Ultrastructural changes and proliferation of pituicytes in mouse posterior lobe during water deprivation and rehydration

Ultrastructural changes and proliferation of pituicytes during water deprivation and rehydration were studied in the posterior lobe of C57BL/Tw mice. Deprivation for 3 days brought about a significant increase in the number of electron-dense bodies (lysosomes) in pituicyte perikarya and their processes. The frequency of pituicytes enclosing neurosecretory axons in their cytoplasm significantly decreased as compared with that of the controls. 12-hour rehydration following deprivation for 3 days induced extensive development of rough endoplasmic reticulum and Golgi apparatus and an increase in frequency of neurosecretory axons enwrapped by pituicyte cytoplasm. However, at 2 days of rehydration the morphology of pituicytes was no more different from that of the controls. Mitotic figures of pituicytes were not encountered throughout the deprivation period of 6 days, but rehydration for 12 h and 1, 2, or 3 days following deprivation for 3 or 6 days was effective in eliciting an increase in mitotic activity. The present results indicate that pituicytes in the mouse posterior lobe are intimately related with the secretory mechanism of neurosecretory material from the neurosecretory axons and that the proliferation of pituicytes is stimulated in conditions of reaccumulation of neurosecretory material.     

Growth hormone and prolactin response to rehydration during exercise: effect of water and carbohydrate solutions

The effect of progressive rehydration with either water or a carbohydrate solution on the plasma growth hormone (GH) and prolactin (PRL) response to exercise was examined together with plasma somatostatin. Five subjects underwent four 3-h experimental sessions at 36 degrees C in which 25-min exercise periods alternated with 5-min rest periods. The sessions were conducted without fluid replacement (DH) or under rehydration with either water or isosmotic carbohydrate solutions AISO (acid) or NISO (neutral). The fluid was given every 10 min after the 1st h of exercise. Plasma GH increased significantly (p less than 0.01) under DH after 2 and 3 h of exercise; this increase was prevented by rehydration with water, AISO and NISO. Plasma glucose was significantly higher following AISO and NISO rehydration compared with DH. This possibly influenced the GH response, but there was no difference between plasma glucose levels under DH and water rehydration at any time. The solutions tended to attenuate the increase in heart rate, rectal temperature and plasma cortisol, suggesting that the lack of GH response under rehydration conditions is a result of decreasing physiological stress levels. The GH response could not be explained by plasma somatostatin, which tended to decline in all sessions. Plasma PRL did not increase in any of the sessions, confirming that exercise without rehydration is a more potent stimulator of GH than of PRL. It is concluded that progressive rehydration with water is sufficient to prevent the exercise-induced increase in plasma GH.     

Seasonal, diurnal and rehydration-induced variation of pressure-volume relationships in Pseudotsuga menziesii

Seasonal and diurnal variation and rehydration effects of pressure-volume parameters in Pseudotsuga menziesii (Mirb.) Franco from a plantation in central Pennsylvania, USA, were evaluated during May-September, 1989. Predawn elastic modulus was lowest in overwintering and newly expanded shoots in May and June, respectively, whereas predawn osmotic potentials at full and zero turgor were lowest in May and in early September, following an August drought. Seasonal variation in predawn relative water content at zero turgor was highly correlated with increases and decreases in elastic modulus and osmotic potential. Diurnal osmotic adjustment resulted in nearly constant turgor pressure, despite decreases in bulk shoot water potential. Elastic modulus decreased diurnally on 1 August and increased on 3 September. Decreases in osmotic potential and/or elastic modulus on 24 June and 1 August lowered the relative water content at zero turgor. Plateaus in pressure-volume data caused by excess apoplastic water, were present in 67% of naturally rehydrated shoots and in all of the shoots artificially rehydrated for 3, 6, 12 and 24 h, and they increased in volume with rehydration time. Plateaus represented 80–95% of the excess apoplastic water lost during pressure-volume analysis. Correcting for plateaus via linear regression had no significant effect on osmotic potential at full turgor; however, uncorrected elastic modulus and relative water content at zero turgor were often significantly lower than the plateau-corrected values, particularly in artificially rehydrated shoots. Plateau-corrected osmotic potential at full turgor and osmotic potential at zero turgor were significantly higher in most artificially rehydrated shoots than in those naturally rehydrated as the result of loss of symplastic solutes. Corrected elastic modulus decreased following 12 and 24 h of rehydration and corrected relative water content at zero turgor increased in as little as 3 h of rehydration. These results indicate that seasonal and diurnal patterns of tissue-water parameters in Pseudotsuga menziesii vary with plant phenology and drought conditions, and that the length of rehydration period is an important consideration for pressure-volume studies.     

