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2.
SARAH M. AYLING 《The Annals of applied biology》1989,114(3):567-577
The effect of root-pruning on shoot growth was investigated in winter wheat growing in lysimeters. Removal of half of the root axes at the beginning of stem elongation reduced shoot dry matter, determined 1 month after pruning, by 13% and grain yield by 8%. Removal of either the seminal or nodal root system during tillering reduced shoot dry weight, measured during the growing season, by 7% and grain yield by 25%. Root-pruning had negligible, or only transient, effects on the concentration of nitrogen, phosphorus, potassium, magnesium and manganese in the shoots. The harvest index was not affected by root-pruning. 相似文献
3.
CARL R. PRATT Jr. 《The Annals of applied biology》1986,108(3):649-658
Germination of gray birch (Betula populifolia) seed collected from anthracite mine spoils in northeastern Pennsylvania was studied. Environmental conditions of the spoil banks are such that high mortality may occur at seed and germination stages because of low moisture availability and thermal stress. The mine spoil banks are harsh environments with respect to key seed germination factors: percent soil moisture as low as 1.8% and soil surface temperatures reaching 59°C. In the field, gray birch typically germinated in mid-April prior to severe environmental stress. Trends in germination success were inversely related to rising soil temperature and decreasing soil moisture availability. Although seeds were capable of survival and germination under laboratory conditions of constant temperatures in excess of 55°C, dramatic decline in germination was observed under fluctuating temperature regimes likely to be experienced in the field. No germinations occurred under fluctuating temperatures in excess of 30°C. Germinations in the field were seen to end after mid-June when substrate temperatures exceeded 30°C. 相似文献
4.
SARAH L. BALL 《The Annals of applied biology》1983,102(2):257-264
Cultivars of pearl millet were challenged by isolates of downy mildew collected from various locations in West Africa and India in order to ascertain whether variability in cultivar response was genetically or environmentally determined. Results of experiments, in Polythene tunnels which imitated tropical field conditions, were confirmed by more precise experiments in an isolation plant propagator. The most important conclusion was that variation is determined by host and pathogen genotypes. West African isolates of the pathogen were generally more pathogenic than Indian isolates. However, there were also substantial differences between two isolates collected from different host cultivars at the same location in Upper Volta. Cultivar ICH105 differentiated between West African and Indian isolates. Cultivars 700516 and MBH110 also showed differential responses between isolates. In contrast two distinct types of symptom expression were recorded and found to be characteristic of cultivar genotype, independent of pathogen isolate. The possibility that both race specific and race non-specific resistance may coexist in this little understood pathosystem is discussed and the practical implications are considered. 相似文献
5.
JAYNE A. BUFFEY SARAH E. HILL STANLEY S. BLEEHEN ANTHONY J. THODY S. MAC NEIL 《Pigment cell & melanoma research》1991,4(3):112-119
Previous work from our laboratory has shown that both cyclic AMP and calcium/calmodulin appear to be involved in the regulation of melanogenesis in murine B16 melanoma cells. In these cells as in murine Cloudman S91 cells, melanogenic responsiveness to melanocyte-stimulating hormone (MSH) varies with cell density in culture. Our objective in this study was to learn more about the intracellular systems involved in the control of melanogenesis, particularly the role played by calcium. The melanogenic response to αMSH was compared to the response to drugs affecting intracellular free calcium and calmodulin over a range of cell densities in B16F1 cells. αMSH-stimulated melanin production was extremely density-dependent but αMSH-stimulated cyclic AMP production was independent of cell density. The melanogenic response to agents that increased intracellular calcium (A23187) or inhibited intracellular calmodulin varied with cell density. A drug (TMB8) that lowered intracellular free calcium, however, increased melanogenesis independently of cell density. At high cell density it was found that an elevation in calcium decreased melanogenesis, whereas agents that reduced calcium or inhibited calmodulin activity increased melanogenesis. At low cell density, however, the inhibitory response to A23187 was lost and in some experiments even stimulated melanogenesis. These data suggest that the calcium/calmodulin signalling system has an inhibitory influence on melanogenesis, and its expression, which depends upon cell density, may also modulate the response to stimulatory agents such as αMSH. 相似文献
6.
Wintering site fidelity and movement patterns of Western Sandpipers Calidris mauri in the San Francisco Bay estuary 总被引:1,自引:0,他引:1
Western Sandpipers Calidris mauri are the most numerous shorebird species in the San Francisco Bay estuary during winter. A sample of 106 Western Sandpipers was captured in mist nets and radio-marked with 1-g transmitters to examine their wintering site fidelity and movements. Differences in distances moved, home range extent and core area size were examined by age, sex, season, site, time of day and tide. All birds remained in the south San Francisco Bay region during winter and exhibited strong site fidelity, with a mean home range of 22.0 km2 or only 8% of the study area. First-year birds had larger home ranges (26.6 ± 3.6 km2 ) than adults (17.2 ± 2.5 km2 ) in winter, but home range sizes of males and females were not significantly different in any period. Home range sizes were similar between seasons, but core areas were smaller in spring (6.3 ± 1.2 km2 ) than in early (9.6 ± 4.0 km2 ) or late (11.6 ± 1.6 km2 ) winter. Movements and home range size were similar for radio-marked birds located during day and night. The high degree of regional and local site fidelity demonstrated that the mixture of natural mud fiats and artificial salt ponds in southern San Francisco Bay provided sufficient resources for large wintering populations of Western Sandpipers. 相似文献
7.
