New chlorophyll-b forms in a chlorophyll-detergent photosynthetic model system.

The absorption spectra of chlorophyll b in Triton X-100 micelles at room temperature are superpositions of components with absorption maxima at 640.8, 648.9, 659.5, 669.6, 682.1 and 695.7 nm, obtained from Gaussian analysis of the spectra. The last four forms strongly overlap the chlorophyll a forms of this system obtained with maxima at 659.3, 667.6, 674.3, 680.8, 686.5, 692.8, 701.9, 713.6 and 722.0 nm. Since the in vivo chlorophyll a forms practically coincide with the forms found in this system, the possible existence of in vivo overlapping chlorophyll b and a forms eventually should be taken into consideration. In this case, however, the Gaussian analysis of in vivo absorption bands in itself in the proper spectrum range cannot discriminate between chlorophyll a and b components.

Energy transfer by chlorophyll beta in detergent micelles.

The concentration-dependent depolarization, concentration-dependent quenching, absorption and fluorescence spectra in solutions of chlorophyll beta-containing detergent micelles with Triton X-100 were studied in a concentration range of c equal to 0.4 muM-0.6mM chlorophyll beta and cd equal to 0.4-7.0 mM Triton X-100. The concentration-dependent depolarization obeys Förster's theory of depolarization of fluorescence with a transfer distance parameter R0 equal to 43 plus or minus 2 A. The concentration-dependent quenching is described by an empirical formula for the relative fluorescence yield n/n0 equal to 1/[1+(c/c1/2)-2] given by Kelly and Porter (Kelly A. R. and Porter, G. (1970) Proc. R. Soc. Lond. Ser. A. 315, 149-161). With increasing chlorophyll beta concentration the red absorption band at 650 nm is shifted toward a longer wavelength and its width increases by 10nm, the intensity of the long wave fluorescence band increases about 720 nm. The results analysed in terms of these findings lead to the conclusions that chlorophyll beta molecules are (a) locally concentrated in the micelles up to the concentration range of in vivo conditions, (b) partly in an aggregated state capable for fluorescence, (c) the chlorophyll beta yields chlorophyll beta homotransfer may be about 3-26% of the homotransfer chlorophyll alpha yields chlorophyll-alpha depending on the ratio of their concentrations.

Dichlorophenylurea-resistant oxygen evolution in Chlorella after cerulenin treatment.

Fluorescence spectra at 77 K, oxygen evolution at 30 degrees C and delayed fluorescence at 25 degrees C were measured in Chlorella pyrenoidosa cultures with and without cerulenin and subsequent 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (DCMU) treatment, respectively. In pure algal cultures the oxygen evolution was inhibited by DCMU and the long-time component of fluorescence was highly influenced by DCMU, as expected. In contrast, both oxygen evolution and delayed fluorescence became DCMU-resistant in cerulenin-treated cultures. The DCMU-resistance is correlated with a change in the fatty acid distribution of the thylakoid membrane, which also leads to changes in the prompt fluorescence. Cerulenin appears to be a promising new tool of diagnostics for the hitherto unsatisfactorily understood processes of oxygen evolution in photosynthesizing organisms.

Energy transfer by chlorophyll a in detergent micelles.

The process of energy transfer was studied in the chlorophyll a-containing detergent micelle, serving as a possible model of the photosynthetic unit. Chlorophyll a was added to aqueous solutions of the detergent Triton X-100 and incorporated into the micelles. The energy transfer process was studied by investigating the concentration depolarization of fluorescence of chlorophyll a. On the basis of the experimental depolarization curves as well as the value of the Förster parameter Ro equals to 56 A calculated from the overlap of absorption and fluorescence spectra it was concluded that energy transfer between chlorophyll a molecules in this model follows the Förster-type mechanism of inductive resonance. Furthermore it was found that the local concentration of chlorophyll a in the micelles is higher by 1-3 orders of magnitude than its overall concentration in the solution and by choosing the appropriate ratio between the consentration of chlorophyll a and the detergent it is possible to reach the in vivo chlorophyll concentration of 0.1 M withing the micelles. Thus the chlorophyll-detergent micelle model may be applied as a model of the separate package-type photosynthetic unit.

