Temperature Stress Tolerance Research Articles

Temperature induction response (TIR) as a rapid screening protocol to dissect the genetic variability in acquired thermotolerance in rice and to identify novel donors for high temperature stress tolerance

Rice is the major cereal food crop in the world. The predicted 2–4 °C increment in temperature by the end of the twenty-first century and the occurrence of drought coupled with high temperature stress situation poses a threat to rice production. There is a wealth of unexplored rice germplasm and landraces which show significant genetic variation in response to temperature stress. Hence, the present study was designed to develop a rapid screening protocol based on the principle of “acquired tolerance” in which seedlings were subjected to a gradual temperature increase from 38 to 48 °C for 3 h (induction treatment), immediately followed by challenging at 54 °C for 3 h. Among the landraces, Apo and Norungan showed a mortality of 12 %, coupled with a less reduction in percent root and shoot growth when subjected to induction treatments. Thus their intrinsic thermo-tolerance was found to be comparable with that of N22. The physiological basis of thermo-tolerance in these lines was further confirmed, as these lines recorded a higher chlorophyll stability index and a strong antioxidant enzyme system with lesser lipid peroxidation in terms of malondialdehyde content values. Finally, TIR studies revealed that, apart from N22, landraces such as Apo, Norungan, Ottadiayan and Vellaikudaivazhai can also be used as new sources of donors in breeding programmes to overcome combined drought and temperature stresses.

Effect of low temperature on profilins and ADFs transcription and actin cytoskeleton reorganization in Arabidopsis

In the present study, we found that the expression patterns of the vegetative profilins and actin depolymerizing factors (ADFs) were specifically altered under low temperature (17 °C) stress using a real-time PCR. Our results show that also reorganization of the actin cytoskeleton was triggered by a low temperature. Facilitation of microfilament (MF) assembly by phalloidin treatment resulted in an enhanced low temperature stress tolerance, whereas blocking MF assembly with latrunculin B resulted in enhanced low temperature stress sensitivity. Our results show that the specific members of the vegetative profilins and ADFs might participate in regulating the response of plants to a low temperature stress, and the actin cytoskeleton is vital for the tolerance of Arabidopsis seedlings to low temperature stress.

Constitutive Expression of a Tomato Small Heat Shock Protein Gene LeHSP21 Improves Tolerance to High-Temperature Stress by Enhancing Antioxidation Capacity in Tobacco

It is well established that small heat shock proteins (sHSPs) play an important role in thermotolerance in various organisms due to their abundance and diversity. In the present study, a chloroplast small heat shock protein gene (LeHSP21) from tomato (Lycopersicon esculentum cv PKM-1) was constitutively expressed in tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants via Agrobacterium-mediated transformation. When compared to wild-type control plants, transgenic tobacco plants constitutively expressing LeHSP21, driven by the cauliflower mosaic virus 35S promoter, exhibited improved tolerance to both high temperature and oxidative stress. Furthermore, when the seedlings were subjected to high temperature treatment, the activities of anti-oxidative enzymes and the content of proline were significantly higher in transgenic plants than those in the wild-type plants. Our results presented here demonstrate the feasibility of improving high temperature and oxidative stress tolerance in plants through the expression of LeHSP21 gene.

Indices and their Applicability under High Temperature in Potato (<i>Solanum tuberosum</i> L.) Cultivars

The increasing temperature is going to be more vulnerable for cool season crops like potato which requires an optimum productivity temperature of 18 to 20 °C. Thus, breeding for heat tolerance has become very important. Therefore, some previously used indices for abiotic stress tolerance have been used in our study for screening of high temperature stress tolerance in potato. Three high yielding (Kufri jyoti, Kufri megha and Kufri pokraj) and two local (Rangpuria and Badami) commonly grown potato cultivars were selected for our experiment. Potato cultivars were sown under normal condition and two high temperature conditions (polyhouse and early season) and indices such as HSI (heat susceptibility index), HTI (heat tolerance index), GM (geometric mean) and HII (heat intensity index) were used to evaluate the performance of the cultivars under all the three temperature conditions. The positive and significant correlation between HTI (heat tolerance index), and GM (geometric mean) as well as with tuber yield under all the conditions revealed that these indices were efficient in selecting the high temperature tolerant potato cultivars. We recorded the equal applicability of these two indices for both high yielding and local group of potato cultivars. Our study revealed that cultivar Kufri megha and Rangpuria showed higher heat tolerance between high yielding and local cultivars respectively.

