Expression of phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxylase kinase genes. Implications for genotypic capacity and phenotypic plasticity in the expression of crassulacean acid metabolism.
In plants with crassulacean acid metabolism (CAM), dark CO2 uptake is mediated by phosphoenolpyruvate carboxylase (PEPC), an enzyme that can be regulated at transcriptional and posttranslational levels. Reversible phosphorylation of PEPC is catalyzed by a dedicated PEPC kinase, which in turn is regulated at the transcriptional level over the 24-h cycle in CAM plants. PEPC kinase controls the day/night regulation of PEPC during the CAM cycle, thus facilitating plasticity for optimizing CO2 uptake under different environmental conditions. To understand the importance of PEPC kinase in relation to its target PEPC in terms of CAM performance, the expression of the genes encoding the two enzymes was investigated in four species of Clusia that have photosynthetic patterns ranging from C3 photosynthesis to constitutive CAM. By linking changes in the expression of PEPC and PEPC kinase to day/night patterns of leaf gas exchange, organic acid, and soluble sugar contents under different environmental conditions, the genetic and metabolic limitations to CAM plasticity were assessed. The results indicate that PEPC expression is a major factor underpinning the genotypic capacity for CAM and that PEPC kinase expression does not appear to limit CAM. The day/night regulation of Ppck transcript abundance was found to be a consequence of CAM and the day/night cycling of associated metabolites, rather than the primary controlling factor for the temporal separation of carboxylation processes. (+info)
The mutagenic potential of Clusia alata (Clusiaceae) extract based on two short-term in vivo assays.
We examined the genotoxic and mutagenic effects of a crude extract of Clusia alata (a potential medicinal plant) on peripheral leukocyte and bone marrow cells of mice, using the comet and chromosome aberration assays. Extracts at doses of 1000, 1500 and 2000 mg/kg were administered by gavage, and a positive control, N-nitroso-N-ethylurea (50 mg/kg) was injected intraperitoneally. Peripheral blood leukocytes were collected 4 and 24 h after the treatments for the comet assay, and bone marrow cells were collected 24 h after the treatments, for the chromosome aberration assay. The comet assay showed that C. alata extract causes an increase in damage to DNA in the peripheral blood leukocytes, but it was significant only with the 2000 mg/kg dose after 24 h; the extract also induced a small but significant increase in the mean number of chromosome aberrations in the bone marrow cells at doses of 1500 and 2000 mg/kg. No evidence of a significant decrease in the mitotic index was observed. Acute consumption of high concentrations of C. alata extract produced some mutagenic effects in bone marrow cells. (+info)
Canopy CO2 exchange of two neotropical tree species exhibiting constitutive and facultative CAM photosynthesis, Clusia rosea and Clusia cylindrica.