Synergistic interaction between UVB radiation and temperature increases susceptibility to parasitic infection in a fish

Levels of UVB radiation (UVB) and mean temperatures have increased substantially over recent decades in many regions of the world. Both stressors independently can compromise immune function, disease resistance and fitness in fish. The impact of UVB can also be exacerbated by interactions with environmental temperatures. In this paper, we test the hypothesis that UVB and temperature act synergistically to influence patterns of energy consumption and susceptibility to disease. We exposed mosquitofish, Gambusia holbrooki, to a factorial design of low and high UVB levels and low (18°C) and high (25°C) temperatures. The combination of high UVB and high temperature interacted synergistically to suppress metabolism and exacerbate infection intensity by the fish pathogen whitespot (Ichtyhophthirius multifiliis). Given the rapid changes in the thermal environment globally, the interaction between UVB and temperatures on energy use and disease resistance could pose significant problems for aquatic animal health in the context of both pre-existing and emerging diseases.     

Autophagy in unicellular eukaryotes

Cells need a constant supply of precursors to enable the production of macromolecules to sustain growth and survival. Unlike metazoans, unicellular eukaryotes depend exclusively on the extracellular medium for this supply. When environmental nutrients become depleted, existing cytoplasmic components will be catabolized by (macro)autophagy in order to re-use building blocks and to support ATP production. In many cases, autophagy takes care of cellular housekeeping to sustain cellular viability. Autophagy encompasses a multitude of related and often highly specific processes that are implicated in both biogenetic and catabolic processes. Recent data indicate that in some unicellular eukaryotes that undergo profound differentiation during their life cycle (e.g. kinetoplastid parasites and amoebes), autophagy is essential for the developmental change that allows the cell to adapt to a new host or form spores. This review summarizes the knowledge on the molecular mechanisms of autophagy as well as the cytoplasm-to-vacuole-targeting pathway, pexophagy, mitophagy, ER-phagy, ribophagy and piecemeal microautophagy of the nucleus, all highly selective forms of autophagy that have first been uncovered in yeast species. Additionally, a detailed analysis will be presented on the state of knowledge on autophagy in non-yeast unicellular eukaryotes with emphasis on the role of this process in differentiation.     

Assessment of oxidative stress in the planktonic diatom Thalassiosira pseudonana in response to UVA and UVB radiation

Induction of oxidative stress by UVA and UVB in the diatom Thalassiosirapseudonana was experimentally studied. Cells, pre-grown in alight-limited continuous culture, were incubated for 4 h at175 µmol m^-2s^-1photosynthetically active radiation, withoptional supplementary UVA at an unweighted dose rate of 0.70W m^-2, or 2.79 W m^-2UVA plus 0.45 W m^-2UVB (unweighted). A fluorescence-basedmeasure of photosynthetic efficiency (F_v/F_m) decreased from0.69 to 0.58 in the presence of UVB, whereas UVA caused a minordecrease of F_v/F_m. Quantitative analysis of confocal imagesshowed a minor increase of active oxygen production associatedwith supplemental UVA alone, and a 100% increase with additionalUVB. Cellular malondialdehyde, an indicator of lipid peroxidationby active oxygen, almost doubled under UVA and increased three-foldwith additional UVB. Activities of superoxide dismutase (scavengingactive oxygen) and glutathione reductase (reducing GSSG to GSH)increased in response to UVB exposure, whereas ascorbate peroxidaseactivities did not. UVB caused a minor decrease in the glutathioneratio GSH : (GSH + 0.5GSSG), which indicates a moderate oxidativestress.     

Inorganic phosphate uptake in unicellular eukaryotes

Background

Inorganic phosphate (P_i) is an essential nutrient for all organisms. The route of P_i utilization begins with P_i transport across the plasma membrane.

Scope of review

Here, we analyzed the gene sequences and compared the biochemical profiles, including kinetic and modulator parameters, of P_i transporters in unicellular eukaryotes. The objective of this review is to evaluate the recent findings regarding P_i uptake mechanisms in microorganisms, such as the fungi Neurospora crassa and Saccharomyces cerevisiae and the parasite protozoans Trypanosoma cruzi, Trypanosoma rangeli, Leishmania infantum and Plasmodium falciparum.

