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971.
- 1. 1. Desert bees do not show significant differences in most thermal parameters; mean endothermic warm-up rates are similar to those of temperate species, with no special cooling mechanisms, and normal upper critical temperatures (unlike desert ants and beetles). Thermoregulatory abilities may however be improved.
- 2. 2. They show the whole range of possible water balance problems; small species are acutely water-stressed when foraging, but large bees suffer from excessive generation of metabolic water in flight.
- 3. 3. Activity patterns are therefore either matinal, crepuscular or bimodal; essentially desert bees avoid heat and adapt to cold desert dawns and dusks. Desert plants must be coevolved to offer appropriate rewards and match the physiological constraints on their pollinators.
- 4. 4. Endothermy in bees may have evolved primarily in arid zones, and served as a pre-adaptation for subsequent invasion of cool temperate biomes.
972.
Immunogold labeling was used to study the distribution of (1 → 3)-β-glucans and (1 → 3, 1 → 4)-β-glucans in the rice grain
during cellularization of the endosperm. At approximately 3–5 d after pollination the syncytial endosperm is converted into
a cellular tissue by three developmentally distinct types of wall. The initial free-growing anticlinal walls, which compartmentalize
the syncytium into open-ended alveoli, are formed in the absence of mitosis and phragmoplasts. This stage is followed by unidirectional
(centripetal) growth of the anticlinal walls mediated by adventitious phragmoplasts that form between adjacent interphase
nuclei. Finally, the periclinal walls that divide the alveoli are formed in association with centripetally expanding interzonal
phragmoplasts following karyokinesis. The second and third types of wall are formed alternately until the endosperm is cellular
throughout. All three types of wall that cellularize the endosperm contain (1 → 3)-β-glucans but not (1 → 3, 1 → 4)-β-glucans,
whereas cell walls in the surrounding maternal tissues contain considerable amounts of (1 → 3, 1 → 4)-β-glucans with (1 → 3)-β-glucans
present only around plasmodesmata. The callosic endosperm walls remain thin and cell plate-like throughout the cellularization
process, appearing to exhibit a prolonged juvenile state.
Received: 7 January 1997 / Accepted: 11 February 1997 相似文献
973.
Conley Michael S.; Stone Michael H.; Nimmons Michael; Dudley Gary A. 《Journal of applied physiology》1997,83(6):2105-2111
Conley, Michael S., Michael H. Stone, Michael Nimmons, andGary A. Dudley. Resistance training and human cervical muscle recruitment plasticity. J. Appl.Physiol. 83(6): 2105-2111, 1997.This studyexamined cervical neuromuscular adaptations to resistance training. TheResX group performed conventional resistance training plushead-extension exercise. Another group performed only conventional resistance training, and the control group performed no resistance exercise. Muscle use during head extension was determinedby quantifying shifts in T2 in serial-transaxial magnetic resonanceimages of the neck. ResX was the only group that showed a trainingeffect. Training decreased (P < 0.05) the cross-sectional area (CSA) of cervical muscle used to performsubmaximal head extension by 31%. This reflected a decrease(P < 0.05) in relative use of thesplenius capitis, semispinalis capitis, and semispinalis cervicis andmultifidus muscles by about one-third; their percentage of CSA showingcontrast shift was reduced from 60 to 40% on average. This sameexercise evoked no contrast shift in the levator scapulae, longissimus capitis and cervicis, and scalenus medius and anterior muscles posttraining, yet 20% or more of their CSA was engaged pretraining. The relative CSA of cervical musculature that was used to perform maximal head extension was increased(P < 0.05) 16% bytraining. The findings suggest functional redundancy ofneck musculature that can be modified by training; submaximal tasks canbe performed despite cessation of recruitment of individual muscles,yet recruitment can be increased for maximal efforts. These resultsalso suggest that neuromuscular adaptations to training require aspecific cervical exercise 相似文献
974.
Crystallization and preliminary structural analysis of Bacillus subtilis adenylosuccinate lyase, an enzyme implicated in infantile autism. 下载免费PDF全文
M. R. Redinbo S. M. Eide R. L. Stone J. E. Dixon T. O. Yeates 《Protein science : a publication of the Protein Society》1996,5(4):786-788
Adenylosuccinate lyase (ASL) from Bacillus subtilis has been crystallized and structural analysis by X-ray diffraction is in progress. ASL is a 200-kDa homotetramer that catalyzes two distinct steps of de novo purine biosynthesis leading to the formation of AMP and IMP; both steps involve the beta-elimination of fumarate. A single point mutation in the human ASL gene has been linked to mental retardation with autistic features. In addition, ASL plays an important role in the bioprocessing of anti-HIV therapeutics. B subtilis ASL, which shares 30% sequence identity and 70% sequence similarity with human ASL, has been crystallized and data to 3.3 A have been collected at 100 K. The space group is P6(1)22 or P6(5)22 with a = b = 129.4 A; the length of the c-axis varies between 275 and 290 A, depending on the crystal. An analysis of solvent content indicates a dimer in the asymmetric unit, although a self-rotation function and an analysis of native Pattersons failed to identify unambiguously the location of any noncrystallographic symmetry axes. Structure determination by isomorphous replacement is in progress. 相似文献
975.
