Influence of Abscisic Acid on K⁺ absorption by leaf tissues ofSolanum tuberosum L. (cv. Bintje). Relation with calcium fluxes and with calmodulin

Abstract

Previous results with potato leaf tissues revealed that a treatment with ABA (10 -4 M) induced an increase of K + uptake (Suleiman et al., 1990a).In this study, we investigate the relationship between increased K § uptake, Ca 2 § fluxes and calmodulin by treating potato leaf discs with Ca 2 § channel blockers (La 3 § verapamil and nifedipine) and with calmodulin inhibitors (chlorpromazine, WT: N-(6-aminohexyl)-5-chloro-l-naphthalene-sulfonamide, and compound 4880).We found: a) all these inhibitors decreased K § uptake in the same ratio in tissues treated or not with ABA; b) a synergistic effect between ABA and the Ca 2 § ionophore A 23187 on K + uptake.The results suggest that the hormone may act on K + uptake like a Ca 2+ agonist, in accord with HUDDART's hypothesis.In a previous pa~per we reported that treatment of foliar tissue of Solanum tuberosum with abscisic acid (ABA) stimulated K § uptake (Suleiman et al. 1990b). By using metabolic inhibitors, it appeared that stimulation was due both to an increase in active and passive components. Elliott (1986) has suggested that in some circumstances hormonal action could involve calmodulin (CAM) and a participation of second messengers especially Ca 2+.Recently, we proposed (Suleiman et al., 1988) a scheme (Fig. 1) based upon data from Elliott (1986), Rincon and Hanson (1986) and Roux et al. (1986) to explain the positive effect of ABA on K § uptake.According to this hypothesis, ABA acts like a Ca 2 § agonist (Huddart et al. 1986) ; a change in cytosolic free [Ca 2 § will activate diverse protein-kinases, (Mg 2 § + Ca 2 §