PLANT PHYSIOLOGY , Vol 104, Issue 4 1201-1208, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Cells of the Upper and Lower Epidermis of Barley (Hordeum vulgare L.) Leaves Exhibit Distinct Patterns of Vacuolar Solutes
W. Fricke, J. Pritchard, R. A. Leigh and A. D. Tomos
School of Biological Sciences, University College of North Wales, Bangor, Gwynedd, LL57 2UW, Wales, United Kingdom (W.F., J.P., A.D.T.)
Vacuolar saps were extracted from individual, anatomically uniform cells of
the upper (adaxial) and lower (abaxial) epidermis of the third leaf of
barley (Hordeum vulgare L.) using a modified pressure probe. Saps (volume
80-200 pL) were sampled at various times between 3 d before and 7 d after
full-leaf expansion and were analyzed for their osmolality and their
concentrations of NO3-, malate, CI-, K+, and Ca2+. The osmolalities of
upper and lower epidermis both increased with time but were similar to each
other. In young leaves, K+ and Ca2+ were evenly distributed between the two
epidermal layers, but as the leaf aged, the upper epidermis accumulated
high (40-100 mM) Ca2+, whereas cells of the lower epidermis accumulated K+
instead. Nitrate concentration was 100 to 150 mM higher in the upper than
in the lower epidermis, whereas CI- was 50 to 120 mM higher in the lower
epidermis. These differences did not depend on the leaf developmental
stage. The uneven distribution of epidermal NO3- and CI- was maintainedover
a wide range of epidermal sap concentrations of these ions and was not
affected by NO3- or CI- starvation or by an increase in the light intensity
from 120 to 400 [mu]mol m-2 s-1. However, the latter did cause a decrease
in epidermal NO3- and the appearance and accumulation of epidermal malate,
particularly in the upper epidermis. The physiological implications of the
results for solute storage in leaves and for the pathways of ion
distribution to the epidermis are discussed.
