Generation of rhythmic and arrhythmic behaviour of Crassulacean acid metabolism in Kalancho� daigremontiana under continuous light by varying the irradiance or temperature: Measurements in vivo and model simulations

Abstract

Abstract. Leaves of Kalancho6 daigremontiana Hametet Perr. at a photon flux density (PFD) above 220 I~mol" m-2 s-1 (400-700 nm) or at leaf temperatures above 27.0 ~ showed a rapid loss of rhythmicity, and a more or less pronounced damping-out of the endogenous circadian rhythm of CO2 exchange under continuous illumination. This rhythm was reinitiated after reduction of the PFD by 90-120 I~mol" m -2" s-1 or reduction of leaf temperature by 3.5-11.0~ under otherwise unchanged external conditions. The reduction in the magnitude of the external control parameter of the Crassulacean acid metabolism (CAM) rhythm (i.e. PFD or leaf temperature) set the phase of the new rhythm. The maxima of CO2 uptake occurred about 5, 28, 51, 75 h after the reduction. Simulations with a CAM model under comparable conditions showed a similar behaviour. The influence of temperature on the endogenous CAM rhythm observed in K. daigremontiana in vivo could be simulated by incorporating into the model temperature-dependent switch modes for passive efflux of malate from the vacuole to the cytoplasm. Thus, the model indicates that tonoplast function plays an important role in regulation of the endogenous CAM rhythm in K. daigremontiana.

On the Mechanism of Reinitiation of Endogenous Crassulacean Acid Metabolism Rhythm by Temperature Changes

“…Measurements were performed in a walk-in climate chamber using a minicuvette system (CMS 400, Walz, Effeltrich, Germany), as described elsewhere (Grams et al, 1996). One fully developed leaf was enclosed in a Plexiglas cuvette.…”

“…This model is explained in detail by Liittge and Beck (1992) and was subsequently improved for the use of simulation of the endogenous CAM rhythm (Liittge and Beck, 1992;Grams et al, 1996). Further refinement of the model with respect to vacuolar malate concentration is presented in "Results.…”

“…In a more detailed study, Liittge and Beck (1992) presented pronounced threshold values of the control parameters temperature and irradiance for the disappearance of the rhythm. Under continuous light, when temperature (or irradiance) is reduced from values above threshold (evoking arrhythmicity) to values below threshold, the circadian C0,-exchange rhythm is reinitiated and set in phase (Wilkins, 1962;Anderson and Wilkins, 1989;Grams et al, 1996). The mechanism of this reinitiation is not yet understood, but Wilkins (1983) proposed that high temperature opens "gates" in the tonoplast, which also may be related to the effect of temperature on the state of order of isolated tonoplast vesicles of K. daigremontiana (Kluge et al, 1991).…”

“…This could modulate the passive efflux of malate from the vacuole to the cytoplasm (Lüttge and Smith, 1984). Using this temperaturedependent behavior of the tonoplast to model the influence of temperature on the endogenous CAM rhythm, Grams et al (1996) were able to reproduce the experimental net C0,-exchange data, although simulated leaf malate concentrations did not fit with the observed values. Thus, as presented in this work, we made another effort to improve Crams et al…”

Oscillatory model of crassulacean acid metabolism with a dynamic hysteresis switch

“…With respect to temperature, the loss of regular oscillations occurs not only when a critical high level, but also when a critical low level, is passed. It has been shown that these transitions between rhythmicity and steady states are reversible (Grams et al 1996). Thus, temperature, T, and light intensity, L, appear as important state-determining control parameters of the endogenous CAM rhythm.…”