Major conclusion

P_i uptake is the key step of P_i homeostasis and in the subsequent signaling event in eukaryotic microorganisms.

General significance

Biochemical and structural studies are important for clarifying mechanisms of P_i homeostasis, as well as P_i sensor and downstream pathways, and raise possibilities for future studies in this field.     

Mitochondrial uncoupling proteins in unicellular eukaryotes

Uncoupling proteins (UCPs) are members of the mitochondrial anion carrier protein family that are present in the mitochondrial inner membrane and mediate free fatty acid (FFA)-activated, purine nucleotide (PN)-inhibited proton conductance. Since 1999, the presence of UCPs has been demonstrated in some non-photosynthesising unicellular eukaryotes, including amoeboid and parasite protists, as well as in non-fermentative yeast and filamentous fungi. In the mitochondria of these organisms, UCP activity is revealed upon FFA-induced, PN-inhibited stimulation of resting respiration and a decrease in membrane potential, which are accompanied by a decrease in membranous ubiquinone (Q) reduction level. UCPs in unicellular eukaryotes are able to divert energy from oxidative phosphorylation and thus compete for a proton electrochemical gradient with ATP synthase. Our recent work indicates that membranous Q is a metabolic sensor that might utilise its redox state to release the PN inhibition of UCP-mediated mitochondrial uncoupling under conditions of phosphorylation and resting respiration. The action of reduced Q (QH₂) could allow higher or complete activation of UCP. As this regulatory feature was demonstrated for microorganism UCPs (A. castellanii UCP), plant and mammalian UCP1 analogues, and UCP1 in brown adipose tissue, the process could involve all UCPs. Here, we discuss the functional connection and physiological role of UCP and alternative oxidase, two main energy-dissipating systems in the plant-type mitochondrial respiratory chain of unicellular eukaryotes, including the control of cellular energy balance as well as preventive action against the production of reactive oxygen species.     

The behaviour of unicellular eukaryotes.

The field of ciliated protozoa behaviour is reconsidered. The simple-complexity of their behaviour is seen in its basic nature and adaptive meaning. The Laboratory Conditions (LABCON) are discussed in comparison with those occurring in nature (NATCON). The nature of the arc, the behavioural element commonly performed by a ciliate, is discussed in detail. Several indexes and rates can perfectly describe the tracks of the ciliates. The behaviour can be considered as a kind of adaptive interface between the environment and the organism.     

Regulation of the life span in unicellular eukaryotes

The review considers the mechanisms of nucleic and mitochondrial control of the life span of unicellular eukaryotes. Special attention is given to analysis of the mechanisms of functioning of telomerase complex, the mechanisms of varied expression of the genes regulating the cell cycle, and the mitochondrial retrograde pathway.     

Identification of organelles in bacteria similar to acidocalcisomes of unicellular eukaryotes

Acidocalcisomes are acidic calcium storage compartments described in several unicellular eukaryotes, including trypanosomatid and apicomplexan parasites, algae, and slime molds. In this work, we report that the volutin granules of Agrobacterium tumefaciens possess properties similar to the acidocalcisomes. Transmission electron microscopy revealed that each intracellular granule was surrounded by a membrane. X-ray microanalysis of the volutin granules showed large amounts of phosphorus, magnesium, potassium, and calcium. Calcium in the volutin granules increased when the bacteria were incubated at high extracellular calcium concentration. Immunofluorescence and immunoelectron microscopy, using antisera raised against peptide sequences conserved in the A. tumefaciens proton pyrophosphatase, indicated localization in intracellular vacuoles. Purification of the volutin granules using iodixanol density gradients indicated a preferential localization of the pyrophosphatase activity in addition to high concentrations of phosphate, pyrophosphate, short- and long-chain polyphosphate, but lack of markers of the plasma membrane. The pyrophosphatase activity was potassium-insensitive and inhibited by the pyrophosphate analogs, amynomethylenediphosphonate and imidodiphosphate, by dicyclohexylcarbodiimide, and by the thiol reagent N-ethylmaleimide. Polyphosphate was also localized to the volutin granules by 4',6'-diamino-2-phenylindole staining. The organelles were acidic, as demonstrated by staining with LysoSensor blue DND-167, a dye especially used to detect very acidic compartments in cells, and cycloprodigiosin, a compound isolated from a marine bacterium that has been shown to uncouple proton pyrophosphatase activity acting as a chloride/proton symport. The results suggest that acidocalcisomes arose before the prokaryotic and eukaryotic lineages diverged.     

