STRUCTURAL MODIFICATIONS OF THE PHOTOSYNTHETIC APPARATUS IN THE REGION OF PHOTOSYSTEM-I IN NICOTIANA-TABACUM AS A CONSEQUENCE OF AN INCREASED CO2-CONTENT OF THE ATMOSPHERE

Nicotiana tabacum was grown with a CO2-content in the atmosphere of 35 0 ppm and 700 ppm. After three weeks of growth in the respective atmos phere we were able to show that chloroplasts from plants grown under 7 00 ppm CO2 exhibited an 18% higher photosystem I-mediated electron tra nsport activity. Furthermore, we were able to show that in plants grow n under the higher CO2-concentration the peptide composition of photos ystem I had been quantitatively changed. It appeared that the CPI-pept ides were increased, whereas the LHCPI peptides were decreased. Corres ponding to this change in the peptide composition the ratio chlorophyl l/carotenoids/protein changes from 1:0.16:3.6 in the control plants to 1:0.23:5 in the ''CO2-plants''. The chlorophyll a/b ratio changes fro m 1.9 in the control plants to 2.3 in the ''CO2 plants''. Furthermore, the carotenoid composition appears to be changed. beta-carotene incre ases by 60% as expected from the increased CPI-content. The xanthophyl ls lutein, violaxanthin, neoxanthin and zeaxanthin increase also but t o a lesser extent. Using specific antisera to lipids, we were able to show that photosystem I contains only the membrane lipids monogalactos yldiglyceride and phosphatidylglycerol. Both lipids are specifically b ound in a restricted number onto peptides of the photosystem I complex . Both lipids differ with respect to their binding strength on the pep tides of photosystem I. The changes in the peptide and lipid compositi on were established by chemical analyses and by immunological techniqu es (Western blot) using monospecific antisera to the photosystem I pep tides, to the chloroplast lipids as well as to the chloroplast caroten oids. From the quantitative and qualitative analyses of the peptides, carotenoids and lipids, the molecular distribution of the carotenoids and lipids in the CPI and LHCPI complex of photosystem I was establish ed.