I. Heilmann et al., Changes in phosphoinositide metabolism with days in culture affect signal transduction pathways in Galdieria sulphuraria, PLANT PHYSL, 119(4), 1999, pp. 1331-1339
The metabolism of phosphatidylinositol-4,5-bisphosphate (PIP,) changed duri
ng the culture period of the thermoacidophilic red alga Galdieria sulphurar
ia. Seven days after inoculation, the amount of PIP2 in the cells was 910 /- 100 pmol g(-1) fresh weight; by 12 d, PIP2 levels increased to 1200 +/-
150 pmol g(-1) fresh weight. In vitro assays indicated that phosphatidylino
sitol monophosphate (PIP) kinase specific activity increased from 75 to 230
pmol min(-1) mg(-1) protein between d 7 and 12. When G. sulphuraria cells
were osmostimulated, transient increases of up to I-fold could be observed
in inositol-1,4,5-trisphosphate (IP3) levels within 90 s, regardless of the
age of the cells. In d-12 cells, the increase in IP3 was preceded by a tra
nsient increase of up to 5-fold in specific PIP kinase activity, whereas no
such increase was detected after osmo-stimulation of d-7 cells. The increa
se in PIP kinase activity before IP3 signaling in d-12 cells indicates that
there is an additional pathway for regulation of phosphoinositide metaboli
sm after stimulation other than an initial activation of phospholipase C. A
lso, the rapid activation of PIP2 biosynthesis in cells with already-high P
IP, levels suggests that the PIP2 present was not available for signal tran
sduction. By comparing the response of the cells at d 7 and 12, we have ide
ntified two potentially distinct pools of PIP2.