The stimulatory effect of the organic sulfur supplement, mercaptopropane sulfonic acid on cellulolytic rumen microorganisms and microbial protein synthesis in cattle fed low sulfur roughages

Two metabolism trials (experiments 1 and 2) were conducted to examine the effect of the organic S compound, sodium 3-mercapto-1-propane sulfonic acid (MPS) on feed intake, fiber digestibility, rumen fermentation and abundance of cellulolytic rumen microorganisms in cattle fed low S (<0.11%) roughages. Urea was provided in all treatments to compensate for the N deficiency (<0.6%) in the roughages. In experiment 1, steers (333 ± 9.5 kg liveweight) were fed Angleton grass (Dicanthium aristatum) supplemented with S in equivalent amounts as either MPS (6.0 g/day) or sodium sulfate (9.56 g/day). Supplementation of Angelton grass with either sulfate or MPS resulted in an apparent increase in flow of rumen microbial protein from the rumen. Sulfur supplementation did not significantly change whole tract dry matter digestibility or intake, even though sulfate and MPS supplementation was associated with an increase in the relative abundance of the fibrolytic bacteria Fibrobacter succinogenes and anaerobic rumen fungi. Ruminal sulfide levels were significantly higher in the sulfate treatment, which indicated that the bioavailability of the two S atoms in the MPS molecule may be low in the rumen. Based on this observation, experiment 2 was conducted in which twice the amount of S was provided in the form of MPS (8.0 g/day) compared with sodium sulfate (6.6 g/day) to heifers (275 ± 9 kg liveweight) fed rice straw. Supplementation with MPS compared with sulfate in experiment 2 resulted in an increase in concentration of total volatile fatty acids, and ammonia utilization without a change in feed intake or whole tract fiber digestibility even though S and N were above requirement for growing cattle in both these treatment groups. In conclusion, supplementation of an S deficient low-quality roughage diet with either MPS or sodium sulfate, in conjunction with urea N, improved rumen fermentation, which was reflected in an increase in urinary purine excretion. However, MPS appeared to have a greater effect on stimulating short-chain fatty acid production and ammonia utilization when provided at higher concentrations than sulfate. Thus, the metabolism of MPS in the rumen needs to be investigated further in comparison with inorganic forms of S as it may prove to be more effective in stimulating fermentation of roughage diets.     

Moisture distribution and texture of spaghetti rehydrated under different conditions

Dried spaghetti was rehydrated to its optimal cooking state, known as al dente, at 60, 80, and 100 °C, in distilled water or 0.1, 1.0, and 2.0 mol/L sodium chloride solutions. Then, the moisture distributions and stress–strain curves were examined to identify the major factors governing the texture of rehydrated spaghetti. The difference in moisture content between the inner and peripheral regions of rehydrated spaghetti and its breaking stress were greater at higher rehydration temperatures; however, rehydration temperature did not affect breaking strain. The sodium chloride concentration of the immersion solution did not affect moisture distribution or breaking stress, while breaking strain was decreased by rehydration at higher sodium chloride concentrations. The results obtained in this study suggest that moisture distribution within spaghetti and its material properties govern its breaking stress and strain, respectively.     

