Acclimation of photosynthesis to nitrogen deficiency in Phaseolus vulgaris

Nitrogen deficiency diminishes consumption of photosynthates in anabolic metabolism. We studied adjustments of the photosynthetic machinery in nitrogen-deficient bean plants and found four phenomena. First, the number of chloroplasts per cell decreased. Chloroplasts of nitrogen starved leaves contained less pigments than those of control leaves, but the in vitro activities of light reactions did not change when measured on chlorophyll basis. Second, nitrogen deficiency induced cyclic electron transfer. The amounts of Rubisco and ferredoxin-NADP⁺ reductase decreased in nitrogen starved plants. Low activities of these enzymes are expected to lead to increase in reduction of oxygen by photosystem I. However, diaminobenzidine staining did not reveal hydrogen peroxide production in nitrogen starved plants. Measurements of far-red-light-induced redox changes of the primary donor of photosystem I suggested that instead of producing oxygen radicals, nitrogen starved plants develop a high activity of cyclic electron transport that competes with oxygen for electrons. Nitrogen starvation led to decrease in photochemical quenching and increase in non-photochemical quenching, indicating that cyclic electron transport reduces the plastoquinone pool and acidifies the lumen. A third effect is redistribution of excitation energy between the photosystems in favor of photosystem I. Thus, thylakoids of nitrogen starved plants appeared to be locked in state 2, which further protects photosystem II by decreasing its absorption cross-section. As a fourth response, the proportion of non-Q_B-reducing photosystem II reaction centers increased and the redox potential of the Q_B/Q_B⁻ pair decreased by 25 mV in a fraction of photosystem II centers of nitrogen starved plants.     

Ultraviolet screening by slug tissue and tight packing of plastids protect photosynthetic sea slugs from photoinhibition

Photosynthesis Research - One of the main mysteries regarding photosynthetic sea slugs is how the slug plastids handle photoinhibition, the constant light-induced damage to Photosystem II of...     

SP3-Enabled Rapid and High Coverage Chemoproteomic Identification of Cell-State–Dependent Redox-Sensitive Cysteines

Proteinaceous cysteine residues act as privileged sensors of oxidative stress. As reactive oxygen and nitrogen species have been implicated in numerous pathophysiological processes, deciphering which cysteines are sensitive to oxidative modification and the specific nature of these modifications is essential to understanding protein and cellular function in health and disease. While established mass spectrometry-based proteomic platforms have improved our understanding of the redox proteome, the widespread adoption of these methods is often hindered by complex sample preparation workflows, prohibitive cost of isotopic labeling reagents, and requirements for custom data analysis workflows. Here, we present the SP3-Rox redox proteomics method that combines tailored low cost isotopically labeled capture reagents with SP3 sample cleanup to achieve high throughput and high coverage proteome-wide identification of redox-sensitive cysteines. By implementing a customized workflow in the free FragPipe computational pipeline, we achieve accurate MS1-based quantitation, including for peptides containing multiple cysteine residues. Application of the SP3-Rox method to cellular proteomes identified cysteines sensitive to the oxidative stressor GSNO and cysteine oxidation state changes that occur during T cell activation.     

The use of aquatic mosses in assessment of metal pollution: appraisal of type-specific background concentrations and inter-specific differences in metal accumulation

Tissue concentrations of Al, As, Cd, Cu, Fe, Pb and Zn were analysed from 73 river sites, including 29 unpolluted reference sites and 44 sites differently affected by land use and industrial and municipal waste waters. Concentrations were measured both in the youngest terminal parts (reflecting the most current exposure conditions) and in the whole vegetative shoot (indicating long-term exposure) of mosses. For the dominant moss species, Fontinalis antipyretica Hedw., the concentration data were stratified according to the river type (small, medium, or large peatland or moraine land rivers) and assessed for background concentrations and patterns of concentration gradients and explored possibilities for setting criteria for environmental quality standards (EQSs). Further, we analysed species-specific differences in metal concentrations of F. antipyretica, Dichelyma falcatum (Hedw.) and Hygrohypnum ochraceum (Turn. ex Wils.). The background concentrations varied more or less according to the river type; in general, peatland rivers had higher concentration than moraine land rivers. The highest metal concentrations were found in rivers contaminated by acid sulphate soils. For most metals, concentrations in D. falcatum and H. ochraceum were higher than in F. antipyretica. Prerequisites for using mosses in pollution assessment and preliminary suggestions for defining EQSs are presented.     

