Electron transport and chloroplast ultrastructure of a chlorophyll deficient mutant of wheat

Estimation of the light distribution between photosystems I and II in intact wheat leaves by fluorescence and photoacoustic measurements

Usisng intact leaves, the extent of the decrease in chlorophyll a fluorescenece caused by the addition of continuous 710 nm light superimposed on modulated (20 Hz) 550 nm light was used to determine the distribution of this absorbed light between photosystems I (α) and II (β). The Fo and Fm levels, which defined the total variable fluorescenece, were taken as equal to those obtained with excess 710 nm light and with saturating blue-green light, respectively.An analogous procedure was used with a photoacoustic detector, saturating white light defining a base line for oxygen yield, the levels with an without 710 nm light being used to define β and α respectively.The two methods gave similar values for the distribution of light between the two photosystems for the experimental conditions used, β averaging 0.55 for a range of Triticum genotypes and Brachypodium sylvaticum grown in high or low light.

A clover mutant lacking the chlorophyll a- and b-containing protein antenna complexes

A chlorophyll deficient mutant of clover has been examined by SDS-PAGE, spectrophotometric and electron microscopic methods. By a comparison of the absorption and first derivative spectra of acetone extracts from the mutant and normal biotypes, we observed a deficiency in chlorophyll b for the mutant biotype. The calculated chlorophyll a/b ratios, using the method of Arnon (Plant Physiol. 24, 1-15, 1949), approached infinity for the mutant whereas it ranged from 3.0-3.3 in the wild-type. The low temperature (77 degrees K) fluorescence emission bands in the 685-695 nm region could not be differentiated for the biotypes; however, the long wavelength emission band (near 740 nm in the wild-type) was shifted to shorter wavelengths (ca 720-725 nm) in the mutant indicating loss of photosystem I antenna. The SDS-PAGE profile of the mutant biotype showed a dramatic decline in the Coomassie stained polypeptides of apparent molecular weights similar to those of LHC II. Transmission electron micrographs of the mutant and normal tissue exhibited similar extents of grana-stacking, indicating that a component(s) other than the LHC II may be responsible for membrane adhesion in this mutant.