Changes of soluble protein expression and leaf metabolite levels in Arabidopsis thaliana grown in elevated atmospheric carbon dioxide

Abstract

Plant responses to elevated atmospheric CO 2 vary with species and with environmental conditions. Rates of dry matter formation were initially enhanced in response to CO 2 enrichment but these accelerated growth rates typically were not maintained over long periods of time. The objective of this study was to better understand the basis for this acclimation process. Changes of metabolite levels and of total protein expression in response to CO 2 enrichment were studied using biochemical assays and two-dimensional gel electrophoresis. Arabidopsis thaliana (L.) Henyh. (Columbia ecotype) plants were grown for 2–6 weeks in controlled environment chambers providing 36 (ambient) or 100 (elevated) Pa CO 2. Averaged over all harvest dates above-ground biomass was greater ( P < 0.05) in the elevated than in the ambient CO 2 treatment but shoot biomass did not differ between treatments on the final harvest. Flowering was delayed by CO 2 enrichment. One or more flowers were observed for 52% and 100% of the elevated and ambient CO 2 grown plants, respectively, after 4-weeks growth. Starch and sucrose levels were increased 132 and 43%, respectively, in leaves of 6-week-old plants in response to CO 2 enrichment. Nitrate varied with plant age, although mean nitrate levels in rosettes were decreased 31% by CO 2 enrichment when averaged over all harvest dates. Chlorophyll, the chlorophyll a/ b ratio, carotenoids and total soluble protein did not differ between CO 2 treatments. Total Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity decreased with plant age and was lower ( P < 0.01) in the elevated compared to the ambient CO 2 treatment. The above results suggested that acclimation to elevated CO 2 occurred in Arabidopsis without developing symptoms of N-deficiency. A total of 400 major proteins were separated and compared by two-dimensional gel electrophoresis. No proteins appeared de novo or disappeared in response to CO 2 enrichment, although pixel densities for 13 protein spots differed significantly between CO 2 treatments on at least one harvest date. Six of these proteins were identified by mass spectrometry. Three of these identified proteins were involved in plant growth and development or were associated with stress. Two other proteins were encoded by genes with putative functions. Only one protein, the 23 kDa subunit of the oxygen evolving complex (OEC23), was involved in photosynthesis. It was concluded that long-term plant growth in elevated CO 2 caused only small changes in the Arabidopsis proteome.