Phase resetting of the circadian rhythm of carbon dioxide assimilation inBryophyllum leaves in relation to their malate content following brief exposure to high and low temperatures,darkness and 5% carbon dioxide |
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Authors: | Clare M Anderson Malcolm B Wilkins |
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Institution: | (1) Botany Department, Glasgow University, G128QQ Glasgow, UK;(2) Present address: Botany Department, Cambridge University, Downing Street, CB2 3EA Cambridge, UK |
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Abstract: | Leaves ofBryophyllum fedtschenkoi show a persistent circadian rhythm in CO2 assimilation when kept in continuous illumination and normal air at 15°C. The induction of phase shifts in this rhythm by
exposing the leaves for four hours at different times in the circadian cycle to 40° C, 2° C, darkness and 5% CO2 have been investigated. Exposure to high temperature has no effect on the phase at the apex of the peak but is effective
at all other times in the cycle, whereas exposure to low temperature, darkness or 5% CO2 is without effect between the peaks and induces a phase shift at all other times. The next peak of the rhythm occurs 17 h
after a 40° C treatment and 7–10 h after a 2° C, dark or 5% CO2 treatment regardless of their position in the cycle. When these treatments are given at times in the cycle when they induce
maximum phase shifts, they cause no change in the gross malate status of the leaf. The gross malate content of the leaf in
continuous light and normal air at 15% shows a heavily damped circadian oscillation which virtually disappears by the time
of the third cycle, but the CO2 assimilation rhythm persists for many days. The generation of the rhythm, and the control of its phase by environmental factors
are discussed in terms of mechanisms that involve the synthesis and metabolism of malate in specific localised pools in the
cytoplasm of the leaf cells. |
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Keywords: | Bryophyllum Carbon dioxide assimilation Circadian rhythm Malate Phosphoenolpyruvate carboxylase |
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