Light-stimulated inositolphospholipid turnover in Samanea saman leaf pulvini

Abstract

Leaflets of Samanea saman open and close rhythmically, driven by an endogenous circadian clock. Light has a rapid, direct effect on the movements and also rephases the rhythm. We investigated whether light signals might be mediated by increased inositolphospholipid turnover, a mechanism for signal transduction that is widely utilized in animal systems. Samanea motor organs (pulvini) labeled with H3llinositol were irradiated briefly (5-30 sec) with white light, and membrane-localized phosphatidylinositol phosphates and their aqueous breakdown products, the inositol phosphates, were examined. After a 15-sec or longer light pulse, labeled phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate decreased and their labeled metabolic products inositol 1,4-bisphosphate and inositol 1,4,5-trisphosphate increased, changes characteristic of inositolphospholipid turnover. We conclude that inositolphospholipid turnover may act as a phototransduction mechanism in Samanea pulvini in a manner that is similar to that reported in animal systems.

Separation and Characterization of Inositol Phospholipids from the Pulvini of Samanea saman

“…We have previously demonstrated that the levels of two lipids, tentatively identified as PIP and PIP2, decrease on illumination of S. saman pulvini, simultaneously with increasing levels of inositol phosphates (19). The present unequivocal confirmation of these tentative identifications strengthens our hypothesis of PI cycle involvement in light reception in pulvini.…”

“…We have demonstrated the existence of inositol phosphate and inositol phospholipid components of the PI cycle in S. saman pulvini (5,18) and have shown light-stimulated metabolism of these components (19). In these studies the inositol phospholipids were separated by TLC.…”

Characterization of Inositol Phosphates in Carrot (Daucus carota L.) Cells

“…There are few reports in the literature concerning polyphosphoinositide turnover in plants in response to stimuli. Recently, light-induced polyphosphoinositide turnover in Samanea saman pulvini and auxin-induced polyphosphoinositide turnover in Catharanthus roseus cells have been reported (8,17). However, the connection between the time course of the polyphosphoinositide turnover and the elevation of free Ca2+ in the cytosol in response to light or auxin has not been delineated.…”

Diacylglycerol Metabolism in the Green Alga Dunaliella salina under Osmotic Stress

“…A few studies of DAG levels in plants or plant organelles (20) have reported higher DAG concentrations. For example, Morse et al (21) found DAG of Samanea saman pulvinus to vary from 3.5 nmol/100 nmol PL in darkacclimated tissue to 4.2 nmol/100 nmol PL following exposure to light conditions that induce PIP2 hydrolysis.…”