D.N. Matorin

Membrane lipid peroxidation, cell viability and Photosystem II activity in the green alga Chlorella pyrenoidosa subjected to various stress conditions

Abstract The unicellular green alga Chlorella pyrenoidosa was subjected to a variety of stress conditions (strong illumination, incubation with Cu 1+ or Zn 2+ , exposure to high temperatures). The amplitude of thermoluminescence (TL) peak at 125°C, accumulation of thiobarbituric acid reactive substances (TBARS), which indicate an accumulation of lipid peroxidation products, efficiency of Photosystem II reactions ( F v / F M ratio) and the percentage of viable cells were measured in stressed culture. Exposure of algae to strong (5000 μmol photons m 2 s 1 ) or to low (60 μmol photons m −2 s −1 ) light combined with the addition of 1.6 μM Cu 2+ or 30 μM Zn 2+ inactivated Photosystem II, decreased the viability of Chlorella cells, and, finally, significantly enhanced TL and the accumulation of TBARS, which was accompanied by chlorophyll bleaching. TL emission started to rise after a lag-period of about 30 min in algae subjected to strong illumination, 2–3 h in copper-treated algae, and 10 h in zinc-treated algae. A vast majority of cells were nonviable to the end of the lag-period. The addition of Cu 2+ or ZN 2+ in darkness caused a slight decrase in the F v / F M ratio without significant changes in TL emission. Incubation of algae at 50°C for 10 min did not affect the F v / F M ratio nd cell viability, whereas no viable cells and Photosystem II activity were detected in the culture incubated at 55°C. Heat stress at temperatures above 55°C significantly enhanced the amplitude of the 125°C TL peak and the accumulation of TBARS when the algae were further incubated at low light at room temperature. We conclude that, under the stress conditions used in this study, (i) lipid peroxides and products of their degradation are not responsible for the cytolethal effect in Chlorella and (ii) lipid peroxidation arises mainly upon illumination of dead cells.

Sublethal concentrations of copper stimulate photosystem II photoinhibition in Chlorella pyrenoidosa

Summary The effect of copper (CuSO 4 , 0.16-1.56 μM) on photosystem II (PS II) was investigated by measuring the chlorophyll fluorescence in Chlorella pyrenoidosa cells exposed to different irradiance levels and different temperatures. The algal culture remained viable only if less than 0.7-0.8 μM Cu 2+ was added. In darkness, PS II inactivation was indicated by a decrease in F v /F m ratio and was detected only at Cu 2+ concentrations higher than 0.7 μM. In the light, Cu 2+ stimulated PS II photoinhibition throughout the whole range of copper concentrations. Low temperature significantly enhanced the PS II photoinhibition in the presence of Cu 2+ . Kinetics of PS II inactivation monitored at algal growth light intensity in the presence of chloramphenicol were only slightly affected by the addition of Cu 2+ . However, Cu 2+ markedly slowed down (0.16 μM) or completely suppressed (0.7 μM) the recovery of PS II activity after the photoinhibitory treatment of the algae with a strong light. The results suggest that sublethal concentrations of copper can nonspecifically retard synthesis of the PS II D 1 protein in Chlorella cells , thus causing PS II inactivation under light.

Effect of silver nanoparticles on the parameters of chlorophyll fluorescence and P700 reaction in the green alga Chlamydomonas reinhardtii

Acute toxicity of silver nanoparticle (AgNP) for photosynthesis in Chlamydomonas reinhardtii was studied using an M-PEA2 fluorimeter. Analysis of the fluorescence induction curves in the presence of AgNP at low concentrations revealed inhibited electron transport on the PS2 photosystem and increased content of QB-nonreducing centers. No direct effect of AgNP on the reactions of P700 oxidation in PS1 was found, while the energization of the photosynthetic membranes was affected. Investigation of the parameters of the prompt and delayed fluorescence is proposed as a method for early detection of AgNP in the environment.

Present-Day State of Coral Reefs of Nha Trang Bay (Southern Vietnam) and Possible Reasons for the Disturbance of Habitats of Scleractinian Corals

Our investigations were conducted from 1990 to 2002. Sampling of bottom sediments and biological objects, as well as photo and video shooting, were performed during scuba diving. The state of the environment and coral reef communities was assessed using the chemical–analytical, fluorometric, and luminometric methods, as well as the Ames test and the transect technique. The research results suggest that the spectrum and distribution pattern of persistent congeners of PCDD/Fs (dioxins) in bottom sediments are similar to those of the defoliant “Agent Orange” and that the bottom sediments are toxic and display photo inhibition and a mutagenic effect. The bottom of the bay is heavily silted throughout its depth. Many large dead colonies of corals without mechanical damage were observed everywhere. The total coverage by live corals in all sites investigated does not exceed 30%. Although, without a doubt, many factors contributed much to the disturbance of the bay ecosystems, the actual trigger for the degradation of the coral reefs seems to be the input of dioxin-containing chemicals used as defoliants during the American–Vietnamese war (Vietnam War).

