Blood respiratory properties of rainbow trout,Salmo gairdneri: Responses to hypoxia acclimation and anoxic incubation of blood in vitro

Summary Blood respiratory properties of rainbow trout were determined following acclimation to normoxia and two levels of hypoxia.The most prominent response appeared to be an increase in blood O₂ affinity graded to the level of hypoxia. TheP ₅₀ values (at pH 7.8 and 20°C) were 24.1 21.7 and 16.8 mm Hg when specimens were acclimated to water O₂ tensions of 150, 80 and 50 mm Hg, respectively. The blood O₂ affinity was closely correlated with the erythrocytic ATP concentration. The stepwise correlation of ATP andP ₅₀, when trout were exposed to graded oxygen lack in the water, indicates that the blood O₂ affinity is precisely regulated.Anoxic incubation of trout blood in vitro induced a rapid reduction in erythrocytic ATP concentration (t _1/2=75 min), which was closely correlated to theP ₅₀ value. The drop inP ₅₀ value during anoxic exposure can be explained partly by the direct allosteric effect of a decreased erythrocytic ATP concentration and partly by the modified Donnan distribution of protons across the red cell membrane. Reoxygenation of the incubated blood, however, only partly re-established the erythrocytic ATP concentration, with a concurrent rise inP ₅₀ value.The results invite discussion about the mechanism, by which fish regulate their blood O₂ affinity. It is concluded, that it is regulated at the organismal rather than at the red cell level.Abbreviation (E) erythrocytes, erythrocytic     

Respiratory adaptations in carp blood influences of hypoxia, red cell organic phosphates, divalent cations and CO2 on hemoglobin-oxygen affinity

Summary This study concerns the adaptation of oxygen transporting function of carp blood to environment hypoxia, tracing the roles played by erythrocytic cofactors, inorganic cations, carbon dioxide and hemoglobin multiplicity.Carp acclimated to hypoxia ( 30 mmHg) display striking increases in blood oxygen affinity compared to normoxic ( =120–150 mm) specimens (P ₅₀'s are 3.0 and 7.0 mm, respectively, at pH 7.9 and 20°C). This correlates with a marked decrease in erythrocytic concentrations of NTP (nucleoside triphosphates) (Figs. 1, 2, Table 1), permitting investigation of the time-course of the response (Fig. 3). That GTP (guanosine triphosphate) plays a greater role than ATP in the allosteric regulation of blood oxygen affinity, follows from greater decreases in its concentration during hypoxia, and its greater effect on oxygen affinity of the hemoglobin (Figs. 1, 5). It is furthermore shown that divalent cations (which complex with NTP) inhibit the regulatory role of GTP on O₂ affinity to a lesser extent than that of ATP (Fig. 7). However, the divalent cation, Mg²⁺, occurs in similarly high concentrations in the erythrocytes of hypoxic and normoxic fish (Table 1). CO₂ specifically depresses the O₂ affinity of carp hemoglobin, but below pH 8.3, its effect is obliterated by ATP and GTP suggesting that the chains are the main sites for CO ₂ ^– binding. Four carp hemoglobin components are isolated and their oxygen-binding properties compared with those of the cofactor-free hemolysate (Figs. 4, 8, 9). The results are discussed comparatively with special reference to hemoglobin function in fish and mammals.     

Difference in the hypoxia tolerance of the round crucian carp and largemouth bass: implications for physiological refugia in the macrophyte zone

The hypoxia tolerance of larval and juvenile round crucian carp, Carassius auratus grandoculis, and largemouth bass, Micropterus salmoides, was determined using respirometry to examine the potential of hypoxic areas in the macrophyte zone as physiological refugia for round crucian carp. The tolerance, which was measured as the critical oxygen concentration (Pc), was 1.32 mg O₂/l in the round crucian carp and 1.93 mg O₂/l in the largemouth bass. As the round crucian carp tolerated hypoxia better than the largemouth bass, hypoxic areas in the macrophyte zone might function as physiological refugia for round crucian carp.     