Effect of Zinc Source on Performance, Zinc Status, Immune Response, and Rumen Fermentation of Lactating Cows

Two experiments were conducted to examine the effect of zinc (Zn) source on the performance, Zn status, immune response, and rumen fermentation of lactating cows to find the most available Zn source for dairy production. In Experiment 1, a total of 30 multiparous Holstein cows were randomly allocated by body weight and milk yield to one of five treatments in a completely randomized design. Cows were fed a total mixed ration (TMR) with no Zn addition (containing 37.60 mg?Zn/kg TMR by analysis), and the basal TMR supplemented with 40 mg?Zn/kg TMR from either Zn sulfate or one of three organic Zn chelates with weak (Zn-AA W), moderate (Zn-Pro M), or strong (Zn-Pro S) chelation strengths, respectively for 55 days. In Experiment 2, the in vitro rumen fermentation method was used in a completely randomized design involving a 4?×?3 factorial arrangement of treatments. The four Zn sources were the same as those used in Experiment 1, and the three supplemental Zn levels in the rumen fluid were 0, 10, and 20 μg/mL, respectively. The feed intake, milk composition, and somatic cell count (SCC) were unaffected (P?>?0.05) by treatments. However, the milk yield was increased (P?<?0.05) by addition of Zn from both the Zn-AA W and Zn-Pro S. Plasma Zn level at the end of the experiment was increased (P?<?0.05) by addition of Zn from all three organic sources. Serum antibody titers on day 21 after vaccination with foot and mouth disease (FMD) vaccine were increased (P?<?0.05) by both supplemental Zn-AA W and Zn-Pro S. The organic Zn sources with different chelation strengths supplemented at the added Zn level of 10 μg/mL were more effective (P?<?0.05) in improving the rumen fermentation than Zn sulfate, with the most effective being Zn-AA W. In conclusion, Zn source had no influence on the feed intake, milk composition, and SCC; however, both the Zn-AA W and Zn-Pro S were more effective than Zn-Pro M and Zn sulfate in enhancing the rumen fermentation, Zn status, and humoral immune response as well as improving milk yield of lactating cows. The improved milk production might be attributed to the improved rumen fermentation, Zn status, and immune function.     

Rehydration with glycerol: endocrine, cardiovascular, and thermoregulatory responses during exercise in the heat.

The impact of rehydration with glycerol on cardiovascular and thermoregulatory responses during exercise in the heat was studied in eight highly trained male cyclists. Each subject completed three dehydration-rehydration experimental trials that differed only in the rehydration treatment, each separated by 7 days. Before each experimental day, subjects dehydrated to -4% of their body weight by exercise and water restriction. The experimental treatments were as follows: no fluid (NF), glycerol bolus (1 g/kg body wt) followed by water (G), and water alone (W). Rehydration (3% body weight) was given over an 80-min period. After rehydration, subjects cycled (74% peak O2 uptake) to exhaustion in a hot and wet (37 degrees C and 48% relative humidity) environment. For G, plasma volume was expanded (P < 0.05) during rehydration and remained higher than W (P < 0.05) during exercise. Exercise time to exhaustion during G (33 +/- 4 min) was longer (P < 0.05) compared with both W (27 +/- 3 min) and NF (19 +/- 3 min). Cutaneous vascular conductance was significantly elevated (P < 0.05) during G, but G provided no other thermoregulatory or cardiovascular benefits compared with W and NF. Fluid-regulating hormones (vasopressin, aldosterone, atriopeptin, and plasma renin activity) decreased during rehydration and increased during exercise (except atriopeptin), but there were no differences between G and W. These data indicated that glycerol had little or no major effect on fluid-regulating factors during rehydration or exercise, and the improved exercise capacity in G was likely due to a greater plasma volume during exercise.     

