Poster: Photosynthesis

Abs # 379: Isolation and analysis of CAM-defective mutants in the common ice plant, Mesembryanthemum crystallinum.

Presenter:	Cushman, John C, jcushman@unr.edu
Authors	Cushman, John C (A)   Branco, Josh B (A)   Agarie, Sakae  (B)   Elliot, Stewart  (C)   Borland, Anne M (C)
Affiliations:	(A): University of Nevada, Department of Biochemistry (B): Saga University, Faculty of Agriculture (C): University of Newcastle, School of Biology

Crassulacean acid metabolism (CAM), an important adaptation of photosynthetic carbon fixation to limited water or CO₂ availability, is present in approximately 7% of vascular plant species. However, the molecular genetic mechanisms that regulate this alternative photosynthetic carbon fixation pathway are poorly understood. In contrast to C₃ and C₄ plants for which well-studied genetic models are available, no genetic model for CAM plants currently exists. To overcome this deficiency, we have established large mutant collections using fast neutron mutagenesis in the common ice plant, Mesembryanthemum crystallinum, as well as a facile screening method for the isolation of CAM-defective mutants. Two CAM-defective mutants have been identified and characterized to date that fail to conduct significant nocturnal CO₂ fixation or reciprocal diel fluctuations in C₄ acids and starch. Interestingly, the mutants also display increased daytime accumulation of soluble sugars (e.g., glucose and fructose). The mutants also show reduced seed set and seed weight and display C₃-like carbon isotope ratios in their seeds. The mutants confirm that a failure to maintain a transitory starch pool within leaves has a direct impact upon the capacity for nocturnal PEP synthesis, CO₂ fixation, and C₄ acid production during Phase I of CAM. The availability of CAM-defective mutants should provide novel insights into the complex interplay between metabolites and the circadian clock that regulates CAM. Efforts are underway to characterize the molecular genetic defects of these mutants using representational difference and oligonucleotide-based microarray analyses. This work is supported by NSF (IBN-0196070).