Maya D. Lambreva

Trapping of the quenched conformation associated with non-photochemical quenching of chlorophyll fluorescence at low temperature.

The kinetics of non-photochemical quenching (NPQ) of chlorophyll fluorescence was studied in pea leaves at different temperatures between 5 and 25°C and during rapid jumps of the leaf temperature. At 5°C, NPQ relaxed very slowly in the dark and was sustained for up to 30xa0min. This was independent of the temperature at which quenching was induced. Upon raising the temperature to 25°C, the quenched state relaxed within 1xa0min, characteristic for qE, the energy-dependent component of NPQ. Measurements of the membrane permeability (ΔA515) in dark-adapted and preilluminated leaves and NPQ in the presence of dithiothreitol strongly suggest that the effect of low temperature on NPQ was not because of limitation by the lumenal pH or the de-epoxidation state of the xanthophylls. These data are consistent with the notion that the transition from the quenched to the unquenched state and vice versa involves a structural reorganization in the photosynthetic apparatus. An eight-state reaction scheme for NPQ is proposed, extending the model of Horton and co-workers (FEBS Lett 579:4201–4206, 2005), and a hypothesis is put forward concerning the nature of conformational changes associated with qE.

Computational Biology, Protein Engineering, and Biosensor Technology: a Close Cooperation for Herbicides Monitoring

Application of herbicides has led to a marked increase in the productivity and preservation of agricultural products, as a result of which, cultural techniques for weed control, such as altering soil pH, salinity, fertility levels or mechanical approaches, have been abandoned. These compounds are also used extensively in industrial sites, roadsides, ditch banks, irrigation canals, fence lines, recreational areas, lawns, railroad embankments, and power line rights-of-way, to remove undesirable plants that might cause damage, present fire hazards, or impede work crews. They also reduce costs of mowing procedures. However, due to the toxic effect, their control is carried out by a system of national registration which limits the manufacture and/or sale of pesticide products to those who have been approved (Montesinos 2003). In this context, herbicides were classified into families based on their chemical similarity or, as proposed by the global Herbicide Resistance Action Committee (HRAC) group, according to their target sites and modes of action (Table 1). Standards and regulations for the classifications, labelling, and packaging of pesticides were first set up by the EUROPEAN ECONOMIC COMMUNITY (EEC) Council Directive 67/548/ in 1967. At present the issue regarding herbicides is quite intricate, because according to the Food and Agriculture Organization (FAO), their exclusion would lead to a strong reduction in farming production; however, several toxic effects on biological systems associated with their use were proved by epidemiological and experimental studies (Waller et al., 2010; Roberts et al., 2010; Frazier 2007). After the first cases of animals poisoned by heavy utilization of herbicides, the monitoring of these compounds to avoid accumulation in the human body were strongly intensified. In particular in 1963, the World Health Organization (WHO) and FAO created the Codex Alimentarius Commission, which joined 173 signatories from the European Community (EC) countries in order to control the tolerable limits of pollutants in food. Twenty years later, the EC established a legal framework for the regulation of pesticides in all member countries. The Commission is responsible for the registration of pesticides actively used in all European countries. This authority is granted

Electrokinetic and light scattering properties of pea and Chlamydomonas reinhardtii thylakoid membranes: Effect of phytohemagglutinin

The effects of phytohemagglutinin (PHA) and illumination on the surface charge densities and 90° light scattering properties of pea and Chlamydomonas reinhardtii thylakoids were investigated. The electrophoretic mobility (EPM) of pea thylakoids decreased after treatment by various concentrations of PHA at ionic strengths of I = 0.01 and I = 0.02, while that of C. reinhardtii thylakoids remained stable except for a drop after treatment by PHA at a concentration of 6 ng/mL in a medium with an ionic strength of I = 0.01. Illumination did not influence the EPM of untreated thylakoids. However, if the EPM of thylakoids had been retarded by pretreatment with PHA, light exposure stimulated a recovery of the reduced negative surface charge density up to at least the initial values. In addition to reducing EPM, PHA also induced a decrease of the basal light scattering property of pea thylakoids, which is an indicator of thylakoid aggregation. The physiological role of the membrane surface charges of thylakoid particles in lectin regulated processes of thylakoid stacking and activity is discussed.

The plastoquinol–plastoquinone exchange mechanism in photosystem II: insight from molecular dynamics simulations

In the photosystem II (PSII) of oxygenic photosynthetic organisms, the reaction center (RC) core mediates the light-induced electron transfer leading to water splitting and production of reduced plastoquinone molecules. The reduction of plastoquinone to plastoquinol lowers PSII affinity for the latter and leads to its release. However, little is known about the role of protein dynamics in this process. Here, molecular dynamics simulations of the complete PSII complex embedded in a lipid bilayer have been used to investigate the plastoquinol release mechanism. A distinct dynamic behavior of PSII in the presence of plastoquinol is observed which, coupled to changes in charge distribution and electrostatic interactions, causes disruption of the interactions seen in the PSII–plastoquinone complex and leads to the “squeezing out” of plastoquinol from the binding pocket. Displacement of plastoquinol closes the second water channel, recently described in a 2.9xa0Å resolution PSII structure (Guskov et al. in Nat Struct Mol Biol 16:334–342, 2009), allowing to rule out the proposed “alternating” mechanism of plastoquinol–plastoquinone exchange, while giving support to the “single-channel” one. The performed simulations indicated a pivotal role of D1-Ser264 in modulating the dynamics of the plastoquinone binding pocket and plastoquinol–plastoquinone exchange via its interaction with D1-His252 residue. The effects of the disruption of this hydrogen bond network on the PSII redox reactions were experimentally assessed in the D1 site-directed mutant Ser264Lys.

Photosystem-II D1 protein mutants of Chlamydomonas reinhardtii in relation to metabolic rewiring and remodelling of H-bond network at QB site

Photosystem II (PSII) reaction centre D1 protein of oxygenic phototrophs is pivotal for sustaining photosynthesis. Also, it is targeted by herbicides and herbicide-resistant weeds harbour single amino acid substitutions in D1. Conservation of D1 primary structure is seminal in the photosynthetic performance in many diverse species. In this study, we analysed built-in and environmentally-induced (high temperature and high photon fluency – HT/HL) phenotypes of two D1 mutants of Chlamydomonas reinhardtii with Ala250Arg (A250R) and Ser264Lys (S264K) substitutions. Both mutations differentially affected efficiency of electron transport and oxygen production. In addition, targeted metabolomics revealed that the mutants undergo specific differences in primary and secondary metabolism, namely, amino acids, organic acids, pigments, NAD, xanthophylls and carotenes. Levels of lutein, β-carotene and zeaxanthin were in sync with their corresponding gene transcripts in response to HT/HL stress treatment in the parental (IL) and A250R strains. D1 structure analysis indicated that, among other effects, remodelling of H-bond network at the QB site might underpin the observed phenotypes. Thus, the D1 protein, in addition to being pivotal for efficient photosynthesis, may have a moonlighting role in rewiring of specific metabolic pathways, possibly involving retrograde signalling.