Effect of chronic hypernatremic dehydration and rapid rehydration on brain carbohydrate, energy, and amino acid metabolism in weanling mice

Abstract: This is a study of the effects of chronic hypernatremic dehydration and rehydration on carbohydrate, energy, and amino acid metabolism in the brains of weanling mice. Chronic hypernatremic dehydration induced by 4 days of water deprivation and salt loading was associated with severe weight loss (no other observed clinical effects), increased brain Na⁺ levels, and a decreased brain water content. Changes in the concentrations of brain glucose, glycolytic and citric acid cycle metabolic intermediates, and phosphocreatine were compatible with reduced cerebral metabolic rate. In adaptation to chronic hypernatremia, there was a significant increase in the content of the measured brain amino acids. Rapid rehydration over a 4-h period with 2.5% dextrose in water returned plasma Na⁺ levels and brain Na⁺ and water contents to normal. After rehydration, metabolites were altered in a manner consistent with increased fluxes through the glycolytic pathway and citric acid cycle; the brain glycogen content almost tripled. Brain taurine and glutamine levels were not lowered by rehydration, and the total content of the measured amino acids in brain was still significantly higher than in controls. We speculate that these metabolic perturbations may relate to the development of cerebral edema and seizures or coma following rapid rehydration of humans with chronic hypernatremic dehydration.     

Concurrent measurements of stem density, leaf and stem water potential, stomatal conductance and cavitation on a spaling of Thuja occidentalis L.

Abstract Concurrent estimates of stem density, leaf and stem water potential, stomatal conductance and ultrasonic acoustic emissions (cavitations) in an excised sapling of Thuja occidentalis L. were made. As the sapling dehydrated in air, the decline in leaf water potential to about - 2.0 MPa was followed by apparent rehydration of the foliage while the stem showed no sign of rehydration. The rate of acoustic emissions peaked prior to the onset of rehydration which coincided with virtual stomatal closure. There was a significant decline in stem density until maximum foliage rehydration level was reached. From this point, leaf water potential, stem water potential and stem density continued a relatively slow decline while acoustic emission rate and stomatal conductance remained low. Removal of the bark and majority of foliage from the sapling resulted in increased cavitation and more rapid deelines in leaf and stem water potential and stem density.     

Cut-shoot vs root rehydration: Effects on pressure-volume analysis of shoots and fascicles of Pinus resinosa seedlings

Two methods of rehydrating red pine ( Pinus resinosa Ait.) shoots for pressure-volume (PV) analysis were compared to clarify the effects of rehydration on estimated tissue water relations of shoots and fascicles. The commonly employed cut-shoot method was compared to rehydration by means of water uptake through the roots of intact plants. Cut-shoot rehydration and increased duration of rehydration significantly decreased estimates of tissue elasticity and relative water content at zero turgor for both shoots and fascicles. Rehydration of cut shoots for 2 days significantly increased the slope of the linear region of shoot pressure-volume (PV) curves and decreased estimates of the apoplastic water fraction. Changes in these and estimates of other water relations attributes were correlated with increased initial water content during rehydration. Estimated apoplastic water fraction was higher for needle fascicles than shoots despite the large amount of woody stem tissue contained in shoots. Fascicle water status strongly influenced shoot water relations, in part due to apparent apoplastic loading with water of fascicles during rehydration.     

Fate of Bacteria in Chicken Meat During Freeze-Dehydration, Rehydration, and Storage

Total plate counts were determined on boneless cooked, cubed chicken meat obtained from a commercial processor. Survival of the natural flora was determined after the meat was freeze-dehydrated and rehydrated at room temperature for 30 min and 50, 85, and 100 C for 10 min. Total counts of bacteria in the rehydrated samples were determined during storage of the meat at 4, 22, and 37 C until spoilage odor was detectable. Meat samples were inoculated with Staphylococcus aureus, then dried, rehydrated, and stored at the same temperatures. Numbers of surviving organisms in the inoculated samples were determined with use of both selective and nonselective media. Representative genera surviving the various rehydration treatments were determined. Approximately 32% of the bacteria in the meat survived during dehydration and rehydration at room temperature. Many numbers and types of vegetative bacteria also survived rehydration at 50 C. When meat was rehydrated at 85 or 100 C, the initial count was less than one per gram. The only organisms isolated from samples rehydrated at 85 or 100 C were of the genus Bacillus. S. aureus in inoculated samples survived dehydration and rehydration at 60 C. Storage of all rehydrated samples at 4 C gave a good shelf life (18 or more days). The study indicates that freeze-dehydrated meat should be produced with adequate microbiological control and that such meat should be rehydrated in very hot water.     

