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Water loss in a desiccation-sensitive moss resulted in destruction of chlorophyll, loss of carotenoids and increased lipid peroxidation, indicating the presence of damaging forms of activated oxygen. These effects were exaggerated when the plants were desiccated at high light intensities. During water-deprivation there was a build up of a free radical, detected in vivo, with a close correlation between molecular damage and radical accumulation. In contrast, in a desiccation-tolerant moss there was almost no indication of molecular (oxidative) damage. However a stable radical similar in type and concentration to that found in the desiccation-sensitive species accumulated, particularly under high irradiances. The stable radical appears to be one of the end-products of a process initiated by environmental stress, desiccation and high irradiance: its association with molecular damage depending on the degree to which the species is tolerant of desiccation. Identification of the radical in intact tissue from EPR and ENDOR studies, suggests that this is not a short-lived peroxy-radical but instead is relatively stable and carbon-centred.
The resurrection plant Craterostigma plantagineum tolerates an extreme loss of cellular water. Therefore this plant is being studied as model system to analyse desiccation tolerance at the molecular level. Upon dehydration, new transcripts are abundantly expressed in different tissues of the plant. One such desiccation-related nuclear gene (dsp-22 for desiccation stress protein) encodes a mature 21 kDa protein which accumulates in the chloroplasts. Sequence analysis indicates that dsp-22 is closely related to early light inducible genes (Elip) of higher plants and to a carotene biosynthesis related gene (cbr) isolated from the green alga Dunaliella bardawil. In contrast to other desiccation-related genes, light is an essential positive factor regulating the expression of dsp-22: ABA-mediated gene activation leads to the accumulation of the transcript only in the presence of light. During the desiccation process, light acts at the transcriptional and post-transcriptional levels. The implications of these different controls and the possible role of the dsp-22 protein in the desiccation/rehydration process are discussed.
The gaia hypothesis, formulated by J.E. Lovelock, asserts the composition of the reactive gases, the oxidation-reduction state and the temperature of the lower atmosphere of the planet Earth are actively regulated by the biota. Lovelock and Watson, using highly simplified mathematical models, have shown that the modulation of atmospheric temperature can be achieved by exponentially growing populations of differently colored organisms ("dark and light daisies"). It is more likely that the modulation of atmospheric gas composition is based on the colligative properties of exponentially growing mixed populations of microorganisms rather than on "daisies". Exponential growth of one population of microorganisms leads to gaseous and other metabolic products released to the environment, which favor the exponential growth of different populations, each with their own unique emissions. Extremely high densities of mixed populations of microorganisms ensue. These populations form structured microbial communities composed of members in varying states of activity. Growth potential of metabolically diverse populations most likely provides the basis for the responsiveness of the biota to changing environments. We have attempted to measure an aspect of the growth potential and diversity of one microbial community, that from a flat laminated microbial mat dominated by the cyanobacterium, Microcoleus. Microbial mat samples collected at yearly intervals between 1977 and 1982 were allowed to dry. Subsamples were revived under laboratory conditions by rewetting, and the resulting complex microbial populations were analyzed. Greater than 10(4) viable organisms per ml were estimated to be present in the desiccated samples. Only a portion of the diverse community could be characterized. There were at least 115 different types of desiccation resistant microorganisms present in these samples, primarily bacteria. However, more than a dozen types of rather uncommon fungi and protoctists were removed from naturally desiccated material. Several did not fit descriptions of previously known species or strains. Neither animals nor plants were recovered from these tiny samples. We present minimal diversity estimates for microorganisms in both the desiccated samples and the corresponding fresh laminated microbial mat community from which they were taken. We found that many organisms in laboratory samples capable of immediate growth from a desiccated state were not common components of growing mats in the field.(ABSTRACT TRUNCATED AT 400 WORDS)
First-stage larvae of pure strains of M. capillaris and N. linearis (Nematoda: Protostrongylidae) from goats were used to assess the influence of rapid desiccation on survival. M. capillaris survived desiccation of faeces better than N. linearis. The latter species was particularly susceptible to duration of storage after desiccation (0 to 10 days). Surviving larvae of desiccated batches of M. capillaris were less able to infect the land-snail Candidula intersecta. Resistance of first-stage larvae to desiccation is a key factor in infectivity and may partly account for the geographical distribution of the two species of protostrongylids.
