Kalanchoe blossfeldiana, a tool for comparatively studying stomatal physiology, guard cell and mesophyll metabolism in C3 and crassulacean acid metabolism tissues

Abstract

Engineering crassulacean acid metabolism (CAM) into C3 crops has potential to significantly improve crop plant water usage efficiency (WUE) without significantly effecting yield. Despite the importance of stomata in efforts to engineer CAM into C3 plants our understanding of CAM stomatal physiology and guard cell metabolism are still lacking. In C3 plants, guard cell metabolism provides energy and osmolytes essential for proper stomatal regulation. Recent studies have suggested that CAM stomata differ in the timing of guard cell metabolism compared to C3. Guard cell metabolism may be of especial importance in CAM plants as it needs to provide energy to sustain nocturnal stomatal opening without photosynthesis. Furthermore, this thesis tackles a key question in CAM engineering, will stomata follow the pattern of mesophyll driven changes in Ci or will guard cells require separate changes to their regulation and metabolism to support nocturnal opening and diurnal closure? These questions will be tackled using C3 and CAM tissues in Kalanchoe blossfeldiana and a CAM deficient Kalanchoe fedtschenkoi pepc1 mutant. This thesis provides evidence of the retiming of guard cell starch metabolism in CAM tissues and suggests that nocturnal carboxylation driven reductions in Ci are not enough to drive nocturnal stomatal opening in C3 tissues. To date, most sequenced inducible CAM plants require inducement through an abiotic stress e.g. drought or salt stress, whereas CAM in K. blossfeldiana is also induced with ageing. This thesis develops the inducible CAM plant K. blossfeldiana as a system for investigating C3 and CAM physiologies and mesophyll and guard cell metabolism by presenting a physiological and biochemical characterisation of K. blossfeldiana along with its genome and a comparative C3/CAM dusk transcriptome; identifying key components of the CAM cycle upregulated in response to age-induced CAM induction.