Nocturnal periodic breathing at altitudes of 6,300 and 8,050 m

Nocturnal periodic breathing was studied in eight well-acclimatized subjects living at an altitude of 6,300 m [barometric pressure (PB) 350-352 Torr] for 3-5 wk and in four subjects during one night at 8,050 m altitude (PB 281-285 Torr). The measurements at 6,300 m included tidal volume by inductance plethysmography, arterial O2 saturation by ear oximetry (calibrated by arterial blood samples), electrocardiogram (ECG), and electrooculogram. At 8,050 m, periodic breathing was inferred from the cyclical variation in heart rate obtained from a night-long ECG record. All subjects at 6,300 m altitude showed well-marked periodic breathing with apneic periods. Cycle length averaged 20.5 s with 7.9 s apnea. Minimal arterial O2 saturation averaged 63.4% corresponding to a PO2 of approximately 33 Torr, i.e., approximately 6 Torr lower than the normal value at rest during daytime. This was probably the most severe hypoxemia of the 24-h period. At 8,050 m altitude, the cycle length averaged 15.4 s, much longer than predicted by a theoretical model. Cyclical variations in heart rate caused by periodic breathing occurred in all subjects, but abnormal cardiac rhythms such as ventricular premature contractions were uncommon. The severe arterial hypoxemia caused by periodic breathing may be an important determinant of tolerance to these great altitudes.     

Comparison of phosphorus distribution and cycling between adjacent native semidesert shrub and cultivated grass-dominated ecosystems

Summary P concentrations at several soil profile depths and for various plant parts were monitored over most of one year in adjacent native semidesert shrub and cultivated crested wheatgrass ecosystems. When multiplied by appropriate soil bulk densities and phytomass values, it was possible to calculate P mineralomasses in these two ecotessera. Knowledge of new to old growth ratios allowed estimation of P turnover. Although there was greater P in the vegetation of the native stand, the tissues lived longer and decomposed less rapidly than those in the grass stand that has been established in a portion of the original shrub dominated semidesert. The grass stand showed higher net primary productivity and had a much higher fraction of phytomass that is consumable by livestock. There was thus, at least a five-fold greater turnover of P in the tilled and seeded system. The introduced grasses are also withdrewing more P from the soil reserves. Whether nutrient export from the systems could lead to long-term declines in productivity will require further monitoring and experimental effort.     

Specific recognition of calmodulin from Dictyostelium discoideum by the ATP, ubiquitin-dependent degradative pathway

Calmodulin purified from Dictyostelium discoideum is selectively degraded by rabbit reticulocyte extracts in the presence of ubiquitin and ATP. This protein forms a 1:1 covalent conjugate with ubiquitin. Analyses of the cyanogen bromide fragments of the protein conjugate indicate that lysine 115 on calmodulin is the ubiquitin conjugation site. Bovine brain calmodulin which contains a trimethyllysine residue at this position is not a substrate for conjugation with ubiquitin, and its degradation rate is not affected by ATP and ubiquitin. These results suggest that the trimethyllysine residue in mammalian calmodulin may function in protecting the protein from degradation by the ATP, ubiquitin-dependent pathway. Since there are eight lysine residues in Dictyostelium calmodulin, the specific conjugation of ubiquitin to lysine 115 may provide a good model system to delineate the structural features required for the conjugation and to follow the degradative steps in the pathway.     

The life history of Petrocelis franciscana

Tetraspores from Petrocelis franciscana Setch. et Gardn. collected at Rockaway Beach, San Mateo County, California, 11 January 1971 were isolated into unialgal culture with Provasoli's enriched seawater medium at 10° and 15° C, 16:8 daily photoregime, 2000–2500 lx cool white fluorescent lighting. The germlings developed as crustose discs with marginal meristems until about 300–500 µm in diameter when erect multiaxial blades were established. The erect plants grew to reproductive maturity in 15° C but not in 10° C. By the fifth month of growth the erect axes flattened and branched dichotomously. At the end of 7 months the plants were reproductively mature. These cultured plants were morphologically similar to Gigartina agardhii Setch. et Gardn. (subgenus Mastocarpus) which occurs abundantly at Rockaway Beach. Male plants were non-papillate with spermatangia forming on the entire blade surface except at the growing tip and near the stipe. The female plants developed papillae which bore many procarps. Many of these procarps were penetrated and seemingly destroyed by intrusive filaments from adjacent vegetative branches but apparently a number were functional since a number of cystocarps developed on plants in both stationary and shake culture after 5 months. Some viable spores were released and germinated.     

The auricularia-to-doliolaria transformation in two aspidochirote holothurians, Holothuria mexicana and Stichopus californicus

Abstract. The fragmentation and rearrangement of the ciliary bands that occurs during the auricularia-to-doliolaria transformation is described for the non-feeding auricularia larva of Holothuria mexicana and the more typical planktotrophic auricularia of Stichopus californicus. The ciliary band of the auricularia larva runs along a series of ridges that project from the sides of the body. Fragmentation results from a loss of ciliary band cells from the zones between the ridges. The remaining fragments then reorient, elongate, and fuse to form the 5 circumferential bands of the doliolaria. The fate of the band cells lost during this process could not be determined with certainty, but they disappear after being sequestered beneath the epithelium for a time, probably through histolysis. Cell counts indicate that significant numbers of cells are also lost from the ridges. Normal swimming ceases just before transformation begins, probably because the nerve supply to all or parts of the band is disrupted, and this may play a role in initiating morphogenesis.