Cell biological mechanism for triggering of ABA accumulation under water stress in Vicia faba leaves

Water stress-induced ABA accumulation is a cellular signaling process from water stress perception to activation of genes encoding key enzymes of ABA biosynthesis, of which the water stress-signal perception by cells or trigg ering mechanism of the ABA accumulation is the center in the whole process of ABA related-stress signaling in plants. The cell biological mechanism fo r triggering of ABA accumulation under water stress was studied in leaves o f Vicia faba. Mannitol at 890 mmol . kg(-1) osmotic concentration induced a n increase of more than 5 times in ABA concentration in detached leaf tissu es, but the same concentration of mannitol only induced an increase of less than 40 % in ABA concentration in protoplasts. Like in detached leaf tissu es, ABA concentration in isolated cells increased more than 10 times under the treatment of mannitol at 890 mmol . kg(-1) concentration, suggesting th at the interaction between plasmalemma and cell wall was essential to trigg ering of the water stress-induced ABA accumulation. Neither Ca2+-chelating agent EGTA nor Ca2+ channel activator A23187 nor the two cytoskeleton inhib itors, colchicine and cytochalasin B, had any effect on water stress-induce d ABA accumulation. Interestingly water stress-induced ABA accumulation was effectively inhibited by a non-plasmalemma-permeable sulfhydryl-modifier P CMBS (p-chloromercuriphenyl-sulfonic acid), suggesting that plasmalemma pro tein(s) may be involved in the triggering of water stress-induced ABA accum ulation, and the protein may contain sulfhydryl group at its function domai n.