Chapter 6 Effects of Sugars on the Stability and Structure of Lipid Membranes During Drying

Effect of Five Different Antioxidants on the Effectiveness of Goat Semen Cryopreservation

The effective combination of semen cryopreservation and artificial insemination has a positive effect on the conservation of germplasm resources, production and breeding, etc. However, during the process of semen cryopreservation, the sperm cells are very susceptible to different degrees of physical, chemical, and oxidative stress damage. Oxidative damage is the most important factor that reduces semen quality, which is affected by factors such as dilution equilibrium, change of osmotic pressure, cold shock, and enzyme action during the freezing-thawing process, which results in the aggregation of a large amount of reactive oxygen species (ROS) in sperm cells and affects the quality of semen after thawing. Therefore, the method of adding antioxidants to semen cryoprotective diluent is usually used to improve the effect of semen cryopreservation. The aim of this experiment was to investigate the effects of adding five antioxidants (GLP, Mito Q, NAC, SLS, and SDS) to semen cryoprotection diluent on the cryopreservation effect of semen from Saanen dairy goats. The optimal preservation concentrations were screened by detecting sperm viability, plasma membrane integrity, antioxidant capacity, and acrosomal enzyme activities after thawing, and the experimental results were as follows: the optimal concentrations of GLP, Mito Q, NAC, SLS, and SDS added to semen cryopreservation diluent at different concentrations were 0.8 mg/mL, 150 nmol/L, 0.6 mg/mL, 0.15 mg/ mL, 0.6 mg/mL, and 0.15 mg/mL. The optimal concentrations of the five antioxidants were added to the diluent and analyzed after 1 week of cryopreservation, and it was found that sperm viability, plasma membrane integrity, and mitochondrial activity were significantly enhanced after thawing compared with the control group (P < 0.05), and their antioxidant capacity was significantly enhanced (P < 0.05). Therefore, the addition of the above five antioxidants to goat sperm cryodilution solution had a better enhancement of sperm cryopreservation. This study provides a useful reference for exploring the improvement of goat semen cryoprotection effect.

Membrane permeabilizers enhance biofortification of Brassica microgreens by interspecific transfer of metabolites from tea (Camellia sinensis)

Interspecific metabolite transfer (ISMT) is a novel approach for plants biofortification. In this study, the effect of tea (Camellia sinensis; Cs), with or without membrane permeabilizers EDTA and Tween, as a donor plant on broccoli, cauliflower and kale sprouts was investigated. As a result, caffeine- and catechin-enriched broccoli, cauliflower and kale microgreens were produced. Kale sprouts were most permeable for catechins from Cs, while cauliflower was most permeable for caffeine. Cs + EDTA significantly increased vitamin C in broccoli and kale. Among the tested enzymes activity, pancreatic lipase was the most affected by the treatment with broccoli and cauliflower biofortified with Cs or Cs combined with permeabilizers. Broccoli sprouts biofortified with Cs most significantly inhibited α-amylase, while those biofortified with Cs combined with permeabilizers most significantly inhibited α-glucosidase. Results point to ISMT combined with membrane permeabilizers as a promising and eco-friendly biofortification strategy to improve the biopotential of Brassica microgreens.

Assessing the Role of Selected Osmolytes in Mediterranean High-Mountain Specialists

Despite the constraining weight of summer drought over plant life which distinguishes Mediterranean high-mountains, and its anticipated exacerbation under the current climate crisis, there is still little knowledge of the underlying drought-endurance mechanisms in Mediterranean high-mountain species, such as osmolyte accumulation. To fill this gap, we studied the role of two of the most frequent osmoregulators in plants, proline and osmotically active carbohydrates (OAC), as pointers of the drought-stress response in seven high-mountain plant species representative of the high-mountain plant communities in Central Spain, along an elevation gradient. Overall, our results are consistent with the escalation of summer drought and suggest the involvement of osmolytes to sustain plant activity in these specialists during the growing season. Proline content showed a steadily increasing pattern in line with the seasonal aggravation of summer drought. The significant rise in mean proline in most species, coinciding with the periods with the greatest decline in soil water content, suggests the recurrent role of proline in the drought-stress response in the studied specialists. The lack of significant differences between elevations and the minimal seasonal variations in the OAC content suggest a fixed OAC content independent of functional type to sustain metabolic functions under summer drought. Moreover, these findings allow inferring the action of both OAC and proline as osmoregulators, allowing to support plant functions in these specialists under atypically dry conditions. Overall, our findings are consistent with proline as a major osmoprotectant strategy over OAC buildup in these specialists, which may be related to an adaptation strategy associated with the briefness of the growing season and the incidence of less favorable conditions in Mediterranean high-mountains.

