Differential effects of UV-B radiation fluence rates on growth, photosynthesis, and phosphate metabolism in two cyanobacteria under copper toxicity

摘要

This work was undertaken to ascertain the impact of different fluence rates of ultraviolet-B (UV-B) radiation on two cyanobacterial biofertilizers, Phormidium foveolamm and Nostoc muscorum, growing under copper toxicity. Copper (2 and 5 μmol L~(-1)) and high UV-B fluence rate (UV-B_H; 1.0 umol m~(-2)s~(-1)) decreased the growth, pigment content, photosynthetic oxygen yield, phosphate uptake, and acid phosphatase activity in both the strains analyzed after 24 and 72 h of experiments, and combined exposure further enhanced the toxic effects. Respiration and alkaline phosphatase activities were stimulated appreciably. The damaging effect was shown on the order on pigments: phycocyanin > chlorophyll a > carotenoids, and on photosystems: whole chain photosynthetic reaction > photosystem II > photosystem I. Partial recovery in the photosystem II activity in the presence of artificial electron donors; diphenyl carbazide (DPC), hydroxylamine (NH_2OH), and manganese chloride (MnCl_2) pointed out the interruption of electron flow on the oxidation side of photosystem II. Unlike UV-B_H, low UV-B fluence rate (UV-B_L; 0.1 umol m~(-2)s~(-1)), rather than causing damaging effect partially, alleviated the toxic effects of Cu. This study suggests that the cyanobacterium P. foveolamm is less sensitive against UV-B_H and excess Cu (2 and 5μmol L~(-1)), thus P. foveolamm may be used as a biofertilizer for sustainable agriculture.