Multiple action sites for photosystem II herbicides as revealed by delayed fluorescence.

DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) at concentrations higher than 10 μM suppresses the second time range delayed fluorescence (DF) of pea chloroplasts, due to inhibition of the oxidizing side of photosystem II (PS II). The inhibition of the reducing side of PS II resulting in the suppression of millisecond DF takes place at much lower (∼0.01 μM) DCMU concentrations. The variation in the herbicide-affinities of the reducing and oxidizing sides of PS II is not the same for DCMU and phenol-type herbicides. The DCMU-affinity of the oxidizing side considerably increases and approximates that of the reducing side upon mild treatment of chloroplasts with oleic acid. Probably this is a result of some changes in the environment of the binding site at the oxidizing side. At DCMU concentrations higher than 1 mM, the chaotropic action of DCMU leads to the generation of millisecond luminescence which is not related to the functioning of the reaction centres.

Cryptomonad alga Rhodomonas sp. ( Cryptophyta, Pyrenomonadaceae ) bloom in the redox zone of the basins separating from the White Sea

Bloom of a cryptomonad alga Rhodomonas sp. (Cryptophyta, Pyrenomonadaceae) was observed in the chemocline of saline basins separating from the White Sea, resulting in red coloration of the relevant water layer. According to the sequence of the 18S nuclear rRNA gene, this species was identical to Rhodomonas sp. RCC2020 (GenBank accession no. JN934672) from the Beaufort Sea. The presence of the red layer formed by mass development of Rhodomonas sp. is considered an indicator of a certain stage of separation of a basin from the sea.

Effects of far-red light on fluorescence induction in infiltrated pea leaves under diminished ΔpH and Δφ components of the proton motive force.

Chlorophyll fluorescence induction curves induced by an actinic pulse of red light follow different kinetics in dark-adapted plant leaves and leaves preilluminated with far-red light. This influence of far-red light was abolished in leaves infiltrated with valinomycin known to eliminate the electrical (Δφ) component of the proton-motive force and was strongly enhanced in leaves infiltrated with nigericin that abolishes the ΔpH component. The supposed influence of ionophores on different components of the proton motive force was supported by differential effects of these ionophores on the induction curves of the millisecond component of chlorophyll delayed fluorescence. Comparison of fluorescence induction curves with the kinetics of P700 oxidation in the absence and presence of ionophores suggests that valinomycin facilitates a build-up of a rate-limiting step for electron transport at the site of plastoquinone oxidation, whereas nigericin effectively removes limitations at this site. Far-red light was found to be a particularly effective modulator of electron flows in chloroplasts in the absence of ΔpH backpressure on operation of the electron-transport chain.

Influence of carbon nanotubes on chlorophyll fluorescence parameters of green algae Chlamydomonas reinhardtii

It has been shown that carbon nanotubes are capable of decreasing the development speed of Chlamydomonas reinhardtii algae culture and significantly changing the parameters of chlorophyll fluorescence that characterize the prime processes of light energy storage throughout photosynthesis. The quantum yield reduction of photochemical light energy transformation during photosynthesis and the relative speed of noncycle electron transfer calculated using the fluorescence parameters have been observed. The inhibition of the electrochemical proton gradient involved in ATP synthesis has been determined using delayed fluorescence. A conclusion on the prospects of implementing highly sensitive fluorescent methods for evaluating the toxic effect of modern nonmaterials on water objects is made.

Increased toxic effect of methylmercury on Chlorella vulgaris under high light and cold stress conditions

The toxic effect of methylmercury on the photosynthetic activity of Chlorella vulgaris was shown to increase under high illumination and unfavorable low temperature. Increased toxic action of methylmercury resulted from the decreased capacity of photosystem II (PS II) for reparation. It was proposed that mild stress conditions might be used to enhance the detection limit of toxicants by microalgae used as test objects.

Promising microbial consortia for producing biofertilizers for rice fields

Two cyanobacterial cultures from rice paddies of Kyzylorda Provence, Kazakhstan were isolated and characterized: Anabaena variabilis and Nostoc calsicola. Based on these cultures, new consortia of cyanobacteria, microalgae and Azotobacter were developed: ZOB-1 (Anabaena variabilis, Chlorella vulgaris, and Azotobacter sp.) and ZOB-2 (Nostoc calsicola, Chlorella vulgaris, and Azotobacter sp.). High growth rate and photosynthetic activity of microalgae were observed in these consortia. The active consortium ZOB-1 was selected, which improved germination and growth of rice plants. ZOB-1 was recommended as a biostimulator and biofertilizer for crops.