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Photomotility behavior in green flagellate algae is mediated by rhodopsin-like receptors, which was initially suggested on the basis of physiological evidence. The cascade of rapid Ca(2+)-dependent electrical responses in the plasma membrane plays a key role in the signal transduction chain during both phototaxis and the photophobic response. The photoreceptor current through the plasma membrane is the earliest detectable event upon photoexcitation of the photoreceptors. Analysis of this current revealed that it consists of at least two components with different characteristics. Genes encoding two archaeal-type rhodopsins (type I rhodopsins) were recently identified in the genome of Chlamydomonas reinhardtii and named (Chlamydomonas Sensory Rhodopsins A and B CSRA and CSRB). The measurements of photoelectric and motor responses in genetic transformants of C. reinhardtii enriched in each of these receptor proteins showed that the two components of the photoreceptor current are mediated by the two rhodopsins, and that both CSRA and CSRB are involved in phototaxis and the photophobic response. The CSRA-mediated current dominates at high light intensities and contributes primarily to the photophobic response. The CSRB-initiated transduction involves an efficient amplification cascade and mediates the highly sensitive phototaxis at low light intensities. CSRA and CSRB expressed heterologously in oocytes of Xenopus laevis act as light-gated proton channels, although it is unclear whether this channel activity plays a functional role in the initiation of motor responses and/or occurs in the native system.

Three types of mutants (pigment, non-photosynthesizing and pigment non-photosynthesizing ones) were used to identify the chlorophyll-containing bands in gel slices. The pigment mutants with an impaired light-harvesting chlorophyll a/b-protein complex possess photochemically active reaction centers of photosystems and are capable of phototrophic growth. Using these mutants, the heterogeneity of the chlorophyll-containing bands, LH2 and LH3, in gel slices and the dependence of LH2 on chlorophyll a-protein and that of LH3 on chlorophyll b-protein in the light-harvesting complex were established. The non-photosynthesizing mutants with an inactive photosystem I (or II) are devoid of antennae forms of chlorophyll a and are not capable of phototrophic growth. Using these mutants, it was demonstrated that in gel slices the chlorophyll-containing band, CPI, corresponds to the chlorophyll a-protein complex of photosystem I, while CPII to the chlorophyll a-protein complex of photosystem II. It was also found that the presence of the chlorophyll-containing band, LH0 (CPIa) in gel slices correlates with the preservation of the light-harvesting complex and is independent of photosystem I. The spectral properties of chlorophyll complexes in gel slices are not identical to those of native chlorophyll. It was assumed that chloroplasts contain at least 4 types of chlorophyll proteins that are controlled by independent genes.

Investigations of non-photosinthesizing mutants of Chlamydomonas reinhardii with damaged activity of both or one of the photosystems have shown that the chlorophyll a form with the absorption maximum at 685 nm and low temperature fluorescence band at 696 nm is a part of the pigment-protein complex of PS-2. Chlorophyll a forms with absorption maxima at 689, 698 and 703 nm belong to the pigment-protein complex of PS-1. They seem to be responsible for the long-wave band of chlorophyll fluorescence with the maximum at 707--718 nm. Chlorophyll a forms with absorption at 661, 667 and 678 nm and a short-wave fluorescence band at 685--690 nm rank among the pigments of the light-converging complex, as well as chlorophyll b with the absorption maximum at 644 and 649 nm.

The analysis of a group of recombinant strains of phenotypically yellow mutant Y-4 Chlamydomonas reinhardii has shown a considerable variability in displaying the degree of pigmentation. Chlorophyll "a" is the first to accumulate in chloroplasts. Chlorophyll "b" was found in strains when the content of chlorophyll "a" reached 1% of its concentration in cells of the wild type, The occurrence of spectral forms of chlorophyll "a" at 661, 667, 678, 685, 698 and 703 does not correlate with its quantitative accumulation. Variability in pigment accumulation is accompanied by changes both in the structural organization of the membrane system of chloroplasts and in the functional activity of photosystems. The degree of development of chloroplast structure in the group of recombinant strains varies from the formation of vesicules to well developed tilakoids and their arrangement in grains.

