Desiccation tolerance in diapausing spider mites Tetranychus urticae and T. kanzawai (Acari: Tetranychidae)

We investigated the effects of changes in vapor pressure deficit (VPD) on the survival of diapausing (winter form) and non-diapausing (summer form) spider mites Tetranychus urticae Koch and Tetranychus kanzawai Kishida (Acari: Tetranychidae). Adult females of both species were kept without food at VPDs of 0.0, 0.4, 0.7, 1.5, 1.9, or 2.7 kPa for 3, 6, 9, 12, or 15 days at 25 °C. Diapausing females of both species kept at a VPD of ≥0.4 kPa for ≥6 days clearly tolerated desiccation. Under water-saturated conditions (VPD = 0.0 kPa), in which no desiccation occurred, diapausing females showed high starvation tolerance: 90 % survived for up to 15 days. No interspecific differences in tolerance to desiccation or starvation were observed under most conditions. These results indicate that diapause functions increase tolerance to desiccation and starvation. Such multiple tolerances to harsh environments might support winter survival in spider mites.     

Freezing and desiccation injury resistance in the filamentous green alga Klebsormidium from the Antarctic, Arctic and Slovakia

The freezing and desiccation tolerance of 12 Klebsormidium strains, isolated from various habitats (aeroterrestrial, terrestrial, and hydro-terrestrial) from distinct geographical regions (Antarctic — South Shetlands, King George Island, Arctic — Ellesmere Island, Svalbard, Central Europe — Slovakia) were studied. Each strain was exposed to several freezing (−4°C, −40°C, −196°C) and desiccation (+4°C and + 20°C) regimes, simulating both natural and semi-natural freeze-thaw and desiccation cycles. The level of resistance (or the survival capacity) was evaluated by chlorophyll a content, viability, and chlorophyll fluorescence evaluations. No statistical differences (Kruskal-Wallis tests) between strains originating from different regions were observed. All strains tested were highly resistant to both freezing and desiccation injuries. Freezing down to −196°C was the most harmful regime for all studied strains. Freezing at −4°C did not influence the survival of studied strains. Further, freezing down to −40°C (at a speed of 4°C/min) was not fatal for most of the strains. RDA analysis showed that certain Antarctic and Arctic strains did not survive desiccation at +4°C; however, freezing at −40°C, as well as desiccation at +20°C was not fatal to them. On the other hand, other strains from the Antarctic, the Arctic, and Central Europe (Slovakia) survived desiccation at temperatures of +4°C, and freezing down to −40°C. It appears that species of Klebsormidium which occupy an environment where both seasonal and diurnal variations of water availability prevail, are well adapted to freezing and desiccation injuries. Freezing and desiccation tolerance is not species-specific nor is the resilience only found in polar strains as it is also a feature of temperate strains. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. This paper is dedicated to the memory of the late Dr. Bohuslav Fott (1908–1976), Professor of Botany at the Charles University in Prague, to mark the centenary of his birth.     

Cold,freezing, and desiccation tolerance of the limpet Acmaea digitalis (Eschscholtz)

Cold, freezing, and desiccation tolerance were examined in the limpet, Acmaea digitalis (Eschscholtz). Fifty percent of the experimental population survived freezing at temperatures between ?10 ° and ?12 °C for at least 24 hr. In this temperature range, 60–80 % of the body water was frozen. The LD₅₀ for water loss by desiccation was 76.5% ± 1.3_δ. At 70–80% body water loss, solutes were concentrated between 350 and 500%. Some limpets failed to survive immersion in 450% seawater for 6 hr (100% scawater = salinity of 31‰), suggesting that much of the damage from freezing and desiccation was from an increased solute concentration. No glycerol could be detected in extracts of the foot and the visceral mass of A. digitalis during winter, confirming similar results in studies carried out on other intertidal molluscs.     

