Osmotic properties of a purified fraction of plasma membran vesicles isolated from Beta vulgaris storage root.

KARINA ALLEVA; RICARDO DORR; J. GÜCLU; P. GERBEAU; M. PARISI; G. AMODEO

Buenos Aires, Argentina

Congreso; XIV International Biophysics Congress; 2002

The osmotic water permeability (Pf) of a purified fraction of plasma membrane vesicles from Beta vulgaris storage root was studied by means of stopped-flow spectrophotometry. Plasma membrane vesicles were purified by aqueous two-phase partitioning, with an enrichment factor ³ 4 compared to the crude microsomal fraction. From the specific activities of membrane markers for mitochondria (0.55±0.55 mmoles.min-1.mg1-protein, n=5), endoplasmic reticulum (0.28±0.09 mmoles.min-1.mg-1 protein, n=6) and tonoplast (1.29±0.63 mmoles Pi.h-1mg-1 protein, n=7), it can be deduced that the contamination of the obtained membrane vesicles is very low. Scattered light intensity was used to follow plasma membrane vesicles volume changes when they were exposed to hyperosmotic shock. The Pf observed was 449±123 mm s-1 with very low associated activation energy (Ea) between 10oC and 28oC. The Pf  was reduced by 50% in the presence of 1 mM HgCl2. The high water permeability values, the inhibition by HgCl2, and the reduced Ea points suggest the presence of channel-mediated water transport in the plasma membrane of Beta vulgaris.