Clone-specific responses in leaf phenolics of willows exposed to enhanced UVB radiation and drought stress

The effects of enhanced UVB radiation and drought stress on willow secondary phenolics were studied using the leaves of 8‐week‐old micropropagated plantlets from interspecific hybrids (Salix myrsinites L. ×S. myrsinifolia Salisb.) and pure species (S. myrsinifolia). The plantlets were subjected for 4 weeks to two levels of UVB radiation (ambient, enhanced) and two levels of watering (well‐watered, drought‐stressed) according to a 2 × 2 factorial design. Enhanced UVB radiation increased the total concentration of flavonoids and phenolic acids in all plantlets, while the total concentration of salicylates remained unaffected. Drought stress reduced the total concentration of salicylates and phenolic acids in S. myrsinifolia plantlets, while in hybrids only phenolic acids were affected. The response of phenolic acids to enhanced UVB in drought‐stressed plantlets was different from that in well‐watered ones, indicating that drought stress limited the accumulation of phenolic acids under enhanced UVB radiation. Flavonoids increased in response to enhanced UVB radiation in drought‐stressed plantlets, although drought caused serious physiological stress on growth. There were significant differences between hybrid and S. myrsinifolia plantlets with respect to the composition of phenolics and between families and clones with respect to their concentration. In addition, the response of salicylates, flavonoids and phenolic acids to enhanced UVB and drought stress was clone‐specific, which may indicate that climatic changes will alter the genetic composition of northern forests.     

Pathways of transduction of apoptotic signals in unicellular eukaryotes

The review summarizes current data about transduction mechanism of apoptotic signals by caspase-like enzymes and mitochondrial apoptogenic proteins in unicellular eukaryotes. The role of receptor-dependent and receptor-independent caspase cascades is rewieved. The special attention is given to evolution aspects of problem of apoptosis.     

Posttranslation regulation of programmable cell events in unicellular eukaryotes

The review considers the up to date achievements about posttranslational regulation of programmable cell events: growth, development, and apoptosis in unicellular eukaryotes mediated by histone modifications and DNA metylation. Special attention is given to the evolution aspects of the problem.     

Potassium channels in the mitochondria of unicellular eukaryotes and plants

The functional characterisation of potassium channels found in the mitochondria of plants and unicellular eukaryotes is critically discussed herein, with a focus on the ATP-sensitive potassium channel and the large-conductance Ca²⁺-activated potassium channel (mitoBK_Ca channel). The physiological functions of these channels are not completely understood. We discuss the functional connections and roles of potassium channels, uncoupling protein and alternative oxidase, three energy-dissipating systems that exist in the mitochondrial respiratory chain of plants and some unicellular eukaryotes, which include preventing the production of reactive oxygen species.     

Resistance to UVB radiation in Antarctic yeasts

Yeast cells were used as a model system to study the inter-relationship among free radicals, antioxidants and UV-induced cell damage. In particular, the effects of UV-radiation in newly isolated yeasts from the Antarctic have been studied.     

Signaling mechanisms of apoptosis-like programmed cell death in unicellular eukaryotes

In unicellular eukaryotes, apoptosis-like cell death occurs during development, aging and reproduction, and can be induced by environmental stresses and exposure to toxic agents. The essence of the apoptotic machinery in unicellular organisms is similar to that in mammals, but the apoptotic signal network is less complex and of more ancient origin. The review summarizes current data about key apoptotic proteins and mechanisms of the transduction of apoptotic signals by caspase-like proteases and mitochondrial apoptogenic proteins in unicellular eukaryotes. The roles of receptor-dependent and receptor-independent caspase cascades are reviewed.     