Incorporation of N from intravenously administered 15N labelled urea into the bacterial protein in the sheep.

The experiment carried out on two wethers demonstrated that nitrogen of intravenously injected urea, labelled with 15N was incorporated into total and bacterial nitrogen fraction of the digesta flowing through the rumen and duodenum. The amount of 15N in the bacterial fraction flowing throught the rumen and duodenum was relatively low in comparison with the amount of 15N in the total nitrogen (14,8% and 8,1% in the rumen and 6,6% and 7,9% in the duodenum. The ratio of the amount of bacterial-N to total-N in the rumen content (12,7 and 7,5%) was only slightly lower than the ratio of bacterial 15N to total 15N. In the duodenum this ratio was a little higher (8,7 and 10,0%). Blood urea nitrogen was utilized only partly in biosynthesis of bacterial protein. The results showed that only a small amount of blood urea nitrogen retained in the organism was utilized for microbial protein synthesis and the majority in some different way.     

Prompt response of superoxide dismutase and peroxidase to dehydration and rehydration of the resurrection plant <Emphasis Type="Italic">Haberlea rhodopensis</Emphasis>

The relic endemic nature of Haberlea rhodopensis, which grows in Balkan Peninsula, in combination with its high vegetative desiccation-tolerance, makes this species a good model to study mechanisms behind plant adaptation to severe drought stress. The aim of this study was to evaluate the antioxidant protection provided by Superoxide dismutase (SOD) and Peroxidase (PO) in H. rhodopensis after exposure to and recovery from dehydration at different developmental stages. During dehydration the electrolyte leakage from leaf tissue increased more significantly in post-flowering plants than in flowering plants, while upon subsequent rehydration this parameter showed a very fast decrease to the basic value of fresh leaves and did not depend on developmental stage. Like other higher plant species, SOD and PO demonstrated in H. rhodopensis an ability to adjust their activity very promptly to changing water supply. In addition, the leaves of this resurrection species retained significant activities of SOD and PO even in air-dried state, considered as the most severe form of water stress. The enhanced activity of antioxidant enzymes may either enable the scavenging of the active oxygen species produced at very severe water deficit, and/or carry a potential for resurrection on subsequent rehydration. Upon stress treatment total activities of both enzymes were higher in flowering than post-flowering plants which reveals that developmental stage might be a factor affecting plant stress tolerance. This work identified for the first time SOD isoforms of H. rhodopensis. Native PAGE showed at least six multiple isoforms in the protein extract from leaf tissue of flowering plants, and the differential visualization revealed that four of them were Cu, Zn-SOD isoforms, one was Mn-SOD and one Fe-SOD. These findings provide a good starting point for future study of the SOD gene family of this rare resurrection plant at the molecular level.     

The physiological basis of adaptation in goats to harsh environments

Goat living in harsh environments represents a climax in the capacity of domestic ruminants to adjust to such areas. This ability is multifactorial: low body mass, and low metabolic requirements of goats can be regarded as an important asset to them for it minimise their maintenance and water requirements, in areas where water sources are widely distributed and food sources are limited by their quantity and quality. An ability to reduce metabolism allows goats to survive even after prolonged periods of severe limited food availability. A skillful grazing behaviour and efficient digestive system enable goats to attain maximal food intake and maximal food utilisation in a given condition. There is a positive interaction between the better recycling rate of urea and a better digestion of such food in desert goats. The rumen plays an important role in the evolved adaptations by serving as a huge fermentation vat and water reservoir. The water stored in the rumen is utilised during dehydration, and the rumen serves as a container, which accommodates the ingested water upon rehydration. The rumen, the salivary glands and the kidney coordinately function in the regulation of water intake and water distribution following acute dehydration and rapid rehydration. Goats in the tropics, when possible, eat a diet composed of tree-leaves and shrubs (browse), which ensure a reliable and steady supply of food all year around, albeit, from a low to medium quality food. Some of the physiological features of ruminants defined as intermediate feeders like large salivary gland, the large absorptive area of their rumen epithelium, and the capacity to change rapidly the volume of the foregut in response to environmental changes are most likely responsible for the goat’s superior digestion capacity.     

