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Interactive effects of UV-B and Cd on growth, pigment, photosynthesis. and lipid peroxidation have been studied in Anahaena, Mirrucystis, and Nustoc; all the tested cyanobacteria showed differential sensitivity to different dosage of UV-B and Cd alone as well as in combination. Phycocyanin was severely affected by UV-B and Cd by all the strains; the degree of pigment bleaching was most pronounced in Anabaena followed by Microcystis and Nosfoc. UV-B₂+Cd₂produced nearly 83.78, and 65% inhibition of phycocyanin in Anabaena, Microcystis, and Nostoc, respectively. The above treatment also significantly decreased the contents of Chl a and carotenoid. Presence of capsule in Microcyslic protected the phycocyanin bleaching as compared to decapsulated cells. Laboratorygrown Micruqsfis revealed about 75 and 80% inhibition. following UV-BaCd, treatment, respectively, in capsukated and decapsulated cells. Damage caused by Cd was more pronounced than UV-B. Inhibition of photosynthesis did occur in all the test strains, being maximum in Anabaena. PS 11 was the most sensitive component of the electron transport chain, showing 84. 80, and 70% inhibition in Anubuena, Microcysfis, and Nosfuc, respectively. As compared to conuol, significant lipid peroxidation (6.5-fold higher) was observed in Anuburna with UV-B,+C&. "C-upt&e was more susceptible to Cd and UV-B than oxygen-evolution. Approximately 84, 80, and 76% inhibition of "C-uptake was observed in Annbaena, Microcystis, and Nostoc, respectively. Similarly. UV-B,+Cdl inhibited ATP content olAnal~aenrr by 87%. This study suggests that inhibition of carbon fixation was due lo decreased ATP content of the test cyanohacteria by W-B+Cd, where Anabaena was the most sensitive and Nostor the most tolerant.
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