Correlation between photorespiration, CO₂-assimilation and spatiotemporal dynamics of photosynthesis in leaves of the C₃-photosynthesis/crassulacean acid metabolism-intermediate species Clusia minor L. (Clusiaceae)
2007
Duarte, H. M | Lüttge, U
The tree Clusia minor L. (Clusiaceae) operates with different modes of photosynthesis in response to different combinations of environmental parameters. Here plants were subjected to experimental conditions eliciting performance of C₃-photosynthesis and crassulacean acid metabolism (CAM), respectively. A combination of instruments was used to determine CO₂ and water vapour gas exchange, relative quantum use efficiency of photosynthesis (ΦPSII) and for the first time in such studies also photorespiration simultaneously with the other parameters. In the C₃-mode photorespiration was constant during the light period, where oxygenase activity of ribulose-bis-phosphate carboxylase/oxygenase (RubisCO) [graphic removed] was ranging between 32.1 and 35.7% of total RubisCO activity. In the CAM-mode photorespiration depended on the CAM phases. In phase II in the morning [graphic removed] was 15.6%. In phase IV in the afternoon initially it was 37.9% and then declined to 17.6% of total RubisCO activity towards the evening. Anatomically leaves of C. minor are differentiated in palisade and spongy parenchyma with an internal air space of 9.3% of the total volume and therefore could be structurally homobaric. However, heterogeneity of ΦPSII under both non-photorespiratory and photorespiratory conditions in the C₃- and CAM-mode indicated that lateral diffusion of CO₂ and O₂ were subject to limitations showing that leaves are functionally heterobaric.
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