Circadian regulation of gene expression and carbon dioxide fixation in Bryophyllum fedtschenkoi

[摘要] Many plants are known to exhibit circadian rhythms in the expression of the genes for chlorophyll a/b binding proteins (CAB genes). Detached leaves of the plant Bryophyllum fedtschenkoi show circadian oscillations in carbon dioxide (CO2) metabolism and in the regulation of phosphoenolpyruvate carboxylase (PEPc) by PEPc kinase. The aim of this work was to investigate the relationship between circadian rhythms of CAB gene expression and CO2 metabolism in Bryophyllum fedtschenkoi. A CAB cDNA from Bryophyllum fedtschenkoi has been cloned and sequenced. This was shown to be one member of a CAB multigene family. When detached leaves of the plant Bryophyllum fedtschenkoi (adapted to a 8 h light/16 h dark cycle) are placed in constant darkness and CO2 free air, or constant light and normal air, at a constant temperature, the CAB gene transcript level shows circadian regulation. If the leaves are placed in constant darkness and normal air, one period of CAB gene expression still occurs, but a continuous cycling rhythm is not observed. The leaves that show maximal CAB expression are smaller than those which show the clearest rhythms in CO2 release/uptake, hi the larger leaves, CAB gene expression was detected but at a much lower level of expression than in the smaller leaves. The Bryophyllum fedtschenkoi leaves, which show circadian cycling in CAB gene expression, show some differences in the pattern of CO2 release/uptake compared to larger leaves. The smaller leaves (2.5 cm to 4.0 cm in length) show a circadian rhythm in CO2 metabolism but the amplitude is greatly reduced and the rhythm dampens out more rapidly than in larger leaves. CAB gene expression is affected by temperature, constant darkness and normal air, the pattern of CAB gene expression is altered by extremes of temperature (5°C and 35°C). CAB gene expression was totally inhibited at low temperatures (5°C) whereas at high temperatures (35°C) CAB gene expression was detectable but the expression showed no clear time dependent pattern. The data indicate that Bryophyllum fedtschenkoi leaves show rhythms of both CO2 metabolism and CAB gene expression. Possible physiological and mechanistic links between these rhythms are discussed.

[发布机构] University:University of Glasgow

[关键词] Physiology