Leaf anthocyanin, photosynthetic light-use efficiency, and ecophysiology of the South African succulent Anacampseros rufescens (Anacampserotaceae)

• in plants grown at high light, leaf anthocyanin concentrations correlated with daytime photosynthetic quantum-use efficiency in Anacampseros rufescens, i.e., leaf anthocyanin appeared to reduce daytime photoinhibition.
• plants were incapable of long-term growth under low light.
• plants grown under medium light exhibited no evidence of photoinhibition.
• drought stress also resulted in some daytime photoinhibition.

Anacampseros rufescens (Anacampserotaceae), a succulent with C4(?)/CAM-cycling photosynthesis, grows on rock outcrops in South Africa and has purple leaves (abaxial and adaxial surfaces) as a result of high anthocyanin contents. Past studies of other plants indicate that this anthocyanin might protect the leaves from photodamage, yet such studies rarely include succulents that grow in high-insolation, arid habitats. Thus, plants of A. rufescens were grown at three light levels for several years to investigate the relationships between leaf anthocyanin amounts and photosynthetic light-use efficiency. This species is shade-intolerant, as plants grown at the lowest light level died early in the experiment. For plants grown at the highest light level, high leaf anthocyanin concentrations correlated with reduced photoinhibition, whereas no evidence for photoinhibition was observed in plants grown at the intermediate light level. Evidence of temporary photoinhibition was also obtained for drought-stressed plants grown under high light. The results of this study contribute to an increased understanding of the photoprotective role of anthocyanin in succulents found in highly exposed arid regions of South Africa.