SPECTRAL AND PHOTOCHEMICAL PROPERTIES OF THE XANTHA MUTANT OF COTTON

The cotyledon leaves of an original line and a chlorophyll-deficient m utant of cotton (Gossypium hirsutum L.) were studied after exposing 4- day-old ethiolated seedlings to light for 1.5, 2.5, and 6 days. The ch lorophyll (a + b) content in the mutant leaves was lower by a factor o f 10 than in the leaves of the parent plants. Analysis of low-temperat ure spectra of leaf absorption and fluorescence emission, and their se cond derivatives showed that chloroplasts in the mutant leaves maintai ned their ability to build up PS I and LHC, whereas PS Il complex deve lopment lagged behind. Measurements of O2 evolution and delayed light emission allowed us to suggest that the water-oxidizing complex in the xantha mutant was inactive. These data could be related to decreased thylakoid development and grana absence. It was likely that low chloro phyll accumulation diminished the number of reaction centers in the ph otosystems and produced only trace amounts of pigment-protein complexe s. However, the mutation did not influence the mechanism of pigment-pr otein complex formation itself. The mutation probably disturbed the co ntrol reactions of the light-dependent biosynthesis of aminolevulinic acid.