The role of the chloroplastic glucose transporter in the operation of CAM in Kalanchoë fedtschenkoi

Starch degradation in the leaves of crassulacean acid metabolism (CAM) plants is thought to primarily occur via the phosphorylytic pathway, and the hydrolytic pathway is believed to serve as a secondary route for starch breakdown. Here it is hypothesized that a chloroplastic glucose transporter, involved in the hydrolytic pathway, is fundamental for the process of starch breakdown, and as such is needed for optimal CAM activity. A knock-down mutant of the chloroplastic glucose transporter (GlcT 12) was generated for the CAM plant Kalanchoë fedtschenkoi. The GlcT12 mutant had significantly impaired growth compared to that of wild type. Data for leaf succulence, chlorophyll content, 24 h and circadian patterns of leaf gas-exchange also showed differences between the mutant and wild type. In the GlcT12 mutant, gas exchange data showed an impact upon the daytime phases of CAM, with enhanced release of CO2 from the mutant compared to wild type, indicating incomplete closure of stomata during the day. Increased maltose and sucrose concentrations in leaves of the mutant additionally infer the use of the hydrolytic pathway to generate maltose for export from the chloroplast when glucose export is curtailed.status: publishe