Response of Antarctic, temperate, and tropical microalgae to temperature stress

The global temperature increase has significant implications on the survival of microalgae which form the basis of all aquatic food webs. The aim of this study was to compare the response of similar taxa of microalgae from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237, and Navicula glaciei UMACC 231), temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248, and Navicula incerta UMACC 249), and tropical (C. augustae UMACC 246, C. vulgaris UMACC 001, and Amphiprora UMACC 239) regions to changing temperature. The Antarctic, temperate, and tropical strains were grown over specific temperature ranges of 4 °C to 30 °C, 4 °C to 32 °C, and 13 °C to 38 °C, respectively. The three Antarctic strains survived at temperatures much higher than their ambient regime. In comparison, the tropical strains are already growing at their upper temperature limits. The three Chlorella strains from different regions are eurythermal, with a large overlap on tolerance ranging from 4 °C to 38 °C. The specific growth rate (μ) of the Antarctic Navicula decreased (<0.34 day^?1) at temperatures above 4 °C, showing it to be sensitive to temperature increase. If further warming of Earth occurs, N. glaciei UMACC 231 is likely to have the most deleterious consequences than the other two Antarctic microalgae studied. The percentage of polyunsaturated fatty acids (PUFA) decreased with increasing temperature in the Antarctic Navicula. As temperature increases, the growth and nutritional value of this commonly occurring diatom in the Antarctic may decrease, with consequences for the aquatic food web. Of the three Chlamydomonas strains, only the Antarctic strain produced predominantly PUFA, especially 16:3 (48.4–57.2 % total fatty acids).     

Production of microsclerotia by Brazilian strains of Metarhizium spp. using submerged liquid culture fermentation

We investigated the potential production and desiccation tolerance of microsclerotia (MS) by Brazilian strains of Metarhizium anisopliae (Ma), M. acridum (Mc) and M. robertsii (Mr). These fungi were grown in a liquid medium containing 16 g carbon l^?1 with a carbon:nitrogen ratio of 50:1. One hundred milliliters cultures were grown in 250 ml Erlenmeyer flasks in a rotary incubator shaker at 28 °C and 200 rpm for 5 days. Five-day-old MS were harvested, mixed with diatomaceous earth (DE) and air-dried for 2 days at 30 °C. The air-dried MS–DE granular preparations were milled by mortar + pestle and stored in centrifuged tubes at either 26 or ?20 °C. Desiccation tolerance and conidia production were assessed for dried MS granules by measuring hyphal germination after incubation for 2 days on water agar plates at 26 °C and for conidia production following 7 days incubation. Yields of MS by all strains of Metarhizium were 6.1–7.3 × 10⁶ l^?1 after 3 days growth with maximum MS yields (0.7–1.1 × 10⁷ l^?1) after 5 days growth. No differences in biomass accumulation were observed after 3 days growth, whereas Ma-CG168 showed the highest biomass accumulation after 5 days growth. Dried MS–DE preparations of all fungal strains were equally tolerant to desiccation (≥93 % germination) and the highest conidia production was obtained by MS granules of Mc-CG423 (4 × 10⁹ conidia g^?1). All MS granules showed similar stability after storage at either 26 or ?20 °C for 3.5 months.     

Divergence of water balance mechanisms in two sibling species (Drosophila simulans and D. melanogaster): effects of growth temperatures

