Chlorophyll composition of photosystems II alpha, II beta and I in tobacco chloroplasts.
The antenna composition of the Photosystems II alpha, II beta and I was studied in tobacco chloroplasts. Absorbance spectra, recorded at 4 K, were analyzed for the wild type and the mutants Su/su and Su/su var. Aurea, containing higher concentrations of the photosystems. With chloroplasts of Su/su we measured the action spectra of the three photosystems from 625 to 690 nm. Above 675 nm absorption by Photosystem I dominated. This system had a maximum at 678 nm and a shoulder at 660 nm. Of the long-wavelength chlorophyll a forms, absorbing at 690, 697 and 705 nm at 4 K, which are generally assigned to Photosystem I, the 697 nm form occurred in an amount of four molecules per reaction center of Photosystem I in each type of chloroplast. The Photosystem II alpha spectrum was characterized by maxima at 650 and 672 nm, showing clearly the participation of the chlorophyll a and b containing light-harvesting complex. In the mutants the light-harvesting complex has a chlorophyll a to chlorophyll b ratio of more than 1; the amount of the 672 nm chlorophyll a was normal, whereas the amount of chlorophyll b was markedly decreased in the mutants relative to the wild type. The Photosystem II beta spectrum mainly consisted of a band at 683 nm.
D002734:Chlorophyll / Q000032:analysis*; D002736:Chloroplasts / Q000032:analysis*; D010788:Photosynthesis; D010944:Plants / Q000032:analysis; D010947:Plants, Toxic; D013053:Spectrophotometry; D013696:Temperature; D014026:Nicotiana / Q000032:analysis
D002734:Chlorophyll