This investigation monitored the response of established contact lens wearers using contact lenses made from Filcon 4a 77% water-content material in three different thicknesses (0.08, 0.10 and 0.12 mm) over a 6-hour period of wear under adverse environmental conditions. The results obtained showed the following. (1) In accordance with previous studies carried out with lenses of similar water content, the present lenses produced corneal desiccation staining under the challenging conditions of use. However, the staining produced was similar for all three lens thicknesses tested. (2) Corneal desiccation staining was present despite the good and stable fitting characteristics observed during the study, confirming that mechanical trauma is not a necessary cause for soft-lens-induced desiccation staining. (3) Corneal desiccation staining was associated with a rapidly destabilizing pre-lens tear film (PLTF) and a thinning lipid layer. The initial break-up of the PLTF and corneal staining were recorded with a higher incidence in the vertical quadrants than in the horizontal quadrants. The PLTF is thinnest and most unstable at the tear prism margin border, hence least efficacious at preventing evaporation. Corneal desiccation staining may be due, at least partly, to excessive evaporation at the contact lens front surface.
Total body water (TBW) determination by tritium space could be factitiously elevated by exchangeable H+ contained within water-soluble chemical configurations. Should this nonaqueous (molecular) exchangeable H+ turn out to be a large fraction of total exchangeable H+, TBW measurement by tritiated water (THO) dilution would display a systematic upward and non-random error. TBW was measured by THO dilution and subsequently by total body desiccation in 21 rats (weight 227+/-83 g, mean+/-SD). TBW was 71.38+/-2.4% by THO dilution and 70.20+/-1.5% by body desiccation. Analysis of variance of TBW vs. body weight showed a highly significant correlation both with desiccation (P less than 0.0005, r=-0.78) and dilution (P less than 0.03, r= -0.50). Convariance analysis of both methods showed no difference in slope (P greater than 0.9). There was a difference in variance (P less than 0.001) and means (P less than 0.03). Tritium space is 1.2% of body weight larger than TBW measured by desiccation. TBW measured by THO dilution gives a 1.71% overestimation of TBW as measured by desiccation. TBW measurement by THO dilution is accurate within less than 2% error. These findings have particular significance in the light of our theoretical model of the total nonaqueous exchangeable H+ in fat, protein, and carbodhydrate in the living vertebrate.
The effect of incubation temperature and pH on the hatch rate of eggs of Necator americanus, and the desiccation tolerance of the resulting infective stage-3 larvae were investigated in the laboratory under controlled conditions. Hatching did not occur below 15 C and above 35 C. A 21% hatch rate was obtained at 15 C while a 10.6% hatch rate was obtained at 35 C. The highest hatch rate (93.7%) was obtained at 30 C. The optimum pH for hatching was 6.0, but the larvae did not reach the infective stage. Incubation temperature of the eggs affected the longevity and desiccation tolerance of resultant infective larvae. Larvae hatched at 30 C and maintained at 26 C under bright fluorescent light had a 50% survival time (S50) of 4 days. In the dark or shade, the S50 for larvae raised at 30 C was 5 weeks, while that of larvae hatched at 20 C was 7 weeks. Incubation temperature also affected the desiccation tolerance of larvae. Larvae developed at 20 C were more resistant to desiccation at various relative humidity values than larvae hatched at 30 C.
