Cobalt (Co) affords both beneficial as well as toxic effects to plants. The present study was performed with an aim to find out the varietal differences among five tomato cultivars against the Co induced changes in growth, photosynthesis, nitrate reductase (E.C.184.108.40.206), carbonic anhydrase (E.C.220.127.116.11), antioxidative enzymes i.e. peroxidase (E.C.18.104.22.168), catalase (E.C.22.214.171.124), superoxide dismutase (E.C.126.96.36.199) and that of proline content. Seeds of tomato (varieties, K-25, NTS-9, NBR-Uday, Sarvodya, and Malti) were soaked in 0, 100, 200 or 300 µM CoCl2 for 0, 4, 8, 12 h (shotgun approach) and sampled at 30 days after sowing. All the varieties showed significantly different response to different treatment combinations. Despite substantial varietal difference, increased Co concentration caused concomitant decrease in growth, photosynthesis and the activity of nitrate reductase and carbonic anhydrase. However, the activity of antioxidant enzymes and that of proline content increased with the increased concentration of Co as well as duration of soaking in all the varieties. Out of the varieties, K-25 possessed maximum antioxidative enzyme and proline content that represent its most resistant nature against the toxic effect of Co. The order of susceptibility/sensitivity was K-25 > NTS-9 > NBR-Uday > Sarvodya > Malti.
antioxidative enzyme; carbonic anhydrase; cobalt; nitrate reductase; photosynthesis; tomato