Assessing the Applicability of Singlet Oxygen Photosensitizers in Leaf Studies.

Singlet oxygen ((1) O2 ) is of special interest in plant stress physiology. Studies focused on internal, chlorophyll-mediated production are often complemented with the use of artificial (1) O2 photosensitizers. Here, we report a comparative study on the effects of Rose Bengal (RB), Methylene Violet (MVI), Neutral Red (NR) and Indigo Carmine (IC).

Effect of light on the gene expression and hormonal status of winter and spring wheat plants during cold hardening.

The effect of light on gene expression and hormonal status during the development of freezing tolerance was studied in winter wheat (Triticum aestivum var. Mv Emese) and in the spring wheat variety Nadro. Ten-day-old plants (3-leaf stage) were cold hardened at 5°C for 12 days under either normal (250 µmol m(-2) s(-1) ) or low (20 µmol m(-2) s(-1) ) light conditions.

Transcriptome analysis of germinating maize kernels exposed to smoke-water and the active compound KAR1.

Background: Smoke released from burning vegetation functions as an important environmental signal promoting the germination of many plant species following a fire. It not only promotes the germination of species from fire-prone habitats, but several species from non-fire-prone areas also respond, including some crops. The germination stimulatory activity can largely be attributed to the presence of a highly active butenolide compound, 3-methyl-2H-furo[2,3-c]pyran-2-one (referred to as karrikin 1 or KAR1), that has previously been isolated from plant-derived smoke.

M234Glu is a component of the proton sponge in the reaction center from photosynthetic bacteria.

Bacterial reaction centers use light energy to couple the uptake of protons to the successive semi-reduction of two quinones, namely Q(A) and Q(B). These molecules are situated symmetrically in regard to a non-heme iron atom. Four histidines and one glutamic acid, M234Glu, constitute the five ligands of this atom.

The local electric field within phospholipid membranes modulates the charge transfer reactions in reaction centres.

Three different cholesterol derivatives and phloretin, known to affect the local electric field in phospholipid membranes, have been introduced into Rhodobacter sphaeroides reaction centre-containing phospholipid liposomes. We show that cholesterol and 6-ketocholestanol significantly slow down the interquinone first electron transfer (approximately 10 times), whereas phloretin and 5-cholesten-3beta-ol-7-one leave the kinetics essentially unchanged. Interestingly, the two former compounds have been shown to increase the dipole potential, whereas the two latter decrease it.

Evidence for delocalized anticooperative flash induced proton binding as revealed by mutants at the M266His iron ligand in bacterial reaction centers.

Bacterial reaction centers (RCs) convert light energy into chemical free energy via the double reduction and protonation of the secondary quinone electron acceptor, QB, to the dihydroquinone QBH2. Two RC mutants (M266His --> Leu and M266His --> Ala) with a modified ligand of the non-heme iron have been studied by flash-induced absorbance change spectroscopy. No important changes were observed for the rate constants of the first and second electron transfers between the first quinone electron acceptor, QA, and QB.

Thermodynamics of light-induced and thermal degradation of bacteriochlorins in reaction center protein of photosynthetic bacteria.

The rate constants of thermal (irreversible) damage of bacteriochlorin pigments (bacteriochlorophyll monomer [B], bacteriochlorophyll dimer [P] and bacteriopheophytine [H]) in reaction center [RC] protein from the photosynthetic bacterium Rhodobacter sphaeroides were studied in the dark and during intense (400 mW x cm(-2)) laser light excitation (wavelengths 488 and 515 nm) under deoxygenated conditions. While the kinetics of degradation of P and B were monoexponential, the decay kinetics of H were overlapped by an initial lag phase at elevated (>40 degrees C) temperature. This is explained by removal of the central metal ion from the bacteriochlorophylls as part of their degradation processes.

Light- and redox-dependent thermal stability of the reaction center of the photosynthetic Bacterium rhodobacter sphaeroides.

Irreversible loss of the photochemical activity and damage of the pigments (bacteriochlorophyll [Bchl] monomer, Bchl dimer [P] and bacteriopheophytin) by combined treatment with intense and continuous visible light and elevated temperature have been studied in a deoxygenated solution of reaction center (RC) protein from the nonsulfur purple photosynthetic bacterium Rhodobacter sphaeroides. Both the fraction of RC in the charge-separated redox state (P+Q-, where Q is a quinone electron acceptor) and the degradation of the pigments showed saturation as a function of increasing light intensity up to 400 mW cm(-2) (488/515 nm) or 1100 microE m(-2) s(-1) (white light). The thermal denaturation curves of the RC in the P+Q- redox state demonstrated broadening and 10-20 degrees C shift to lower temperature (after 30-90 min heat treatment) compared with those in the PQ redox state.

A mathematical model for quinone-herbicide competition in the reaction centres of Rhodobacter sphaeroides.

A quantitative model describing the amplitude of semiquinone absorption in photosynthetic reaction centres after successive flashes in the presence of increasing inhibitor concentration is presented. By using relatively simple algebra, the semiquinone signals can be calculated and fitted to the oscillation pattern by optimizing only two parameters; the electron and quinone equilibrium constants, Ke and Kq, respectively. In this work we expand our earlier model [Tandori et al.

Proton uptake of rhodobacter capsulatus reaction center mutants modified in the primary quinone environment.

Flash-induced absorbance spectroscopy was used to analyze the proton uptake and electron transfer properties of photosynthetic reaction centers (RC) of Rhodobacter capsulatus that have been genetically modified near the primary quinone electron acceptor (Q(A)). M246Ala and M247Ala, which are symmetry-related to the positions of two acidic groups, L212Glu and L213Asp, in the secondary quinone electron acceptor (QB) protein environment, have been mutated to Glu and Asp, respectively. The pH dependence of the stoichiometry of proton uptake upon formation of the P+Q(A)- (H+/P+Q(A)-) and PQ(A) (H+/Q(A)-) (P is the primary electron donor, a noncovalently linked bacteriochlorophyll dimer) states have been measured in the M246Ala --> Glu and the M247Ala --> Asp mutant RC, in the M246Ala-M247Ala --> Glu-Asp double mutant and in the wild type (WT).