MICROSOMAL ATP-DEPENDENT CA-2+ TRANSPORT AS AFFECTED BY ENVIRONMENTAL-STRESS IN BRYONIA-DIOICA INTERNODES

Mechanical perturbation of Bryonia dioica internodes results in an increase of microsomal ATP-dependent Ca2+ transport for 4 h, followed by a decline after 8 h. As evidenced by the inhibition by the protonophores CCCP and DNP and by the plasma membrane Ca2+-ATPase inhibitor erythrosine B, the higher rate of ATP-dependent Ca2+ transport observed after mechanical stress may result from the stimulation of both Ca2+-ATPase activity (associated with the plasma membrane and possibly the endoplasmic reticulum) and H+/Ca2+ antiport (attributable to the tonoplast). The subsequent decrease in Ca2+ transport corresponds to a decline in the H+/Ca2+ antiport activity. Although calmodulin antagonists fail to impair Ca2+ transport, addition of calmodulin activates it. Membrane-bound calmodulin increases after mechanical perturbation, for at least 8 h. It is suggested that a cellular redistribution of endogenous calmodulin is involved in the stress-induced changes in Ca2+ transport.