Comparison of the composition of the energy-trapping apparatus of normal barley photosynthetic membranes and those lacking chlorophyll b shows that not only is chlorophyll b absent from the mutant, but all constituents (chlorophyll a, chlorophyll b, carotenoids and the protein moiety) of the major chlorophyll-protein complex of normal higher plant chloroplast membranes are also missing ; other chlorophyll-containing components, as far as can be ascertained, are essentially unaffected by the mutation. The nuclear gene which codes for the protein moiety of this complex is suggested as a possible site of the mutation in this barley mutant. This chlorophyll a/b-protein complex which accounts for such a large proportion of the chlorophyll and protein of the photosynthetic apparatus of higher plants is thus not essential for a plant to grow photosynthetically, and therefore a new name, light-harvesting chlorophyllprotein, is proposed for the complex, which was formerly termed the photosystem I1 chlorophyll-protein. The biosynthetic machinery in the mutant is unable to compensate for the loss of the light-harvesting chlorophyll-protein by adding extra chlorophylls into alternative sites in the membrane, thus the chlorophyll/P700 ratio in the mutant is two-thirds that of the normal plant. The light-harvesting chlorophyll-protein is the major location for chlorophyll b in higher plant membranes. The function of the complex is thought to be analogous to that of the algal biliproteins, i.e. light energy absorbed by the complex is fed preferentially, but not exclusively, to the photosystem I1 reaction-center or trap. It is reasoned that the complex exerts a strong influence on the organization of photosynthetic lamellae in higher plant chloroplasts by maintaining lamellae in contact with each other.Photosynthetic membranes of higher plants and green algae contain two major chlorophyll-protein complexes which account for approximately onehalf of the chlorophyll in the membrane [1,2]. One complex, the P700-chlorophyll a-protein, is the heart of photosystem1 and represents 8--15O/, of the chlorophyll in a higher plant [3] or green algal chloroplasts (K. Kan and J. P. Thornber, unpublished data), and 70°/, in blue-green algal membranes[4]. This complex has a red wavelength maximum of 677 nm and a chlorophyll/P700 ratio of 75 & 5/1 in all chlorophyll-a-containing organisms studied [3,4]. Scenedesmus, mutant 8, which lacks P700, and therefore does not live photosynthetically, is devoid of this component [5]. The second complex contains 25-50°/, of the chlorophyll of photosynthetic membranes of all higher plants [1,2,6] and green algae (K. Kan and J. P. Thornber, unpublished data) examined. The component has a molecular weight of 32000, and each protein molecule contains one molecule of chlorophyll a and one of chlorophyll b [1,6]. The precise function of this component has not been delineated ; however, the complex has been termed the photosystem I1 chlorophyll-protein [6] since it is predominantly associated with photochem...

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Abstract. A chlorophyll-deficient mutant of pea (Pisum sativum) was found as a spontaneous mutation of the variety Greenfeast. Total chlorophyll of the mutant leaves was about one-half that of normal pea leaves per mg dry weight, and the ratio of chl a:chl b ranged from 10 to 18, compared with 3 for normal pea. In each generation the mutant plants gave rise to normal and mutant plants and lethal plants with yellow leaves.For a normal pea plant, CO2 uptake was saturated at about 60,000 lux, whereas with mutant leaves, the rate of CO2 uptake was still increasing at 113,000 lux. At 113,000 lux the mutant and normal leaves showed similar rates of CO2 fixation per unit area of leaf surface, but on a chlorophyll basis the mutant leaves were twice as active. Hill reaction measurements on isolated chloroplasts also showed that the mutant chloroplasts werc saturated at higher intensities than the normal, and that the activity of the mutant was at least double that of the normal on a chlorophyll basis.It is suggested that the photosynthetic units of the mutant chloroplasts contain about half the number of chlorophyll molecules as compared to the normal photosynthetic units.Electron microscopy of leaf sections of normal and mutant leaves showed that the mutant chloropla,sts oontain fewer lamellae per chloroplast and fewer lamellae per granum. The lethal chloroplasts, which were virtually devoid of chlorophyll, were characterized by an absence of grana.

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