MICHAEL H. SILVER JEAN-MICHEL FOIDART ROBERT M. PRATT 《Differentiation; research in biological diversity》1981,18(1-3):141-149
Indirect immunofluorescence has been used to study the distribution of fibronectin and collagen types I, II, and III in the developing primary and secondary palatal processes and forelimb buds of the Swiss Webster (NIH) mouse. In the palatal processes fibronectin and types I and III collagen are distributed throughout the mesenchyme. Fibronectin is present in the basement membrane, while types I and III collagen are localized in a linear, discontinuous fashion beneath the basement membrane. Fibronectin is not observed in the epithelium, including the presumptive fusion areas. In the forelimb bud these components show a similar distribution prior to chondrogenesis (early day 11). When chondrogenesis commences (late day 11 or early day 12) fibronectin and, to a lesser degree, types I and III collagen are apparently concentrated in the core mesenchyme, suggesting that fibronectin has a role in initiating chondrogenesis, perhaps by increasing cellular aggregation. Type II collagen is observed only in chondrogenic regions. The codistribution of fibronectin and types I and III collagen supports in vitro studies which indicate that cells use fibronectin to bind to collagen in the matrix. The developing chondrogenic regions appear to lose fibronectin gradually, concomitant with the appearance of type II collagen, suggesting that fibronectin is not involved in the maintenance of functional chondrocytes in their matrices. 相似文献
8.
Manipulating resource availability to assess the strength and effects of resource limitation on an animal population is relatively straightforward, and thus, common in the scientific literature. Resource quality, however, is rarely manipulated, as this requires a priori knowledge of a relationship between some measurable variation in the resource and individual preference and/or fitness. Recent research on nest‐site selection was used to inform the design of custom‐built nest‐boxes for an endangered hollow‐nester, the Gouldian finch (Erythrura gouldiae). By provisioning breeding populations with these ‘high quality’ artificial nest sites over 3 years, we experimentally investigated the strength and effects of nest‐site limitation in this species. Breeding pairs using nest‐boxes initiated nesting earlier, produced larger clutches and fledged more offspring per season than those in natural hollows. Total and mean reproductive output also increased in nest‐box provisioned sites over the duration of the study. All of these effects were predominantly driven by pairs initiating clutches earlier, potentially because of the reduced intra‐ and interspecific competition for nest sites at optimal breeding times. Our findings suggest that reproduction in wild Gouldian finch populations may be limited by the availability of high quality nest sites in the landscape, and that nest‐boxes could be used as a tool for enhancing reproduction in recovering populations. Furthermore, we conclude that resource quality is equally, if not more important than quantity when supplementing resource‐limited habitats. 相似文献
9.
Although microsatellite markers have become exceedingly popular in molecular studies of wild organisms, their development in some taxonomic groups is challenging. This is partly because of repetitive flanking sequences, which lead to the simultaneous amplification of alleles from multiple loci. Until now, these microsatellite DNA families have been considered unsuitable for population genetics studies, but here we describe our development of these repetitive flanking sequences (ReFS) as novel molecular markers. We illustrate the utility of these markers by using them to address an outstanding taxonomic question in the moth genus Schrankia. 相似文献
10.
Use of PCR for detection of subpatent infections of lizard malaria: implications for epizootiology 总被引:1,自引:0,他引:1
The estimated prevalence of a malaria parasite, Plasmodium mexicanum , of western fence lizards, Sceloporus occidentalis , was compared using two techniques: microscopic examination of blood smears, and nested PCR amplification of the 18S small subunit rRNA gene. Two sites in northern California, USA were investigated, one with known long-term high prevalence of the parasite (30% by blood smear scanning), and one with low prevalence (6%). The nested PCR readily detected very low-level infections (< 1 parasite per 10 000 erythrocytes); such infections are often subpatent by normal microscopic examination. False negatives (scored as not infected after scanning the blood smear, but found infected via PCR) were rare at both sites (4% at the high-prevalence site, 6% at the low-prevalence site). However, a greater proportion of infections was detected only by PCR at the low-prevalence site (50% vs. 9%). If 50% of the infections sustain very weak parasitaemia where lizards are rarely infected, this would accord with hypotheses that predict that parasites should reduce infection growth when transmission is uncommon. The study demonstrates that PCR is a powerful tool to detect very low-level malarial infections in vertebrate hosts, including those with nucleated erythrocytes. 相似文献