Microspectrophotometric and scanning microphotometric studies of carp (Cyprinus carpio L.) erythrocytes

Summary Carp (Cyprinus carpio) hemoglobin readily autoxidizes in blood smears. Quantification of Soret-band absorbance in individual erythrocytes by means of scanning cytophotometry therefore requires more elaborate methods of preparation of blood samples. Of the fixatives that have been tested, suspension of whole blood in isotonic salt solutions containing glutaraldehyde was most suitable. Glutar-aldehyde-fixed red blood cells are totally resistant to hemolysis. In the course of fixation, hemoglobin is transformed to methermoglobin. Spectrophotometry indicated extensive similarities between glutaraldehyde-fixed carp methemoglobin and human methemoglobin. In aqueous solutions, the intensity of the Soret-peak was pH-dependent. The allosteric modifier organic polyphosphate caused anR↔T transition, resulting in increased molar extinctions. Dried preparations showed Soret-spectra that were not influenced from either pH or organic polyphosphate concentration of the aqueous suspensions in which the erythrocytes had been stored. The same was true for slide preparations of cyano-methemoglobin, easily derived from methemoglobin on addition of potassium cyanide. In the absence of oxygen fresh blood cells from carp slowly transform their hemoglobin into deoxyhemoglobin. Spectra of the intermediate stages of deoxygenation, Hb₄(O₂)₃, Hb₄(O₂)₂ and Hb₄(O₂), as well as mixtures of these intermediates, could be monitored.     

Changes in the respiratory properties of the blood in the carp,Cyprinus carpio, induced by diurnal variation in ambient oxygen tension

Summary Effects of diurnal variation in ambient oxygen tension on acid-base balance and blood respiratory properties were investigated in carp (Cyprinus carpio). The carp were subjected to two cycles in ambient between about 130 mm Hg and about 12 mm Hg at 17°C (cf. Figs. 1 and 2). The first period of hypoxia was characterized by a non-compensated respiratory alkalosis, i.e. whole blood showed an increase in pH from 7.92 to 8.14. During the second hypoxic period, 24 h later, a significantly smaller respiratory alkalosis was present, whole blood pH changed from 7.95 (the value found during the intermediate return to normoxia) to 8.08. The latter increase was associated with a significant increase of 25% in plasma bicarbonate concentration compared with the first period of hypoxia (Fig. 1, Table 1). The erythrocytic concentrations of hemoglobin and ATP were lowered by about 10%, compared with the normoxic values, during the two episodes of hypoxia, and this was due to a swelling of the erythrocytes during hypoxia. The red cell GTP concentration showed an altogether different change during the O₂ cycling: the absolute concentration of red cell GTP changed to a steady level, 50% below that present at the onset of the experiment and the major part of this change took place between the two hypoxic periods (Fig. 2, Table 2).The results are discussed with reference to the respiratory function of the blood of carps during subjection to cyclic changes in nature.     

Respiratory and metabolic responses of the Australian Yabby Cherax destructor to progressive and sustained environmental hypoxia

The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was assessed during progressive hypoxia and during 3 h at a water PO₂ of 1.33 kPa. The O₂ affinity of haemocyanin from C. destructor was increased by lactate (Δlog P ₅₀/Δlog[lactate] = −0.111) and by Ca (Δlog P ₅₀/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO₃ ⁻]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation, which induced a respiratory alkalosis, until the water O₂ partial pressure declined below 2.67 kPa, after which the O₂ uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O₂ affinity maintained haemolymph O₂ content during progressive hypoxia despite the normally low arterial O₂ partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O₂ saturation. The importance of regulated haemocyanin-O₂ affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O₂ requirement. Anaerobiosis became important only at very low PO₂ but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after 3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important hypoxic response but severe hypoxia may encourage the crayfish to breathe air. Accepted: 26 February 1998     

Cationic composition and acid–base state of the extracellular fluid,and specific buffer value of hemoglobin from the branchiopod crustacean <Emphasis Type="Italic">Triops cancriformis</Emphasis>

Recent insights into the allosteric control of oxygen binding in the extracellular hemoglobin (Hb) of the tadpole shrimp Triops cancriformis raised the question about the physico-chemical properties of the protein’s native environment. This study determined the cationic composition and acid–base state of the animal’s extracellular fluid. The physiological concentrations of potential cationic effectors (calcium, magnesium) were more than one order of magnitude below the level effective to increase Hb oxygen affinity. The extracellular fluid in the pericardial space had a typical bicarbonate concentration of 7.6 mM but a remarkably high CO₂ partial pressure of 1.36 kPa at pH 7.52 and 20°C. The discrepancy between this high CO₂ partial pressure and the comparably low values for water-breathing decapods could not solely be explained by the hemolymph-sampling procedure but may additionally arise from differences in cardiovascular complexity and efficiency. T. cancriformis hemolymph had a non-bicarbonate buffer value of 2.1 meq L⁻¹ pH⁻¹. Hb covered 40–60% of the non-bicarbonate buffering power. The specific buffer value of Hb of 1.1 meq (mmol heme)⁻¹ pH⁻¹ suggested a minimum requirement of two titratable histidines per heme-binding domain, which is supported by available information from N-terminal sequencing and expressed sequence tags.     

