| Research Abstract |
RELATION BETWEEN THE REGULATION OF PHOTOTROPIC RESPONSE AND ABILITY OF TURGOR REGULATION IN TWO, VAUCHERIA SPECIES,A FRESH WATER SPECIES V.terrestris (VT) AND BRACKISH WATER SPECIES V.dichotoma (VD) WAS INVESTIGATED.VT HAS LOW SALINITY TOLERANCE,AND EXHIBITS NEGATIVE PHOTOTROPISM TO WHITE LIGHT OF THE INTENSITY HIGHER THAN 50Wm^<-2>, WHILE VD CAN SURVIVE EVEN IN SEA WATER AND SHOWS POSITIVE PHOTOTROPIC RESPONSE TO DIRECT SUN LIGHT.ADDITION OF Ca VERY MUCH IMPROVES SALT TOLERANCE IN BOTH VT AND VD.DIAMETER IN GROWING CELL APICES OF THE TWO SPECIES DECREASES WHEN THEY ARE CULTURED IN MEDIA OF HIGH OSMOLARITY.NEGATIVE PHOTOTROPISM OF VT IS INDUCED BY NaCl AND SORBITOL OF THE SAME OSMOLARITY,HIGHER THAN 50mOsm ; THAT OF VD IS,ON THE OTHER HAND,INDUCED ONLY BY SORBITOL,NOT BY NaCl OF THE SAME OSMOLARITY.THIS INDICATES THAT PHOTOTROPIC INVERSITION AND APICAL CONTRACTION ARE INDEPENDENTLY CORRELATING WITH LOW TURGOR PRESSURE.
TO COMPARE AND ANALYZE THE ABILITY OF TURGOR REGULATION OF VT AND VD,CELLULAR IONIC COMPOSITION WAS DETERMINED BY MEANS OF NEWLY IMPROVED ION CHROMATOGRAPHY SYSTEM.IN THE PRESENCE OF 5mM Ca, AND UNDER BLUE LIGHT,VT REGAIN ITS ORIGINAL TURGOR BY ABSORBING MAINLY Na^+ AND Cl^-. IN SORBITOL-MEDIUM,HOWEVER,VT,BEING A Na-PLANT,CANNOT REGULATE TURGOR,BECAUSE OF LACK OF Na. UNDER WHITE LIGHT CONDITION (12L/12D) VT PARTIALLY LOOSES ITS ABILITY TO REGULATE TURGOR,BUT NOT VD.VD,SUPPOSED TO BE A K-PLANT , ABSORBS MUCH K^+, Na^+, Cl^-, AND SO_4^<2-> TO REGULATE ITS TURGOR.IT HAS TURGOR AT THE EXTERNAL OSMOLARITY AS HIGH AS 400mOsm. THE PRESENT RESULTS STRONGLY SUGGEST THAT THE EXPRESSION OF NEGATIVE PHOTOTROPISM OF VAUCHERIA IS LINKED WITH THE FAILURE OF TURGOR REGULATION OR SUSTAINED LOW TURGOR PRESSURE.THE UNDERLYING MECHANISM BETWEEN THE SENSING OF LOW TURGOR AND EXPRESSION OF NEGATIVE PHOTOTROPISM AWAITS FURTHER INVESTIGATION.
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