Indices and their Applicability under High Temperature in Potato (<i>Solanum tuberosum</i> L.) Cultivars

The increasing temperature is going to be more vulnerable for cool season crops like potato which requires an optimum productivity temperature of 18 to 20 °C. Thus, breeding for heat tolerance has become very important. Therefore, some previously used indices for abiotic stress tolerance have been used in our study for screening of high temperature stress tolerance in potato. Three high yielding (Kufri jyoti, Kufri megha and Kufri pokraj) and two local (Rangpuria and Badami) commonly grown potato cultivars were selected for our experiment. Potato cultivars were sown under normal condition and two high temperature conditions (polyhouse and early season) and indices such as HSI (heat susceptibility index), HTI (heat tolerance index), GM (geometric mean) and HII (heat intensity index) were used to evaluate the performance of the cultivars under all the three temperature conditions. The positive and significant correlation between HTI (heat tolerance index), and GM (geometric mean) as well as with tuber yield under all the conditions revealed that these indices were efficient in selecting the high temperature tolerant potato cultivars. We recorded the equal applicability of these two indices for both high yielding and local group of potato cultivars. Our study revealed that cultivar Kufri megha and Rangpuria showed higher heat tolerance between high yielding and local cultivars respectively.

A wheat salinity-induced WRKY transcription factor TaWRKY93 confers multiple abiotic stress tolerance in Arabidopsis thaliana

Wheat is an important crop in the world. But most of the cultivars are salt sensitive, and often adversely affected by salt stress. WRKY transcription factors play a major role in plant responses to salt stress, but the effective salinity regulatory WRKYs identified in bread wheat are limited and the mechanism of salt stress tolerance is also not well explored. Here, we identified a salt (NaCl) induced class II WRKY transcription factor TaWRKY93. Its transcript level was strongly induced by salt (NaCl) and exogenous abscisic acid (ABA). Over-expression of TaWRKY93 in Arabidopsis thaliana enhanced salt (NaCl), drought, low temperature and osmotic (mannitol) stress tolerance, mainly demonstrated by transgenic plants forming longer primary roots or more lateral roots on MS plates supplemented with NaCl and mannitol individually, higher survival rate under drought and low temperature stress. Further, transgenic plants maintained a more proline content, higher relative water content and less electrolyte leakage than the wild type plants. The transcript abundance of a series of abiotic stress-related genes was up-regulated in the TaWRKY93 transgenic plants. In summary, TaWRKY93 is a new positive regulator of abiotic stress, it may increase salinity, drought and low temperature stress tolerance through enhancing osmotic adjustment, maintaining membrane stability and increasing transcription of stress related genes, and contribute to the superior agricultural traits of SR3 through promoting root development. It can be used as a candidate gene for wheat transgenic engineering breeding against abiotic stress.

Genome-wide Scanning and Characterization of Sorghum bicolor L. Heat Shock Transcription Factors.

A genome-wide scanning of Sorghum bicolor resulted in the identification of 25 SbHsf genes. Phylogenetic analysis shows the ortholog genes that are clustered with only rice, representing a common ancestor. Promoter analysis revealed the identification of different cis-acting elements that are responsible for abiotic as well as biotic stresses. Hsf domains like DBD, NLS, NES, and AHA have been analyzed for their sequence similarity and functional characterization. Tissue specific expression patterns of Hsfs in different tissues like mature embryo, seedling, root, and panicle were studied using real-time PCR. While Hsfs4 and 22 are highly expressed in panicle, 4 and 9 are expressed in seedlings. Sorghum plants were exposed to different abiotic stress treatments but no expression of any Hsf was observed when seedlings were treated with ABA. High level expression of Hsf1 was noticed during high temperature as well as cold stresses, 4 and 6 during salt and 5, 6, 10, 13, 19, 23 and 25 during drought stress. This comprehensive analysis of SbHsf genes will provide an insight on how these genes are regulated in different tissues and also under different abiotic stresses and help to determine the functions of Hsfs during drought and temperature stress tolerance.

