Structural Modifications of the Photosynthetic Apparatus in the Region of Photosystem I in Nicotiana tabacum as a Consequence of an Increased C 0 2-Content of the Atmosphere

Nicotiana tabacum was grown with a C 0 2-content in the atm osphere of 350 ppm and 700 ppm. A fter three weeks of growth in the respective atm osphere we were able to show that chloroplasts from plants grown under 700 ppm C 0 2 exhibited an 18% higher pho to ­ system I-m ediated electron transport activity. Furtherm ore, we were able to show that in plants grown under the higher C Ö 2-concentration the peptide composition of photosystem I had been quantitatively changed. It appeared that the CPI-peptides were increased, w hereas the LHCPI peptides were decreased. C orresponding to this change in the peptide com posi­ tion the ratio chlorophyll/carotenoids/protein changes from 1:0.16:3.6 in the control plants to 1:0.23:5 in the “C 0 2-plants”. The chlorophyll a/b ratio changes from 1.9 in the control plants to 2.3 in the “C 0 2 p lan ts”. Furtherm ore, the carotenoid composition appears to be changed, ß-carotene increases by 60% as expected from the increased C PI-content. The xanthophylls lutein, violaxanthin, neoxanthin and zeaxanthin increase also but to a lesser extent. Using specific antisera to lipids, we were able to show that photosystem I contains only the m em brane lipids monogalactosyldiglyceride and phosphatidylglycerol. Both lipids are specifically bound in a restricted num ber onto peptides of the photosystem I complex. Both lipids differ with respect to their binding strength on the peptides of photosystem I. The changes in the peptide and lipid com position were established by chemical analyses and by immunological techniques (W estern blot) using monospecific antisera to the photosys­ tem I peptides, to the chloroplast lipids as well as to the chloroplast carotenoids. From the quantitative and qualitative analyses of the peptides, carotenoids and lipids, the m olecular distribution of the carotenoids and lipids in the CPI and LHCPI complex of photosystem I was established.