Mortality and growth responses of Daphnia carinata to increases in temperature and salinity

1.  Daphnia carinata King, a freshwater cladoceran, occurs in Lake Waihola, a tidal lake with seasonal fluctuations in temperature (4–21 °C), and salinity (30–2000 mg L^–1 Cl). We hypothesise that these fluctuations influence the seasonal changes in D. carinata abundance.
2. To test this hypothesis, adults and juveniles were exposed to combinations of temperature and salinity. We measured mortality of adults and juveniles, growth of juveniles over 20 days, and their age at first reproduction.
3. The salinity tolerance of adult D. carinata was temperature-dependent. Juveniles were more sensitive to salinity, but more tolerant of temperature increases.
4. Growth rates were higher at elevated temperatures, but reduced by elevated salinities. The onset of reproduction was earlier at elevated temperatures.
5. We conclude that seasonal changes in temperature and salinity contribute to seasonal population changes of D. carinata .     

The conserved regulation of mitochondrial uncoupling proteins: From unicellular eukaryotes to mammals

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier protein family and mediate regulated proton leak across the inner mitochondrial membrane. Free fatty acids, aldehydes such as hydroxynonenal, and retinoids activate UCPs. However, there are some controversies about the effective action of retinoids and aldehydes alone; thus, only free fatty acids are commonly accepted positive effectors of UCPs. Purine nucleotides such as GTP inhibit UCP-mediated mitochondrial proton leak. In turn, membranous coenzyme Q may play a role as a redox state-dependent metabolic sensor that modulates the complete activation/inhibition of UCPs. Such regulation has been observed for UCPs in microorganisms, plant and animal UCP1 homologues, and UCP1 in mammalian brown adipose tissue. The origin of UCPs is still under debate, but UCP homologues have been identified in all systematic groups of eukaryotes. Despite the differing levels of amino acid/DNA sequence similarities, functional studies in unicellular and multicellular organisms, from amoebae to mammals, suggest that the mechanistic regulation of UCP activity is evolutionarily well conserved. This review focuses on the regulatory feedback loops of UCPs involving free fatty acids, aldehydes, retinoids, purine nucleotides, and coenzyme Q (particularly its reduction level), which may derive from the early stages of evolution as UCP first emerged.     

Maize growth and developmental responses to temperature and ultraviolet-B radiation interaction

Plant response to the combination of two or more abiotic stresses is different than its response to the same stresses singly. The response of maize (Zea mays L.) photosynthesis, growth, and development processes were examined under sunlit plant growth chambers at three levels of each day/night temperatures (24/16°C, 30/22°C, and 36/28°C) and UV-B radiation levels (0, 5, and 10 kJ m^?2 d^?1) and their interaction from 4 d after emergence to 43 d. An increase in plant height, leaf area, node number, and dry mass was observed as temperature increased. However, UV-B radiation negatively affected these processes by reducing the rates of stem elongation, leaf area expansion, and biomass accumulation. UV-B radiation affected leaf photosynthesis mostly at early stage of growth and tended to be temperature-dependent. For instance, UV-B radiation caused 3–15% decrease of photosynthetic rate (P _N) on the uppermost, fully expanded leaves at 24/16°C and 36/28°C, but stimulated P _N about 5–18% at 30/22°C temperature. Moreover, the observed UV-B protection mechanisms, such as accumulation of phenolics and waxes, exhibited a significant interaction among the treatments where these compounds were relatively less responsive (phenolics) or more responsive (waxes) to UV-B radiation at higher temperature treatments or vice versa. Plants exposed to UV-B radiation produced more leaf waxes except at 24/16°C treatment. The detrimental effect of UV-B radiation was greater on plant growth compared to the photosynthetic processes. Results suggest that maize growth and development, especially stem elongation, is highly sensitive to current and projected UV-B radiation levels, and temperature plays an important role in the magnitude and direction of the UV-B mediated responses.