Excipient selection for thermally stable enveloped and non-enveloped viral vaccine platforms in dry powders

Two enveloped viral vectors, vesicular stomatitis virus and influenza virus, and a non-enveloped viral vector, human adenovirus type 5, were encapsulated by spray drying to enhance thermal stability.Results with these candidates led to the hypothesis that stability performance of chosen excipients may be less virus-specific, as previously postulated in the literature, and more differentiated based on whether the virus has a lipid envelope. Spray dried samples were characterized for their thermal properties, RNA viability and in vitro viral activity after storage at 37 °C for up to 30 days or at 45 °C for up to 3 days. The enveloped viral vectors, as a group, were more thermally stable in trehalose while the non-enveloped viral vector showed higher activity with mannitol as the primary excipient in blends. Trehalose shows strong hydrogen bonds with the envelope's lipid membrane than the other carbohydrates, more effectively replacing water molecules while maintaining the fluidity of the membrane. Conversely, the small size of mannitol molecules was attributed to the more effective hydrogen bonding between water and the protein capsid of non-enveloped viral vectors. In all cases, a matrix with high glass transition temperature contributed to thermal stabilization through vitrification. This work suggests that carbohydrate stabilizer selection may be more dependent on the envelope rather than the specific viral vector, which, if universally true, will provide a guideline for future formulation development.

Induced, Imprinted, and Primed Responses to Changing Environments: Does Metabolism Store and Process Information?

Metabolism is the system layer that determines growth by the rate of matter uptake and conversion into biomass. The scaffold of enzymatic reaction rates drives the metabolic network in a given physico-chemical environment. In response to the diverse environmental stresses, plants have evolved the capability of integrating macro- and micro-environmental events to be prepared, i.e., to be primed for upcoming environmental challenges. The hierarchical view on stress signaling, where metabolites are seen as final downstream products, has recently been complemented by findings that metabolites themselves function as stress signals. We present a systematic concept of metabolic responses that are induced by environmental stresses and persist in the plant system. Such metabolic imprints may prime metabolic responses of plants for subsequent environmental stresses. We describe response types with examples of biotic and abiotic environmental stresses and suggest that plants use metabolic imprints, the metabolic changes that last beyond recovery from stress events, and priming, the imprints that function to prepare for upcoming stresses, to integrate diverse environmental stress histories. As a consequence, even genetically identical plants should be studied and understood as phenotypically plastic organisms that continuously adjust their metabolic state in response to their individually experienced local environment. To explore the occurrence and to unravel functions of metabolic imprints, we encourage researchers to extend stress studies by including detailed metabolic and stress response monitoring into extended recovery phases.

Functional characterization of galactinol synthase and raffinose synthase in desiccation tolerance acquisition in developing Arabidopsis seeds

Raffinose family oligosaccharides (RFOs) accumulate during seed development, and have been thought to be associated with the acquisition of desiccation tolerance (DT) by seeds. Here, comprehensive approaches were adopted to evaluate the changes of DT in developing Arabidopsis seeds of wild type, overexpression (OX-AtGS1/GS2/RS5), and mutant lines by manipulating the expression levels of the GALACTINOL SYNTHASE (GS) and RAFFINOSE SYNTHASE (RS) genes. Our results indicate that seeds of the double mutant (gs1, gs2) and rs5 delayed the timing of DT acquisition as compared to wild type. Subsequent detection confirmed that seeds from OX-AtGS1/GS2 plants with high levels of galactinol, raffinose, and stachyose, and OX-AtRS5 plants possess more raffinose and stachyose but less galactinol compared to wild type. These lines all showed greater germination percentage and shorter time to 50% germination after desiccation treatment at 11 and 15 days after flower (DAF). Further analysis revealed that the role of RFOs is time limited and mainly affects the middle stage (9-16 DAF) of seed development by enhancing seed viability and the ratio of GSH to GSSH in cells, but there is no significant difference in DT of mature seeds. In addition, RFOs could reduce damage to seeds caused by oxidative stress. We conclude that GALACTINOL SYNTHASE and RAFFINOSE SYNTHASE play important roles in DT acquisition during Arabidopsis seed development, and that galactinol and RFOs are crucial protective compounds in the response of seeds to desiccation stress.

