MYOINOSITOL TRISPHOSPHATE MOBILIZES CALCIUM FROM FUSOGENIC CARROT (DAUCUS-CAROTA L) PROTOPLASTS

To determine whether or not inositol trisphosphate (IP3) mobilizes calcium in higher plant cells, we investigated the effect of IP3 on Ca2+ fluxes in fusogenic carrot (Daucus carota L.) protoplasts. The protoplasts were incubated in 45Ca2+-containing medium and the 45Ca2+ associated with the protoplasts was monitored with time. Addition of IP3 (20 micromolar) caused a 17% net loss of the accumulated 45Ca2+ within 4 minutes. There was a reuptake of 45Ca2+ and the protoplasts recovered to their initial value by 10 minutes. Phytic acid (IP6), also stimulated 45Ca2+ efflux from the protoplasts. Both the IP3- and the IP6-induced 45Ca2+ efflux were inhibited by the calmodulin antagonist, trifluoperazine.