Physiological and morphological processes in the Alpine snow alga Chloromonas nivalis (Chlorophyceae) during cyst formation

Amongst a specialised group of psychrophilic microalgae that have adapted to thrive exclusively in summer snow fields, Chloromonas nivalis has been reported as a species causing green, orange or pink blooms in many alpine and polar regions worldwide. Nevertheless, the cytology, ecophysiology and taxonomy of this species are still unresolved. Intracellular processes during cyst formation, which is the dominant stage on snow fields, were examined with samples from the European Alps to better understand the cellular strategies of a green alga living in this harsh habitat. We show with two different methods, i.e. oxygen optode fluorometry and by chlorophyll fluorescence, that the cysts are photosynthetically highly active, although they do not divide, and that Chloromonas nivalis can cope with low as well as high light conditions. During cyst formation, the chloroplast is fragmented into several smaller parts, enlarging the surface to volume ratio. The pool of xanthophyll-cycle pigments is significantly enlarged, which is different from other snow algae. The cytoplasm is filled with lipid bodies containing astaxanthin, a secondary carotenoid that causes the typical orange colour. The cyst wall surface possesses characteristic elongate flanges, which are assembled extracellulary by accumulation of material in the periplasmatic interspace. Comparison of Chloromonas nivalis samples from different locations (Austrian Alps, Spitsbergen) by molecular methods indicates genetic variations due to spatial isolation, while a North American strain has no close relationship to the taxon.     

Water balance of over-wintering beetles in relation to strategies for cold tolerance

The vapour pressure of the haemolymph of a supercooled insect is higher than the vapour pressure of the haemolymph of a frozen insect at the same temperature. The aim of the study was to see whether this may affect the water loss of freeze-avoiding and freezetolerant, over-wintering beetles. The rates of water loss were determined on freeze-tolerant Pytho depressus larvae and Upis ceramboides adults. Within each species one group was kept supercooled whereas another group was frozen. All groups were incubated at-5°C. Both species displayed significantly lower rates of water loss when they were frozen than when they were supercooled. Values of respiratory rate and water loss of freeze-avoiding and freeze-tolerant species were compared to corresponding values of desert beetles. The results indicate that the freeze-avoiding species have lower rates of cuticular water loss than freeze-tolerant species. This indicates that the freeze-avoiding species have developed more efficient water-saving mechanisms than freeze-tolerant species. The reason for this may be that the haemolymph in frozen animals will be in vapour pressure equlibrium with the ice in the hibernaculum and thus there is no danger of desiccation during winter. The supercooled insects will have a vapour pressure of the haemolymph that is higher than the vapour pressure of water in the surrounding air and will thus lose water.Abbreviations BW body weight - BW_i initial body weight - BW_t body weight at time t - P vapour pressure difference between the water in the haemolymph and the water in the air - DWL_t dry weight loss at time t - M _w rate of metabolic water production - MF_w mol fraction of water, in the haemolymph - MO₂ rate of oxygen consumption - Osm osmolality of the haemolymph - P _a vapour pressure of water in the air - P _h vapour pressure of water in the haemolymph - P _w vapour pressure of pure water - Q a constant (2,02 1 oxygen per g fat metabolized) relating oxygen consumption to dry weight loss when fat is metabolized - R a constant (1,89 1 oxygen per g water produced) relating metabolic water production to oxygen consumption when fat is metabolized - R _dwl rate of dry weight loss - RH relative humidity of the air - RWC_i initial relative water content measured by weighing - RWC_t relative water content at time t - STP standard temperature and pressure     

Vertical distribution of the snow alga Chlamydomonas nivalis (Chlorophyta,Volvocales)

Summary Chlamydomonas nivalis commonly forms large blooms, visible as a red coloration, in the snow during summer. Fewer algae are seen in the top layer of snow during days of intense sunlight than on cloudy days. The present experiments were done to investigate this change of vertical distribution of algae. Apparently the algae are able to associate with the watersurface surrounding snow crystals. Due to this association they avoid being washed away by the water from melting snow. Intense sunlight, however, decreases the degree to which the algae associate with the water-surface, and thereby increasing the number of algae being removed from the top layer of snow by the melting water. If the weather becomes cloudy again, the algae do not move upwards, but stay attached to the water-surfaces. Thus when the snow above melts, they will reappear in the top layer.     