In Concert: Orchestrated Changes in Carbohydrate Homeostasis Are Critical for Plant Abiotic Stress Tolerance

The sessile lifestyle of higher plants is accompanied by their remarkable ability to tolerate unfavorable environmental conditions. This is because, during evolution, plants developed a sophisticated repertoire of molecular and metabolic reactions to cope with changing biotic and abiotic challenges. In particular, the abiotic factors light intensity and ambient temperature are characterized by altering their amplitude within comparably short periods of time and are causative for onset of dynamic plant responses. These rapid responses in plants are also classified as 'acclimation reactions' which differ, due to their reversibility and duration, from non-reversible 'adaptation reactions'. In this review, we demonstrate the remarkable importance of stress-induced changes in carbohydrate homeostasis of plants exposed to high light or low temperatures. These changes represent a co-ordinated process comprising modifications of (i) the concentrations of selected sugars; (ii) starch turnover; (iii) intracellular sugar compartmentation; and (iv) corresponding gene expression patterns. The critical importance of these individual processes has been underlined in the recent past by the analyses of a large number of mutant plants. The outcome of these analyses raised our understanding of acclimation processes in plants per se but might even become instrumental to develop new concepts for directed breeding approaches with the aim to increase abiotic stress tolerance of crop species, which in most cases have high stress sensitivity. The latter direction of plant research is of special importance since abiotic stress stimuli strongly impact on crop productivity and are expected to become even more pronounced because of human activities which alter environmental conditions rapidly.

Effects of flavonol glycosides on liposome stability during freezing and drying

Flavonoids are a large and diverse group of plant secondary metabolites that are mainly present as glycosides. They are often accumulated in response to abiotic stresses such as UV radiation, drought, cold and freezing. The most extensively studied function of flavonoids is their antioxidant activity although their importance as antioxidants in plants has been questioned. We therefore aim to study effects of flavonols on cellular stress tolerance that are independent of their antioxidant function. Here we investigate the effects of the glycosylated flavonols kaempferol-3-O-glucoside, kaempferol-7-O-glucoside, quercetin-3-O-glucoside and quercetin-3-O-rhamnoside on liposome stability after freezing and drying. Insertion of flavonols in lipid bilayers destabilized egg phosphatidylcholine (EPC) liposomes and to a lesser extent vesicles made from equal proportions of EPC and egg phosphatidylethanolamine (EPE) during a freeze-thaw cycle, while liposomes containing the unsaturated non-bilayer lipid 18:2 PE were either unaffected or slightly stabilized. In general, the kaempferol derivatives were more destabilizing for liposomes during freezing than the quercetin derivatives. Fourier-transform infrared spectroscopy revealed that all flavonols were localized in the interfacial region of the lipid bilayers, forming H-bonds with the lipid phosphate and carbonyl groups. The phase transition temperature of dry 16:0/18:1 PC (POPC) and POPC/EPE liposomes was decreased by 75°C and 55°C, respectively. Changes in the vibration bands attributed to the phenolic ring structures of the flavonols in the presence of liposomes provided further evidence of interactions of these molecules in particular with the interfacial region of the bilayers.

Wheat stem reserves and salinity tolerance: molecular dissection of fructan biosynthesis and remobilization to grains