Drosophila simulans is more abundant under colder and drier montane habitats in the western Himalayas as compared to its sibling D. melanogaster but the mechanistic bases of such climatic adaptations are largely unknown. Previous studies have described D. simulans as a desiccation sensitive species which is inconsistent with its occurrence in temperate regions. We tested the hypothesis whether developmental plasticity of cuticular traits confers adaptive changes in water balance-related traits in the sibling species D. simulans and D. melanogaster. Our results are interesting in several respects. First, D. simulans grown at 15 °C possesses a high level of desiccation resistance in larvae (~39 h) and in adults (~86 h) whereas the corresponding values are quite low at 25 °C (larvae ~7 h; adults ~13 h). Interestingly, cuticular lipid mass was threefold higher in D. simulans grown at 15 °C as compared with 25 °C while there was no change in cuticular lipid mass in D. melanogaster. Second, developmental plasticity of body melanisation was evident in both species. Drosophila simulans showed higher melanisation at 15 °C as compared with D. melanogaster while the reverse trend was observed at 25 °C. Third, changes in water balance-related traits (bulk water, hemolymph and dehydration tolerance) showed superiority of D. simulans at 15 °C but of D. melanogaster at 25 °C growth temperature. Rate of carbohydrate utilization under desiccation stress did not differ at 15 °C in both the species. Fourth, effects of developmental plasticity on cuticular traits correspond with changes in the cuticular water loss i.e. water loss rates were higher at 25 °C as compared with 15 °C. Thus, D. simulans grown under cooler temperature was more desiccation tolerant than D. melanogaster. Finally, desiccation acclimation capacity of larvae and adults is higher for D. simulans reared at 15 °C but quite low at 25 °C. Thus, D. simulans and D. melanogaster have evolved different strategies of water conservation consistent with their adaptations to dry and wet habitats in the western Himalayas. Our results suggest that D. simulans from lowland localities seems vulnerable due to limited acclimation potential in the context of global climatic change in the western Himalayas. Finally, this is the first report on higher desiccation resistance of D. simulans due to developmental plasticity of both the cuticular traits (body melanisation and epicuticular lipid mass) when grown at 15 °C, which is consistent with its abundance in temperate regions.     

Measurement of individual cell strength of <Emphasis Type="Italic">Botryococcus braunii</Emphasis> in cell culture

Botryococcus braunii is a microalga considered for biofuel production and may require physical disruption of cells/colonies for efficient hydrocarbon extraction. In this study, the strength of individual cells of B. braunii was measured using a nanoindenter. From the load and cell size, the pressure for bursting the cell was calculated to be 56.9 MPa. This value is 2.3–10 times those of Saccharomyces cerevisiae and Chlorella vulgaris found in another research, because B. braunii has two types of cell walls with different thicknesses. The energy required to disrupt 1 g of dry B. braunii cells, estimated by load-displacement curves, is 3.19 J g^?1 which is 0.19–1.2 times higher than those of S. cerevisiae and C. vulgaris. When using a high-pressure homogenizer for disrupting B. braunii cells, the cell disruption degree increased with the treatment pressure at above 30 MPa, and 70% of cells were disrupted at 80 MPa.     

A comparison of desiccation tolerance among 12 species of chironomid larvae

Tolerance to desiccation was compared among 12 Japanese species of chironomid larvae under the condition of 60% in relative humidity at 25.5?°C. Three parameters were assessed: time to 50% survival (T ₅₀), water loss at 50% survival (WL₅₀) and water loss rate (WLR). T ₅₀, WL₅₀ and WLR were determined as measures of desiccation tolerance, dehydration tolerance, and dehydration resistance, respectively. T ₅₀ was 64.4–142 min for most species, except Propsilocerus akamusi (Tokunaga) which took 872 min. WL₅₀ was 60.6–82.4% for all species. WLR was only 0.0664% per minute for Pr. akamusi, while it was 0.629–1.50% for the other species. These results showed that Pr. akamusi had a high desiccation tolerance due to a high preventive ability of evaporation from body surface. T ₅₀ showed no significant relationships to WL₅₀ or WLR among the 12 species, while there was a significant positive relationship between WL₅₀ and WLR. These results suggest that chironomid species have a trade-off tendency that a species has a high tolerance – low resistance or a high resistance – low tolerance for dehydration.     

Melanin production by a yeast strain XJ5-1 of <Emphasis Type="Italic">Aureobasidium melanogenum</Emphasis> isolated from the Taklimakan desert and its role in the yeast survival in stress environments

