Chlorophyll fluorescence quenching in isolated light harvesting complexes induced by zeaxanthin.
(57/2508)
Non-photochemical quenching of chlorophyll fluorescence in plants occurs in the light harvesting antenna of photosystem II and is regulated by the xanthophyll cycle. A new in vitro model for this process has been developed. Purified light harvesting complexes above the detergent critical micelle concentration have a stable high fluorescence yield but a rapidly inducible fluorescence quenching occurs upon addition of zeaxanthin. Violaxanthin was without effect, lutein and antheraxanthin induced a marginal response, whereas the violaxanthin analogue, auroxanthin, induced strong quenching. Quenching was not caused by aggregation of the complexes but was accompanied by a spectral broadening and red shift, indicating a zeaxanthin-dependent alteration in the chlorophyll environment. (+info)
Organization of the pigment molecules in the chlorophyll a/b/c containing alga Mantoniella squamata (Prasinophyceae) studied by means of absorption, circular and linear dichroism spectroscopy.
(58/2508)
In order to obtain information on the organization of the pigment molecules in chlorophyll (Chl) a/b/c-containing organisms, we have carried out circular dichroism (CD), linear dichroism (LD) and absorption spectroscopic measurements on intact cells, isolated thylakoids and purified light-harvesting complexes (LHCs) of the prasinophycean alga Mantoniella squamata. The CD spectra of the intact cells and isolated thylakoids were predominated by the excitonic bands of the Chl a/b/c LHC. However, some anomalous bands indicated the existence of chiral macrodomains, which could be correlated with the multilayered membrane system in the intact cells. In the red, the thylakoid membranes and the LHC exhibited a well-discernible CD band originating from Chl c, but otherwise the CD spectra were similar to that of non-aggregated LHC II, the main Chl a/b LHC in higher plants. In the Soret region, however, an unusually intense (+) 441 nm band was observed, which was accompanied by negative bands between 465 and 510 nm. It is proposed that these bands originate from intense excitonic interactions between Chl a and carotenoid molecules. LD measurements revealed that the Q(Y) dipoles of Chl a in Mantoniella thylakoids are preferentially oriented in the plane of the membrane, with orientation angles tilting out more at shorter than at longer wavelengths (9 degrees at 677 nm, 20 degrees at 670 nm and 26 degrees at 662 nm); the Q(Y) dipole of Chl c was found to be oriented at 29 degrees with respect to the membrane plane. These data and the LD spectrum of the LHC, apart from the presence of Chl c, suggest an orientation pattern of dipoles similar to those of higher plant thylakoids and LHC II. However, the tendency of the Q(Y) dipoles of Chl b to lie preferentially in the plane of the membrane (23 degrees at 653 nm and 30 degrees at 646 nm) is markedly different from the orientation pattern in higher plant membranes and LHC II. Hence, our CD and LD data show that the molecular organization of the Chl a/b/c LHC, despite evident similarities, differs significantly from that of LHC II. (+info)
Rescuing activity of galactoglycerolipids from cellular lesions induced by 5-aminolevulinic acid.
(59/2508)
An anti-oxygen radical reagent of a bacterial metabolite, M874 monogalactoglycerolipid (di-O-12-methyl-tetradecanoyl-3-O-beta-D-galactopyranosyl-sn-glycerol ), was tested for its ability to protect two organisms against cellular lesions induced by 5-aminolevulinic acid (ALA) and light. In Corynebacterium flavescens ATCC 10340, extracellular uroporphyrin and coproporphyrin were the main porphyrin products. Although less than 2 mM ALA increased porphyrin synthesis, ALA levels above 3 mM inhibited the synthesis. Depending on the light intensity, the amount of porphyrin decreased and ALA-induced cytotoxicity increased. The lesion was more severe in the case of coproporphyrin than uroporphyrin. The porphyrin lesion produced in low intensity light (300 lx) was considerably reduced by 100 microM M874 glycolipid, although the reduction in intense light (3,000 lx) was restricted to a lower level. Similar results were obtained with radish (Raphanus sativus). The ALA concentration that inhibited porphyrin synthesis and stem growth was similar to that seen with C. flavescens. Although the exogenous addition of M874 glycolipid to the radish did not prevent ALA-induced cellular injury, the co-culture of radish and a glycolipid producing bacterium (Microbacterium sp. M874) resulted in a significant prevention of cellular injury. This was true only under enforced adhesion conditions through the action of a polysaccharide flocculant H12. Some species of monogalactoglycerolipids were found in Corynebacterium and radish that showed prominent oxygen radical-protecting activities similar to that of M874 glycolipid. These monogalactoglycerolipids might function in vivo as agents to prevent ALA-induced cytological lesions, although the concentrations were low in Corynebacterium and radish. (+info)
Picosecond detection of an intermediate in the photochemical reaction of bacterial photosynthesis.