Effects of freshwater to seawater transfer on osmoregulation,acid-base balance and respiration in river migrating whitefish (Coregonus lavaretus)

Osmoregulation, acid-base balance and respiratory parameters were investigated in whitefish following transfer from freshwater to salt water. Whitefish acclimated successfully to 25 ppt brackish water but died after direct transfer to 32 ppt sea water. Transfer to brackish water induced rapid (<6 h) and permanent increases in plasma [Na⁺], [Cl^–], total [Ca] and [Mg]. The extracellular hyperosmolality effected a transient (<3 days) muscle tissue dehydration and red blood cell shrinkage. Exposure to brackish water decreased both the arterial O₂ tension and whole body O₂ uptake. The extracellular acid-base status changed from an initial respiratory acidosis at 1 h towards a pronounced metabolic acidosis at 48 h of brackish water exposure. Red cell pH_i decreased in parallel with extracellular pH_e, but the in vivo pH_i/pH_e was only 0.26, suggesting some selective protection of red cell pH_i. Plasma cortisol concentration and gill Na⁺, K⁺-ATPase activity increased after exposure to high ambient salinity, reflecting the induction of hypo-osmoregulatory mechanisms. The physiological changes in whitefish are discussed in relation to salinity-induced effects in other salmonid fishes.Abbreviations CO₂ solubility in plasma - water O₂ capacitance coefficient - BW brackish water - C _T total CO₂ content in plasma - FW fresh water - Hb hemoglobin - Hct hematocrit - M _b body mass of fish - MCHC mean cellular hemoglobin concentration - PCO₂ carbon dioxide tension - pH _e extracellular pH - pH _i intracellular pH - PO_{2 in} oxygen tension in water flowing in - PO_{2 out} oxygen tension in water flowing out - ppt parts per thousand - RBC red blood cell(s) - SW sea water - V _m water flows through chamber - OV ₂ ml O₂ consumed per kg per hour     

Substrate mobilization and hormonal changes in rainbow trout (Oncorhynchus mykiss,L.) and common carp (Cyprinus carpio,L.) during deep hypoxia and subsequent recovery

Common carp (at 20°C) and rainbow trout (at 15°C) were fitted with an indwelling cannula in the dorsal aorta. The fish were exposed to a controlled decline of waterpO₂ followed by 90 min deep hypoxia at 0.3 kPa (carp) or 4.8 kPa (trout). Thereafter, normoxic recovery was monitored in both species for 48 h. At regular intervals blood samples were analysed for glucose, lactate, free fatty acids, adrenaline, noradrenaline and cortisol. The oxygen restriction was maximal in both species and resulted in a significant increase of plasma lactate levels. In carp, adrenaline, noradrenaline and cortisol levels increased to 2, 50, and 753 ng·ml^-1 respectively during anoxia, whereas in trout these hormones increased to 12, 8 and 735 ng·ml^-1 respectively during hypoxia. In hypoxic trout, the plasma levels of glucose (3 mol·l^-1) were increased modestly whereas levels of free fatty acids (0.25 mmol·l^-1) were decreased to 0.15 mmol·l^-1. In carp, however, a marked and prolonged hyperglycaemia (from 5 to 10 mmol·l^-1) and a significant continuous depression of plasma levels of free fatty acids (from 0.4 to 0.2 mmol·l^-1) were observed indicating a difference in metabolic organization. It is suggested that hyperglycaemia is likely to be the result of hepatic glycogenolysis, stimulated by circulating catecholamines and a stimulation of gluconeogenesis by cortisol during recovery. The mechanism for the decline of plasma levels of free fatty acids is most probably a reduction of lipolytic activity, which appears to be an adaptation to hypoxia.     

