Table II.

Permeability of boric acid (in centimeters per second) across different membrane vesicles isolated from squash roots using a stopped-flow device and inhibition by 0.5 mM HgCl₂ and 0.25 mm phloretin

Type of Membrane Vesicle Used	Control	HgCl2	HgCl2+ 2-Mercaptoethanol	Phloretin
Microsomal vesicles	5.29 × 10−8 ± 8.8 × 10−9b	3.56 × 10−8 ± 5.3 × 10−9 (33%)b	4.86 × 10−8 ± 1.2 × 10−9 (8%)	NDa
Plasma membrane  vesicles	3.91 × 10−7 ± 1.4 × 10−8b	1.67 × 10−7 ± 1.5 × 10−8 (57%)b	4.2 × 10−7 ± 8 × 10−8 (0%)	2.38 × 10−7 ± 5.4 × 10−8 (39%)b
Plasma membrane- depleted vesicles	2.41 × 10−8 ± 4.6 × 10−9	2.26 × 10−8 ± 3.6 × 10−9 (6%)	2.32 × 10−8 ± 5.6 × 10−9 (4%)	NDa

Also the permeability coefficient of urea P = 1.46 × 10⁻⁸ ± 1.5 × 10⁻⁹ cm s⁻¹ was determined in microsomal vesicles. The percent of inhibition is given in brackets. The experiment was repeated three times and six to eight replicates were used in every treatment. Statistical significance at the 5% level according to t test.

^a ND, Not determined. 

^b Statistically significant difference between the control and the HgCl₂ and phloretin treatment.