PLANT PHYSIOLOGY , Vol 113, Issue 4 1309-1317, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
On the Mechanism of Reinitiation of Endogenous Crassulacean Acid Metabolism Rhythm by Temperature Changes
TEE. Grams, A. M. Borland, A. Roberts, H. Griffiths, F. Beck and U. Luttge
Institut fur Botanik, Technische Hochschule Darmstadt, Schnittspahnstrasse 3-5, D-64287 Darmstadt, Germany (T.E.E.G., U.L.)
Under continuous light the endogenous Crassulacean acid metabolism (CAM)
rhythm of Kalanchoe daigremontiana Hamet et Perrier de la Bathie disappears
at high (>29.0[deg]C) or low (<8.0[deg]C) temperatures. We
investigated the reinitiation of rhythmicity when temperature was reduced
from above the upper and increased from below the lower threshold level via
measurements of (a) short-term changes in carbon-isotope discrimination to
illustrate shifts between C3 and C4 carboxylation in vivo, and (b) the
malate sensitivity of phosphoenolpyruvate carboxylase (PEPC) in vitro. When
the net CO2-exchange rhythm disappears at both temperatures, the
instantaneous discrimination indicates low PEPC activity. Leaf malate
concentration and osmolarity attain high and low values at low and high
temperatures, respectively. After small temperature increases or reductions
from the low and high temperatures, respectively, the rhythm is
reinitiated, with phases shifted by 180[deg] relative to each other. This
can be related to the contrasting low and high leaf malate concentrations
due to direct inhibition of PEPC and possibly also of the phosphorylation
of PEPC by malate. The experimental results were satisfactorily simulated
by a mathematical CAM-cycle model, with temperature acting only on the
passive efflux of malate from the vacuole. We stress the important role of
the tonoplast in malate compartmentation and of malate itself for the
reinitiation and generation of endogenous CAM rhythmicity.