Many International Standards, Reference Preparations and Reference Reagents are routinely prepared by lyophilization in the presence of 'inert' carriers followed by an extensive period of secondary desiccation. In this study we have used high-performance liquid chromatography (HPLC) to analyse the effects of lyophilization and secondary desiccation on initial degradation and subsequent stability of a model protein, insulin. Secondary desiccation was found to promote a reaction of the insulin with a carrier consisting of non-volatile buffer salts and a sugar. Secondary desiccation did not improve the stability of the insulin as determined by accelerated thermal degradation and analysis using the Arrhenius equation. We conclude that careful consideration needs to be given, on a case-by-case basis, to the selection of the procedures for the preparation of International Standards, particularly those ampouled in the absence of carrier proteins and intended for physicochemical analysis such as HPLC.
Ascospores of a strain of Saccharomyces cerevisiae Hansen were less sensitive to desiccation and heat than vegetative cells. Desiccation resistance was acquired earlier during sporulation and lost later during spore germination than heat resistance. As spores matured, resistance to both stresses increased. With the exception of the first few hours in sporulation medium, when proline appeared to be utilized, the intracellular free proline content increased during sporulation and decreased during spore germination. Not all the proline lost could be detected in the germination medium, indicating that some was metabolically utilized by the germinating spores. Since exogenous proline supplied to vegetative or sporulating cells before desiccation increased their survival, it is suggested that the high level of free proline in mature spores may protect against desiccation stress.
Previously we found that Drosophila melanogaster lines selected for increased desiccation resistance have lowered metabolic rate and behavioral activity levels, and show correlated responses for resistance to starvation and a toxic ethanol level. These results were consistent with a prediction that increased resistance to many environmental stresses may be genetically correlated because of a reduction in metabolic energy expenditure. Here we present experiments on the genetic basis of the selection response and extend the study of correlated responses to other stresses. The response to selection was not sex-specific and involved X-linked and autosomal genes acting additively. Activity differences contributed little to differences in desiccation resistance between selected and control lines. Selected lines had lower metabolic rates than controls in darkness when activity was inhibited. Adults from selected lines showed increased resistance to a heat shock, 60Co-gamma-radiation, and acute ethanol and acetic acid stress. The desiccation, ethanol and starvation resistance of isofemale lines set up from the F2s of a cross between one of the selected and one of the control lines were correlated. Selected and control lines did not differ in ether-extractable lipid content or in resistance to acetone, ether or a cold shock.
Sperm quality has been studied using different microscopic methods. Light microscopy gives similar percentages of sperm typologies (mature, immature and aberrant) as scanning electron microscope (SEM) techniques using both normal (critical-point drying) and simple desiccation techniques. Artefactual forms, which are easily recognizable, are not taken into account. The artefactual forms observed by the simple desiccation SEM method were spermatozoa with tails folded in a simple loop, and spermatozoa with short tails coiled at their extreme. The simple desiccation SEM method is a useful and rapid technique for the testing of porcine sperm quality.
Triiodothyronine (T3) and thyroxine (T4) were measured by radioimmunoassay in Pronase hydrolysates of four lots each of 1- and 2-grain tablets of desiccated thyroid (Thyroid, Armour) and thyroglobulin (Proloid, Warner-Chilcott). The methodology used was verified by studies of tablets containing known quantities of T4 and T3. One grain of desiccated thyroid contained 12 +/- 1 and 64 +/- 3 microgram (mean +/- SD) of T3 and T4 per tablet, respectively (T4/T3 molar ratio, 4.3). A 1-grain tablet of thyroglobulin contained 16 +/- 2 and 55 +/- 5 microgram of T3 and T4, respectively with a T4/T3 ratio of 2.9. Two-grain tablets generally contained twice the quantity of T3 and T4 in the 1-grain preparations. The variation in T3 and T4 content between the four lots of each tablet strength for each product was 10% or less. These estimates of T3 and T4 content are 1.5- to 2-fold greater than those previously published. This difference probably results from the more sophisticated methodology now available which does not require chromatographic separation of T3 and T4 or iodometry. Using calculations based on published estimates of T4 and T3 absorption and of the T3/T4 potency ratio, it would appear that the T3 content of desiccated thyroid and thyroglobulin provide approximately 39% and 51%, respectively, of the thyromimetic activity of these two medications.