Sclerotinia nivalis, sp. nov., the pathogen of snow mold of herbaceous dicots in Northern Japan

A newSclerotinia, previously reported asS. intermedia from Japan, is described asSclerotinia nivalis on the morphological basis of the sclerotial anamorph and teleomorph produced in culture. The characters assigning this species to the genusSclerotinia are the tuberoid sclerotia superficially produced on suscepts, the small sclerotia produced on aerial mycelium in culture, the interhyphal spaces in medullary tissue of sclerotia, and the globose cells constructing the ectal excipulum of apothecia. It is distinguishable fromS. sclerotiorum, S. minor, andS. trifoliorum by the intermediate sized sclerotia in culture, binucleate ascospores, the molecular mass of major proteins of sclerotia, and the patterns of esterase isozymes in sclerotial extracts. AlthoughS. nivalis causes snow mold of various dicots, it is a mesophile having an optimum temperature for mycelial growth of around 20°C. It attacks edible burdock(Arctium lappa), Chryhsanthemum morifolium, Ambrosia elatior, carrot(Daucus carota), Angelica acutiloba, Ajuga reptans, andPlantago lanceolata.     

Relationship between plasma potassium and ventilation during successive periods of exercise in men

During and after two successive incremental cycle ergometer tests (tests A and B), plasma potassium concentration ([K+]p), plasma pH (pHp), plasma partial pressure of carbon dioxide, blood lactate concentration ([Lac-]b) and ventilation (VE) were measured. While there was a good correlation between the increase in [K+]p and VE or pHp, respectively, in test A, in test B a close correlation was found only between the increase in VE and [K+]p (r greater than 0.9 for nearly all single cases; r was 0.84 and 0.89 for all (pooled) cases in tests A and B, respectively; the correlation coefficients between changes in pHp and VE in tests A and B were r = 0.74 and r = 0.28, respectively, and r = 0.89 and r = 0.10 between the changes in [Lac-]b and VE in tests A and B). The close relationship for individuals between VE and [K+]p in tests A and B supported the hypothesis that the extracellular increase in [K+] may contribute to the ventilatory drive during exercise. The comparison of the results of tests A and B further indicated that the relationship between pHp and VE was dependent on the experimental design, and that pHp and VE changes are unlikely to be cause and effect.     

Associations between body composition and helminths of lesser snow geese during winter and spring migration

Costs of parasitism are predicted to be higher with greater parasite intensities and higher inter-parasite competition (diversity). We tested whether greater helminth intensities and diversity were associated with poorer body composition (whole-body fat, protein, mineral and true body mass) in lesser snow geese, Chen caerulescens caerulescens. As part of a larger study on nutritional ecology, 828 wintering or migrating geese were shot between January and May 1983 in 27 different date-locations (samples) during their northward migration through mid-continental North America. A large proportion of overall variation in body composition and parasite communities was among samples, so we analyzed data within each of the 27 samples, controlling for structural body size (the first principal component of 10 body size measurements), sex and the age of geese. There was no compelling evidence that cestodes, trematodes or helminth diversity were associated with variation in body composition but nematodes had several negative associations with fat reserves. However, negative associations between fat reserves and nematodes occurred most often in geese collected between March and May when nematode prevalences and intensities were relatively low. This suggests several possibilities: that the most common nematodes (Heterakis dispar and Trichostrongylus tenuis) were more virulent at this time, that infected individuals had been chronically infected and suffered cumulative nutrient deficits that lasted until late in the spring migration, or that geese became more vulnerable to the effects of parasites at this time of year, possibly because they redirected resources away from immunity toward fat storage in preparation for reproduction.     

