Metabolic relations of inositol 3,4,5,6-tetrakisphosphate revealed by cellpermeabilization. Identification of inositol 3,4,5,6-tetrakisphosphate 1-kinase and inositol 3,4,5,6-tetrakisphosphate phosphatase activities in mesophyll cells

Using a permeabilization strategy to introduce Ins(3,4,5,6) P-4 into mesoph yll protoplasts of Commelina communis, we have identified Ins(3,4,5,6) P-4 l-kinase activity in mesophyll cells. Multiple InsP(3) isomers were identif ied in Spirodela polyrhiza and Arabidopsis. Only two of these, Ins(1,2,3) P -3 and Ins(3,4,6) P-3, have previously been identified in plants and only i n monocots. The isomers detected in S. polyrhiza included D- and/or L-Ins(3 ,4,5) P-3, D- and/or L-Ins(3,5,6) P-3, and D- and/or L-Ins(2,4,5) P-3. Ins( 1,4,5) P-3, if present, was only a tiny fraction of total InsP(3) species. We have also identified inositol polyphosphate phosphatase activities, Ins( 3,4,5,6) P-4 6-phosphatase and Ins(3,4,5, 6) P-4 4-phosphatase, whose actio n on endogenous inositol polyphosphates explains the presence of D- and/or L-Ins(3,4,5) P-3 and D- and/or L-Ins(3,5,6) P-4 in mesophyll cells. Inosito l trisphosphates identified in Arabidopsis include Ins(1,2,3) P-3 and D- an d/or L-Ins(3,4,6) P-3, suggesting that dicots may share pathways of InsP(6) biosynthesis and breakdown in common with monocots.