Avaliação da ultraestrutura e morte celular em Cylindrospermopsis raciborskii (Woloszynska) Seenayya & Subba Raju (Cianobacteria) sob efeito da radiação ultravioleta

Abstract

Solar radiation is essential for life on Earth, providing energy for photosynthesis and heat. The total radiation that reaches the Earth surface, 9% is represented by the ultraviolet radiation (UV). Studies with cyanobacterial groups show negative effects of UV radiation on physiological processes such as growth, survival and enzymes of nitrogen metabolism and CO2 fixation. Cylindrospermopsis raciborskii is a filamentous nitrogen fixing cyanobacteria that has become one of the species of cyanobacteria of interest to researchers because of its potential toxicity and its high ecophysiological adaptability. In this work, we investigated the effect of UV-A, UV-B and UV (A + B) on the density, cell viability and occurrence of morphological changes by transmission electron microscopy. Natural intensities were used on strain of C. racirborskii in a period of 6 hours of treatment. The treatments UV-A and UV had significant negative effects on the density and integrity of membrane (99.3 and 95% of dead cells, respectively), while UV-B showed no significant difference in density, but induced alteration of membrane integrity in 57% of the cells at the end of treatment. Ultrastructural analysis showed morphological changes in all treatments characterized mainly by reducing the proportion of thylakoid structures and pigments accessories storage. Our results demonstrate the induction of cell death in strains of C. racirborskii treatments by UV-A and UV. However, the UV-B treatment seems to be less lethal to this strain in the intensity used. The understanding of processes of cell death in phytoplanktoic populations induced by UV radiation opens new perspectives on the influence of such radiation on aquatic ecosystems and its consequences on the persistence of species, energy flow and biogeochemical cycles.