484:	Photosystem-II activity is reduced by chlorosis of barley primary leaves in response to carbon dioxide enrichment.

Authors:	Sicher, Richard, C. (A)Bunce , James, A.(A)
Affiliations:	(A): USDA/ARS, Climate Stress Laboratory, Bldg 046A, BARC-West, 10300 Baltimore Ave., Beltsville, MD 20705-2350
Presenter:	Sicher, Richard C. , rsicher@asrr.arsusda.gov

Leaf yellowing was observed on barley primary leaves grown in controlled environment chambers between 10 and 18 days after sowing (DAS). Chlorosis was more extensive at elevated (70, 100 and 140 Pa) than at ambient (38 Pa) CO2. Rates of stomatal conductance (Gs) were decreased and internal leaf CO2 levels (Ci) were increased for leaves in the elevated compared to ambient CO2 treatment. Rates of net photosynthesis (Pn) decreased with leaf age and photosynthetic decline was greater for primary leaves from the elevated compared to the ambient CO2 treatment. Quantum absorptance, Fo, Fm, Fv, Fv/Fm and Y were significantly decreased 18 DAS in response to CO2-dependent leaf yellowing. Total thylakoid membrane proteins, the Chl a/b binding protein (LHC-II) and D1 protein levels were lower for chloroplast preparations from the elevated compared to ambient CO2 treatment. Ferricyanide reduction and whole chain electron transport rates by isolated chloroplast preparations were significantly lower for chloroplasts from plants grown at 68 compared to 38 Pa CO2. These results showed that photosystem-II activity was adversely affected by growth in elevated CO2. We suggest that leaf yellowing occurred because growth in elevated CO2 promoted light damage to photosystem-II.