Role of calcium and calmodulin antagonist in photosynthesis and salinity tolerance in Chlorella vulgaris

Abstract

To cast light upon the role of Ca1+ and calmodulin on photosynthetic rate (Pn), dark respiration (RD) and amino acid and protein contents in salinity stressed and non-stressed Chlorella cultures, the Ca2+ chelator EGTA [ethylene glycol-bis-(2-aminoethyl ether)-N,N- tetraacetate] and the calmodulin antagonist TFP (trifluperazine) were used. TFP markedly inhibited PN while EGTA exerted a slight, if any, effect on PN. NaCl tolerance, on the other side, was markedly abolished by TFP that inhibited PN and lowered rate of proline accumulation. Calmodulin might be involved in osmoregulation and salt tolerance of Chlorella. RD, however, was markedly enhanced by EGTA and Ca2+-free medium and hence the Ca2+ deprivation increased stress severity exerted by NaCl. Combinations of Na+ and Ca2+ enhanced PN, decreased RD and proline content in comparison with an osmotically equivalent reference culture containing only NaCl. Addition of Ca2+ to TFP treated cultures failed to reactivate calmodulin for proline synthesis. However, when Ca2+ was added to EGTA-treated cultures, only relatively reduced proline contents were recorded. © 1993 Institute of Experimental Botany.