Evaluation of agronomic and physiological traits associated with high temperature stress tolerance in the winter wheat cultivars

Post-anthesis high temperature stress is a major concern for the winter wheat producing areas in east China, especially in Shandong province. Fourteen agronomic and physiological traits were studied in 58 Chinese wheat accessions under high-temperature conditions in 2012 and 2013. High temperature stress led to reduction in grain yield and other yield component traits. Significant variations were observed for grain yield per plant (GYPP), grain weight per spike (GWS), thousand kernel weight (TKW), grain number of the main-spike, spikelet number and biological yield per plant. Among the physiological traits measured, chlorophyll content and normalized difference vegetation index showed significant variation under high temperature stress. The results indicate that heat susceptibility index estimated for TKW, GYPP, GWS and flag leaf senescence scale (FLSS) could be used as selection criteria for identifying heat tolerant genotypes for the Shandong province. The results also suggest that FLSS is a good, quick visual indicator of stay-green for field selection for heat tolerance. After harvest, TKW can be measured as final indicator of heat tolerance. The varieties Gaoyou 9415, Hemai 13, Jimai 22, Kexin 9, Shannong 8355, Taishan 23, Yannong 5286 and Zimai 7 were heat tolerant and potential germplasm for heat tolerance breeding in Shandong province and other parts of China. The results could be useful for breeding climate resilient varieties for China or other countries in the world suffering high temperature stresses during grain filling period.

Evaluation of wheat chromosome translocation lines for high temperature stress tolerance at grain filling stage.

High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines.

Cytoplasmic effects of Brassica napus and B. juncea on extreme temperature stresses of B. carinata

Alloplasmic lines of Brassica carinata were developed from the interspecific crosses B. napus × B. carinata and B. juncea × B. carinata followed by repeated backcrossing to B. carinata as the recurrent male parent up to the BC7 generation. The BC7 generations with cytoplasm of B. napus and B. juncea were designated NC-7 and JC-7, respectively, and the corresponding euplasmic lines were designated CN-7 and CJ-7, respectively. Four lines (NC-7 vs. CN-7 and JC-7 vs. CJ-7) were grown in a closed vinyl greenhouse at 55 °C and outdoors during winter in two cold regions of China (−3 to −10 °C) to investigate the heat and cold tolerance of the alloplasmic and euplasmic lines. Plants with the cytoplasm of B. napus showed lower leaf chlorophyll content and little difference in heat tolerance, whereas plants with the cytoplasm of B. juncea showed higher severity of heat injury compared with that of the euplasmic lines with cytoplasm of B. carinata. Alloplasmic plants with cytoplasm of B. napus and B. juncea showed decreased cold tolerance compared with that of euplasmic lines with cytoplasm of B. carinata. The difference in cold tolerance also was observed in the lethal temperature of the alloplasmic and euplasmic plants. The results suggest that tolerance of extreme temperature stress was controlled mainly by the nucleus but also was affected by the cytoplasm. Interaction between the maternal genome and nucleus was also observed.

Responses of canola (Brassica napus L.) cultivars under contrasting temperature regimes during early seedling growth stage as revealed by multiple physiological criteria

Investigations were carried out to study the responses of canola (Brassica napus) under contrasting temperature regimes (day/night °C): 35/30 (high temperature) and 15/10 (low temperature) in comparison with optimal temperature (25/20) at early seedling stage. The results indicated that high temperature inhibited seedling establishment, while low temperature restrained seed germination. Both high and low temperatures showed detrimental effects on seedling growth as revealed by reduced establishment percentage, seedling vigor index, and fresh weight due to accumulated reactive oxygens. The antioxidant enzymes responded to high and low temperature differently. Under high temperature, superoxide dismutase (SOD) and peroxidase (POD) activities reduced, while catalase (CAT) activities increased. Under low temperature, however, SOD activities increased, while POD activities reduced, with CAT activities unchanged. Proline played an important role in temperature stress tolerance and can be used as an indicator for tolerance to unfavorable temperature conditions in canola seedlings. Huayouza 9 showed much stronger tolerance to both high and low temperature compared with other cultivars tested in this study. The full extent of tolerance mechanisms need to be further studied.

