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The effect of a dangerous toxic substance, methylmercury, on light dependence curves of chlorophyll fluorescence in Chlamydomonas moewusii was studied. We found low concentration of methylmercury (10(-7) M) to cause a decrease in the relative rate of the non-cyclic electron transport activity of PS 2, a decline in the maximum utilization of light energy (α), and a decline in the saturation light intensity (E(s)). Non-photochemical fluorescence quenching increased after short-term exposure and decreased in the course of prolonged incubation. These parameters were more sensitive to the action of the toxic substance than the widely used parameter F(V)/F(M), which reflects the maximum quantum yield of PS 2. We propose the use of the method of fast measurement of light dependence curves of fluorescence to detect the changes in algal cells at the early stages of exposure to mercury salts.

The effect of methylmercury and copper ions on the kinetics of light induction and dark relaxation of the variable of chlorophyll a fluorescence has been studied on cultures of the microalgae Chlamydomonas moevusii. It was shown that the toxicants added at concentrations that induce no decrease in photochemical activity of PS II (F(v)/F(M)) affect the electron transport on the acceptor side of PS II, the nonphotochemical quenching of excitation in the antenna, and the reoxidation of the quinone pool. At low concentrations, methylmercury produced a more toxic effect. The results obtained indicate that this approach can be used for detecting the changes in plant and algae cells at the early stages of the action of toxicants.

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.

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.

The amounts of ferredoxin, plastocyanin, ferredoxin-NADP-reductase were determined by electrophoresis and differential spectroscopy. The cytochrome levels in the chloroplasts of non-photosynthesizing mutants Chlamydomonas reinhardii were determined both in active and inactive photosystems. It was shown that the loss of PS-1 activity did not affect the amount and activity of the electron carriers. The disturbances of the donor side of PS-2 in the mutants were accompanied by a loss of the reaction center activity and by a decrease of cytochrome b599. The amounts of other protein components in the mutants with inactive PS-2 remained unchanged. The disturbances in the cytochrome c553 content presumably blocked the electron transfer between the photosystems but did not affect the activity of the reaction centers of PS and the levels of other carriers of the chloroplast electron transport chain.

The effect of "hole burning" in absorption spectrum upon monochromatic illumination at 4.2 degrees K has been investigated on the Chlamydomonas reinhardii mutant strain 516-3a which possesses the chlorophyll a/P700 ratio of about 25. This effect has been earlier discovered for the wild type strain of Chlorella. In the strain 516-3a two types of holes differing in width and in shape have been observed. For their assignment the maximal (saturated) holewidth has been studied as a function of the burning wavelength. It has been shown that for the holes of one type photooxidation of P700 is responsible. The other type of holes is caused by electrochromic transition shift of another component of the reaction centre with the absorption maximum at 693 nm. Using measured holewidths it has been estimated that the lifetime of P700 excited state is not less than 50 ps and that the excited state lifetime of the component responsible for the other type of holes is 8.6 ps. The latter, in assumption that it is limited by energy transfer between two components under consideration, gives a distance of 20 A between them. Possible reasons of disagreement between obtained P700* lifetime and considerably shorter times attributed earlier to the primary electron phototransfer in photosystem I on the basis of picosecond studies are discussed.

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.