Fructan accumulation and remobilization to grains under salinity can decrease dependency of the wheat tolerant cultivar on current photosynthesis and protect it from severe yield loss under salt stress. Tolerance of plants to abiotic stresses can be enhanced by accumulation of soluble sugars, such as fructan. The current research sheds light on the role of stem fructan remobilization on yield of bread wheat under salt stress conditions. Fructan accumulation and remobilization as well as relative expression of the major genes of fructan metabolism were investigated in the penultimate internodes of 'Bam' as the salt-tolerant and 'Ghods' as the salt-sensitive wheat cultivars under salt-stressed and controlled conditions and their correlations were analyzed. More fructan production and higher efficiency of fructan remobilization was detected in Bam cultivar under salinity. Up-regulation of sucrose: sucrose 1-fructosyltransferase (1-SST) and sucrose: fructan 6-fructosyltransferase (6-SFT) (fructan biosynthesis genes) at anthesis and up-regulation of fructan exohydrolase (1-FEH) and vacuolar invertase (IVR) genes (contributed to fructan metabolism) during grain filling stage and higher expression of sucrose transporter gene (SUT1) in Bam was in accordance with its induced fructan accumulation and remobilization under salt stress. A significant correlation was observed between weight density, WSCs and gene expression changes under salt stress. Based on the these results, increased fructan production and induced stem reserves remobilization under salinity can decrease dependency of the wheat tolerant cultivar on current photosynthesis and protect it from severe yield loss under salt stress conditions.

Interactions of the amphiphiles arbutin and tryptophan with phosphatidylcholine and phosphatidylethanolamine bilayers in the dry state

BACKGROUND

Water is essential for life, but some organisms can survive complete desiccation, while many more survive partial dehydration during drying or freezing. The function of some protective molecules, such as sugars, has been extensively studied, but much less is known about the effects of amphiphiles such as flavonoids and other aromatic compounds. Amphiphiles may be largely soluble under fully hydrated conditions, but will partition into membranes upon removal of water. Little is known about the effects of amphiphiles on membrane stability and how amphiphile structure and function are related. Here, we have used two of the most intensively studied amphiphiles, tryptophan (Trp) and arbutin (Arb), along with their isolated hydrophilic moieties glycine (Gly) and glucose (Glc) to better understand structure-function relationships in amphiphile-membrane interactions in the dry state.

RESULTS

Fourier-transform infrared (FTIR) spectroscopy was used to measure gel-to-liquid crystalline phase transition temperatures (Tm) of liposomes formed from phosphatidylcholine and phosphatidylethanolamine in the presence of the different additives. In anhydrous samples, both Glc and Arb strongly depressed Tm, independent of lipid composition, while Gly had no measurable effect. Trp, on the other hand, either depressed or increased Tm, depending on lipid composition. We found no evidence for strong interactions of any of the compounds with the lipid carbonyl or choline groups, while all additives except Gly seemed to interact with the phosphate groups. In the case of Arb and Glc, this also had a strong effect on the sugar OH vibrations in the FTIR spectra. In addition, vibrations from the hydrophobic indole and phenol moieties of Trp and Arb, respectively, provided evidence for interactions with the lipid bilayers.

CONCLUSIONS

The two amphiphiles Arb and Trp interact differently with dry bilayers. The interactions of Arb are dominated by contributions of the Glc moiety, while the indole governs the effects of Trp. In addition, only Trp-membrane interactions showed a strong influence of lipid composition. Further investigations, using the large structural diversity of plant amphiphiles will help to understand how their structure determines the interaction with membranes and how that influences their biological functions, for example under freezing or dehydration conditions.

Mobilization of reserves and germination of seeds of Erythrina velutina Willd. (Leguminosae - Papilionoideae) under different osmotic potentials

Some environmental factors, including water availability, may influence seed germination. This study investigated the germination of E. velutina seeds submitted to different osmotic potentials and mobilization of reserves during water-stress. Scarified seeds were arranged in paper rolls and soaked in solutions of Polyethylene Glycol (PEG) prepared in osmotic potentials 0.0, -0.2, -0.4, -0.6, and -0.8 MPa and kept into a seed germinator, at 25 °C, and 12/12 h photoperiod (L/D), during 10 days. The percentage, mean time, mean speed, germination speed index; as well as the germination uniformity coefficient were assessed. During germination process the total soluble sugars, reducing sugars, soluble protein, and total amino acids were quantified in the cotyledon, hypocotyl and radicle of soaked seeds and cotyledons of quiescent seeds (control). There was influence of osmotic potential on E. velutina seed germination. The germination percentage remained at high levels until -0.6 MPa and above this osmotic potential there has been no germination. The mobilization of stored reserves of carbon and nitrogen in E. velutina seeds was also influenced by water-stress. There was sensitiveness between -0.2 and -0.6 MPa; however, the degradation and the mobilization of reserves was slower when the osmotic potential decreased.

Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state

BACKGROUND

Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (HII) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.

