Clusia: Holy Grail and enigma

Area of Science:

• Plant physiology
• Photosynthesis research
• Biochemistry

Background:

• Clusia is the sole genus of dicotyledonous trees capable of Crassulacean acid metabolism (CAM).
• Clusia minor L. demonstrates exceptional plasticity, functioning as a C(3)/CAM intermediate with C(3), CAM, CAM-cycling, and CAM-idling photosynthetic modes.
• Simultaneous C(3) photosynthesis and CAM can occur in different leaves or even within the same leaf.

Purpose of the Study:

• Investigate the photosynthetic flexibility of Clusia minor L.
• Analyze the role of photorespiration in synchronizing photosynthetic activity.
• Examine the impact of circadian rhythms on C(3) and CAM photosynthesis.

Main Methods:

• Chlorophyll fluorescence imaging to visualize Photosystem II activity (PhiPSII) heterogeneity.
• Measurement of CO(2) uptake and photorespiration under varying conditions.
• Observation of plant responses under free-running circadian conditions and constant illumination.

Main Results:

• Photosystem II activity (PhiPSII) is higher under photorespiratory conditions, suggesting photorespiration's energy demands synchronize photosynthesis.
• Photorespiration stabilizes photosynthetic activity by reducing heterogeneity and oscillations under non-photorespiratory conditions.
• Circadian oscillations in photosynthesis are dampened in both C(3) and CAM modes, with photorespiration under circadian control.

Conclusions:

• Photorespiration plays a crucial role in synchronizing and stabilizing photosynthetic activity in Clusia minor L.
• The plant's C(3)/CAM plasticity is influenced by environmental conditions and internal regulatory mechanisms.
• Circadian regulation impacts photosynthetic processes, but its effects are modulated by photorespiration.