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991.
992.
Guoqing Liu Huan Lin Xiaoduan Tang Kevin Bergler Xinwei Wang 《Journal of visualized experiments : JoVE》2014,(83)
The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including conductive, semi-conductive or nonconductive one-dimensional structures. This technique broadens the measurement scope of materials (conductive and nonconductive) and improves the accuracy and stability. If the sample (especially biomaterials, such as human head hair, spider silk, and silkworm silk) is not conductive, it will be coated with a gold layer to make it electronically conductive. The effect of parasitic conduction and radiative losses on the thermal diffusivity can be subtracted during data processing. Then the real thermal conductivity can be calculated with the given value of volume-based specific heat (ρcp), which can be obtained from calibration, noncontact photo-thermal technique or measuring the density and specific heat separately. In this work, human head hair samples are used to show how to set up the experiment, process the experimental data, and subtract the effect of parasitic conduction and radiative losses. 相似文献
993.
Different Responses of Plant Growth and Antioxidant System to the Combination of Cadmium and Heat Stress in Transgenic and Non-transgenic Rice 总被引:1,自引:0,他引:1
A comparative study of just cadmium (Cd) or heat and their combination treatments on some physiological parameters and the antioxidant systems in transgenic rice ( Oryza sativa L. cv. Zhonghua No.11) carrying glutathione-S-transferase (GST, EC. 2.5.1.18) and catalase1 (CAT1, EC. 1.11.1.6) and non-transgenics was conducted. The results revealed improved resistance in the transgenics to Cd and the combined Cd and heat stress than non-transgenics. Data showed that the activities of CAT, GST, superoxide dismutase (EC.1.15.1.1) and all components of the ascorbate-glutathione cycle measured in the stressed transgenics shoots are significantly different from those of non-transgenics. Results indicated that co-expression of GST and CAT1 had an important effect on the antioxidant system, in particular, the whole ascorbate-glutathione cycle. The less oxidative damage induced by Cd and the stress combination in the transgenics resulted not only from the GST and CAT1 transgene but also from the coordination of the whole ascorbate-glutathione cycle. 相似文献
994.
More intense, more frequent, and longer heat-waves are expected in the future due to global warming, which could have dramatic ecological impacts. Increasing nitrogen (N) availability and its dynamics will likely impact plant responses to heat stress and carbon (C) sequestration in terrestrial ecosystems. This field study examined the effects of N availability on plant response to heat-stress (HS) treatment in naturally-occurring vegetation. HS (5 d at ambient or 40.5 ℃) and N treatments (±N) were applied to 16 1 m2 plots in restored prairie vegetation dominated by Andropogon gerardii (warm-season C4 grass) and Solidago canadensis (warm-season C3 forb). Before, during, and after HS, air, canopy, and soil temperature were monitored; net CO2 assimilation (Pn), quantum yield of photosystem Ⅱ (φPsⅡ), stomatal conductance (gs), and leaf water potential (Ψw) of the dominant species and soil respiration (Rsolf) of each plot were measured daily during HS. One week after HS, plots were harvested, and C% and N% were determined for rhizosphere and bulk soil, and above-ground tissue (green/senescent leaf, stem, and flower). Photosynthetic N-use efficiency (PNUE) and N resorption rate (NRR) were calculated. HS decreased Pn, gs, Ψw, and PNUE for both species, and N treatment generally increased these variables (±HS), but often slowed their poat-HS recovery. Aboveground biomass tended to decrease with HS in both species (and for green leaf mass in S. canadensis), but decrease with N for ,4. gerardii and increase with N for S. canadensis. For A. gerardii, HS tended to decrease N% in green tissues with N, whereas in S. canadensis, HS increased N% in green leaves.Added N decreased NRR for A. gerardii and HS increased NRR for S. canadensis. These results suggest that heat waves,though transient, could have significant effects on plants, communities, and ecosystem N cycling, and N can influence the effect of heat waves. 相似文献
995.
996.
This study investigate the potential contribution of
nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N2-fixing cyanobacteria abundance and N2 fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up
to 70 kg N ha-1. No further increase was observed with 140 kg N ha-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from 15N fertilizer. Recovery of applied 15N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only
0.3–1% of applied N was lost by denitrification. Recovery of 15N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was
available to rice plant even at the tillering stage, 20 days after N application.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
997.
We present evidence that plant growth at elevated atmospheric CO2 increases the high‐temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 μ mol mol ? 1) and elevated CO2 (550–1000 μ mol mol ? 1) in three separate growth facilities, including the Nevada Desert Free‐Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2‐grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient‐grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2‐grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2‐grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2‐grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2‐grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high‐temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2‐induced increase in plant high‐temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century. 相似文献
998.
The presented work was conducted on seedlings of spring barley and meadow fescue which differ in the degree of sensitivity
to leaf spot pathogen Bipolaris sorokiniana (Sacc.) Shoem. The seedling reaction to inoculation with mycelium and conidia was examined in glasshouse conditions on the
basis of respiration intensity and heat production. The leaf respiration was measured using Clark-type electrode, while heat
emission was evaluated by means of isotermic microcalorimeter. The measurements were performed after 1, 3, 6, 10, 24, 48,
72, 168 and 240 hours since the inoculation moment.
Leaves of meadow fescue were characterized by the most intense respiration at the 6th hour, while barley leaves at the 24th and 72nd hour after inoculation. In the case of meadow fescue the greatest heat production was noted in the period between 24 and
168 hours after inoculation. Simultaneously, at the 48th hour the smallest rate of respiration was observed. Barley leaves emitted the greatest amount of heat only in the first 3
hours of the pathogenesis. In these hours the smallest respiration rate was noted. The observed, opposing reaction of respiration
intensity and heat emission in the infected seedlings of both species may illustrate a disorder in metabolic processes in
plants during pathogenesis. The plants studied differed in the time of their reaction to pathogen attack: barley responded
earlier in heat production, while fescue extended respiration rate in the first hours after inoculation. This is clearly observable,
when coefficients of metabolic inefficiency (heat rates per mole O2) are compared. In the case of barley the highest rates were noticed just after inoculation, whereas in fescue at the 48th hour. In both species attack of pathogen caused high metabolic efficiency. 相似文献
999.
不同活力玉米种子胚萌发期间热激蛋白的合成 总被引:8,自引:0,他引:8
玉米(Zea mays L.)种子在萌发期间热激处理(42℃)时蛋白质合成率低于对照(25℃);高活力种子胚热激蛋白的合成率最高。在42℃热激处理时玉米种胚子合成的热激蛋白的分子量分别为73、65、62、54、18kD等5种。高活力种胚合成的热激蛋白在最上高于低活力种子,高活力种胚合成的特异性热激蛋白56kD可以作为衡量种子活力的指标。双向电泳表明高低活力种子间热激蛋白的合成有更多质上的差异。 相似文献
1000.