EFFECTS OF PB AND CD ON CUCUMBER DEPENDING ON THE FE-COMPLEX IN THE CULTURE SOLUTION

Modifying effects of EDTA and citrate as Fe(III)-complexes on Pb- and Cd-toxicity were investigated with cucumber (Cucumis sativus L.) grown in culture solution. Pb and Cd were applied in 10 mu M concentration. ph and Cd inhibited the growth of plants with Fe-citrate but with Fe- EDTA only Cd did. Chlorophyll content of Cd-treated plants - independe ntly on the Fe-complex - was very low similarly to the iron deficient plants. Pb is proved to inhibit the chlorophyll accumulation only in p lants supplied with Fe-citrate. photosynthetic activity of 6-week-old plants was characterized by in vivo CO2 fixation. The highest activiti es were observed in the middle (third-fourth) leaf storeys, and decrea sed in the lower and higher leaf storeys. Cd caused more than 50% inhi bition of the photosynthetic activity when applied with Fe-EDTA. With Fe-citrate, the inhibition exceeded 30%. The photosynthetic activities in the Pb-treated plants were not significantly different from the co ntrol plants. The amount of chlorophyll containing complexes, especial ly that of PSI was highly affected by Cd particularly in the lower lea ves. The results correlate with Fe-59 translocation into the shoot. Fe translocation was stimulated by Pb in the presence of Fe-EDTA but it was inhibited in the presence of Fe-citrate. Cd completely inhibited F e translocation from the root to the shoot with both chelators. It is concluded that strong iron deficiency has a great but not exclusive ro le in the observed symptoms, and that the quality of the chelator stro ngly influences the effects of these polluting metals.