Bioethics and political ideology: the case of active voluntary euthanasia

In different countries responses to important bioethical issues are different, as exemplified by the attitudes towards the voluntary and active forms of medical euthanasia. But why is this the case? My suggestion is that the roots of the variety are, to be considerable degree, ideological. The most important present-day political ideologies all have their roots in the prevailing doctrines of moral and social philosophy. In the paper these doctrines are outlined and the predicted response towards active voluntary euthanasia within each model is sketched. The conclusion reached is that while it would in some countries be dangerous to allow euthanasia in the prevailing circumstances, the solution is not to hinder the legalization process but to alter the circumstances.     

AIDS now

Two philosphers from the University of Helsinki argue that, despite beliefs to the contrary in the Western world, AIDS is no longer predominantly a problem limited to homosexuals. First they clarify this claim by presenting epidemiological data. They then consider three ethical issues that have resulted from fearful public reaction to the rapid spread of AIDS: discrimination against those infected with the human immunodeficiency virus (HIV); proposed legal restrictions on personal choices, especially sexual; and screening for HIV antibodies without consent. The H?yrys then discuss whether there is a right not to know one's HIV status. Their essay concludes with suggestions of three ways to fight the spread of AIDS that should be implemented immediately: more support for AIDS research, organization of sociomedical actions such as information campaigns to slow the spread of the disease, and enactment of antidiscrimination legislation.     

Integrated analysis of protein composition, tissue diversity, and gene regulation in mouse mitochondria

Mitochondria are tailored to meet the metabolic and signaling needs of each cell. To explore its molecular composition, we performed a proteomic survey of mitochondria from mouse brain, heart, kidney, and liver and combined the results with existing gene annotations to produce a list of 591 mitochondrial proteins, including 163 proteins not previously associated with this organelle. The protein expression data were largely concordant with large-scale surveys of RNA abundance and both measures indicate tissue-specific differences in organelle composition. RNA expression profiles across tissues revealed networks of mitochondrial genes that share functional and regulatory mechanisms. We also determined a larger "neighborhood" of genes whose expression is closely correlated to the mitochondrial genes. The combined analysis identifies specific genes of biological interest, such as candidates for mtDNA repair enzymes, offers new insights into the biogenesis and ancestry of mammalian mitochondria, and provides a framework for understanding the organelle's contribution to human disease.     

Magnetic field protects plants against high light by slowing down production of singlet oxygen

Recombination of the primary radical pair of photosystem II (PSII) of photosynthesis may produce the triplet state of the primary donor of PSII. Triplet formation is potentially harmful because chlorophyll triplets can react with molecular oxygen to produce the reactive singlet oxygen (1O?). The yield of 1O? is expected to be directly proportional to the triplet yield and the triplet yield of charge recombination can be lowered with a magnetic field of 100-300 mT. In this study, we illuminated intact pumpkin leaves with strong light in the presence and absence of a magnetic field and found that the magnetic field protects against photoinhibition of PSII. The result suggests that radical pair recombination is responsible for significant part of 1O? production in the chloroplast. The magnetic field effect vanished if leaves were illuminated in the presence of lincomycin, an inhibitor of chloroplast protein synthesis, or if isolated thylakoid membranes were exposed to light. These data, in turn, indicate that 1O? produced by the recombination of the primary charge pair is not directly involved in photoinactivation of PSII but instead damages PSII by inhibiting the repair of photoinhibited PSII. We also found that an Arabidopsis thaliana mutant lacking α-tocopherol, a scavenger of 1O?, is more sensitive to photoinhibition than the wild-type in the absence but not in the presence of lincomycin, confirming that the target of 1O? is the repair mechanism.     

Unresolved quenching mechanisms of chlorophyll fluorescence may invalidate MT saturating pulse analyses of photosynthetic electron transfer in microalgae

Chlorophyll a fluorescence is a powerful tool for estimating photosynthetic efficiency, but there are still unanswered questions that hinder the use of its full potential. The present results describe a caveat in estimation of photosynthetic performance with so‐called rapid light curves (RLCs) with pulse amplitude modulation fluorometers. RLCs of microalgae show a severe decrease in photosynthetic performance in high light, although a similar decrease cannot be seen with other methods. We show that this decrease cannot be assigned to energy‐dependent non‐photochemical quenching or photoinhibition or to the geometry of the algal sample. The measured decrease in electron transfer rate is small in the tested siphonaceuous algae and higher plants, but very notable in all planktonic species, exhibiting species‐dependent variation in extent and reversibility. We performed in‐depth analysis of the phenomenon in the diatom Phaeodactylum tricornutum, in which the decrease is the most pronounced and reversible among the tested organisms. The results suggest that quenching of fluorescence by oxidized plastoquinone alone cannot explain the phenomenon, and alternative quenching mechanisms within PSII need to be considered.