Physiotypic Plasticity and Survival of Arido-active Euphorbia triaculeata (Euphorbiaceae) in its Natural Habitat
Turki A. Al-Turki1, Osama H. Sayed2, Yahya S. Masrahi2*
Abstract. Leafless stem succulent Euphorbia triaculeata Forssk. is abundant in arid regions southwest of the Arabian Peninsula. These regions are characterized by short wet season with erratic rainfall and long dry season with high temperature and high irradiance. Field observations indicated that the plant survives the long dry season and acquires a red stem colour under high irradiance and protracted drought. Our work aimed at investigating survival of this arido-active species in its natural habitat by studying diurnal and seasonal changes in stomatal conductance, cell sap acidity, and chlorophyll fluorescence. Results showed that E. triaculeata is obligate crassulacean acid metabolism (CAM) plant. Under protracted drought, low stomatal conductance and dampening of CAM denoted a shift to CAM-idling. Observed stress-induced reduction of Photosystem II activity occurred in concomitance with increased non-photochemical quenching of chlorophyll fluorescence and increased anthocyanin content. These results reflected operation of a photoprotective mechanism involving interplay of non-photochemical energy dissipation via xanthophyll cycle and alleviation of oxidative stress by anthocyanin. It was concluded that E. triaculeata survives in its arid habitat by performing obligate CAM, shifting to CAM-idling under protracted drought, increasing non-photochemical excess energy dissipation, and accumulating anthocyanin pigment for its antioxidant attributes.
Key words: chlorophyll fluorescence, Crassulacean Acid Metabolism (CAM), CAM-idling, Euphorbia triaculeata, photoprotection.
Article № eb.14114, ICID: 1140465 [Full text - PDF]