Regulation of Calcium Ion and Its Effect on Growth and Developmental Behavior in Wild Type and ntcA Mutant of Anabaena sp. PCC 7120 under Varied Levels of CaCl_2

摘要

A study of calcium ion regulation in Anabaena 7120 and its derivative mutant (CSE2) strain impaired in ntcA gene were investigated in terms of altered morphological and physiological responses against various levels of calcium stress (0–100 mM). Calcium concentration of 10 mM was found to be inhibitory while 100 mM proved lethal for both wild type and mutant strain. The involvement of Ca~(2+) in the regulation of cellular processes has been described in terms of an influx or efflux of Ca~(2+) from the cytosol. A biphasic calcium uptake with difference in calcium influx and efflux rate was responsible for differential amount of remaining calcium which followed a decreasing trend both for wild type and mutant. Low K_(s 0.5) and high V_(max) in mutant suggest heavy and less restricted influx of calcium ion. Further, the interactive effect of calcium influx/efflux rate, remaining Ca~(2+) and intracellular levels of Na~+ and K~+ may be attributed for the degree of membrane damage and growth sustenance during exogenous supply of calcium salt. Widening in heterocyst spacing pattern, decreased heterocyst frequency and formation of abnormal cell structures at higher concen- tration (100 mM CaCl_2) suggest that calcium mediated regulatory process modulate heterocyst frequency and maintenance of cell structure. Further, poor regulation of calcium ion homeostasis in ntcA suggests that the calcium level and ntcA gene expression are inter-related.