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N. Firon R. Shaked M.M. Peet D.M Pharr E. Zamski K. Rosenfeld L. Althan E. Pressman 《Scientia Horticulturae》2006
Exposure to high temperatures (heat stress) causes reduced yield in tomatoes (Lycopersicon esculentum), mainly by affecting male gametophyte development. Two experiments were conducted where several tomato cultivars were grown under heat stress, in growth chambers (day/night temperatures of 31/25 °C) or in greenhouses (day/night temperatures of 32/26 °C), or under control (day/night temperatures of 28/22 °C) conditions. In heat-sensitive cultivars, heat stress caused a reduction in the number of pollen grains, impaired their viability and germinability, caused reduced fruit set and markedly reduced the numbers of seeds per fruit. In the heat-tolerant cultivars, however, the number and quality of pollen grains, the number of fruits and the number of seeds per fruit were less affected by high temperatures. In all the heat-sensitive cultivars, the heat-stress conditions caused a marked reduction in starch concentration in the developing pollen grains at 3 days before anthesis, and a parallel decrease in the total soluble sugar concentration in the mature pollen, whereas in the four heat-tolerant cultivars tested, starch accumulation at 3 days before anthesis and soluble sugar concentration at anthesis were not affected by heat stress. These results indicate that the carbohydrate content of developing and mature tomato pollen grains may be an important factor in determining pollen quality, and suggest that heat-tolerant cultivars have a mechanism for maintaining the appropriate carbohydrate content under heat stress. 相似文献
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Bernard Peet 《北方牧业》2014,(3)
正母猪的非生产天数(NPD)是指每个繁殖周期,或每年母猪或青年母猪既非妊娠又非泌乳的天数,它是影响猪群繁殖生产效率最关键的指标。某些记录系统还包括青年母猪从进场到配种的时间,但这段时间的长短与青年母猪的引进程序有关,不同猪场之间存在很大差异,现在只探讨第一胎之后的非生产天数。 相似文献
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Mary M. Peet C. David Raper Jr. Leslie C. Tolley Wayne P. Robarge 《Journal of plant nutrition》2013,36(9):787-798
Tomato (Lycopersicon esculentum L. Mill. ‘Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3 ‐ or 1.0 mM NH4 +. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3 ‐ or NH4 + can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4 +‐fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant. 相似文献
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Ecological theory predicts a positive influence of local-, landscape-, and regional-scale spatial environmental heterogeneity
on local species richness. Therefore, knowing how heterogeneity measured at a variety of scales relates to local species richness
has important implications for conservation of biological diversity. We took a statistical modeling approach to determine
which metrics of heterogeneity measured at which scales were useful predictors of local species richness, and whether the
heterogeneity-local richness relationship was always positive. Local plant species richness data came from 400-m2 vegetation plots in North and South Carolina, USA. At each of four scales from within plots to across regions, we used either
GIS or field data to calculate measures of heterogeneity from abiotic environmental variables, vegetation productivity data,
and land cover classifications. Among all predictors at all scales, we found that no measure of heterogeneity was a better
predictor of local richness than mean pH within plots. However, at scales larger than within plots, measures of heterogeneity
were correlated most strongly with local richness, and each of the three classes of variables we used had a distinct scale
at which it performed better than the others. These results highlight the fact that ecological processes occurring across
multiple scales influence local species richness differently. In addition, relationships between heterogeneity and richness
were usually, though not always, positive, underscoring the importance of processes that occur at a variety of scales to local
biodiversity conservation and management. 相似文献
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Sarina Claassens Peet Jansen van Rensburg Danica Liebenberg Leon van Rensburg 《Water, air, and soil pollution》2012,223(3):1091-1100
Previous studies have made some progress with the use of microbial community properties as assessment criteria for rehabilitation
success of post-mining areas. Currently, there is a need for reference ranges of specific properties in rehabilitated post-mining
sites to make this approach more practical. The aim of this investigation was to compare assessment parameters indicative
of microbial community function (enzymatic assays) and structure (phospholipid fatty acid (PLFA) analysis) in rehabilitated
asbestos and coal discard sites and to establish ranges of minimum and maximum values for these parameters in both types of
sites. The range established for dehydrogenase activity in coal discard sites was 24.3–339.5 μg INF g−1 2 h−1 and for asbestos 44.5–544.6 μg INF g−1 2 h−1. Ranges were also established for β-glucosidase, urease, acid phosphatase and alkaline phosphatase. Complete PLFA profiles
were determined and ranges established for major PLFA groups and ratios in both types of discard. From the PLFA profiles,
viable microbial biomass was determined as 6,080–29,851 and 8,128–47,242 pmol g−1 dry weight for the coal and asbestos discard sites, respectively. While similar ranges were observed for both types of discard,
a canonical correspondence analysis that accounts for functional and structural characteristics showed that sites clustered
according to the origin of the samples. 相似文献
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OBJECTIVE: To develop an assay to measure canine von Willebrand factor (vWF):collagen-binding activity (CBA) to screen for type 2 von Willebrand disease (vWD) in dogs. SAMPLE POPULATION: 293 plasma samples submitted for analysis of canine vWF antigen (vWF:Ag) and 12 control plasma samples from dogs with inherited type 2 or 3 vWD. PROCEDURE: Bovine collagens were evaluated for suitability as binding substrate for vWF. Assay sensitivity to depletion, proteolytic degradation, or a genetic deficiency of high-molecular-weight vWF were determined. Amounts of vWF:Ag and vWF:CBA were measured. The ratio of vWF:Ag to vWF:CBA was used to discriminate between type 1 and type 2 vWD. RESULTS: An assay for canine vWF activity was developed by use of mixed collagen (types I and III). When vWF:Ag was used to subtype vWD, 48% of the dogs were classified as clinically normal, 9% as indeterminate, and 43% as type 1 vWD. Inclusion of vWF activity resulted in reclassification of 5% of those identified as type 1 to type 2 vWD. However, vWF:CBA of the reclassified dogs was not persistently abnormal, a finding compatible with acquired type 2 vWD. Some Doberman Pinschers had lower antigen-to-activity ratios than other breeds with type 1 vWD, suggesting that Doberman Pinschers have more functional circulating vWF. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of canine vWF activity should be included among the vWF-specific assays used to confirm type 2 vWD. The prevalence of inherited forms of type 2 vWD in screened dogs is lower than acquired forms that can result secondary to underlying disease. 相似文献