Abstract:
Using onion epidermis layer a v e r y accurate method for
measuring the permeability of epidermis cells to water was
standardized. In this method a 1.4 cm diameter epidermis disc
was soaked in tritiated water ( 5 0 0 curie/ml) fo r about 1 hour.
Next the disc was mounted in a specially designed elution
chamber where it was held flat and washed on the non-cuticular
side with ordinary water. A constant flow rate, high enough to
minimize unstirred lay er effect, was used. P e rm ea b ility was
calculated in the usual way after separating different exponentials
from the efflux curve of tritiated water. Turgor pressure of
the c e ll was regulated by soaking the disc in mannitol solutions
containing tritiated water and washing it in the chamber with same
concentration mannitol solution containing no radioactivity.
Water permeability values were found to decrease less than 8%
when the turgor pressure was decreased from 8 atmospheres
(fu ll turgor) to ze ro . Turgor pressure had no significant e ffect
on the water permeability of onion epidermal c e lls . Our results
are contradictory to the findings of Zimmerman and Steudle
15
(1974, J. Me mb. Biol. 16:331 -352) but are s im ila r to the
findings of Tarawa and Kamiya (1966, Aust. J. Biol, Sci.
19:399-419).