RESULTS

Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to HII transition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.

CONCLUSIONS

This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

Predicting Arabidopsis freezing tolerance and heterosis in freezing tolerance from metabolite composition

Heterosis, or hybrid vigor, is one of the most important tools in plant breeding and has previously been demonstrated for plant freezing tolerance. Freezing tolerance is an important trait because it can limit the geographical distribution of plants and their agricultural yield. Plants from temperate climates increase in freezing tolerance during exposure to low, non-freezing temperatures in a process termed 'cold acclimation'. Metabolite profiling has indicated a major reprogramming of plant metabolism in the cold, but it has remained unclear in previous studies which of these changes are related to freezing tolerance. In the present study, we have used metabolic profiling to discover combinations of metabolites that predict freezing tolerance and its heterosis in Arabidopsis thaliana. We identified compatible solutes and, in particular, the pathway leading to raffinose as crucial statistical predictors for freezing tolerance and its heterosis, while some TCA cycle intermediates contribute only to predicting the heterotic phenotype. This indicates coordinate links between heterosis and metabolic pathways, suggesting that a limited number of regulatory genes may determine the extent of heterosis in this complex trait. In addition, several unidentified metabolites strongly contributed to the prediction of both freezing tolerance and its heterosis and we present an exemplary analysis of one of these, identifying it as a hexose conjugate.

Fructan and its relationship to abiotic stress tolerance in plants

Numerous studies have been published that attempted to correlate fructan concentrations with freezing and drought tolerance. Studies investigating the effect of fructan on liposomes indicated that a direct interaction between membranes and fructan was possible. This new area of research began to move fructan and its association with stress beyond mere correlation by confirming that fructan has the capacity to stabilize membranes during drying by inserting at least part of the polysaccharide into the lipid headgroup region of the membrane. This helps prevent leakage when water is removed from the system either during freezing or drought. When plants were transformed with the ability to synthesize fructan, a concomitant increase in drought and/or freezing tolerance was confirmed. These experiments indicate that besides an indirect effect of supplying tissues with hexose sugars, fructan has a direct protective effect that can be demonstrated by both model systems and genetic transformation.

Heterosis in the freezing tolerance, and sugar and flavonoid contents of crosses between Arabidopsis thaliana accessions of widely varying freezing tolerance

Heterosis is defined as the increased vigour of hybrids in comparison to their parents. We investigated 24 F(1) hybrid lines of Arabidopsis thaliana generated by reciprocally crossing either C24 or Col with six other parental accessions (Can, Co, Cvi, Ler, Rsch, Te) that differ widely in their freezing tolerance. The crosses differed in the degree of heterosis for freezing tolerance, both in the non-acclimated state and after a 14 d cold acclimation period. Crosses with C24 showed more heterosis than crosses with Col, and heterosis was stronger in acclimated than in non-acclimated plants. Leaf content of soluble sugars and proline showed more deviation from mid-parent values in crosses involving C24 than in those involving Col, and deviations were larger in acclimated than in non-acclimated plants. There were significant correlations between the content of different sugars and leaf freezing tolerance, as well as between heterosis effects in freezing tolerance and sugar content. Flavonoid content and composition varied between accessions, and between non-acclimated and acclimated plants. In the crosses, large deviations from the mid-parent values in the contents of different flavonols occurred, and there were strikingly strong correlations between both flavonol content and freezing tolerance, and between heterosis effects in freezing tolerance and flavonol content.

Plant fructans in stress environments: emerging concepts and future prospects

Plants are sessile and sensitive organisms known to possess various regulatory mechanisms for defending themselves under stress environments. Fructans are fructose-based polymers synthesized from sucrose by fructosyltransferases (FTs). They have been increasingly recognized as protective agents against abiotic stresses. Using model membranes, numerous in vitro studies have demonstrated that fructans can stabilize membranes by direct H-bonding to the phosphate and choline groups of membrane lipids, resulting in a reduced water outflow from the dry membranes. Inulin-type fructans are flexible random-coiled structures that can adopt many conformations, allowing them to insert deeply within the membranes. The devitrification temperature (T(g)) can be adjusted by their varying molecular weights. In addition, above T(g) their low crystallization rates ensure prolonged membrane protection. Supporting, in vivo studies with transgenic plants expressing FTs showed fructan accumulation and an associated improvement in freezing and/or chilling tolerance. The water-soluble nature of fructans may allow their rapid adaptation as cryoprotectants in order to give optimal membrane protection. One of the emerging concepts for delivering vacuolar fructans to the extracellular space for protecting the plasma membrane is vesicle-mediated, tonoplast-derived exocytosis. It should, however, be noted that natural stress tolerance is a very complex process that cannot be explained by the action of a single molecule or mechanism.