Exogenous glutathione confers high temperature stress tolerance in mung bean (Vigna radiata L.) by modulating antioxidant defense and methylglyoxal detoxification system

The present study investigates the role of exogenous glutathione (GSH) in conferring high temperature stress (HT, 42°C) tolerance in mung bean (Vigna radiata L. cv. Binamoog-1) seedlings by modulating the antioxidant defense and methylglyoxal (MG) detoxification systems. Six-day-old seedlings were exposed to HT stress with or without exogenous GSH (0.5mM for 24h as pretreatment) for 24 and 48h. Heat stress at any duration significantly increased lipid peroxidation (MDA), H2O2, MG, and Proline (Pro) content, generation rate of O2− and lipoxygenase (LOX) activity; decreased leaf chlorophyll (chl) and leaf relative water content (RWC), and the level of ascorbate (AsA); increased endogenous GSH and GSSG (glutathione disulfide); decreased the GSH/GSSG ratio. For both treatment durations, activities of ascorbate peroxidase (APX), glutathione reductase (GR), glutathione-S-transferase (GST) increased; the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione peroxidase (GPX), catalase (CAT) and glyoxalase I (Gly I) decreased; the activity of glyoxalase II (Gly II) increased at 48h. Mung bean seedlings pretreated with exogenous GSH under HT improved chl and leaf RWC; increased APX (only after 24h), MDHAR, DHAR, GR, GPX, GST (increased only after 24h), CAT, Gly I and Gly II activities; improved endogenous GSH content and the GSH/GSSG ratio; lowered GSSG content. Glutathione supplementation with drought stress significantly decreased MDA, H2O2 and MG content, O2− generation rate and LOX activity. Pretreatment with GSH resulted in better physiological performance, improved antioxidant and glyoxalase systems, and reduced MG and oxidative stress under 24h of HT stress, compared with that of 48h. The results suggest that exogenous GSH enhances mung bean seedling tolerance of short-term HT stress by modulating the antioxidant and glyoxalase systems and by improving physiological adaptation.

An essential role of a ferritin-like protein in acid stress tolerance of Listeria monocytogenes.

The expression of ten genes of Listeria monocytogenes previously identified as penicillin G-inducible was transcriptionally analyzed in the presence of 0.5 M KCl, pH 5.0 and 42 °C. This study revealed that all the genes are upregulated by osmotic stress, seven by acid stress and four by temperature stress conditions. The contribution of a gene encoding a ferritin-like protein (fri), a two-component phosphate-response regulator (phoP) and an AraC/XylS family transcription regulator (axyR) to temperature, acid and osmotic stress tolerance was further examined by analysis of nonpolar deletion mutants. This revealed that a lack of PhoP or AxyR does not affect the ability to grow under the tested stress conditions. However, the Δ fri strain showed slightly delayed growth under osmotic and clearly impaired growth under acid stress conditions, indicating an important role of the ferritin-like protein in acid stress tolerance.

Identification and expression analysis of cold and freezing stress responsive genes of Brassica oleracea

Cold and freezing stress is a major environmental constraint to the production of Brassica crops. Enhancement of tolerance by exploiting cold and freezing tolerance related genes offers the most efficient approach to address this problem. Cold-induced transcriptional profiling is a promising approach to the identification of potential genes related to cold and freezing stress tolerance. In this study, 99 highly expressed genes were identified from a whole genome microarray dataset of Brassica rapa. Blast search analysis of the Brassica oleracea database revealed the corresponding homologous genes. To validate their expression, pre-selected cold tolerant and susceptible cabbage lines were analyzed. Out of 99 BoCRGs, 43 were differentially expressed in response to varying degrees of cold and freezing stress in the contrasting cabbage lines. Among the differentially expressed genes, 18 were highly up-regulated in the tolerant lines, which is consistent with their microarray expression. Additionally, 12 BoCRGs were expressed differentially after cold stress treatment in two contrasting cabbage lines, and BoCRG54, 56, 59, 62, 70, 72 and 99 were predicted to be involved in cold regulatory pathways. Taken together, the cold-responsive genes identified in this study provide additional direction for elucidating the regulatory network of low temperature stress tolerance and developing cold and freezing stress resistant Brassica crops.

