Protective Role of Ca2+ towards Cu2+ Induced Toxicity on Photosynthetic Pigments, Morphology and Ultra-Structures of the Cyanobacterium Nostoc muscorum Meg 1

Abstract

Ca2+ has been reported to play a protective role in many cyanobacteria against toxic effects of various metals. However there are very few reports of Ca2+ mediated protection in Cu2+ treated cyanobacterial cells. An initial study conducted to assess the influence of Ca2+ over Cu2+ induced effects on morphology, ultra-structure, photosynthetic pigments and total protein content of cyanobacterial Nostoc muscorum Meg 1 revealed that as little as 3 ppm Cu2+ can induce reduction in all these parameters by 50-80%. However when 10 ppm Ca2+ was present along with 3 ppm Cu2+, the Cu2+ induced toxic effects were lessened by 55-85% within 7 days. Bright field and scanning electron microscopic study showed that morphological changes including broken filaments; rupture, elongation and shrivelling of cells were lessened upon inclusion of Ca2+. Ultra-structural studies conducted using transmission electron microscopy showed detachment of cell membrane from cell wall, shrinkage of cellular matter; compromised thylakoid membranes and increased number of polyphosphate bodies in the Cu2+ treated cells whereas these effects were convincingly less in presence of Ca2+. Similarly decrease in protein concentration under the influence of Cu2+ was also positively modulated by the presence of Ca2+.