The yeast strain XJ5-1 isolated from the Taklimakan desert soil was identified to be a strain of Aureobasdium melanogenum and could produce a large amount of melanin when it was grown in the PDA medium, but its melanin biosynthesis and expression of the PKS gene responsible for the melanin biosynthesis was significantly repressed in the presence of (NH₄)₂SO₄. However, A. melanogenum P5 strain isolated from a mangrove ecosystem grown in both the presence and the absence of (NH₄)₂SO₄ did not produce any melanin. The cell size of A. melanogenum XJ5-1 strain was much higher than that of A. melanogenum P5 strain. The melanized cells of the yeast strain XJ5-1 had higher tolerance to UV radiation, oxidation (200.0 mM H₂O₂), heat treatment (40 °C), salt shock (200.0 g/L NaCl), desiccation and strong acid hydrolysis (6.0 M HCl) at high temperature (80 °C) than the non-melanized cells of the same yeast strain XJ5-1. At the same time, the melanized cells of the yeast strain XJ5-1 also had higher tolerance to UV radiation, oxidation (200.0 mM H₂O₂), desiccation and strong acid hydrolysis (6.0 M HCl) at high temperature (80 °C) than A. melanogenum P5 strain, but had similar resistance to heat treatment (40 °C) and salt shock (200.0 g/L NaCl) compared to those of A. melanogenum P5 strain. All the results revealed that many characteristics of A. melanogenum XJ5-1 isolated from the Taklimakan desert soil was different from those of A. melanogenum P5 strain isolated from the mangrove ecosystem.     

Biological control of giant salvinia (Salvinia molesta) in a temperate region: cold tolerance and low temperature oviposition of Cyrtobagous salviniae

Success of Cyrtobagous salviniae Calder & Sands (Coleoptera: Curculionidae) for biological control of Salvinia molesta D. S. Mitchell in temperate regions has been less reliable than in tropical and subtropical regions and this difference is presumed to be due to greater winter mortality. We measured the cold tolerance of C. salviniae by comparing chill coma recovery time and survival of adults after exposure to freezing conditions among four geographic populations collected from Florida, Louisiana, Texas and Australia. Effects of winter temperature acclimation on low temperature oviposition also were determined. The Australian population was more cold tolerant than the three US populations. No oviposition by C. salviniae was observed at a water temperature of 17 °C and the oviposition rate at 19 °C was less than at 21, 23 and 25 °C. We suggest that introduction of cold tolerant strains of C. salviniae could increase its effectiveness in temperate regions of the US.     

Evaluation of an improved strain of Porphyra yezoensis Ueda (Bangiales, Rhodophyta) with high-temperature tolerance

The red algae Porphyra yezoensis has high commercial and nutritional value; however, its cultivation and product quality are jeopardized by global warming. Screening of high-temperature-tolerant strains would greatly reduce cultivation risks and benefit the Porphyra industry. Single somatic cells isolated enzymatically from the wild-type (WT) blades irradiated by ⁶⁰Co-?? rays were screened at 25°C; one strain, T-17, displayed significant high-temperature resistance. Further culture studies showed that conchospore germlings of T-17 showed 76.2% survival at 23°C and 65.7% survival at 24°C, while the WT conchospore germlings survived at significantly lower percentages of 16.9% and 11.5%, respectively, over a period of 16 days. Furthermore, T-17 conchospore germlings divided at higher percentages of 100% at both 23 and 24°C compared to the WT conchospores with 99.8% and 81.8%, respectively. When the 50-day-old F₁ gametophytic blades were transferred from the optimal temperature of 18°C to high temperatures of 23 and 24°C, the T-17 blades sustained growth over a 45-day period without rot, and their mean lengths increased by 20 and 4.2 times, respectively. The mean lengths of WT blades only increased by a factor of 0.6 and 0.4 times and were severely decayed after being cultured for 15 days at high temperatures. The mean wet weights of T-17 blades increased by 418.9 and 195.3 times, but only 7.8 and 4.6 times in WT at 23 and 24°C, respectively. These results indicate that T-17 is superior to WT in growth and high-temperature tolerance, which may offer a new cultivar for the nori industry as a high-temperature-resistant strain to counteract the effects of global warming.     

