Screening of A/Ci-mutant in Arabidopsis thaliana for Identifying Regulatory Elements of the Limiting Factors in Photosynthesis

Abstract

In C3-plants, CO₂-fixation rate at low CO₂ is limited by factors (amount, activity and activation ratio of Rubisco, diffusion of CO₂ to Rubisco) relating to Rubisco-carboxylase reaction, at high CO₂ factors (electron-transport-reaction, enzyme activities in Calvin-cycle, Pi-recovery) relating to RuBP-regeneration. In the present work, for the identification of regulatory elements of the above limiting factors, we try to isolate Arabidopsis mutants having abnormalities in photosynthesis at low or high CO₂. Photosynthesis rate was estimated as quantum yield of PSII (Φ (PSII)) from the two-demensional Chl fluorescence-image-analysis in about 25,000 plants. The isolated photosynthesis mutant were grouped into 4-characteristics: 1, high Φ (PSII) at low CO₂, compared to wild type; 2, low Φ (PSII) and no CO₂-dependence; 3, low Φ (PSII) at low CO₂; 4, slow induction of photosynthesis initiation. Now, we characterize biochemical and physiological traits, and use map-based cloning to locate the causal mutation in these mutants.