Nodule metabolism in cold stress tolerant and susceptible chickpea cultivars

Early maturing short duration cold-tolerant chickpea cultivars are being introduced to avoid yield loss from spell faced by crops. However, the biochemical basis of the low temperature stress tolerance is not known. In the present study carbon and nitrogen metabolizing enzymes in nodules along with physiological indices were measured in early maturing short duration cold- tolerant chickpea cultivars (ICCV 93929 and ICCV 88503) and in normal cold - susceptible (PBG1 and GPF2) cultivars. The higher biomass in nodules of cold-tolerant cultivars might act as a greater sink for attracting photoassimilates to fuel N2-fixation. The simultaneous increase of sucrose synthase and alkaline invertase in nodules of ICCV 93929 and ICCV 88503 at the stage corresponding to lower temperature, ensures hexose supply for meeting the energy and reducing power demands for active nitrogen fixation. The greater activity of glutamine synthetase observed in nodules of cold tolerant cultivars at stages exposed to lower temperature indicates an efficient assimilation of the symbiotically fixed nitrogen into amino acids. The total protein and amino acid contents were also higher in cold tolerant cultivars. There was a greater and more rapid dry matter accumulation in ICCV 88503 and ICCV 93929 as compared to PBG1 and GPF2 in which biomass accumulation extended up to 70 DAS. Sustainable photosynthetic efficiency and activities of carbon and nitrogen metabolizing enzymes for a longer period in ICCV 93929 and ICCV 88503 even after flowering and during the onset of pod setting indicates that period of active nitrogen fixation is extended in cold tolerant chickpea cultivars due to allocation of photosynthates for longer period. This will lead to more transfer of reduced N as amino compounds towards the shoots which will lead to more nitrogen availability to seeds and ultimately better seed filling. The molecular diversity characterized by using RAPD primers and clustering method revealed a greater similarity between cold tolerant cultivars than between the cold susceptible cultivars.

Plant-derived compatible solutes proline betaine and betonicine confer enhanced osmotic and temperature stress tolerance to Bacillus subtilis.

L-Proline is a widely used compatible solute and is employed by Bacillus subtilis, through both synthesis and uptake, as an osmostress protectant. Here, we assessed the stress-protective potential of the plant-derived L-proline derivatives N-methyl-L-proline, L-proline betaine (stachydrine), trans-4-L-hydroxproline and trans-4-hydroxy-L-proline betaine (betonicine) for cells challenged by high salinity or extremes in growth temperature. l-Proline betaine and betonicine conferred salt stress protection, but trans-4-L-hydroxyproline and N-methyl-L-proline was unable to do so. Except for L-proline, none of these compounds served as a nutrient for B. subtilis. L-Proline betaine was a considerably better osmostress protectant than betonicine, and its import strongly reduced the l-proline pool produced by B. subtilis under osmotic stress conditions, whereas a supply of betonicine affected the L-proline pool only modestly. Both compounds downregulated the transcription of the osmotically inducible opuA operon, albeit to different extents. Mutant studies revealed that L-proline betaine was taken up via the ATP-binding cassette transporters OpuA and OpuC, and the betaine-choline-carnitine-transporter-type carrier OpuD; betonicine was imported only through OpuA and OpuC. L-Proline betaine and betonicine also served as temperature stress protectants. A striking difference between these chemically closely related compounds was observed: L-proline betaine was an excellent cold stress protectant, but did not provide heat stress protection, whereas the reverse was true for betonicine. Both compounds were primarily imported in temperature-challenged cells via the high-capacity OpuA transporter. We developed an in silico model for the OpuAC-betonicine complex based on the crystal structure of the OpuAC solute receptor complexed with L-proline betaine.

Ecophysiological responses of two dominant subalpine tree species Betula albo-sinensis and Abies faxoniana to intra- and interspecific competition under elevated temperature

Seedlings of tree species Abies faxoniana and Betula albo-sinensis were grown under different competition regimes (single plant, monoculture or mixture) at ambient temperature (AT) and elevated temperature (ET) to evaluate the impact of inter- and intraspecific competition on photosynthesis capacity, N resorption efficiency, N uptake patterns, water use efficiency (foliar carbon isotope composition, δ13C) and root carbon reserve accumulation. Our results showed that ET did not have significant effects on relative height growth rate (RGRH), relative diameter growth rate (RGRD), chlorophyll fluorescence parameters (Fv/Fm, ΦPSII), light-saturated photosynthetic rate (A1400) and nitrogen uptake in A. faxoniana, but it significantly reduced the values of these parameters in B. albo-sinensis. On the other hand, RGRH of A. faxoniana was not influenced by intraspecific competition irrespective of temperature regimes, while in B. albo-sinensis intraspecific competition was severer under AT than under ET. Decreased photosynthetic capacity and reduced plant size detected in B. albo-sinensis under ET likely contribute to its low intraspecific competitive ability. However, we found positive effects of interspecific competition on A. faxoniana but negative effects on B. albo-sinensis under ET, as A. faxoniana exposed to interspecific competition showed higher RGRH, RGRD, A1400, chlorophyll fluorescence parameters, foliar δ13C, foliar N, and percentages of 15N-ammonium and 15N-nitrate recovery than did A. faxoniana exposed to intraspecific competition or no competition. The results indicate that A. faxoniana is a better competitor than B. albo-sinensis under ET. Further, A. faxoniana altered resource use patterns and had a high plasticity in its ammonium uptake in mixtures compared with monocultures under ET, while B. albo-sinensis did not change its N use pattern. In all, our results showed that high temperature stress tolerance (e.g., higher root carbon accumulation), high ability to keep carbon balance (e.g., higher water use efficiency, lower leaf respiration rate, higher Fv/Fm), as well as a better N acquisition ability make A. faxoniana a better competitor when compared to B. albo-sinensisg under ET.

