Acclimation of photosynthesis and respiration to simulated climatic warming in northern and southern populations of Acer saccharum: laboratory and field evidence

Physiological acclimation and genotypic adaptation to prevailing temperatures may influence forest responses to future climatic warming. We examined photosynthetic and respiratory responses of sugar maple (Acer saccharum Marsh.) from two portions of the species' range for evidence of both phenomena in a laboratory study with seedlings. A field study was also conducted to assess the impacts of temperature acclimation on saplings subjected to an imposed temperature manipulation (4 degrees C above ambient temperature). The two seedling populations exhibited more evidence of physiological acclimation to warming than of ecotypic adaptation, although respiration was less sensitive to short-term warming in the southern population than in the northern population. In both seedling populations, thermal compensation increased photosynthesis by 14% and decreased respiration by 10% in the warm-acclimated groups. Saplings growing in open-top field chambers at ambient temperature and 4 degrees C above ambient temperature showed evidence of temperature acclimation, but photosynthesis did not increase in response to the 4 degrees C warming. On the contrary, photosynthetic rates measured at the prevailing chamber temperature throughout three growing seasons were similar, or lower (12% lower on average) in saplings maintained at 4 degrees C above ambient temperature compared with saplings maintained at ambient temperature. However, the long-term photosynthetic temperature optimum for saplings in the field experiment was higher than it was for seedlings in either the 27 or the 31 degrees C growth chamber. Respiratory acclimation was also evident in the saplings in the field chambers. Saplings had similar rates of respiration in both temperature treatments, and respiration showed little dependence on prevailing temperature during the growing season. We conclude that photosynthesis and respiration in sugar maple have the potential for physiological acclimation to temperature, but exhibit a low degree of genetic adaptation. Some of the potential for acclimation to a 4 degrees C increase above a background of naturally fluctuating temperatures may be offset by differences in water relations, and, in the long term, may be obscured by the inherent variability in rates under field conditions. Nevertheless, physiologically based models should incorporate seasonal acclimation to temperature and permit ecotypic differences to influence model outcomes for those species with high genetic differentiation between regions.     

多功能清雪车单泵多马达液压系统功率分配分析

为研究多功能清雪车单泵多马达液压系统在使用流量分配器和液压变压器条件下的功率分配特性,在理论分析并建立齿轮流量分配器分流排量方程和液压变压器压力控制方程的基础上,运用液压数值分析软件AMESIM对多功能清雪车液压系统的功率分配进行了数值分析,数值分析曲线直观地显示了各马达的流量、压力、转速和转矩特征。对比数值分析结果与实测参数值,二者最大相对误差绝对值小于15.5%,且得到了多功能清雪车单泵多马达液压系统功率分配的特征值;流量分配器和液压变压器能够实现单泵多马达液压系统功率分配和有效避免功率干涉;分配功率存在负向偏移性,最大负向偏差比为-12.5%。流量分配器和液压变压器可有效地解决液压系统的功率分配和负载功率干涉问题。     

Failure to induce neoplasia in nude mice by injection of disrupted cells from continuous cell lines

Nude mice were injected subcutaneously with disrupted cells from three continuous cell lines (HeLa, NCTC clone 2472 and Morris hepatoma). No tumours were observed at either the inoculation site or in other organs taken at 35 or 90 days after injection. Live cells from one line (HeLa) produced tumours at the inoculation site after eight to 12 days.     

Natural scrapie: detection of fibrils in extracts from the central nervous system of sheep

Extracts from the cervical spinal cord and from the medulla, thalamus, cerebellum and cerebral cortex of the brains of 10 sheep, histopathologically confirmed as cases of scrapie, were examined by electron microscopy for the presence of scrapie-associated fibrils. Characteristic fibrils were observed in all the extracts except for that from the thalamus of one sheep. No fibrils were found in any extracts from three control sheep. A comparison of these results with a similar study of 22 cases of bovine spongiform encephalopathy (BSE) suggests that in cases of scrapie the area of the brain chosen for the detection of fibrils is less critical than in cases of BSE, in which fibrils are more readily extracted from areas of the brain stem.     

Cytogenetic study of bovine leukosis

Nine dairy cows aged four to eleven years were subjected to examination by chromosomal analysis. These cows had been found, by haematological examination, to suffer from leucosis. The study also covered one ten-day-old calf - heifer. The test group included two dam-daughter pairs. The animals belonged to the Black-Pied Lowland breed. The blood was sampled from vena jugularis and the karyotypes were processed and evaluated by the method after Moorhead et al. (1960), modified by Lojda et al. (1974). A list was kept for each animal. The tested animals were included in classes by the percentages of the chromosome aberrations: class I - two animals (up to 10% of aberrations), class II - seven animals (from 10% to 20% of aberrations), class III - one animal (above 20% of aberrations). Hyposomy was found in all cases, polysomy and hyperploidy in four cases. Structural aberrations were observed in nine cases, breaks being the most frequent anomalies (7 cases). Breaks on sexual chromosomes were observed in five cases, including the dam-daughter pairs; centric fusion occurred in one case and mixed aberrations in two cases.     

Pre-harvest sprouting in bread wheat (Triticum aestivum) as influenced by cytoplasmic male-sterility derived from T. Timopheevi

Summary An investigation into the inheritance of pre-harvest germination (sprouting) in male sterile wheat is described. Sprouting does not occur in material which is hand emasculated prior to anthesis, but is present in cytoplasmic male-sterile lines. Thus sprouting appears to be associated with the interaction between the T. timopheevi cytoplasm and nuclei from T. aestivum. Different T. aestivum nuclei in T. timopheevi cytoplasm produce different sprouting tendencies.     

Hereditary defects in cattle in relation to chromosome analysis

In the cytogenetic study of karyotypes of breeding bulls and cows aimed at their health and at the hereditary defects in offspring the lymphocytes from the peripheral blood from the jugular vein were employed. On the basis of the percentual evaluation of numerical and structural deviations in karyotypes the following criteria were established: the animals with deviations up to 10%--Ist class, with deviations from 10 to 20%--IInd class, with deviations over 20%--IIIrd class. From 17 breeding bulls of the first group two were included in the Ist class, twelve in the IInd class and three in the IIIrd class. From the second group, two sires belonged to the IInd class and four to the IIIrd class. Both dairy cows (mothers) that delivered calves with lethal factors, as well as the leukosis-suffering mother with daughter, were included in the IIIrd class. The chromosome analyses are given in tables.