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Two photosystem I (PSI) preparations were purified by non-denaturing SDS-PAGE or sucrose gradient ultracentrifugation and examined as to their chlorophyll-protein composition. In both preparations a minimum of two chlorophyll-proteins can be distinguished in addition to the 110 kD P-700 Chlo-P 1 complex. One (LHCI-730) is a chlorophyll-protein (Mr 40 kD) having a high chlorophyll a/b ratio, and a major 77 K fluorescence peak at 730 nm. It consists of three polypeptides with apparent molecular weights of 21, 22.5 and 24 kD. Another chlorophyll-protein (LHCI-680) with a lower molecular weight (Mr 25 kD) fluoresces at 77 K with a maximum at 680 nm. This chlorophyll-protein has a high chlorophyll b content and two constituent polypeptides of 20 and 25 kD. Absorption, 77 K fluorescence and circular dichroism spectra of the PSI related chlorophyll-proteins are presented and compared with those of photosystem II chlorophyll-proteins from maize thylakoids. We propose a model for energy transfer in the photosystem I reaction centre with the following sequence: LHCI-730 ~ LHCI-680ChL-P 1. LHCI-680 acts as a connecting antenna which can also transfer energy from ChL/b-P2. This model was used to interpret the 77 K fluorescence emission from two barley mutants.

i n d u c t i o n kinetics, H P L C , polypeptides, SDS-polyacrylamide gel electrophoresisWe have examined 31 new chlorina mutants of barley using in vivo absorption spectroscopy, 77 K fluorescence emission spectroscopy, room temperature fluorescence induction kinetics, HPLC separation of pigments and SDS-PAGE. Based on these properties they can be placed into 4 groups. The first group consists of 10 mutants which are allelic to the chlorophyll b-less chlorina-f2 and comprises five strongly and three slightly leaky mutants at this locus. The decrease in chlorophyll b content was correlated with a corresponding decrease in the amount of chlorophyll a/b-proteins in the thylakoids. One mutant (chlorina 106) was found which had a very low chlorophyll b content and a deficiency in Chl,/~-P2, but was not allelic to chlorina-f2. The second group of chlorina mutants has unusual fluorescence properties, with a high Fm/Fo ratio. Gaussian deconvolution of the 77 K fluorescence emission spectra revealed an increase in the amplitude of components emitting at 694 and 718 rim. The possibility is discussed that these properties result from the absence of the PSI connecting antenna LHCI-680. The third group has a Fs/Fo ratio < 1, and other properties consistent with a partial deficiency in the chlorophyll a-proteins of PSII reaction centres. The fourth group consists ofchlorina mutants which are very similar to wild-type in the properties examined, differing mainly in having a lower chlorophyll content. I N T R O D U C T I O NO n e of the most extensively studied higher plant nuclear gene m u t a n t is the chlorophyll b-less barley m u t a n t chlorina-f2, and its alleles 2800, 2807 and 3613 (12, 19, 26). This mutation has proved invaluable in determining the role of chlorophyll b in photosynthetic m e m b r a n e s and the function of the chlorophyll a/b-proteins.

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