Diurnal changes in malate-decarboxylation activity in the leaves of a CAM plant, Bryophyllum daigremontianum

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Bryophyllum diagremontianum plants grown under light-dark regimes were exposed to one more cycle of the regime or to continuous darkness for 24 hr. Photosynthetic O_2 evolution by leaf segments from these plants was investigated in the presence of 15 mM NaHCO_3 (CO_2-dependent O_2 evolution) or in the absence of CO_2 (malate-dependent O_2 evolution). The malate-dependent O_2 evolution served as an index of the activity of malate decarboxylation. Malate content was respectively 67, 64 and 85 μmoles/g・fw in leaves measured at 7 hr 30 min in light and 6 hr 26 min in the dark from plants under the light-dark regime (light 12 hr/dark 12 hr) and those measured at 6 hr 26 min in the dark from plants under the continuous dark regime. The malate- and CO_2-dependent photosynthetic O_2 evolutions in the same leaves were 9.7 and 22, 0.2 and 17, and 16 and 26 μμmoles/g・fw・hr, respectively. Thus, the diurnal change in capacity for malate-dependent O_2 evolution was relieved by continuous dark treatment. These results suggest that the diurnal change in malate decarboxylation in this crassulacean acid metabolism plant does not occur by an endogenous rhythm. This further indicates lack of an endogenous rhythm for the influx-efflux of malate across the vacuole and in malate decarboxylation enzyme activity.
日本植物生理学会の論文