Protection of liposomes against fusion during drying by oligosaccharides is not predicted by the calorimetric glass transition temperatures of the dry sugars

Sugars play an important role in the desiccation tolerance of most anhydrobiotic organisms. It has been shown in previous studies that different structural families of oligosaccharides have different efficacies to interact with phospholipid headgroups and protect membranes from solute leakage during drying. Here, we have compared three families of linear oligosaccharides (fructans (inulins), malto-oligosaccharides, manno-oligosaccharides) for their chain-length dependent protection of egg phosphatidylcholine liposomes against membrane fusion. We found increased protection with chain length up to a degree of polymerization (DP) of 5 for malto-oligosaccharides, and a decrease for inulins and manno-oligosaccharides. Differential scanning calorimetry measurements showed that for all sugars the glass transition temperature (T_g) increased with DP, although to different degrees for the different oligosaccharide families. Higher T_g values resulted in reduced membrane fusion only for malto-oligosaccharides below DP5. Contrary to expectation, for inulins, manno-oligosaccharides and malto-oligosaccharides of a DP above five, fusion increased with increasing T_g, indicating that other physical parameters are more important in determining the ability of different sugars to protect membranes against fusion during drying. Further research will be necessary to experimentally define such parameters.

Effects of cholesterol on dry bilayers: interactions between phosphatidylcholine unsaturation and glycolipid or free sugar

Cholesterol and other sterols are important components of biological membranes and are known to strongly influence the physical characteristics of lipid bilayers. Although this has been studied extensively in fully hydrated membranes, little is known about the effects of cholesterol on the stability of membranes in the dry state. Here, we present a Fourier transform infrared spectroscopy study on the effects of cholesterol on the phase behavior of dry liposomes composed of phosphatidylcholines with different degrees of fatty acid unsaturation or of mixtures of phosphatidylcholine with a plant galactolipid. In addition, we have analyzed the H-bonding of cholesterol, galactose, and a combination of the two additives to the P=O and C=O groups in dry phosphatidylcholine bilayers. The data indicate a complex balance of interactions between the different components in the dry state and a strong influence of fatty acid unsaturation on the interactions of the diacyl lipids with both cholesterol and galactose.

Extender osmolality and sugar supplementation exert a complex effect on the cryopreservation of Iberian red deer (Cervus elaphus hispanicus) epididymal spermatozoa

We have carried out two experiments to study the cryobiology of red deer epididymal spermatozoa and to improve freezing extenders: (1) effect of extender (Tris-citrate-fructose) osmolality (300-600 mOsm/kg), and (2) effect of sugar (0.4M) supplementation to the extender (no sugar, glucose, fructose, mannose, sucrose, maltose, threalose and raffinose). Sperm quality was assessed pre-freezing, post-thawing, and after 2h at 37 degrees C post-thawing: sperm motility index (SMI), acrosome integrity and membrane integrity (HOS test) were assessed subjectively; mitochondrial activity (JC-1) and membrane stability (merocyanine 540) were assessed by flow cytometry. In experiment 2, DNA status was assessed using acridine orange and flow cytometry. To find an optimal osmolality, we fitted the data to a quadratic curve. Four hundred Osmolal per kilogram rendered better results pre-freezing and post-thawing. However, post-thawing viability and most parameters after 2h incubation fitted a linear model. Osmolalities above 425 mOsm/kg were deleterious (P<0.05). In experiment 2, fructose had a positive effect respect to control after 2h of incubation at 37 degrees C post-thawing. Di and trisaccharides were deleterious. Trehalose showed impaired DNA status after 2h incubation. In conclusion, the osmolality of the extenders should be around 400 mOsm/kg, although the change from quadratic to lineal may indicate a complex effect that must be further studied. Monosaccharides may enhance red deer epididymal sperm cryopreservation, especially fructose, whereas di and trisaccharides may not be adequate.