PLANT PHYSIOLOGY , Vol 109, Issue 1 187-194, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Properties of Proton Pumping in Response to Blue Light and Fusicoccin in Guard Cell Protoplasts Isolated from Adaxial Epidermis of Vicia Leaves
C. H. Goh, T. Oku and Ki. Shimazaki
Biophysics Laboratory, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka 812, Japan (C.-H.G., T.O.)
Guard cell protoplasts (GCPs) were isolated from the adaxial epidermis of
Vicia leaves. The properties of isolated adaxial GCPs (ad GCPs) were
compared with those of abaxial GCPs (ab GCPs) with respect to H+-pumping
activity. A saturating pulse of blue light (200 [mu]mol m-2 s-1, 30 s)
induced H+ pumping in both ad GCPs and ab GCPs under red light. The maximum
rate of blue-light-dependent H+ pumping was slightly higher in ad GCPs than
in ab GCPs, but the magnitude of H+ pumping in ad GCPs was 68% of that in
ab GCPs. H+ pumping was responsive to the second pulse, and the rate and
magnitude of the pumping increased with the time between two pulses. The
periods required to achieve 50% of the maximum rate were 12 and 22 min for
ad GCPs and ab GCPs, respectively. The rates of blue-light-dependent H+
pumping were saturable, with half-saturation at 630 [mu]mol m-2 (21 [mu]mol
m-2 s-1, 30 s) for ad GCPs and 105 [mu]mol m-2 (3.5 [mu]mol m-2 s-1, 30s)
for ab GCPs. In contrast, fusicoccin, an activator of the plasma membrane
H+- ATPase, induced H+ pumping with a slightly higher rate in ad GCPs than
in ab GCPs. Both types of protoplast swelled similarly in response to
fusicoccin. These results suggest that ad GCPs have almost the same
activity for H+ pumping as ab GCPs, whereas ad GCPs require a larger number
of photons to activate the H+ pump than ab GCPs.