The emersion response of the Australian Yabby Cherax destructor to environmental hypoxia and the respiratory and metabolic responses to consequent air-breathing

The Australian Yabby Cherax destructor voluntarily emerges from water to breathe air with increased frequency as water PO₂ decreases. When the water PO₂ declined below 2.7 kPa the crayfish spent >50% of time breathing air. The respiratory gas transport, acid-base, ionic and energetic status were quantified in simulations of this emersion behaviour to determine the benefits that the crayfish may gain from switching to air-breathing. C. destructor initially showed an elevated O₂ uptake rate on emerging from hypoxic water, but after 1 h the O₂ uptake rate was not different from that of crayfish in normoxic water. During 3 h of air breathing, subsequent to 2.7 kPa aquatic hypoxia, the haemolymph PO₂ increased while oxygen content was essentially unchanged, although cardiac output increased 5-fold. The haemolymph PCO₂ increased from 0.44 to 1.21 kPa after 3 h while the CO₂ content increased from 3.47 to 8.66 mmol · l⁻¹ and the pH decreased from 7.73 to 7.57 after 1 h in air. In air C. destructor eventually achieved an O₂ uptake rate similar to that achieved in water. A general hyperglycaemia occurred without anaerobiosis. In air-breathing C. destructor, small changes in lactate appear to offset the decrease in haemocyanin-O₂ affinity caused by acid Bohr shift. During air-breathing, decreased haemocyanin-O₂ affinity assisted in maintaining O₂ diffusion into the tissues, but the ATP content of the tail muscle decreased so that after 3 h in air the energy charge was only 0.59. The data are consistent with a specific depression of the Emden-Meyerhof pathway, preventing either lactate formation or oxidative phosphorylation in the tail muscle, despite a concomitant glycogenolysis. Accepted: 26 February 1998     

Vitreoscilla Hemoglobin (VHb) Overexpression Increases Hypoxia Tolerance in Zebrafish (Danio rerio)

Aquaculture farming may benefit from genetically engineering fish to tolerate environmental stress. Here, we used the vector pCVCG expressing the Vitreoscilla hemoglobin (vhb) gene driven by the common carp β-actin promoter to create stable transgenic zebrafish. The survival rate of the 7-day-old F₂ transgenic fish was significantly greater than that of the sibling controls under 2.5% O₂ (dissolved oxygen (DO), 0.91 mg/l). Meanwhile, we investigated the relative expression levels of several marker genes (hypoxia-inducible factor alpha 1, heat shock cognate 70-kDa protein, erythropoietin, beta and alpha globin genes, lactate dehydrogenase, catalase, superoxide dismutase, and glutathione peroxidase) of transgenic fish and siblings after hypoxia exposure for 156 h. The expression profiles of the vhb transgenic zebrafish revealed that VHb could partially alleviate the hypoxia stress response to improve the survival rate of the fish. These results suggest that that vhb gene may be an efficient candidate for genetically modifying hypoxia tolerance in fish.     

Brittle star fauna (Echinodermata: Ophiuroidea) of the arctic northwestern Barents sea: composition,abundance, biomass and spatial distribution

 Epibenthic brittle star assemblages were investigated on the northwestern Barents Sea shelf between 81° and 77°N in July 1991. At 9 drift stations in water depths between 80 and 360 m, series of 35–71 photographs, each depicting about 1 m² of the seabed, were taken along transects of about 150- to 300-m length to assess abundances and spatial distribution patterns of adult brittle stars (disc diameter ≥1 mm). Biomass values were derived by combining abundances with size-weight relationships and size frequencies established using specimens from trawl catches. Six brittle star species were identified on the seabed images. Ophiocten sericeum was the most abundant species on shallow shelf banks (≤100 m). Up to 2,800 individuals were counted on a single photograph; median abundances per station ranged from 32 to 524 ind.m^-2 and biomass from 0.3 to 5.0 g ash-free dry weight (AFDW) m^-2. The spatial distribution along the transects (i.e. on the 100-m scale) was, however, extremely patchy. Disc diameters of O. sericeum ranged between 1.6 mm and 15.4 mm. In deeper shelf habitats (>150 m), O. sericeum was rare or absent, and Ophiacantha bidentata dominated the brittle star fauna with median densities and biomasses of 2–49 ind.m^-2 and 0.07–1.9 g AFDW m^-2, respectively. Its disc diameters ranged from 2.9 to 14.4 mm. The other species (Ophiura sarsi, Ophiopholis aculeata, Ophioscolex glacialis, Ophiopleura borealis) occurred in distinctly lower numbers. Our findings provide further evidence that brittle stars dominate epibenthic communities on Arctic shelves and locally reach very high abundances. Dense beds of Ophiocten sericeum seem to be a general phenomenon on high-Arctic shallow shelf banks. Received: 30 March 1995/Accepted: 30 June 1995     

