Metabolic Relations of Inositol 3,4,5,6-Tetrakisphosphate Revealed by Cell Permeabilization. Identification of Inositol 3,4,5,6-Tetrakisphosphate 1-Kinase and Inositol 3,4,5,6-Tetrakisphosphate Phosphatase Activities in Mesophyll Cells

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Abstract
Using a permeabilization strategy to introduce Ins(3,4,5,6) P4 into mesophyll protoplasts ofCommelina communis, we have identified Ins(3,4,5,6) P4 1-kinase activity in mesophyll cells. Multiple InsP3 isomers were identified in Spirodela polyrhiza and Arabidopsis. Only two of these, Ins(1,2,3) P3 and Ins(3,4,6) P3, have previously been identified in plants and only in monocots. The isomers detected inS. polyrhiza included d- and/orl-Ins(3,4,5) P3, d- and/orl-Ins(3,5,6) P3, and d- and/orl-Ins(2,4,5) P3. Ins(1,4,5) P3, if present, was only a tiny fraction of total InsP3 species. We have also identified inositol polyphosphate phosphatase activities, Ins(3,4,5,6) P4 6-phosphatase and Ins(3,4,5, 6) P4 4-phosphatase, whose action on endogenous inositol polyphosphates explains the presence of d- and/orl-Ins(3,4,5) P3 and d- and/orl-Ins(3,5,6) P3 in mesophyll cells. Inositol trisphosphates identified in Arabidopsis include Ins(1,2,3) P3 and d- and/or l-Ins(3,4,6) P3, suggesting that dicots may share pathways of InsP6 biosynthesis and breakdown in common with monocots.