The active centre of triose phosphate isomerase

1. Cystamine (2,2'-diaminodiethyl disulphide) caused an unmasking of mitochondrial adenosine triphosphatase and a leakage of Mg(2+) from the mitochondria, and decreased the stimulation of adenosine triphosphatase by 2,4-dinitrophenol. When Mg(2+) was added, cystamine potentiated the activation of adenosine triphosphatase by 2,4-dinitrophenol. 2. Cystamine was without effect on the adenosine triphosphatase of disrupted mitochondria. 3. Cystamine was moderately potent as an uncoupling agent and as an inhibitor of the [(32)P]P(i)-ATP exchange reaction. 4. Cysteamine (2-aminoethanethiol) was without the above effects, when special precautions were taken to counteract its autoxidation. 5. The effects of cystamine should probably be ascribed to its disulphide group, since the diamine cadaverine protected slightly against the loss of Mg(2+) and the decrease of 2,4-dinitrophenol-stimulated adenosine-triphosphatase activity caused by aging of the mitochondria. It is suggested that cystamine acts by a breakdown of mitochondrial permeability barriers.     

Breeding Systems of Three Tree Ferns: Alsophila firma (Cyatheaceae), Cyathea stipularis (Cyatheaceae), and Lophosoria quadripinnata (Lophosoriaceae)

Abstract Breeding-system data have been available for a large number and diverse array of angio-sperms for a relatively long time. In contrast, breeding systems of ferns and their allies (pteridophytes) have only recently been examined, and breeding-system data from natural populations of sporophytes are still lacking for pteridophytes representing many life-history strategies. Few studies, for example, have examined breeding systems of tropical pteridophytes, and no breeding-system data are available for tree ferns. We therefore examined the breeding systems of three species of tree ferns from Costa Rica, Alsophila firma (Cyatheaceae), Cyathea stipularis (Cyatheaceae), and Lophosoria quadripinnata (Lophosoriaceae) using enzyme electro-phoresis. Genetic data were used to estimate intragametophytic self-fertilization and F , the fixation index. Analysis of genetic data indicates that the gametophytes of these three species predominantly cross-fertilize; all three species would be characterized as outcrossers. However, some population-to-population variation in breeding system was detected in all three species. Outcrossing also typifies a diverse array of temperate ferns. Thus, despite the potential for self-fertilization, outcrossing appears to characterize the majority of pteridophytes representing a variety of evolutionary lineages, life-history strategies, and environments.     

Annual nitrous oxide flux and soil nitrogen characteristics in sagebrush steppe ecosystems

Soil nitrogen transformations and nitrous oxide fluxes were measured in a range of sagebrush steppe ecosystems in south-central Wyoming. Net nitrate production, measured in laboratory incubations, was highest in the ecosystem type dominated by Artemisia tridentata ssp. vaseyana, especially early in the growing season. Fluxes of nitrous oxide, measured in closed chambers and analyzed by gas chromatography, also tended to be higher in the same type, but only for short periods in the spring. Thereafter, all nitrous oxide fluxes were low and did not differ consistently among types. Estimated average annual fluxes for three Artemisia ecosystem types (dominated by Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, and Artemisia nova) were 0.32, 0.23 and 0.13 kg N₂O-N ha^–1 y^–1 repsectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N₂O-N ha^–1y^–1. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 × 10⁹ g y^–1 of N₂O-N from U.S. sagebrush steppe, and a flux of 1.1 × 10¹¹ g y^–1 of N₂0-N from analogous desert and semi-desert shrublands of the world.     

