The uptake of (+)-S- and (-)-R-abscisic acid by suspension culture cells of hopbush (Dodonaea viscosa)

Abstract

The uptake of (+)-S- and (-)-R-abscisic acid (ABA) by suspension culture cells of hopbush (Dodonaea viscosa L. Jacqu.) was followed over a range of temperatures, pH values, and time intervals. The natural (+)-S-ABA was taken up about five times faster than the unnatural (-)-R-ABA. Each 10°C rise in temperature from 1 to 31°C increased the rate of uptake (Q10) of (+)-S-ABA about 2.2-fold, whereas that of the (-)-R increased with a Q10 of 1.4. (+)-ABA was taken into the cells by a saturable carrier, but (-)-ABA and both enantiomers of 2-trans-ABA were not; they appeared to enter by passive diffusion. The uptake of (+)-ABA was linear over the first 8 hours but concentrations within the cells decreased after 2 hours to remain constant after 4 hours as rapid metabolism was induced. Electron microscopy of thin sections of the cells, combined with a stereological analysis of their shape, showed that the vacuoles comprised 80% of the cell volume and the cytoplasm plus nucleus comprised 20%. There were no photosynthetically active plastids in the cells. Concentrations of the endogenous ABA in the cytoplasm (pH 7.32) and vacuoles (pH 5.88) were calculated by applying the Henderson-Hasselbalch equation (ABA pKa 4.7) so that, provided no active metabolic redistribution occurred, the concentration in the cytoplasm was 7.9 micromolar and that in the vacuole was 0.3 micromolar. In vivo pH was measured by 31P nuclear magnetic resonance spectroscopy.