Potent antisense oligonucleotides to the human multidrug resistance-1 mRNA are rationally selected by mapping RNA-accessible sites with oligonucleotide libraries. 总被引:13,自引:5,他引:8 下载免费PDF全文
S P Ho D H Britton B A Stone D L Behrens L M Leffet F W Hobbs J A Miller G L Trainor 《Nucleic acids research》1996,24(10):1901-1907
976.
Chorea-acanthocytosis: genetic linkage to chromosome 9q21. 总被引:2,自引:0,他引:2
J P Rubio A Danek C Stone R Chalmers N Wood C Verellen X Ferrer A Malandrini G M Fabrizi M Manfredi J Vance M Pericak-Vance R Brown G Rudolf F Picard E Alonso M Brin A H Nmeth M Farrall A P Monaco 《American journal of human genetics》1997,61(4):899-908
Chorea-acanthocytosis (CHAC) is a rare autosomal recessive disorder characterized by progressive neurodegeneration and unusual red-cell morphology (acanthocytosis), with onset in the third to fifth decade of life. Neurological impairment with acanthocytosis (neuroacanthocytosis) also is seen in abetalipoproteinemia and X-linked McLeod syndrome. Whereas the molecular etiology of McLeod syndrome has been defined (Ho et al. 1994), that of CHAC is still unknown. In the absence of cytogenetic rearrangements, we initiated a genomewide scan for linkage in 11 families, segregating for CHAC, who are of diverse geographical origin. We report here that the disease is linked, in all families, to a 6-cM region of chromosome 9q21 that is flanked by the recombinant markers GATA89a11 and D9S1843. A maximum two-point LOD score of 7.1 (theta = .00) for D9S1867 was achieved, and the linked region has been confirmed by homozygosity-by-descent, in offspring from inbred families. These findings provide strong evidence for the involvement of a single locus for CHAC and are the first step in positional cloning of the disease gene. 相似文献
977.
Cross-Polarized Magic-Angle Spinning (sup13)C Nuclear Magnetic Resonance Spectroscopic Characterization of Soil Organic Matter Relative to Culturable Bacterial Species Composition and Sustained Biological Control of Pythium Root Rot 下载免费PDF全文
M. J. Boehm T. Wu A. G. Stone B. Kraakman D. A. Iannotti G. E. Wilson L. V. Madden H. Hoitink 《Applied microbiology》1997,63(1):162-168
We report the use of a model system that examines the dynamics of biological energy availability in organic matter in a sphagnum peat potting mix critical to sustenance of microorganism-mediated biological control of pythium root rot, a soilborne plant disease caused by Pythium ultimum. The concentration of readily degradable carbohydrate in the peat, mostly present as cellulose, was characterized by cross-polarized magic-angle spinning (sup13)C nuclear magnetic resonance spectroscopy. A decrease in the carbohydrate concentration in the mix was observed during the initial 10 weeks after potting as the rate of hydrolysis of fluorescein diacetate declined below a critical threshold level required for biological control of pythium root rot. Throughout this period, total microbial biomass and activity, based on rates of [(sup14)C]acetate incorporation into phospholipids, did not change but shifts in culturable bacterial species composition occurred. Species capable of inducing biocontrol were succeeded by pleomorphic gram-positive genera and putative oligotrophs not or less effective in control. We conclude that sustained efficacy of naturally occurring biocontrol agents was limited by energy availability to this microflora within the organic matter contained in the potting mix. We propose that this critical role of organic matter may be a key factor explaining the variability in efficacy typically encountered in the control of pythium root rot with biocontrol agents. 相似文献
978.
Barbara R. Stucki Malcolm M. Dow Donald Stone Sade 《American journal of physical anthropology》1991,84(2):181-191
Differential rates of intrinsic growth for the population of Macaca mulatta on Cayo Santiago partitioned by social group and dominance rank of genealogies indicate that the potential for increase is not uniformly distributed throughout the population. In the period from 1973 to 1974, high-ranking genealogies were growing at a faster rate than low-ranking genealogies. Large differences in r among the social groups indicate the possible existence of demographic, genetic, or social differences between groups. A random resampling procedure was employed to assess the statistical significance of differences in the intrinsic rate of growth among the 5 natural social groups and the 3 partitions formed by, respectively, lumping members of high-, middle-, and low-ranking genealogies across several social groups. Comparisons among social groups shows that there are significant differences in the rate of growth between Group J and Group M, and between Group J and Group F for the period from 1973 to 1974. Among dominance ranks of genealogies, significant differences in r were found between the partitions of the high- and middle-ranking genealogies. These findings suggest that differential reproductive success is influenced and maintained by underlying variations in the distribution of behavioral traits in the population. 相似文献
979.
S. Hockaday T. A. Beddow M. Stone P. Hancock L. G. Ross 《Journal of fish biology》2000,57(4):981-1000
Truss and length measurements were made on 463 tilapia Oreochromis niloticus of known mass. These measurements were then used to build mathematical models to estimate tilapia biomass. Two different approaches were used to build the models. The first was to take some simple mathematical models, and to optimize them using least squares regression. The second approach was to build models using artificial neural network software. Models were built for two different but overlapping size ranges and both approaches were successful in creating models that estimated the total biomass to within ±1%. The truss measurements were also used to assess the principal shape components of different sized tilapia. 相似文献
980.