MULTIPLE EFFECTS OF GLYCEROL ON PLANT-CELL METABOLISM - PHOSPHORUS-31NUCLEAR-MAGNETIC-RESONANCE STUDIES

The effects of glycerol on plant cell metabolism were studied with syc amore (Acer pseudoplatanus L.) cells using (31)p nuclear magnetic reso nance spectroscopy. After a long period of sucrose starvation, the add ition of 50 mM glycerol to the medium did not restore the original glu cose-6-P pool and led to a rapid accumulation of sn-glycerol-3-P in th e cytoplasmic compartment. The synthesis of sn-glycerol-3-P was rapid and occurred first at the expense of cytoplasmic P-i. Accumulated sn-g lycerol-3-P competitively inhibited glucose-6-phosphate isomerase acti vity when fructose-6-P was the varied substrate. Such a situation prev ented the rapid recycling of triose phosphates back to hexose phosphat es and led to an arrest of the functioning of the cytosolic and plasti dial pentose phosphate pathways. Under these conditions, the flow of c arbon to drive eel respiration derived almost exclusively from glycero l, and this polyalcohol was not used as a source of carbon skeletons f or biosynthesis. Glycerol also induced the accumulation of O-phosphoho moserine in the cytoplasmic compartment as long as the cell culture me dium contained sucrose. Finally glycerol added to sucrose starved cell s stopped the accumulation of phosphocholine (Roby, C., Martin J.-B., Bligny, R., and Douce, R. (1987) J. Biol. Chem. 262, 5000-5007) and pr evented a further decline in the uncoupled rate of O-2 consumption by the cells (Journet, E. P., Bligny, R., and Douce, R. (1986) J. Biol. C hem. 261, 3193-3199). These last observations strongly suggest that gl ycerol prevented the triggering of autophagy induced by sucrose starva tion in sycamore cells.