PLANT PHYSIOLOGY , Vol 101, Issue 1 251-257, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Patterns of Effective Permeability of Leaf Cuticles to Acids
H. D. Hauser, K. D. Walters and V. S. Berg
Biology Department, University of Northern Iowa, Cedar Falls, Iowa 50614-0421
Plants in the field are frequently exposed to anthropogenic acid
precipitation with pH values of 4 and below. For the acid to directly
affect leaf tissues, it must pass through the leaf cuticle, but little is
known about the permeability of cuticles to protons, or about the effect of
different anions on this permeability. We investigated the movement of
protons through isolated astomatous leaf cuticles of grapefruit (Citrus X
paradisi Macfady.), rough lemon (Citrus limon [L.] Burm. fils cv
Ponderosa), and pear (Pyrus communis L.) using hydrochloric, sulfuric, and
nitric acids. Cuticles were enzymically isolated from leaves and placed in
a diffusion apparatus with pH 4 acid on the morphological outer surface of
the cuticle and degassed distilled water on the inner surface. Changes in
pH of the solution on the inner surface were used to determine rates of
effective permeability of the cuticles to the protons of these acids. Most
cuticles exhibited an initial low permeability, lasting hours to days, then
after a short transition displayed a significantly higher permeability,
which persisted until equilibrium was approached. The change in effective
permeability appears to be reversible. Effective permeabilities were higher
for sulfuric acid than for the others. A model of the movement of protons
through the cuticle is presented, proposing that dissociated acid groups in
channels within the cutin are first protonated by the acid, accounting for
the low initial effective permeability; then protons pass freely through
the channels, resulting in a higher effective permeability.
