Calcium, Calmodulin and the Control of Respiration in Protoplasts Isolated from Meristematic Tissues8

Owen, J. H., Hetherington, A. M. and Wellburn, A. R. 1987. Calcium,calmodulin and the control of respiration in protoplasts isolatedfrom meristematic tissues by abscisic acid.—J. exp. Bot.38: 1356–1361. A study was made of the possible involvement of calcium channelsand calmodulin during the calcium-dependent inhibition of mitochondrialrespiration by abscisic acid (ABA) in meristematic protoplastsobtained from light-grown barley (Hordeum vulgare L. cv. Patty)seedlings. The calcium channel blockers lanthanum, verapamiland nifedipine were all found to reduce the Ca²⁺-dependent inhibitionof protoplast respiration by ABA. The ionophore A23187 GenBank] itselfcaused an inhibition of protoplast respiration, possibly becauseit mimicked the action of ABA by increasing plasmalemma permeabilityto extracellular calcium. By contrast, calmodulin antagoniststrifluoperazine and compound 48/80 both caused a partial decreasein the Ca²⁺-dependent inhibition of protoplast respiration byABA. In contrast to the action of ABA, gibberellic acid markedlyincreased the rates of protoplast respiration but this did notappear to require the presence of extracellular calcium ions.These results support the hypothesis that ABA increases plasmalemmapermeability to extracellular calcium which might then directlyor indirectly act as a second messenger, possibly in conjunctionwith calmodulin, to regulate mitochondrial dark respirationwhich is an important part of early meristematic cell development. Key words: Abscisic acid, calcium, calmodulin, meristematic respiration