Cardiac development in crayfish: ontogeny of cardiac physiology and aerobic metabolism in the red swamp crayfish Procambarus Clarkii

The cardiovascular system performs key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval development in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25°C, 20 kPa O₂). Prior to eclosion, heart rate (ƒH) decreases significantly. Previous data suggests that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation of the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption primarily increased while egg surface area remains constant. The limited area for gas exchange of the egg membrane, in combination with the increasing oxygen demand of the embryo could result in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late stage embryos were exposed to hyperoxic water (PO₂ =40 kPa O₂). The ƒH in late stage embryos increased significantly over control values when exposed to hyperoxic water suggesting that the suppression in cardiac function observed in late stage embryos is likely due to a limited oxygen supply.     

Methemoglobin and the Activities of Catalase and Superoxide Dismutase in Nucleated Erythrocytes of Scorpaena porcus (Linnaeus, 1758) under Experimental Hypoxia (in vitro)

The effect of hypoxia on nucleated red blood cells of the black scorpionfish (Scorpaena porcus) was studied in vitro. Deep hypoxia (the oxygen concentration was less than 1 mg O₂ L^–1; the norm was 7–8 mg O₂ L^–1) led to the transition of a part of the hemoglobin molecules to the ferric state (methemoglobin). The maximum increase in the concentration of methemoglobin was 32%. The accumulation of methemoglobin in red blood cells was accompanied by an increase in the activity of catalase and superoxide dismutase and a decrease in the content of reactive oxygen species in the cytoplasm of cells. It was shown that the formation of methemoglobin did not cause damage to the cytoplasmic membranes of red blood cells. The percentage of red blood cell lysis in deoxygenated (less than 1.0 mg O₂ L^–1) suspensions quantitatively coincided with the control values.

     

Investigating the effects of opioid drugs on electrocortical activity using wavelet transform

 Fetal electrocortical activity (ECoG) is characterized by two distinct patterns: HVSA (high voltage, slow activity) and LVFA (low voltage, fast activity). Using the wavelet transform (WT), we recently reported that the frequency characteristics of these two ECoG patterns undergo significant maturational changes prior to birth (Akay et al. 1994a). We now report that fetal ECoG can also be significantly affected by pharmacological agents. In this paper, we compared the effects of two opioid drugs (morphine and [D-Pen², D-Pen⁵]enkephalin, DPDPE) on fetal ECoG, using the chronically instrumented fetal lamb model. Morphine was infused intravenously (i.v.) at 2.5 mg/h, while DPDPE was infused into the lateral cerebroventricle (i.c.v.) at 30 μg/h. The ECoG was analyzed using WT. We performed multiresolution decomposition for four sets of parameters D _{2 j} where −1<j<−4. The four series WTs represent the detail signal bandwidths: (1) 16–32 Hz, (2) 8–16 Hz, (3) 4–8 Hz, (4) 2–4 Hz. The data were subjected to statistical analysis using the Kolmogorov–Smirnov (KS) test. Both morphine and DPDPE resulted in a significant increase in power in the first wavelet band, while power was reduced in the second, third and fourth wavelet bands. In addition, both drugs resulted in a disruption of the normal cyclic pattern between the two ECoG patterns. There was a difference in the time course of action between morphine and DPDPE. This is the first occasion in which continuous ECoG has been subjected to rigorous statistical analysis. The results suggest that the WT-KS method is most suitable for quantitating changes in the ECoG induced by pharmacological agents. Received: 21 January 1994/Accepted in revised form: 15 September 1994     

Class-1 hemoglobin and antioxidant metabolism in alfalfa roots

In the course of nitric oxide (NO) scavenging, hemoglobin (Hb) turnover is linked to antioxidant metabolism and affects the cellular redox level. The influence of Hb presence on the ascorbate-glutathione cycle enzymes and the levels of H₂O₂ and ascorbate was investigated in alfalfa root cultures transformed to over-express (Hb+) or down-regulate (Hb–) class-1 Hb. Hb+ lines had substantially increased ascorbate levels as well as elevated monodehydroascorbate reductase and ascorbate peroxidase activities. Hb– lines showed significant increases in dehydroascorbate reductase and glutathione reductase activities. The observed changes in ascorbate and ascorbate-glutathione cycle enzymes were pronounced both at high (40 kPa) and low (3 kPa) O₂ pressures. Hb– lines had significantly reduced levels of the NO- and H₂O₂-sensitive enzyme, aconitase, as compared to Hb+ lines. This reduced activity was likely due the higher levels of NO in Hb– lines, as treatment of plant extracts with the NO-donor DEANO also affected aconitase activity. The H₂O₂ levels were not significantly different amongst the lines and showed no variation with change in oxygen partial pressure. In conclusion, the expression of class-1 Hb improves the antioxidant status through increased ascorbate levels and increased activity of enzymes involved in H₂O₂ removal.     