Cerulenin-induced Changes in Lipid and Fatty Acid Content of Chloroplasts in Detached Greening Barley Leaves.

Measurements were made of the monogalactosyl diglyceride, digalactosyl diglyceride, total phospholipid, and total fatty acid contents, the fatty acid compositions of the glycerolipids of plastids from detached barley leaves before and after 72 hours of greening in the presence or absence of the fatty acid biosynthesis inhibitor cerulenin. At the final stage of greening the incorporation of 1-(14)C-acetate into leaf tissue and that of U-(14)C-galactose into chloroplast galactolipids as well as the ultrastructure of chloroplasts were also studied. Cerulenin caused a marked reduction in the rate of accumulation of chloroplast lipids and fatty acids during the greening period. In addition, specific alterations were observed in the fatty acid composition of monogalactosyl diglyceride, phosphatidyl choline, and phosphatidyl inositol following cerulenin treatment, the possible reasons of which are discussed. 1-(14)C-acetate incorporation into leaf slices was only slightly reduced in cerulenin-treated leaves after 72 hours of greening, whereas nearly 3 times as much U-(14)C-galactose incorporated into chloroplast galactolipids as in the control. The chloroplasts of cerulenin-treated leaves displayed a marked membrane deficiency, probably due to the shortage of galactolipids.

[Excitation energy transfer between chlorophyll a molecules in detergent solutions]. / Peredacha énergii vozbuzhdeniia mezhdu molekulami khlorofilla a v rastvorakh detergenta

Chlorophyll-a absorption and luminescence as well as the transfer of electronic excitation energy between chlorophyll-a molecules were studied in micellar solutions of triton X-100 as a function of both chlorophyll-a and detergent concentrations. It is shown that the spectral properties of chlorophyll-a are closely related to the ratio between the concentrations of X-100 and chlorophyll-a. Concurrent evaluation of the curves for depolarization and relative quantum yield of fluorescence show that two different mechanisms of energy transfer are involved: energy transfer between monomers of chlorophyll-a, and energy transfer from excited monomers to aggregates of chlorophyll-a. Using the theoretical value for the critical distance of energy transfer (Ro=56-58 A) as well as experimental data from depolarization and fluorescence curves for solutions containing 3-10-3 M triton X-100 we determined the local concentration of chlorophyll-a in the detergent micelles.

Changes in the xanthophyll cycle and fluorescence quenching indicate light-dependent early events in the action of paraquat and the mechanism of resistance to paraquat in Erigeron canadensis (L.) cronq.

Violaxanthin de-epoxidation, chlorophyll fluorescence quenching, and photosynthetic O(2) evolution in the presence of paraquat (Pq) were studied in intact attached leaves of Pq-susceptible, and Pq-resistant (PqR) biotypes of Erigeron canadensis under different light conditions. Initially, similar changes were induced in the two biotypes, but the effects relaxed only in the PqR plants, indicating a Pq elimination process. The penetration of Pq into the chloroplasts of PqR plants proved to be somewhat restricted and highly light-dependent, as revealed by both the light response curves of violaxanthin de-epoxidation and fluorescence quenching and the short-term high-light pre-illumination experiments. An irregular down-regulation of the non-photochemical fluorescence quenching processes was observed, reflected by lower steady-state zeaxanthin and non-photochemical fluorescence quenching levels as compared with the corresponding non-treated high-light controls. It is concluded that light is essential not only for the initiation of the mechanism of resistance to Pq, but also for the penetration of Pq into the chloroplasts in the PqR E. canadensis. Also, the Pq elimination process may cause a modification to the regulation of the non-radiative energy dissipation in PqR plants in the presence of Pq.

Photosynthetic characteristics of detached barley leaves during greening in the presence of SAN 9785.

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by(14)CO2 fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.