Systematic overestimation of Salicaceae seed survival using radicle emergence in response to drying and storage: implications for ex situ seed banking

Biodiversity conservation programmes are underpinned by seed banking following drying to low water contents (WC), and supported by both the assessment and prediction of seed viability over time. The means of judging viability is thus crucial to the comprehension of seed vigour. We selected seeds of three species and one hybrid in the Salicaceae likely to have variation in tolerance to drying, processing and storage, including in relation to cryobanking, and compared survival growth as radicle emergence (germination) and normal seedling production. With three seed lots of Salix gracilistyla, air-drying to 8–10 % WC enhanced seed survival after 40 days’ storage at 5 °C as compared with non-treated seeds at 14–20 % WC. Four seed lots of Populus alba × P. glandulosa showed equally high germination (88–100 %) and proportions of normal seedlings (81–99 %) when stored at 5 °C for 7–10 weeks. Among seven seed lots of S. gracilistyla, two groups with different storage behaviour could be statistically distinguished with normal seedling production ranging from 0 to 45 % after storage at 5 °C for 13 weeks. Seed tolerance to WC manipulation and cryopreservation was very variable among species and seed lots. Seed lots of S. hallaisanensis and S. gracilistyla with ~80 % germination survived cryopreservation at 10 % WC, but were sensitive to lower WCs. In contrast, Populus seeds had greater desiccation tolerance combined with cryopreservation capability. With seed lots of all species and hybrids, cryopreservation had little effect on viability unless the high moisture freezing limit had been exceeded (~10–20 % WC, depending on seed lot). However, under all conditions of handling (drying, rehydration, storage at 5 °C or cryopreservation) using germination as the only indicator of viability over-estimated survival compared with normal seedling production.     

Saccharomyces cerevisiae strains from traditional fermentations of Brazilian cachaça: trehalose metabolism, heat and ethanol resistance

Nine indigenous cachaça Saccharomyces cerevisiae strains and one wine strain were compared for their trehalose metabolism characteristics under non-lethal (40°C) and lethal (52°C) heat shock, ethanol shock and combined heat and ethanol stresses. The yeast protection mechanism was studied through trehalose concentration, neutral trehalase activity and expression of heat shock proteins Hsp70 and Hsp104. All isolates were able to accumulate trehalose and activate neutral trehalase under stress conditions. No correlation was found between trehalose levels and neutral trehalase activity under heat or ethanol shock. However, when these stresses were combined, a positive relationship was found. After pre-treatment at 40°C for 60 min, and heat shock at 52°C for 8 min, eight strains maintained their trehalose levels and nine strains improved their resistance against lethal heat shock. Among the investigated stresses, heat treatment induced the highest level of trehalose and combined heat and ethanol stresses activated the neutral trehalase most effectively. Hsp70 and Hsp104 were expressed by all strains at 40°C and all of them survived this temperature although a decrease in cell viability was observed at 52°C. The stress imposed by more than 5% ethanol (v/v) represented the best condition to differentiate strains based on trehalose levels and neutral trehalase activity. The investigated S. cerevisiae strains exhibited different characteristics of trehalose metabolism, which could be an important tool to select strains for the cachaça fermentation process.     

Modulation in fatty acid composition influences salinity stress tolerance in Frankia strains

Frankia strains, isolated from Hippöphae salicifolia D. Don, were utilized to examine the utility of lipid amendments in the strains’ strategic survival against salinity. Frankia strains are known to withstand severe temperature fluctuations (?20 °C to +30 °C), nitrogen deprivation and low soil water content. It was interesting to note that these strains were also able to tolerate a considerable range of salinity. Strains were subjected to 250 mM (500 mM for HsIi10) and 750 mM NaCl treatment, which were the critical and inhibitory NaCl concentrations, respectively, for the experimental strains. Their lipid profiles showed dynamic modifications in saline environment; 16–18 carbon chain fatty acids were of predominant occurrence in the lipid membrane. In the critical NaCl environment, there was an increase in fatty acid unsaturation (measured in terms of MUFA/PUFA ratio), which preserved normal membrane fluidity. Conversely, at the inhibitory salinity level, increased fatty acid saturation made the membrane highly rigid and susceptible to breakage and electrolyte loss. The differential capability of fatty acid desaturation could be a major factor in variation of salt sensitivity/tolerance patterns among these strains. Also, management of the lipid profile in response to salinity was found to be a strain-specific character.     

