Acclimation to elevated CO2 is improved by low Rubisco and carbohydrate content, and enhanced Rubisco transcripts in the G132 barley mutant

Abstract

Variations induced by mutagenesis may identify targets for adapting to rising atmospheric CO2 concentrations. G132 is a barley mutant with strong decreases in photosynthesis, Rubisco and carbohydrate content, but increased Rubisco transcripts. We tested the hypothesis that G132 will record a greater stimulation of photosynthesis and dry mass gain than the wild-type (WT) in response to CO2 enrichment. A growth chamber experiment compared the mutant G132 and the WT developed in ambient (∼390μmolmol−1) and elevated (1200μmolmol−1) CO2. Photosynthesis, protein and carbohydrate contents, Rubisco and nitrate reductase activities, leaf morphology, plant dry matter and leaf area were determined. The transcriptome responses of fully expanded leaves of G132 and WT to elevated CO2 were investigated using microarrays and qRT-PCR. Growth in elevated CO2 stimulated photosynthesis more in G132 than in WT, in association with a lack of Rubisco down-regulation and lower carbohydrate levels in G132. Electron transport-related proteins increased in G132 and decreased in WT. Elevated CO2 induced more changes in gene expression in WT than G132. Clustering of the corresponding transcripts showed that the expression of genes involved in carbohydrate synthesis and nitrogen assimilation was enhanced, while that for stress-related genes was repressed in both genotypes, and gene expression for jasmonate metabolism was activated in G132. Elevated CO2 decreased the transcript levels for a greater number of transcription factors in WT than in G132. CO2 enrichment increased leaf area in G132 but not in WT, and induced greater dry mass increases in the mutant. The low Rubisco and carbohydrate content and enhanced Rubisco transcripts recorded in G132 are traits that may improve adaptation to rising CO2.