Comparison among the effects of oral,intraperitoneal and intravenous fluid-loading on kidney function and drinking in goats

The effects of hyperhydration, induced by oral loading via a stomach tube (41 of 0.9% NaCl within 2–3 min), intra-peritoneal and intra-jugular infusions (41 of 0.9% NaCl solution at a rate of 21 hr⁻¹) in normally hydrated goats, on fluid retention, plasma expansion, kidney function and drinking response were compared. Higher fluid retention (67 and 65% vs. 40% at 3 hr after the termination of the infusion, P < 0.01), attenuated diuretic (P < 0.01) and natriuretic (P < 0.01) responses and lower expansion of plasma volume (P < 0.05) were recorded in the orally and intra-peritoneally treated goats in comparison with the intra-jugularly treated animals. Portal expansion apparently induces acceleration of saliva secretion which recycles water to the gut. Recycling of water to the gut reduced excessive expansion of plasma fluid and load on the kidney. Retention of water in the rumen satiated the urge to drink in the orally and intra-peritoneally treated goats for at least 24 hr. The intra-jugularly treated goats consumed a significant amount of water (11), which was approximately half of their normal requirement. Under arid conditions, these responses are appropriate to the animals' regular exposure to severe dehydration and rapid rehydration.     

Fluid balance in exercise dehydration and rehydration with different glucose-electrolyte drinks

After exercise dehydration (3% of body weight) the restoration of water and electrolyte balance was followed in 6 male subjects. During a 2 h rest period after exercise, a drink of one of four solutions was given as 9 X 300 ml portions at 15 min intervals: control (C-drink), high potassium (K-drink), high sodium (Na-drink) or high sugar (S-drink). An exercise test (submaximal and supramaximal work) was performed before dehydration and after rehydration. Dehydration reduced plasma volume by 16%, a process reversed on resting even before fluid ingestion began, due to release of water accumulated in the muscles during exercise. After 2 h rehydration, plasma volume was above the initial resting value with all 4 drinks. The final plasma volumes after the Na-drink (+14%) and C-drink (+9%) were significantly higher than after the K- and S-drinks. The Na-drink favoured filling of the extracellular compartment, whereas the K- and S-drinks favoured intracellular rehydration. In spite of the higher than normal plasma volume after rehydration, mean heart rate during the submaximal test was 10 bpm higher after rest and rehydration than in the initial test, and was not different between the drinks. The amount of work which could be performed in the supramaximal test (105% VO2max) was 20% less after exercise dehydration and subsequent rest and rehydration than before. This reduction was similar for all drinks, and may be due to a decreased muscle glycogen content (70% of initial) at the time of the second test.     