Improvement of heat and desiccation tolerance in <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis> through cross-breeding of tolerant strains and successive genetic selection

Genetic selection can be a powerful tool to increase beneficial traits in biological control agents. In this study the heat and desiccation tolerance of the entomopathogenic nematode Heterorhabditis bacteriophora Poinar (Rhabditidomorpha: Strongyloidea) were significantly increased by cross breeding tolerant parental strains and successive genetic selection. These strains originated from a prior screening among 60 strains for increased stress tolerance. During genetic selection, the selection pressure was constantly increased and only the most tolerant 10% of the nematode populations were propagated for further selection steps. Assessment of tolerance and selection for both traits was performed with and without prior adaptation to the stress conditions. Eleven selection steps were performed to increase heat tolerance. A final overall increase in mean heat tolerance of 5.5°C was achieved when nematodes had been adapted to heat stress. For non-adapted tolerance an increase of 3.0°C from 40.1°C to 43.1°C was recorded. For comparison, a commercial strain had a mean tolerated temperature after adaptation of 38.2°C and of 36.5°C without adaptation. For assessment of the desiccation tolerance the mean tolerated water activity (a_w-value) of a population was measured. Cross-breeding most tolerant strains reduced the a_w-value from 0.67 to 0.65 after adaptation and from 0.9 to 0.7 without prior adaptation. The following six selection steps could not increase the tolerance whether nematodes had been adapted to stress or not. In comparison, the commercial strain tolerated a mean a_w-value of 0.985 after adaptation and 0.951 without adaptation. Further investigation will have to assess trait stability and possible trade-off effects. This study is a first important step on the road towards domestication of the entomopathogenic nematode H. bacteriophora.     

Survival of Bactrocera latifrons (Diptera: Tephritidae) adults under constant and fluctuating low temperatures

Bactrocera latifrons (Hendel) is believed to have originated in Southeast Asia but has invaded Hawaii and most recently East Africa. This insect has also been recorded on Okinawa Island, the far south of Kyushu Island, Japan. To assess the overwintering ability of B. latifrons adults, survival at constant temperatures (8, 10, 12, 14, 15 °C) and under fluctuating thermal regimes (FTRs) was investigated. At 14 or 15 °C, more than 30 % of females survived for 90 days. Time required to kill 95 % of B. latifrons at 8 °C was estimated to be 13 days; at 10 °C, 29 days; and at 12 °C, 38 days for females, and 8, 17, and 24 days at the same above temperatures, respectively, for males, suggesting low cold tolerance of this species. The results show that females survive cold temperatures better than males. Under an FTR of 11 °C (22 h)/20 °C (2 h) (average 11.8 °C) survival of females drastically increased compared to that at a constant temperature of 12 °C, whereas the survival of males increased slightly. Survival under FTRs indicates that adult B. latifrons may not overwinter in the north of Tanegashima Island, located 30 km south of Kyushu Island, Japan.     

Hybridisation and selective breeding for improvement of low temperature activity of the entomopathogenic nematode Steinernema feltiae

Steinernema feltiae is used to control overwintering larvae of the codling moth Cydia pomonella L. Application is in autumn when efficacy can be limited by low temperature. The objective of this study was to screen for low temperature activity among wild type populations of S. feltiae, hybridise most active strains and further improve low temperature activity by subjection of a hybrid strain to selective breeding. Significant variation was recorded among 22 S. feltiae strains. The temperature at which 50 % (AT₅₀) and 10 % (AT₁₀) of the dauer juveniles (DJs) were active ranged between 2.9 to 5.8 °C and 0.95 to 3.5 °C, respectively. The mean AT₅₀ of 22 S. feltiae strains was 3.83 °C. The five most active strains were crossed. The hybrid strain HYB01 was more active at low temperature than parental and other hybrid strains with an AT₅₀ of 0.52 °C and an AT₁₀ of 0.09 °C. The tolerance was lost after few reproductive cycles in the insect Galleria mellonella, but was recovered after seven selection cycles with exposure to lowering temperatures. The heritability for the low temperature activity was calculated at h ² = 0.45. Negative trade-off effects on virulence against C. pomonella and reproduction on the same insect were not reported. The most virulent strain was a commercial strain with an LD₅₀ of 30.2 at 8 °C and 37.2 DJs per cocooned instar at 15 °C, followed by the selected hybrid with 48.1 and 47.4 DJs, respectively. Offspring production reached 15.000 DJs per instar at 8 °C and was only half at 15 °C. The results well document the potential of a breeding programme for enhancement of the activity of S. feltiae at lower temperature with the objective to improve the control potential of overwintering codling moth C. pomonella.     

