Variations in δ 13C Rates and Crassulacean Acid Metabolism of Six Coleus species

Abstract

Photosynthetic adaptations and biomass productivity of six Coleus species namely Coleus aromaticus, spicatus, blumei, zeylanicus, forskholii, and ambonicus were studied by determining their photosynthetic rates, Crassulacean acid metabolism (CAM) and carbohydrate levels. CAM metabolism was investigated by studying the activities of phosphoenol pyruvate carboxylase (PEPC), PEP carboxykinase and diurnal fluctuations of malate dehydrogenase along with levels of total organic acids, malic acid and citric acids. Carbohydrates such as sucrose, starch, glucose and fructose were assayed spectrophotometrically. Significant differences among the six Coleus species were observed in photosynthesis levels and CAM metabolic pathway enzymes whose activities were correlated with the aerial biomass. Our study indicates that Coleus is a CAM plant with nicotineamine Adenine Di nucleotide (Phosphate) (NAD (P)) as a preponderant malic enzyme and diurnal fluctuations in the levels of carbohydrates reveals that Coleus utilizes reservoir of starch for the synthesis of malic acid. Δ13C accumulation is more in Coleus aromaticus and ambonicus whose aerial biomass values are also high indicating the correlation between carbon fixation and biomass accumulation.