Calcium transients in response to salinity and osmotic stress in the nitrogen‐fixing cyanobacterium Anabaena sp. PCC7120, expressing cytosolic apoaequorin

Abstract

We show here that both salinity and osmotic stress trigger transient increases in intracellular free Ca2+ concentration ([Ca2+]i) in cells of the nitrogen‐fixing filamentous cyanobacterium Anabaena sp. PCC7120, which constitutively expresses apoaequorin. Isoosmolar concentrations of salt (NaCl) and osmoticum (sucrose) induced calcium transients of similar magnitude and shape, suggesting that cells sense, via Ca2+ signalling, mostly osmotic stress. The Ca2+ transients induced by NaCl and sucrose were completely blocked by the calcium chelator ethylene glycol‐bis(b‐aminoethylether)N,N,N¢,N¢‐tetraacetic acid (EGTA) and were partially inhibited by the calcium channel blocker verapamil. Increased external Ca2+ and the Ca2+ ionophore calcimycin (compound A23187) enhanced Ca2+ influx further, suggesting the involvement of extracellular Ca2+ in the observed response to salinity and osmotic stress. However, the plant hormone abscisic acid (ABA) did not provoke any effect on the Ca2+ transients induced by both stresses, indicating that it may not be acting upstream of Ca2+ in the signalling of salinity and/or osmotic stress in Anabaena sp. PCC7120.

Principles of demineralization: Modern strategies for the isolation of organic frameworks

“…In cyanobacteria, as in all organisms, intracellular calcium is tightly regulated at the cost of energy through independent processes of calcium uptake and efflux. The normal levels of intracellular calcium are maintained at about 0.1-0.2 mM, to prevent toxicity to the cell metabolism, but transient levels may rise to 5 mM in cyanobacteria (Torrecilla et al, 2001). If external Ca 2+ concentrations exceed these concentration levels, as is typically the case, calcium uptake may involve low passive permeability and/or Ca 2+ -sensitive trans-membrane channels.…”

ABA in bryophytes: how a universal growth regulator in life became a plant hormone?

“…For instance, ABA did not induce calcium transients in response to salinity and osmotic stress in the Anabaena sp. PCC7120 (Torrecilla et al 2001). A-40 kDa protein immunologically related to plant dehydrins was detected in osmostressed filamentous, heterocyst-forming cyanobacteria, Anabaena sp.…”

Light‐to‐dark transitions trigger a transient increase in intracellular Ca2+ modulated by the redox state of the photosynthetic electron transport chain in the cyanobacterium Anabaena sp. PCC7120

“…Many of these processes have been largely studied, but little is known about the signal transduction that couples light perception with cell responses. Among many (Smith 1988;Torrecilla et al 2000Torrecilla et al , 2001. Thus, the aim of this work was to determine whether intracellular free calcium levels are altered by light-to-dark transitions in the filamentous, heterocyst-forming cyanobacterium Anabaena sp.…”