Kinase that can phosphorylate various inositol polyphosphate such as Ins(3,4,5,6)P4 or Ins(1,3,4)P3 and participates in phytic acid biosynthesis in developing seeds. Phosphorylates Ins(3,4,5,6)P4 at position 1 to form Ins(1,3,4,5,6)P5. This reaction is thought to have regulatory importance, since Ins(3,4,5,6)P4 is an inhibitor of plasma membrane Ca(2+)-activated Cl(-) channels, while Ins(1,3,4,5,6)P5 is not. Also phosphorylates Ins(1,3,4)P3 on O-5 and O-6 to form Ins(1,3,4,6)P4, an essential molecule in the hexakisphosphate (InsP6) pathway. Also able to phosphorylate Ins(3,5,6)P3 but not Ins(1,4,5)P3, Ins(2,4,5)P3, Ins(1,3,4,6)P4 nor Ins(1,3,5,6)P4. Has higher specific activity on Ins(3,4,5,6)P4 than Ins(1,3,4)P3 and Ins(3,5,6)P3. Can also could use Ins(1,2,5,6)P4 as a substrate. 1D-myo-inositol 3,4,5,6-tetrakisphosphate + ATP = 1D-myo-inositol 1,3,4,5,6-pentakisphosphate + ADP + H(+) 1D-myo-inositol 1,3,4-trisphosphate + ATP = 1D-myo-inositol 1,3,4,5-tetrakisphosphate + ADP + H(+) 1D-myo-inositol 1,3,4-trisphosphate + ATP = 1D-myo-inositol 1,3,4,6-tetrakisphosphate + ADP + H(+) Binds 2 magnesium ions per subunit. Monomer. Expressed in the embryo of 15 day after pollination. Expressed in kernels at earlier stages but at very low levels. Expression in the embryo peaks at 15 days after pollination and then declines. No expression is detected from endosperm and vegetative tissues. Plants display reduced phytic acid content in seeds. Belongs to the ITPK1 family.