C-10-1 BEAN DEFENCE GENE EXPRESSION UNDER ELEVATED CARBONDIOXIDE.

David E. Lincoln and Ying Liu
Dept. of Biological Sciences, University of South Carolina, 700 SumterStreet, Columbia, SC 29208, USA.

Carbon-based secondary metabolite production may increase with the continuingrise of atmospheric carbon dioxide according to the carbon/nutrient balancehypothesis. Utilizing bean plants, Phaseolus vulgaris L., grownin different CO₂ regimes, we investigated the impact of elevatedcarbon availability on the production of phenolic and flavonoid metabolitesand the regulation of this effect. Plants grown under a CO₂concentration of 700 µmol mol-1 produced significantlyhigher amounts of total phenols than those grown under a CO₂concentration of 400 µmol mol-1 (P<0.01).The stimulation effect of CO₂ may be mediated by specific regulationof the biosynthetic pathway, rather than simply by increased substrateavailability. This was indicated by the increased expression of one ofthe committed enzymes in the flavonoid pathway, chalcone synthase, underelevated CO₂ growth conditions. The activity of chalcone synthaseshowed a 2.1-fold increase under CO₂ enrichment. Further, chalconesynthase mRNA level was induced about 3-fold in enriched CO₂grown plants. Neither the leaf phenolic content nor the expression of chalconesynthase was significantly stimulated by wounding in our study, apparentlydue to insufficient wound treatment. Our results suggest the defensiveand UV screening properties of leaves may be increased as phenolic andflavonoid production is stimulated by the elevated atmospheric carbon dioxideexpected in the future.