Does methyl jasmonate modify the oxidative stress response in Phaseolus coccineus treated with Cu?

The contribution of methyl jasmonate (MJ) as a signal molecule able to take part in the defense mechanism against copper (Cu)-imposed oxidative stress was studied in the leaves and roots of runner bean (Phaseolus coccineus) plants. Roots of plants cultivated hydroponically were preincubated in MJ (10µM) for 1h or 24h and subsequently exposed to Cu (50µM) for 5h (short-term experiment) or 5 days (long-term experiment). Enzymatic (activity of superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; guaiacol peroxidase, POX) and non-enzymatic (accumulation of malondialdehyde, MDA; homoglutathione, hGSH; proline; anthocyanins; low molecular weight organic acids, LMWOAs) responses were determined in the leaves and roots.

Molecular architecture of plant thylakoids under physiological and light stress conditions: a study of lipid-light-harvesting complex II model membranes.

In this study, we analyzed multibilayer lipid-protein membranes composed of the photosynthetic light-harvesting complex II (LHCII; isolated from spinach [Spinacia oleracea]) and the plant lipids monogalcatosyldiacylglycerol and digalactosyldiacylglycerol. Two types of pigment-protein complexes were analyzed: those isolated from dark-adapted leaves (LHCII) and those from leaves preilluminated with high-intensity light (LHCII-HL). The LHCII-HL complexes were found to be partially phosphorylated and contained zeaxanthin.

Organization and functionality of chlorophyll-protein complexes in thylakoid membranes isolated from Pb-treated Secale cereale.

In this study, Secale cereale seedlings cultivated under 0 (control), 2 or 5mM Pb(NO3)2 concentrations were used to examine alterations in the organization and functionality of chlorophyll-protein complexes in thylakoid membranes under Pb ion stress. The studies were conducted on whole leaves of rye seedlings or thylakoid membranes isolated from Pb-treated and control plants. Using non-denaturing electrophoresis, it was assessed that increasing Pb concentrations resulted in an increase in the value of the ratio of the content of LHCII oligomers (mainly trimers) to the content of LHCII monomers.

Strong light-induced reorganization of pigment-protein complexes of thylakoid membranes in rye (spectroscopic study).

The supramolecular reorganization of LHCII complexes within the thylakoid membrane in Secale cereale leaves under low and high light condition was examined. Rye seedlings were germinated hydroponically in a climate chamber with a 16 h daylight photoperiod, photosynthetic photon flux density (PPFD) of 150 μmo lm(-2)s(-1) and 24/16°C day/night temperature. The influence of pre-illumination of the plants with high light intensity on the PSII antenna complexes was studied by comparison of the structure and function of the LHCII complexes and organization of thylakoid membranes isolated from 10-day-old plants illuminated with low (150 μmo lm(-2)s(-1)) or high (1200 μmo lm(-2)s(-1)) light intensity.

The photoprotective mechanisms in Secale cereale leaves under Cu and high light stress condition.

The influence of excess Cu ions and high light treatment on the function of photosystem II was investigated in order to examine how this heavy metal modifies the photoprotective mechanisms operating at the molecular level in Secale cereale plants. Thus, non-treated plants and those treated with 5 or 50 microM Cu, simultaneously illuminated with 150 micromol m(-2) s(-1) or 1200 micromol m(-2) s(-1) light intensity, were studied. To analyze the PSII reaction to the stress conditions, Chl a fluorescence induction was applied.

Structural and functional modifications of the major light-harvesting complex II in cadmium- or copper-treated Secale cereale.

The effects of 50 microM cadmium (Cd) or copper (Cu) ions on the supramolecular conformation of the light-harvesting pigment-protein complex of PSII (LHCII) isolated from rye seedlings were studied. It was found that the action of these two metal ions on the LHCII structure and organization is dissimilar. The Fourier transform infrared (FTIR) measurements indicated inhibition or stimulation of formation of parallel beta-structures and aggregates in the presence of Cd or Cu ions, respectively.

Xanthophyll-induced aggregation of LHCII as a switch between light-harvesting and energy dissipation systems.

The xanthophyll cycle pigments, violaxanthin and zeaxanthin, present outside the light-harvesting pigment-protein complexes of Photosystem II (LHCII) considerably enhance specific aggregation of proteins as revealed by analysis of the 77 K chlorophyll a fluorescence emission spectra. Analysis of the infrared absorption spectra in the Amide I region shows that the aggregation is associated with formation of intermolecular hydrogen bonding between the alpha helices of neighboring complexes. The aggregation gives rise to new electronic energy levels, in the Soret region (530 nm) and corresponding to the Q spectral region (691 nm), as revealed by analysis of the resonance light scattering spectra.

Variation in oxidative stress and photochemical activity in Arabidopsis thaliana leaves subjected to cadmium and excess copper in the presence or absence of jasmonate and ascorbate.

We have presented changes in the photosynthetic apparatus activity of Arabidopsis thaliana plants occurring within 15-144 h of 100 microM Cu or Cd action with regard to jasmonate (JA) as well as expression of the oxidative stress and non-enzymic defense mechanisms. The inhibitory effect of both heavy metals related to developing dissipative processes and lipid peroxide formation was expressed in dark-adapted state after the longest time as a decrease in potential quantum yield of PSII. In dark- and light-adapted state the heavy metals affected the enzymic phase of photosynthesis already from the 15th hour, which was related to the lipid peroxide formation.

The level of jasmonic acid in Arabidopsis thaliana and Phaseolus coccineus plants under heavy metal stress.

The effect of heavy metal stress as a potent abiotic elicitor for triggering an accumulation of jasmonic acid (JA) was investigated. Copper and cadmium in in vivo conditions induced accumulation of jasmonates in mature leaves of Arabidopsis thaliana and in young and oldest Phaseolus coccineus plants. The dynamics of jasmonate accumulation showed a biphasic character in both plants.

A study of molecular interactions in light-harvesting complexes LHCIIb, CP29, CP26 and CP24 by Stark effect spectroscopy.

Electric field-induced absorption changes (electrochromism or Stark effect) of the light-harvesting PSII pigment-protein complexes LHCIIb, CP29, CP26 and CP24 were investigated. The results indicate the lack of strong intermolecular interactions in the chlorophyll a (Chl a) pools of all complexes. Characteristic features occur in the electronic spectrum of Chl b, which reflect the increased values of dipole moment and polarizability differences between the ground and excited states of interacting pigment systems.

Spectral analysis of pigment photobleaching in photosynthetic antenna complex LHCIIb.

Light-induced photooxidation of chlorophyll (Chl) a, b and xanthophylls was investigated in LHCIIb, the antenna pigment-protein complex of photosystem II. Absorption difference spectra at normal and low temperatures show initially (at less than 25% Chl a decay) a selective bleaching of a red-shifted Chl b with absorption bands at 487 and 655 nm, Chl b (460/650 nm) and Chl a (433/670 nm), which changes to a less selective photooxidation pattern at deeper bleaching stages. Difference absorption spectra and HPLC analyses indicate different photooxidation rates of pigments in the order neoxanthin>Chl a>lutein approximately Chl b.

Conformational rearrangements in light-harvesting complex II accompanying light-induced chlorophyll a fluorescence quenching.

Light-induced chlorophyll a (Chl a) fluorescence quenching was studied in light-harvesting complex of photosystem II (LHCII). Fluorescence intensity decreased by ca. 20% in the course of 20 min illumination (412 nm, 36 micromol m(-2) s(-1)) and was totally reversible within 30 min dark adaptation.