Attractiveness of the male Acheta domesticus calling song to females

1. Most crickets first demonstrated positive phonotaxis to 65 dB CSs having a 53-62 ms SP by day 3 following the imaginal molt (Fig. 3B). The onset of copulatory readiness occurred on average at 3.2 days. 2. The attractive range of SPs for most females became progressively broader as they aged (Fig. 4). Three to 4-day-old females were attracted to a smaller number of CS SPs than were 20-21 day old females (Fig. 4). 3. Older, less selective females did not typically respond to the same range of CS SPs (Fig. 6). However, they were more likely to respond to some SPs (especially 50 ms) than to others (Fig. 7). 4. The phonotactic threshold decreased from 95 dB or greater on day 0 to a mean of 55 dB by day 3, during a period of increasing JHIII biosynthesis, and thereafter remained at that level (Fig. 8). 5. During a period of maximal JHIII production, 3-5 day-old females usually responded to 4 of the 7 SPs presented (Fig. 8). Females older than 12 days were unselective for CS SP, and JHIII synthesis remained at a level below the peak production on day 4 (Fig. 8). 6. Older females, that were unselective for CS SP, became as selective as 3 to 5-day-old females within 4 days of topical application of JHIII (Figs. 9-11).     

Increased dependence on blood glucose after acclimatization to 4,300 m

To evaluate the hypothesis that altitude exposure and acclimatization result in increased dependency on blood glucose as a fuel, seven healthy males (23 +/- 2 yr, 72.2 +/- 1.6 kg, mean +/- SE) on a controlled diet were studied in the postabsorptive condition at sea level (SL), on acute altitude exposure to 4,300 m (AA), and after 3 wk of chronic altitude exposure to 4,300 m (CA). Subjects received a primed continuous infusion of [6,6-2D]glucose and rested for a minimum of 90 min, followed immediately by 45 min of exercise at 101 +/- 3 W, which elicited 51.1 +/- 1% of the SL maximal O2 consumption (VO2 max; 65 +/- 2% of altitude VO2 max). At SL, resting arterial glucose concentration was 82.4 +/- 3.2 mg/dl and rose significantly to 91.2 +/- 3.2 mg/dl during exercise. Resting glucose appearance rate (Ra) was 1.79 +/- 0.02 mg.kg-1.min-1; this increased significantly during exercise at SL to 3.71 +/- 0.08 mg.kg-1.min-1. On AA, resting arterial glucose concentration (85.8 +/- 4.1 mg/dl) was not different from sea level, but Ra (2.11 +/- 0.14 mg.kg-1.min-1) rose significantly. During exercise on AA, glucose concentration rose to levels seen at SL (91.4 +/- 3.0 mg/dl), but Ra increased more than at SL (to 4.85 +/- 0.15 mg.kg-1.min-1; P less than 0.05). Resting arterial glucose was significantly depressed with CA (70.8 +/- 3.8 mg/dl), but resting Ra increased to 3.59 +/- 0.08 mg.kg-1.min-1, significantly exceeding SL and AA values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Internal carotid flow velocity with exercise before and after acclimatization to 4,300 m.

Cerebral blood flow and O2 delivery during exercise are important for well-being at altitude but have not been studied. We expected flow to increase on arrival at altitude and then to fall as O2 saturation and hemoglobin increased, thereby maintaining cerebral O2 delivery. We used Doppler ultrasound to measure internal carotid artery flow velocity at sea level and on Pikes Peak, CO (4,300 m). In an initial study (1987, n = 7 men) done to determine the effect of brief (5-min) exercises of increasing intensity, we found at sea level that velocity [24.8 +/- 1.4 (SE) cm/s rest] increased by 15 +/- 7, 30 +/- 6, and 22 +/- 8% for cycle exercises at 33, 71, and 96% of maximal O2 uptake, respectively. During acute hypobaric hypoxia in a decompression chamber (inspired PO2 = 83 Torr), velocity (23.2 +/- 1.4 cm/s rest) increased by 33 +/- 6, 20 +/- 5, and 17 +/- 9% for exercises at 45, 72, and 98% of maximal O2 uptake, respectively. After 18 days on Pikes Peak (inspired PO2 = 87 Torr), velocity (26.6 +/- 1.5 cm/s rest) did not increase with exercise. A subsequent study (1988, n = 7 men) of the effect of prolonged exercise (45 min at approximately 100 W) found at sea level that velocity (24.8 +/- 1.7 cm/s rest) increased by 22 +/- 6, 13 +/- 5, 17 +/- 4, and 12 +/- 3% at 5, 15, 30, and 45 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Operation Everest II: preservation of cardiac function at extreme altitude

