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Photosynthetic gas exchange and the stable isotope composition of leaf water: comparison of a xylem-tapping mistletoe and its host 总被引:4,自引:2,他引:2
Photosynthetic gas exchange and the stable isotopic composition of foliage water were measured for a xylem tapping mistletoe, Phoradendron juniperinum, and its host tree, Juniperus osteosperma, growing in southern Utah. The observed isotopic composition of water extracted from foliage was compared to predictions of the Craig-Gordon model of isotopic enrichment at evaporative sites within leaves. Assimilation rates of juniper were higher and stomatal conductance was lower than the values observed for the mistletoe. This resulted in lower intercellular/ ambient CO2 values in the juniper tree relative to its mistletoe parasite. For mistletoe, the observed foliage water hydrogen and oxygen isotopic enrichment was less than that predicted by the model. In juniper, foliage water hydrogen isotopic enrichment was also lower than that predicted by the evaporative enrichment model. In contrast, the oxygen isotopic enrichment in juniper foliage water was slightly greater than that predicted for the evaporative sites within leaves. Hydrogen isotopic enrichment in mistletoe foliage shows systematic variation with stem segment, being highest near the tips of the youngest stems and decreasing toward the base of the mistletoe, where isotopic composition is close to that of stem water in the host tree. In a correlated pattern, mid-day stomatal conductance declined abruptly in mistletoe foliage of increasing age. 相似文献
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ABSTRACT. The cicadelloid leaf-hoppers, Eurymela distincta (Signoret) and Eurymela fenestrata (Le Pelletier & Serville), feed on the phloem sap of Eucalyptus spp. The osmotic pressure profile of haemolymph and gut fluids is consistent with a filtration mechanism based on passive osmosis. This is responsible for shunting water rapidly from foregut to hindgut in the relatively simple filter chamber. The osmotic gradient which drives the system is probably produced by active secretion of sodium and potassium into the Malpighian tubules and posterior midgut. Although the osmotic pressures in all parts of the system are higher, the mechanism is probably similar to that previously described for xylem-feeding cicadas.
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper. 相似文献
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper. 相似文献
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LAURENCE M. COOK 《Biological journal of the Linnean Society. Linnean Society of London》2007,90(1):49-53
A test has been made of the association of heterozygosity with shell breadth in the polymorphic snail Cepaea nemoralis. The material was collected by C. B. Goodhart from a series of paired sites at which individuals reached different adult breadths. Dominant phenotypes, in which a large fraction was heterozygous, had a greater breadth and lower variance than recessive phenotypes regardless of whether the measurement was of shell ground colour, banding or the double recessive vs. the rest. Most of the difference was contributed by samples from the habitat where animals reached the largest size. The result is consistent with existence of heterotic sections of chromosome that include the colour and banding loci, and may help to explain the persistence of the polymorphism. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 49–53. 相似文献
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SYNOPSIS. An examination of research on heredity in the yearsbetween Mendel's scientific work and his multiple rediscovery(approximately 18501900) suggests that at the turn ofthe century the elucidation of the mechanism of the transmissionof hereditary traits from parent to offspring was inevitable.By 1900, a variety of different investigators were either attackingthe problem of genetic transmission directly and successfully,or were examining specific aspects of the issue. However, itappears that the identity of analysis used by Mendel and byhis rediscoverers was primarily the result of the latter allfollowing Mendel's formulation. Had Mendel not been rediscovered,the "Laws of Heredity" would likely have been formulated quitedifferently, and been discovered and refined over a period oftime rather than all being discovered and given their finalform at the very outset. 相似文献
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Kirk, W W., Davies, H. V. and Marshall, B. 1985. The effectof temperature on the initiation of leaf primordia in developingpotato sprouts.J. exp. Bot. 36: 16341643. Initiation of leaf primordia in potato sprouted out of soilin light was an asymptotic function of thermal time and thebase temperature for the process was 3.6 °C. The parametervalues of the asymptotic function were universal for cv. MarisPiper. The estimated rate of leaf primordium initiation decreasedlinearly from 0.033 leaf pnmordia (K day)1 when abouteight leaf primordia were present to zero after a maximum numberof 24 leaf primordia had been initiated. The decrease in rateof development with increasing number of primordia may be dueto depletion of mother tuber resources. The transition of theapex from a vegetative to a reproductive state was not the factorlimiting the initiation of additional leaf primordia. Key words: Potato, Solanum tuberosum L., leaf primordia initiation, temperature, thermal time, development 相似文献
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Reiteration and Clustering of DNA Sequences Complementary to Histone Messenger RNA 总被引:23,自引:0,他引:23
The DNA complements of 9S messenger RNA thought to code for histones in sea urchins are reiterated, closely clustered, relatively stable in evolution and development and potentially separable from other nuclear DNA. 相似文献