Phytotoxicity of cobalt, chromium and copper in cauliflower

Cauliflower (Brassica oleracca L. var. Botrytis cv. Maghi) was grown in ref ined sand with complete nutrition (control) and at 0.5 mM each of Ca, Cr an d Cu. In cauliflower, compared to that of excess Cu or Cr, the visible effe cts of excess Co appeared first and were most pronounced. Excess of each he avy metal restricted the biomass of cauliflower, concentrations of Fe, chlo rophylls a and b, protein and activity of catalase in leaves in the order C o > Cu > Cr. The translocation of Cr from roots to tops was minimum and tha t of Co was maximum when cauliflower was individually supplied with excess Co, Cu or Cr. In cauliflower each heavy metal inhibited the concentration o f most of the macro- and micronutrients. The translocation of P, S, Mn, Zn and Cu from roots to tops of cauliflower were affected most significantly b y Co and least by Cr. In contrast to excess Cu or Cr, Co significantly decr eased the water potential and transpiration rates and increased diffusive, resistance and relative water content in leaves of cauliflower. (C) 2000 El sevier Science Ltd. All rights reserved.