Flavodiiron Proteins in Oxygenic Photosynthetic Organisms: Photoprotection of Photosystem II by Flv2 and Flv4 in Synechocystis sp. PCC 6803

BACKGROUND: Flavodiiron proteins (FDPs) comprise a group of modular enzymes that function in oxygen and nitric oxide detoxification in Bacteria and Archaea. The FDPs in cyanobacteria have an extra domain as compared to major prokaryotic enzymes. The physiological role of cyanobacteria FDPs is mostly unknown. Of the four putative flavodiiron proteins (Flv1-4) in the cyanobacterium Synechocystis sp. PCC 6803, a physiological function in Mehler reaction has been suggested for Flv1 and Flv3. PRINCIPAL FINDINGS: We demonstrate a novel and crucial function for Flv2 and Flv4 in photoprotection of photosystem II (PSII) in Synechocystis. It is shown that the expression of Flv2 and Flv4 is high under air level of CO(2) and negligible at elevated CO(2). Moreover, the rate of accumulation of flv2 and flv4 transcripts upon shift of cells from high to low CO(2) is strongly dependent on light intensity. Characterization of FDP inactivation mutants of Synechocystis revealed a specific decline in PSII centers and impaired translation of the D1 protein in Delta flv2 and Delta flv4 when grown at air level CO(2) whereas at high CO(2) the Flvs were dispensable. Delta flv2 and Delta flv4 were also more susceptible to high light induced inhibition of PSII than WT or Delta flv1 and Delta flv3. SIGNIFICANCE: Analysis of published sequences revealed the presence of cyanobacteria-like FDPs also in some oxygenic photosynthetic eukaryotes like green algae, mosses and lycophytes. Our data provide evidence that Flv2 and Flv4 have an important role in photoprotection of water-splitting PSII against oxidative stress when the cells are acclimated to air level CO(2). It is conceivable that the function of FDPs has changed during evolution from protection against oxygen in anaerobic microbes to protection against reactive oxygen species thus making the sustainable function of oxygen evolving PSII possible. Higher plants lack FDPs and distinctly different mechanisms have evolved for photoprotection of PSII

Photorespiratory 2-phosphoglycolate metabolism and photoreduction of O2 cooperate in high-light acclimation of Synechocystis sp. strain PCC 6803

In cyanobacteria, photorespiratory 2-phosphoglycolate (2PG) metabolism is mediated by three different routes, including one route involving the glycine decarboxylase complex (Gcv). It has been suggested that, in addition to conversion of 2PG into non-toxic intermediates, this pathway is important for acclimation to high-light. The photoreduction of O2 (Mehler reaction), which is mediated by two flavoproteins Flv1 and Flv3 in cyanobacteria, dissipates excess reductants under high-light by the four electron-reduction of oxygen to water. Single and double mutants defective in these processes were constructed to investigate the relation between photorespiratory 2PG-metabolism and the photoreduction of O2 in the cyanobacterium Synechocystis sp. PCC 6803. The single mutants Δflv1, Δflv3, and ΔgcvT, as well as the double mutant Δflv1/ΔgcvT, were completely segregated but not the double mutant Δflv3/ΔgcvT, suggesting that the T-protein subunit of the Gcv (GcvT) and Flv3 proteins cooperate in an essential process. This assumption is supported by the following results: (1) The mutant Δflv3/ΔgcvT showed a considerable longer lag phase and sometimes bleached after shifts from slow (low light, air CO2) to rapid (standard light, 5% CO2) growing conditions. (2) Photoinhibition experiments indicated a decreased ability of the mutant Δflv3/ΔgcvT to cope with high-light. (3) Fluorescence measurements showed that the photosynthetic electron chain is reduced in this mutant. Our data suggest that the photorespiratory 2PG-metabolism and the photoreduction of O2, particularly that catalyzed by Flv3, cooperate during acclimation to high-light stress in cyanobacteria

Feeling of pleasure to high-intensity interval exercise is dependent of the number of work bouts and physical activity status

Objectives: To examine the affective responses during a single bout of a low-volume HIIE in active and insufficiently active men. Materials and methods: Fifty-eight men (aged 25.3 ± 3.6 years) volunteered to participate in this study: i) active (n = 29) and ii) insufficiently active (n = 29). Each subject undertook i) initial screening and physical evaluation, ii) maximal exercise test, and iii) a single bout of a low-volume HIIE. The HIIE protocol consisted of 10 x 60s work bouts at 90% of maximal treadmill velocity (MTV) interspersed with 60s of active recovery at 30% of MTV. Affective responses (Feeling Scale, -5/+5), rating of perceived exertion (Borg's RPE, 6-20), and heart rate (HR) were recorded during the last 10s of each work bout. A two-factor mixed-model repeated measures ANOVA, independent-samples t test, and chi-squared test were used to data analysis. Results: There were similar positive affective responses to the first three work bouts between insufficiently active and active men (p > 0.05). However, insufficiently active group displayed lower affective responses over time (work bout 4 to 10) than the active group (p 0.05). Conclusions: Insufficiently active and active men report feelings of pleasure to few work bouts (i.e., 3-4) during low-volume HIIE, while the affective responses become more unpleasant over time for insufficiently active subjects. Investigations on the effects of low-volume HIIE protocols including a fewer number of work bouts on health status and fitness of less active subjects would be interesting, especially in the first training weeks