Variations in gastric acid secretion during periods of fasting between two species of shark

Vertebrates differ in their regulation of gastric acid secretion during periods of fasting, yet it is unknown why these differences occur. Elasmobranch fishes are the earliest known vertebrates to develop an acid secreting stomach and as such may make a good comparative model for determining the causative factors behind these differences. We measured gastric pH and temperature continuously during periods of fasting in captive free-swimming nurse sharks (Ginglymostoma cirratum) using autonomous pH/temperature data-loggers. All nurse sharks secreted strong gastric acids (minimum pH 0.4) after feeding; however, for most of the sharks, pH increased to 8.2-8.7, 2-3 days after feeding. Half of the sharks also exhibited periodic oscillations in pH when the stomach was empty that ranged from 1.1 to 8.7 (acid secretion ceased for 11.3 +/- 4.3 h day(-1)). This is in contrast to the gastric pH changes observed from leopard sharks (Triakis semifasciata) in a previous study, where the stomach remains acidic during fasting. The leopard shark is a relatively active, more frequently feeding predator, and continuous acid secretion may increase digestive efficiency. In contrast, the nurse shark is less active and is thought to feed less frequently. Periodic cessation of acid secretion may be an energy conserving mechanism used by animals that feed infrequently and experience extended periods of fasting.     

Anoxia tolerance in rice roots acclimated by several different periods of hypoxia

Rice (Oryza sativa L.) seedlings were subjected to hypoxic pretreatment (H-PT; incubated in 5% O2 atmosphere) for various lengths of time followed by an anoxic stress. Anoxia tolerance of rice roots was improved with increasing duration of H-PT, but longer H-PT than 12 h gave no additional improvement. Concentrations of ATP and ethanol, and activities of pyruvate decarboxylase (EC 4.1.1.1) and alcohol dehydrogenase (EC 1.1.1.1) in the roots were increased by H-PT, and the times and patterns of increasing in these concentrations and activities were similar to those of increasing in the anoxia tolerance. These results suggest that the H-PT may increase anoxia tolerance due to maintenance of ATP levels with rapid induction of ethanolic fermentation, and hypoxic acclimation may occur within 12 h.     

Correlation between heat tolerance during exercise and maximum aerobic work capacity

Observation of the physiological responses during exercise in a hot environment and measurement of maximal work capacity were made on eight young male subjects, ages 20--22. Exercise was performed on a bicycle ergometer at a constant work load of 450 kg . m/min at a cycling rate of 50 rpm for 30 min in a climatic chamber at 30 degree C with 70% relative humidity. The maximum work capacity was measured by bicycle ergometer exercise. Heat tolerance during exercise was assessed by the magnitude of physiological strain expressed by the combination of relative rise in rectal temperature, relative water loss and relative salt loss. Heat load during exercise was calculated using metabolic rates at rest and during exercise, assuming heat loss through the respiratory tract to be 10 percent of metabolic rate. Fairly good correlations were found between the ratio of work done to maximum work capacity and rise in rectal temperature, ratio of body weight loss to body weight and heat tolerance during exercise. Close correlations were found among relative heat load during exercise and rise in rectal temperature, relative body weight loss and heat tolerance. Heat tolerance during exercise in a hot environment correlated well to capacity of heat dissipation and maximum work capacity.     

Regulation of lipid metabolism in the snow alga Chlamydomonas nivalis in response to NaCl stress: An integrated analysis by cytomic and lipidomic approaches

The cultures of the snow alga Chlamydomonas nivalis in the exponential phage were stressed by NaCl (up to 1.5%) for 0～48 h, followed by Nile Red staining-based cytomic analysis (flow cytometry and confocal laser scanning microscopy). The fluorescent intensities of total lipids, and neutral and polar lipids increased to the maximum within 7 h in the NaCl stressed cells with the highest increase in total lipids by 2-fold (0.75%-NaCl for 7 h), the highest increase in neutral lipids by 68-fold (1%-NaCl for 7 h) and the highest increase in polar lipids by 10-fold (1.25%-NaCl for 5 h), respectively. Seven types and 22 kinds of polar lipid molecules were selected and identified as biomarkers by UPLC/Q-TOF-MS-based lipidomic analysis, which demonstrated differences in total lipids between the stress group (0.75%-NaCl for 7 h) and the control. The biological roles of the biomarkers in the alga under NaCl stress were discussed. The integrated approach based on “omics” technologies developed in the present work is validated as a powerful tool to successfully reveal the regulation of lipid metabolism in microalgae in response to stress stimulation.     