Using antisera to fractions H1, H2a, H3 and H4 of the calf thymus histones, a comparative immunofluorescent investigation of these proteins in the nuclei of Chlamydomonas reinhardii, Haematococcus pluvialis, Dunaliella salina and Euglena gracilis was carried out. It has been shown that according to the immunofluorescent test, the nuclei of these algae contain proteins close to fractions H2a, H3 and H4 of the calf thymus histones. H1 fraction in these algae is either absent or can be considered as a protein immunochemically non-related to H1 fraction of the calf thymus histone. For quantitative evaluation (in units of the immunological distance) of the difference between histones of the algae and of the calf thymus in situ by indirect immunofluorescence, it was suggested to use the ultimate dilutions of antisera to histones. It was shown that the ultimate dilutions were correlated with titres of antisera in the reaction of microcomplement fixation. Such an approach and the data obtained are of interest for studying into the evolution of nucleosome histones in unicellular and multicellular eukaryotes.

The method of hole-burning in absorption spectra at helium temperatures has been applied to the study of primary photoprocesses in photosystem II (PS2) of Chlamydomonas reinhardii mutant strains 420/7 and N-154. The former is enriched in PS2 reaction centers (the chlorophyll a/P680 ratio is about of 50--70) and the latter presumably lacks the pheophytin molecule which is the primary electron acceptor in PS2. For the strain 420/7 samples with ferricyanide addition two types of holes have been observed differing in their width and spectral region of burning. One type could be burned in the region of 678--682 nm (P680 is responsible for burning) and another one -- in the region of 682--688 nm (pheophytin is responsible). The excited states relaxation times evaluated from the hole widths are 3,8 +/- 0,8 ps for P680 and 9,8 +/- 1.5 ps for pheophytin. The new mechanism of PS2 operating has been proposed in which photoexcited phenophytin molecule functions as a primary electron donor. In the case of N-154 strain the only type of holes has been observed for which P680 is responsible. The excited state relaxation time of the latter evaluated from the hole width is 10 +/- 2 ps.

A method for qualitative determination of cytochromes of the wild-type and mutant strains of Chalmydomonas reinhardii was developed. The effect of different techniques of cell disruption (ultrasound, Triton X-100, acetone, etc) on detection of cytochrome maxima in the oxidized minus reduced difference spectra was studied on a comparative basis. The development of the stable difference spectrum of the disrupted cell suspension was shown to be a function of incubation time in the presence of an oxidizing or a reducing agent. Cytochromes of the wild-type and 10 nonphotosynthesizing mutants were determined. Four mutants with lesions in cytochromes B559 and C553 were detected. Mutants with lesions in the reaction center of photosystem 2 were found to have a substantially reduced content of cytochrome B559, whereas those with normal photosystems--of cytochrome C553.

It has been shown in the studies of 6 strains of non-synthesizing Chlamydomonas reinhardi mutants with a damaged electron-transport chain (ETC) in the region of the Photosystem 2 (PS 2) that the damage is localized on the oxidizing side of PS 2. The ESR studies of the mutants have shown that signal 2 is absent in all the mutants, the width of signal 1 in some mutants is lower than in the control, which is, probably, concerned with the differences in the reaction centre structures. The ETC region from electron inlet from the donor--diphenylcarbaside to P700 is capable of functioning. It is suggested that in all the mutants studied the complex responsible for photodissociation of water is damaged.

The light electron transport in non-photosynthetic mutants of Chlamydomonas reinhardii A-36 and A-68 with a decreased content of cytochrome c553 was studied. The light-induced changes of absorption at 520, 559, 563 nm were shown to occur in the films of intact cells and in cell fragments. However, no maximum of the "light minus dark" difference absorption spectra of mutants belonging to cytochrome c553 was revealed. The electron transport from water to NADP+ or ferricyanide in the mutants was completely blocked; however, it was partly restored by an addition of exogenous cytochrome c553 to the cell fragments. A conclusion on the genetic damage of cytochrome c553 in mutants A-36 and A-68 was made. The localization of the cytochrome in the electron transport chain between the photosystems was demonstrated.

A 2-3-fold reduction of chlorophyll content in pigment mutants of Chlamydomonas reinhardii is conditioned by the disturbances in light-harvesting pigments. When the activity of both photosystems is preserved, the reduction of short-wave forms of chlorophyll a (667, 678 nm) is accompanied by a fall of the fluorescence maximum at 685-690 nm; the disturbance of the long-wave forms with the adsorption maxima at 689, 698 an 703 nm results in a decrease of the chlorophyll fluorescence band at 707-718 nm. The long-wave forms of chlorophyll appertain to the pigment-protein complex of PS-1 which is not involved in the formation of contacts between the grand thylacoids.