levels of NADP-malic enzyme (NADP-ME) were determined. Exposure to UV-B radiation for 8 h caused a marked increase of NADP-ME from leaves, stems and roots in the three cultivars studied. A similar induction was observed in the leaves and stems after 8 h of exposure under UV-C, but not in the roots, suggesting that a different signal might be acting to induce the expression of NADP-ME after UV-B and UV-C exposure. In contrast, red light was ineffective in inducing NADP-ME in either tissue, so the regulation of the expression of this enzyme is phytocrome-independent. The activity of superoxide dismutase, ascorbate peroxidase, catalase and peroxidase was also different in plants treated with UV-B, UV-C and photosynthetically active radiation, suggesting that various pathways may be acting in the regulation of these enzymes by UV-B and UV-C. Reactive oxygen species (ROS) were also required for UV-B induction of NADPME, as the addition of ascorbic acid before UV-B treatment prevented NADP-ME induction, whereas salicylic acid was not effective in inducing the enzyme, showing that NADPME induction by UV-B is ROS dependent but salicylic acid independent.