Hypoxia at high altitude could depress cardiac function and decrease exercise capacity. If so, impaired cardiac function should occur with the extreme, chronic hypoxemia of the 40-day simulated climb of Mt. Everest (8,840 m, barometric pressure of 240 Torr, inspiratory O2 pressure of 43 Torr). In the five of eight subjects having resting and exercise measurements at the barometric pressures of 760 Torr (sea level), 347 Torr (6,100 m), 282 Torr (7,620 m), and 240 Torr, heart rate for a given O2 uptake was higher with more severe hypoxia. Slight (6 beats/min) slowing of the heart rate occurred only during exercise at the lowest barometric pressure when arterial blood O2 saturations were less than 50%. O2 breathing reversed hypoxemia but never increased heart rate, suggesting that hypoxic depression of rate, if present, was slight. For a given O2 uptake, cardiac output was maintained. The decrease in stroke volume appeared to reflect decreased ventricular filling (i.e., decreased right atrial and wedge pressures). O2 breathing did not increase stroke volume for a given filling pressure. We concluded that extreme, chronic hypoxemia caused little or no impairment of cardiac rate and pump functions.     

On the role of subunit III in proton translocation in cytochromec oxidase

Mammalian mitochondrial cytochromec oxidase catalyzes the transfer of electrons from ferrocytochromec to molecular oxygen in the respiratory chain, while conserving the energy released during its electron transfer reactions by the vectorial movement of protons across the inner membrane of the mitochondrion. The protein domain that translocates the protons across the membrane is currently unknown. Recent research efforts have investigated the role of one of the transmembrane subunits of the enzyme (III,M _r 29,884) in the vectorial proton translocation reaction. The data that favor subunit III as integral in vectorial proton translocation as well as the data that support a more peripheral role for subunit III in proton translocation are reviewed. Possible experimental approaches to clarify this issue are presented and a general model discussed.     

Floral evolution and phylogeny in the tribeThelymitreae (Orchidaceae: Neottioideae)

The Australian orchid tribeThelymitreae, composed ofCalochilus, Epiblema, andThelymitra, is unique in theOrchidaceae because of the presence of a mitra or staminodal complex. Evidence from floral structure suggests thatEpiblema andThelymitra are sister genera and thatCalochilus is derived from aThelymitra ancestor. A Gene Pool Vortex model and a hypothetical phylogeny illustrate that introgressive hybridization, allopatry, and long distance dispersal have played a major role in the evolution of the tribe. Pollination and hybridization in the tribe are discussed with major emphasis on floral mimicry.     

Halimeda bioherms along an open seaway: Miskito Channel,Nicaraguan Rise,SW Caribbean Sea

A recent research cruise to examine small, detached carbonate platforms situated on the Nicaraguan Rise in the SW Caribbean Sea has revealed the presence of numerous Halimeda bioherms. Based upon interpretations from seismic reflection data some exceed 140 m in relief. This is the first documented occurrence of these green-algal buildups in the Caribbean/Bahama Bank region. The Halimeda bioherms form a nearly continuous band that borders the margins of the Miskito Channel—a shallow, open, 125 km long seaway. This 220 m deep channel bisects the Miskito Bank which is a major carbonate shelf. In seismic profile the bioherms appear acoustically soft and reveal a local relief of 20–30 m. Tops of these features lie in about 40–50 m of water. Samples from dredge hauls are coarse, poorly cemented packstones/grainstones which are dominated by largely unbroken, disarticulated Halimeda segments set in a poorly sorted sandy matrix. Exposed surfaces were stained brown. Very little living material was brought up in the dredges. The significance of these bioherms and their full extent in the Caribbean are not understood. Undoubtedly, further study will provide important answers concerning their role in the geologic development of Caribbean carbonate platforms.