(60/2508)
Preparations of photosynthetic reaction centers from Rhodopseudomonas sphaeroides were excited with flashes lasting approximately 8 psec. Immediately after the excitation, there appeared a transient state which was characterized by new absorption bands near 500 and 680 nm, by a bleaching of bands near 540, 600, 760, and 870 nm, and by a blue shift of a band near 800 nm. The transient state decayed with an exponential decay time,t, of 246 plus or minus 16 psec after the flash. As the transient state decayed, the radical cation of the reaction center bacteriochlorophyll complex appeared. This indicates that the transient state is an intermediate in the photooxidation of the bacteriochlorophyll. The absorpiton spectrum of the transient state shows the state to be identical with a state (P-F) which has been detected previously in reaction centers that are prevented from completing the photooxidation, because of chemical reduction of the electron acceptor. Analysis of the spectrum suggests that the formation of P-F involves electron transfer from one bacteriochlorophyll molecule to another within the reaction center, or possibly from bacteriochlorophyll to the bacteriopheophytin of the complex. The initial absorbance changes after flash excitation also include a bleaching of an absorption band at 800 nm. The bleaching decays with tau approximately equal to 30 pse. The bleaching appers not to be a secondary effect, but rather to revael another early step in the primary photochemical reaction. (+info)
Recruitment of a foreign quinone into the A1 site of photosystem I. Altered kinetics of electron transfer in phylloquinone biosynthetic pathway mutants studied by time-resolved optical, EPR, and electrometric techniques.
(61/2508)
Interruption of the menA or menB gene in Synechocystis sp. PCC 6803 results in the incorporation of a foreign quinone, termed Q, into the A(1) site of photosystem I with a number of experimental indicators identifying Q as plastoquinone-9. A global multiexponential analysis of time-resolved optical spectra in the blue region shows the following three kinetic components: 1) a 3-ms lifetime in the absence of methyl viologen that represents charge recombination between P700(+) and an FeS(-) cluster; 2) a 750-microseconds lifetime that represents electron donation from an FeS(-) cluster to methyl viologen; and 3) an approximately 15-microseconds lifetime that represents an electrochromic shift of a carotenoid pigment. Room temperature direct detection transient EPR studies of forward electron transfer show a spectrum of P700(+) Q(-) during the lifetime of the spin polarization and give no evidence of a significant population of P700(+) FeS(-) for t +info)
fhy3-1 retains inductive responses of phytochrome A.
(62/2508)
The fhy3 mutation of Arabidopsis impairs phytochrome A (phyA)-mediated inhibition of hypocotyl growth without affecting the levels of phyA measured spectrophotometrically or immunochemically. We investigated whether the fhy3-1 mutation has similar effects on very low fluence responses (VLFR) and high irradiance responses (HIR) of phyA. When exposed to hourly pulses of far-red light, etiolated seedlings of the wild type or of the fhy3-1 mutant showed similar inhibition of hypocotyl growth, unfolding of the cotyledons, anthocyanin synthesis, and greening upon transfer to white light. In the wild type, continuous far-red light was significantly more effective than hourly far-red pulses (at equal total fluence). In the fhy3-1 mutant, hourly pulses were as effective as continuous far-red light, i.e. the failure of reciprocity typical of HIR was not observed. Germination was similarly promoted by continuous or pulsed far-red in wild-type and fhy3-1 seeds. Thus, for hypocotyl growth, cotyledon unfolding, greening, and seed germination, the fhy3-1 mutant retains VLFR but is severely impaired in HIR. These data are consistent with the idea that VLFR and HIR involve divergent signaling pathways of phyA. (+info)
The PSI-K subunit of photosystem I is involved in the interaction between light-harvesting complex I and the photosystem I reaction center core.
(63/2508)
PSI-K is a subunit of photosystem I. The function of PSI-K was characterized in Arabidopsis plants transformed with a psaK cDNA in antisense orientation, and several lines without detectable PSI-K protein were identified. Plants without PSI-K have a 19% higher chlorophyll a/b ratio and 19% more P700 than wild-type plants. Thus, plants without PSI-K compensate by making more photosystem I. The photosystem I electron transport in vitro is unaffected in the absence of PSI-K. Light response curves for oxygen evolution indicated that the photosynthetic machinery of PSI-K-deficient plants have less capacity to utilize light energy. Plants without PSI-K have less state 1-state 2 transition. Thus, the redistribution of absorbed excitation energy between the two photosystems is reduced. Low temperature fluorescence emission spectra revealed a 2-nm blue shift in the long wavelength emission in plants lacking PSI-K. Furthermore, thylakoids and isolated PSI without PSI-K had 20-30% less Lhca2 and 30-40% less Lhca3, whereas Lhca1 and Lhca4 were unaffected. During electrophoresis under mildly denaturing conditions, all four Lhca subunits were partially dissociated from photosystem I lacking PSI-K. The observed effects demonstrate that PSI-K has a role in organizing the peripheral light-harvesting complexes on the core antenna of photosystem I. (+info)
White yellow virescent pattern in winter rye: inheritance, plant growth, and ultrastructure of plastids.
(64/2508)
Inbred lines from different varieties of cultivated plants characterized by a white yellow irregular pattern on the leaves obtained after selection in the inbred generation (S3) of winter rye (Secale cereale L.) were the object of the present studies. The feature of a white yellow irregular pattern in all lines was monomeric and recessive. This trait in L158b, wch, and zp was determined by the same recessive gene marked with the symbol wyv1, "white yellow virescent." The gene responsible for the appearance of the above feature in line L24 was nonallelic to the gene wyv1, therefore it was designated as the sequent gene of the same series--wyv2. The studied forms of plants were characterized by a diminution in the number of plastids and in chlorophyll (a plus b) content in mesophyll cells of leaves. Contrary to typical ultrastructure of chloroplasts in dark green plants (control), plastids in lines with the white yellow virescent pattern on the leaves showed variations in ultrastructure from numerous granal and intergranal thylakoids to a reduced number. (+info)