title: The occurrence of crassulacean acid metabolism in Cymbidium (Orchidaceae) and its ecological and evolutionary implications.
abstract: Crassulacean acid metabolism (CAM) is one of the photosynthetic pathways regarded as adaptations to water stress in land plants. Little is known about correlations among the level of CAM activity, environment of habitat, life form, and phylogenetic relationship of a plant group from an evolutionary perspective. We examined these relationships in 18 species of Cymbidium (Orchidaceae) because the genus shows distinctive diversification of habitats and life forms. The photosynthetic type was classed into three categories, strong CAM, weak CAM, and C(3) on the basis of CAM activity. CAM expression in Cymbidium was confined to the epiphytic and lithophytic species. Especially, all of these species from tropical to subtropical rainforest exhibited CAM activity. On the other hand, the terrestrial species always exhibited C(3) metabolism irrespective of their varied habitats. Regarding the evolution of photosynthetic characters, weak CAM was the ancestral state in Cymbidium and strong CAM and C(3) metabolism occurred subsequently. The evolution of strong CAM likely enabled Cymbidium to extend to exposed sites in tropical lowland where marked water stress exists. Further, different levels of CAM activity characterized each species and such potential plasticity of CAM may realize the radiation of Cymbidium into sites with different environmental conditions.
authors.affiliation: Tsukuba Botanical Garden, National Museum of Nature and Science, Tsukuba, Ibaraki, 305-0005, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Motomura
authors.forename: T
authors.initials: T
authors.lastname: Yukawa
authors.forename: O
authors.initials: O
authors.lastname: Ueno
authors.forename: A
authors.initials: A
authors.lastname: Kagawa
mesh_terms: D005075:Biological Evolution; D002247:Carbon Isotopes / Q000378:metabolism; D002940:Circadian Rhythm; D017753:Ecosystem; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D029595:Orchidaceae / Q000033:anatomy & histology / Q000145:classification / Q000201:enzymology*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology
chemical_list: D002247:Carbon Isotopes; D008293:Malates; C030298:malic acid; D008291:Malate Dehydrogenase; C046446:malate dehydrogenase-(oxaloacetate-decarboxylating) (NAD+); C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D019764:Phosphoenolpyruvate Carboxykinase (ATP)