Constitutive and facultative crassulacean acid metabolism (CAM) in Cuban oregano,

Abstract

Plants exhibiting the water-conserving crassulacean acid metabolism (CAM) photosynthetic pathway provide some of the most intriguing examples of photosynthetic diversity and plasticity. Here, a largely unnoticed facet of CAM-plant photosynthesis is highlighted: the co-occurrence of ontogenetically controlled constitutive and environmentally controlled facultative CAM in a species. Both forms of CAM are displayed in leaves of Coleus amboinicus Lour. (Lamiaceae), a semi-succulent perennial plant with oregano-like flavour that is native to southern and eastern Africa and naturalised elsewhere in the tropics. Under well-watered conditions, leaves assimilate CO2 predominantly by the C3 pathway. They also display low levels of CO2 uptake at night accompanied by small nocturnal increases in leaf tissue acidity. This indicates the presence of weakly expressed constitutive CAM. CAM expression is strongly enhanced in response to drought stress. The drought-enhanced component of CAM is reversible upon rewatering and thus considered to be facultative. In contrast to C. amboinicus, the thin-leaved closely related Coleus scutellarioides (L.) Benth. exhibits net CO2 fixation solely in the light via the C3 pathway, both under well-watered and drought conditions. However, low levels of nocturnal acidification detected in leaves and stems indicate that the CAM cycle is present. The highly speciose mint family, which contains few known CAM-exhibiting species and is composed predominantly of C3 species, appears to be an excellent group of plants for studying the evolutionary origins of CAM and for determining the position of facultative CAM along the C3–full CAM trajectory.

The climate changes promoted the chloroplast genomic evolution of Dendrobium orchids among multiple photosynthetic pathways

“…Crassulacean acid metabolism (CAM) is a photosynthetic pathway that has arisen convergently in many plant lineages, especially for the species that live in CO 2 and water-limited environments, such as some aquatic habitats, hot semiarid areas, and tropical forests [ 1 , 2 ]. Recent studies have revealed the multiple independent origins of the CAM pathway, which have occurred in at least 343 genera across 35 plant families, accounting for 6 percent of vascular plants [ 3 – 5 ].…”

Diversity of CAM plant photosynthesis (crassulacean acid metabolism): a tribute to Barry Osmond

“…This paper also contains an updated list of all plant families in which the CAM cycle has been confirmed. Winter et al (2021c) highlight the co-occurrence of both stress-induced facultative and developmentally controlled constitutive CAM in a species of the Lamiaceae, Coleus amboinicus Lour., which is widely cultivated in the tropics as a spice and ornamental plant. Holtum et al (2021) study CAM in two species of Cistanthe (Montiaceae) from the Atacama desert where these species contribute to spectacular desert blooms after rare massive rainfall events.…”