Picophytoplankton biomass, community structure and productivity in the Great Astrolabe Lagoon, Fiji

 Phytoplankton biomass, community structure and productivity of the Great Astrolabe lagoon and surrounding ocean were studied using measurements of chlorophyll concentration and carbon uptake. The contribution of picophytoplankton to biomass, productivity and community structure was estimated by size fractionation, ¹⁴C-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll <3 μm. Consequently, the percentage contribution to chl a<3 μm from each picoplankton group could be calculated using regression estimated values of ψ _i (fg chl a per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m^-3 with 45% of phytoplankton <3 μm. Primary production reached 1.3 g C m^-2 day^-1 with 53% due to phytoplankton <3 μm. Synechococcus was the most abundant group at all stations, followed by Prochlorococcus and picoeukaryotes. At all stations, Prochlorococcus represented less than 4% of the chl a <3 μm, Synechococcus between 85 and 95%, and Picoeukaryotes between 5 and 10%. In the upper 40 m of surrounding oceanic waters, phytoplankton biomass was dominated by the >3 μm size fraction. In deeper water, the <1 μm size fraction dominated. Prochlorococcus was the most abundant picoplankton group and their contributions to the chlorophyll a<3 μm were close to that of the picoeukaryotes (50% each). Accepted: 27 May 1999     

Genetic variation for in vitro sesame pollen germination and tube growth

  In vitro pollen germination and tube length studies are valuable in elucidating mechanisms (germination capacity and rate, tube growth rate) possibly associated with genetic differences in male transmission. On each of two collection dates, the percentage germination and tube length of the binucleate pollen grains from five diverse sesame (Sesamum indicum L.) genotypes were determined at eight times (30, 60, 90, 120, 150, 180, 240, 300 min) after inoculation on a semisolid medium containing 10% (100 g l^-1) sucrose (C₁₂H₂₂O₁₁), 0.4% (4 g l^-1) purified agar (Fisher Lot 914409), 0.1% (1 g l^-1) calcium nitrate [Ca(NO₃)₂ ⋅ 4H₂O] and 0.01% (100 mg l^-1) boric acid (H₃BO₃). Before heating, the pH of the medium was adjusted to 7.0 with a 0.1 N potassium hydroxide (KOH) solution. Over the five genotypes, 5% germination was found 30 min after inoculation and a maximum of 37% germination 120 min after inoculation with no significant changes thereafter. As indicated by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which germination was initiated and maximum germination attained. Over all five genotypes, the tube length was 91 μm 30 min after inoculation, reaching a maximum of 1000 μm 300 min after inoculation. As shown by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which tube length was observed and the maximum tube length was attained. Little or no relationship between percent germination and tube length was observed among the genotypes. For both percent germination and tube length, the statistical significance of collection date and its interactions with genotype and time after inoculation indicated that environment in the form of collection date was also an influencing factor. These results indicated that genetic differences among genotypes were present for in vitro germination capacity, germination rate and tube growth rate and that these factors singly or in combination could alter male transmission of genetic elements. Received: 5 February 1997 / Accepted: 23 June 1997     

Mathematical studies of the interaction of respiratory gases with whole blood II. CO2 absorption

Some progress has been made on the problem of the interaction of respiratory gases with whole blood. A working mathematical model for the O₂−CO₂ interaction phenomena has been developed from mathematical studies of the data. The Edsall-Wyman (1958) model for CO₂ absorption is improved upon in this paper by consolidating it with the O₂ absorption model developed in paper I of this set (Bernard, S. R.,Bull. Math. Biophysics,22, 391–415, 1960). This improved model assumed the effect of O₂ on CO₂ absorption is mediated through the electrical charge possessed by the hemoglobin molecule,i.e., O₂ molecules bound to hemoglobin displace protons from the hemoglobin thereby increasing the negative charge on the hemoglobin and at the same time increasing the acidity of the solution. The model is tested against the data.