Water relations of the pine exine

BACKGROUND AND AIMS: Water adhesion forces, water absorption capacity and permeability of the pine exine were investigated to consider a possible function of sporopollenin coatings in the control of water transport. METHODS: The experiments were carried out with sporopollenin capsules obtained from pine pollen consisting of an empty central capsule and two sacci. Changes in the concentration of excluded dextran molecules in the medium were analysed to quantify water absorption by purified exine fragments and the osmotic volume flow out of the intact central capsule. KEY RESULTS: The contact angle of sporopollenin to water is higher than the one to ethanol and lower than the one to n-heptane. The water-filled pore space in pine sporopollenin amounts to only 20.6 % of the matrix volume. A monosaccharide was excluded from 15 % and a trisaccharide from about 38 % of this space. Shrinkage of the central capsule induced by permeable osmotica was transient, whereas that induced by sodium polyacrylate (2100 g mol(-1)) was stable. Values obtained for the hydraulic conductance L(P) of the exine (0.39-0.48 microm s(-1) MPa(-1)) are comparable in size to those of biomembranes. Sodium sulfate solutions induced a significant osmotic flow through the exine (reflection coefficient at least 0.6). The exine around the central capsule can be ruptured by equilibration of its lumen with a concentrated electrolyte solution and subsequent transfer to water. The denatured protoplast along with the intact intine was ejected when pollen grains were subjected to this osmotic shock treatment. CONCLUSIONS: The pine exine is easily wetted with water and does not represent a significant barrier to water exchange either liquid or gaseous. Through osmotic burst, it can be separated from the intine. The effect of salts and small solute molecules on water fluxes may be functionally significant for rehydration upon pollination.     

PHOTOSYNTHETIC INSENSITIVITY OF THE TERRESTRIAL CYANOBACTERIUM NOSTOC FLAGELLIFORME TO SOLAR UV RADIATION WHILE REHYDRATED OR DESICCATED1

Photosynthetic performance of the terrestrial cyanobacterium Nostoc flagelliforme (M. J. Berkeley et M. A. Curtis) Bornet et Flahault during rehydration and desiccation has been previously characterized, but little is known about the effects of solar UV radiation (280–400 nm) on this species. We investigated the photochemical activity during rehydration and subsequent desiccation while exposing the filamentous colonies to different solar radiation treatments. Photochemical activity could be reactivated by rehydration under full‐spectrum solar radiation, the species being insensitive to both ultraviolet‐A radiation (UVAR; 315–400 nm) and ultraviolet‐B radiation (UVBR). When the rehydrated colonies were exposed for desiccation, the effective PSII photochemical yield was inhibited by visible radiation (PAR) at the initial stage of water loss, then increased with further decrease in water content, and reached its highest value at the water content of 10%–30%. However, no significant difference was observed among the radiation treatments except for the moment when they were desiccated to critical water content of about 2%–3%. At such a critical water content, significant reduction by UVBR of the effective quantum yield was observed in the colonies that were previously rehydrated under indoor light [without ultraviolet radiation (UVR)], but not in those reactivated under scattered or direct solar radiation (with UVR), indicating that preexposure to UVR during rehydration led to higher resistance to UVR during desiccation. The photosynthetic CO₂ uptake by the desiccated colonies was enhanced by elevation of CO₂ but was not affected by both UVAR and UVBR. It increased with enhanced desiccation to reach the maximal values at water content of 40%–50%. The UV‐absorbing compounds and the colony sheath were suggested to play an important role in screening harmful UVR.     

Movement of water within the body of sheep fed at maintenance under thermoneutral conditions

Two mature Border Leicester x Merino wethers were maintained with continuous feeding under thermoneutral conditions. Their water balance was recorded for 2 weeks; at the beginning of each week they were given a dose of tritiated water (TOH) into the pulmonary artery or the rumen and samples were taken from both the pulmonary artery and the rumen. A four-compartment model was developed which simultaneously fitted the balance and tracer data. The half-time of TOH in body water was 6.7 days for one sheep and 7.6 days for the other; TOH space was about 55% of liveweight in both sheep. The bidirectional flux of water between the plasma-accessible compartment and 'bound' intracellular water averaged 45 litres per hour and that between plasma-accessible water and rumen water averaged 3.2 litres per hour. The mean residence times of a water molecule in the rumen were, for the two sheep, 60 and 63 min and the time constants for flow from the rumen were 12.3 and 13.4 h. Consideration of the rumen water balance suggested that there was net movement of water from the rumen to the plasma at about 200 ml/h; diffusion accounted for 86% of the influx to and 92% of the efflux from the rumen.