Seasonal and diel changes in photosynthetic activity of the snow alga Chlamydomonas nivalis (Chlorophyceae) from Svalbard determined by pulse amplitude modulation fluorometry

The seasonal and diel dynamics of the physiological state and photosynthetic activity of the snow alga Chlamydomonas nivalis were investigated in a snowfield in Svalbard. The snow surface represents an environment with very high irradiation intensities along with stable low temperatures close to freezing point. Photosynthetic activity was measured using pulse amplitude modulation fluorometry. Three types of cell (green biflagellate vegetative cells, orange spores clustered by means of mucilaginous sheaths, and purple spores with thick cell walls) were found, all of them photosynthetically active. The pH of snow ranged between 5.0 and 7.5, and the conductivity ranged between 5 and 75 microS cm(-1). The temperature of snow was stable (-0.1 to +0.1 degrees C), and the incident radiation values ranged from 11 to 1500 micromol photons m(-2) s(-1). The photosynthetic activity had seasonal and diel dynamics. The Fv/Fm values ranged between 0.4 and 0.7, and generally declined over the course of the season. A dynamic response of Fv/Fm to the irradiance was recorded. According to the saturating photon fluence values Ek, the algae may have obtained saturating light as deep as 3 cm in the snow when there were higher-light conditions, whereas they were undersaturated at prevalent low light even if on the surface.     

Competition between inoculum strains ofRhizobium japonicum in the process of soybean nodulation during three planting periods

Competition between inoculum strains ofRhizobium japonicum D 216 and 311 B applied to soybean seeds in mixed inocula depended, especially in the year of inoculation, directly on the ratio of the cell numbers of the two inoculum strains in mixtures. Uninoculated plants grown in original soil contaminated in August 1969 by inoculated seed and stored subsequently in original pots without watering for 8 months displayed, after the spring (May) and summer (August) sowing in 1970, a statistically significant nodulation shift in favour of the D 216 strain. The highest nodulatiou was achieved with all inoculation treatments during spring sowing in 1970.     

Influence of simulated snow cover on the cold tolerance and freezing injury of yellow-cedar seedlings

It has been hypothesized that yellow‐cedar [Chamaecyparis nootkatensis (D. Don) Spach] decline may result from root freezing injury following climate change‐induced reductions in protective snow cover. To test this hypothesis, we measured the freezing tolerance and injury expression of yellow‐cedar seedlings in three treatments that differed in the insulative protection they provided to soils during winter and spring: (1) full exposure to ambient temperatures (exposed treatment), (2) continuous protection from ambient temperatures via addition of perlite over pots (full protection), and (3) perlite protection only during winter and exposure to ambient temperatures during spring (partial protection). Foliage from all treatments was cold tolerant enough to prevent foliar freezing injury throughout the study period. However, on all sample dates, roots of seedlings from all treatments were only tolerant to about ?5 °C – a level considerably warmer than the reported maximum cold tolerance for the species and well above the soil temperature recorded in the exposed treatment. As a result of this limited root cold tolerance, visibly uninjured roots of seedlings from the exposed treatment had significantly higher relative electrolyte leakage (REL) throughout the winter and early spring than seedlings in soil protection treatments. Seedlings from the exposed treatment also had significantly higher foliar REL values and greater visual foliar injury than seedlings from the other treatments starting in early spring. For both roots and foliage, REL measurements consistently detected tissue damage before visual injury was evident. Patterns of injury from both REL and visual injury assessments showed the same pattern: damage began with freezing injury to roots and subsequently became evident as foliar browning after spring temperatures increased. All seedlings in the exposed treatment eventually had 100% fine root damage and died. This progression of initial root damage followed by foliar browning and mortality after the onset of warming conditions is consistent with reports of yellow‐cedar decline symptom development in the field.     

Breeding of the bush fly,Musca vetustissima Walker,in an over-wintering area during winter and spring

Field experiments in an area of south-western Australia where bush fly (Musca vetustissima) adults occur permanently, showed that it overwintered by continuous breeding; but only two to three generations occurred between June and September. Low survival of eggs and larvae in the food (cattle dung) from May to August was associated with rainfall rather than low temperatures. High egg-adult survival occurred in late August; lower egg and larval survival in September and early October was attributed partly to dung fauna. Egg and larval survival was high in late October until December but predation or parasitization caused low survival of puparia outside the dung. Experimental and wild adult flies were largest and therefore most fecund in early spring; smaller wild flies in late spring appeared to result from larval competition for food. Simultaneous high egg-adult survival, high fecundity and rapidly decreasing generation times in late winter and early spring provide a basis for explaining the major increase in adult bush fly abundance observed in some areas in mid-spring.