Effect of Silicon on Growth and Temperature Stress Tolerance of Nephrolepis exaltata ‘Corditas’

Effect of silicon (Si) nutrition on growth and temperature stress tolerance of Nephrolepis exaltata 'Corditas' grown in a soilless substrate was examined. In vitro-grown acclimatized plantlets were transplanted into the pots containing a coir-based substrate. A nutrient solution containing 0, 50, or <TEX>$100mg{\cdot}L^{-1}$</TEX> Si was supplied through a drip-irrigation system. After 5 months of cultiv ation, S i-treated and -untreated p lants were grown at 10, 25, or <TEX>$40{\pm}1^{\circ}C$</TEX> under a 12 h photoperiod with <TEX>$530{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX> PPFD and 60% RH. After 7 days, chlorophyll content and chlorophyll fluorescence parameters were measured. Silicon nutrition had a negative effect on growth characteristics of N. exaltata 'Corditas'. However, Si-treated plants had more tolerance to temperature stress than the control plants. The Fv/Fm value was not significantly different when the plants were exposed to <TEX>$25^{\circ}C$</TEX>. However, significant difference in Fv/Fm was recorded when plants were exposed to 10 or <TEX>$40^{\circ}C$</TEX>. Thus, Fv/Fm could be used as an indicator of low and high temperature tolerance in ferns. The present study also suggests that application of Si may be used to enhance temperature tolerance of ferns.

Phenotypic diversity, population structure and stress protein-based capacitoring in populations of Xeropicta derbentina, a heat-tolerant land snail species.

The shell colour of many pulmonate land snail species is highly diverse. Besides a genetic basis, environmentally triggered epigenetic mechanisms including stress proteins as evolutionary capacitors are thought to influence such phenotypic diversity. In this study, we investigated the relationship of stress protein (Hsp70) levels with temperature stress tolerance, population structure and phenotypic diversity within and among different populations of a xerophilic Mediterranean snail species (Xeropicta derbentina). Hsp70 levels varied considerably among populations, and were significantly associated with shell colour diversity: individuals in populations exhibiting low diversity expressed higher Hsp70 levels both constitutively and under heat stress than those of phenotypically diverse populations. In contrast, population structure (cytochrome c oxidase subunit I gene) did not correlate with phenotypic diversity. However, genetic parameters (both within and among population differences) were able to explain variation in Hsp70 induction at elevated but non-pathologic temperatures. Our observation that (1) population structure had a high explanatory potential for Hsp70 induction and that (2) Hsp70 levels, in turn, correlated with phenotypic diversity while (3) population structure and phenotypic diversity failed to correlate provides empirical evidence for Hsp70 to act as a mediator between genotypic variation and phenotype and thus for chaperone-driven evolutionary capacitance in natural populations.

Temperature-stress tolerance of the fungal strain Aspergillus niger 26: physiological and ultrastructural changes

The study focuses on the morphological and physiological cell responses to oxidative stress induced by high temperature treatment in the industrially relevant fungus Aspergillus niger 26. Temperatures above 30°C lead to growth suppression and changes in morphological characteristics: decrease in the size of hyphal elements and increase in "active length" by switching from slightly branched long filaments to a multitude of branched forms containing active cytoplasm. Transmission electron microscopy of fungal cultures heated at 40°C demonstrated abnormal wavy septation with reduced amount of chitin (as shown by WGA-gold labelling), intrahyphal hyphae development, disintegration of mitochondria and extensive autolysis. Temperature-dependent decrease in the total intracellular protein content and a sharp increase (six to tenfold) in oxidatively damaged proteins were also demonstrated. Elevated temperatures caused a two and threefold increase in catalase and superoxide dismutase activities, respectively.