Tham khảo tài liệu 'advances in photosynthesis fundamental aspects part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 382 Advances in Photosynthesis - Fundamental Aspects Codonanthe crassifolia Gesneriaceae CAM cycling was observed in well-watered plants and CAM idling in drought-stressed plants. CAM cycling that scavenges respiratory CO2 appears to be a starting point for CAM evolution Guralnick et al. 2002 . The various forms of weak and strong CAM may be restricted to different individual species or may also be expressed temporarily in one given species. For example Sedum telephium has the potential to exhibit pure C3 characteristics when well-watered and a transition to CAM when droughted including a continuum of different stages of CAM expression which are repeatedly reversible under changing drought and watering regimes Lee and Griffiths 1987 . CAM physiotypes Phase of CO2 fixation Phase of stomatal closure Diel Fluctuation of malate concentration Diel pH Fluctuation Full CAM I II III IV 15 High CAM idling --- I II III IV 15 High CAM cycling II III IV I 5 Low C3 CAM Intermediate C4 CAM Intermediate Table 1. Various CAM physiotypes with different degrees of CAM expression. There are true intermediate species C3 CAM that can switch between full C3 photosynthesis and full CAM. The large genus Clusia comprises three photosynthetic physiotypes . C3 C3 CAM and CAM. There are also some C4 CAM intermediate species . Peperomia camptotricha Portulaca oleracea and Portulaca grandiflora Guralnick et al. 2002 . Only succulent C4 dicotyledons are capable of diurnal fluctuations of organic acids where dark-respiratory CO2 is trapped in bundle sheaths by PEPC and the water storage tissue in the succulent leaves may also participate in the fixation of internally released CO2. In Portulaca this may be a form of CAM cycling in leaves with C4 photosynthesis while stems perform CAM idling Guralnick et al. 2002 . However although C4 photosynthesis and weak CAM occur in the same leaves they are separated in space and do not occur in the same cells. Compatibility of CAM and C4 photosynthesis
