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Redundancy of Stomatal Control for the Circadian Photosynthetic Rhythm in Kalanchoë daigremontiana Hamet et Perrier

2005; Wiley; Volume: 7; Issue: 2 Linguagem: Inglês

10.1055/s-2005-837541

1438-8677

Tomasz P. Wyka, Heitor Monteiro Duarte, Ulrich Lüttge,

Light effects on plants

Abstract: In continuous light, the Crassulacean acid metabolism plant Kalanchoë daigremontiana Hamet et Perrier has a circadian rhythm of gas exchange with peaks occurring during the subjective night. The rhythm of gas exchange is coupled to a weak, reverse phased rhythm of quantum yield of photosystem II (Φ PSII ). To test if the rhythm of Φ PSII persists in the absence of stomatal control, leaves were coated with a thin layer of translucent silicone grease which prevented CO 2 and H 2 O exchange. In spite of this treatment, the rhythm of Φ PSII occurred with close to normal phase timing and with a much larger amplitude than in uncoated leaves. The mechanism underlying the Φ PSII rhythm in coated leaves can be explained by a circadian activity of phosphoenolpyruvate carboxylase (PEPC). At peaks of PEPC activity, the small amount of CO 2 contained in the coated leaf could have become depleted, preventing the carboxylase activity of Rubisco and causing decreases in electron transport rates (observed as deep troughs of Φ PSII at 23‐h in LL and at ca. 24‐h intervals afterwards). Peaks of Φ PSII would be caused by a downregulation of PEPC leading to improved supply of CO 2 to Rubisco. Substrate limitation of photochemistry at 23 h (trough of Φ PSII ) was also suggested by the weak response of ETR in coated leaves to stepwise light enhancement. These results show that photosynthetic rhythmicity in K. daigremontiana is independent of stomatal regulation and may originate in the mesophyll.