Xanthophyceaen assemblages during winter–spring flood: autecology and ecophysiology of Tribonema fonticolum and T. monochloron

The autecology and ecophysiology of two selected periphytic species of Xanthophyceae (Tribonema fonticolum and T. monochloron) were studied from seasonal pools of the inundation area, in the upper part of the Lužnice River (Třeboňsko Biosphere Reserve, Czech Republic) during winter–spring flood. Our studies have shown that these species differ in their ecological requirements (their temperature and light optima; inorganic carbon sources for photosynthesis; and also their ability to survive freezing and desiccation injuries). In our experiments, the optimal growth temperatures for both strains were higher than the temperatures of the water they were collected and isolated from. Tribonema monochloron has the rate of photosynthesis several times higher than T. fonticolum. In addition, the optimal growth temperatures were about 3–4°C lower for Tribonema monochloron than for T. fonticolum. From our results, we concluded that both strains of Tribonema prefer low intensities of irradiance. Both Tribonema strains were determined as CO₂ users, but we revealed the ability of T. fonticolum to use HCO₃⁻ in small amounts. In both Tribonema strains, 100% of the cells survived freezing down to −4°C. The cells’ viability after freezing at −40, −100 and −196°C was much higher for T. monochloron (about 40%) than for T. fonticolum (about 4%). With respect to desiccation damages, at temperatures of +4 and +20°C, T. monochloron (the species better adapted to low temperatures) did not survive. In contrast, about 80% cells of T. fonticolum survived desiccation at both temperatures. Handling editor: J. Padisak.     

Dehydrin, alcohol dehydrogenase, and central metabolite levels are associated with cold tolerance in diploid strawberry (Fragaria spp.)

The use of artificial freezing tests, identification of biomarkers linked to or directly involved in the low-temperature tolerance processes, could prove useful in applied strawberry breeding. This study was conducted to identify genotypes of diploid strawberry that differ in their tolerance to low-temperature stress and to investigate whether a set of candidate proteins and metabolites correlate with the level of tolerance. 17 Fragaria vesca, 2 F. nilgerrensis, 2 F. nubicola, and 1 F. pentaphylla genotypes were evaluated for low-temperature tolerance. Estimates of temperatures where 50 % of the plants survived (LT₅₀) ranged from ?4.7 to ?12.0 °C between the genotypes. Among the F. vesca genotypes, the LT₅₀ varied from ?7.7 °C to ?12.0 °C. Among the most tolerant were three F. vesca ssp. bracteata genotypes (FDP821, NCGR424, and NCGR502), while a F. vesca ssp. californica genotype (FDP817) was the least tolerant (LT₅₀ ?7.7 °C). Alcohol dehydrogenase (ADH), total dehydrin expression, and content of central metabolism constituents were assayed in select plants acclimated at 2 °C. The LT₅₀ estimates and the expression of ADH and total dehydrins were highly correlated (r _adh = ?0.87, r _dehyd = ?0.82). Compounds related to the citric acid cycle were quantified in the leaves during acclimation. While several sugars and acids were significantly correlated to the LT₅₀ estimates early in the acclimation period, only galactinol proved to be a good LT₅₀ predictor after 28 days of acclimation (r _galact = 0.79). It is concluded that ADH, dehydrins, and galactinol show great potential to serve as biomarkers for cold tolerance in diploid strawberry.