At several heights and times of day within a crop of Zea mays, internal leaf diffusion resistance (ri) and external boundary layer diffusion resistance (ra) were evaluated by measuring the temperature of a transpiring and a non-transpiring leaf (simulated by covering both sides of a normal leaf with strips of poly-ethylene tape), and by measuring the immediate air temperature, humidity and windspeed.
Both ra and ri increased with depth into the crop. However, ra generally was less than 10% of ri.
Profiles of latent-heat flux density and source intensity of transpiration showed that transpiration corresponded roughly to foliage distribution (with an upward shift) and were not similar to the profile of radiation absorption.
The data were compared with heat budget data. The 2 approaches yielded quite similar height distributions of transpiration per unit leaf area and total transpiration resistance.
The total crop resistance to transpiration was computed as 0.027 min cm−1. This compares to Monteith's values of 0.017 to 0.040 min cm−1 for beans (Phaseolus vulgaris L.), and Linacre's values of 0.015 to 0.020 min cm−1 for turf.
Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (515 C and 0500µmol m2s1), with CO2 level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO2 fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO2- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO2 level on leaf CO2uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO2-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO2 level, global warming, low temperature 相似文献
Ribulose-1,5-bisphosphate carboxylase activity (RuBPC), chlorophyll (chl) and protein (prot) concentrations and chlorophyll/protein
(chl/prot) ratios were determined in five differentPopulus clones together with their maximal net CO2 uptake rates (Pmax). A classic reference clone (Populus ×euramericana “Robusta” (Dode) Guinier) was compared with four recently selected euramerican and interamerican crossings. Chl/prot ratio
and RuBPC activity varied among the different clones, while chl a/chlb ratio showed only a very low coefficient of variation (1.7%) for the five clones. Poplar clone “Robusta” could be distinguished
from the recent faster growing clones based on the different biochemical characteristics. A significant correlation was found
between both total chl concentration and chl/prot ratio with Pmax for the five clones. 相似文献
Systemic sclerosis, or scleroderma, is a chronic and rare connective tissue disease with negative physical and psychological implications. Sources of emotional distress and the impact they have on the lives of people with scleroderma are not well understood.
Objectives
To gain an in-depth understanding of the emotional experiences and sources of emotional distress for women and men living with scleroderma through focus group discussions.
Methods
Three semi-structured focus group discussions were conducted (two in English, one in French) with a total of 22 people with scleroderma recruited through the Scleroderma Society of Ontario in Hamilton, Ontario and a scleroderma clinic in Montreal, Canada. Interviews were recorded, transcribed, and then coded for emerging themes using thematic inductive analysis.
Results
Core themes representing sources of emotional distress were identified, including: (a) facing a new reality; (b) the daily struggle of living with scleroderma; (c) handling work, employment and general financial burden; (d) changing family roles; (e) social interactions; and (f) navigating the health care system. Collectively, these themes refer to the stressful journey of living with scleroderma including the obstacles faced and the emotional experiences beginning prior to receiving a diagnosis and continuing throughout the participants’ lives.
Conclusion
Scleroderma was portrayed as being an unpredictable and overwhelming disease, resulting in many individuals experiencing multiple sources of emotional distress. Interventions and supportive resources need to be developed to help individuals with scleroderma and people close to them manage and cope with the emotional aspects of the disease. 相似文献
Calpains are Ca(2+)-dependent, intracellular cysteine proteases involved in many physiological functions. How calpains are activated in the cell is unknown because the average intracellular concentration of Ca(2+) is orders of magnitude lower than that needed for half-maximal activation of the enzyme in vitro. Two of the proposed mechanisms by which calpains can overcome this Ca(2+) concentration differential are autoproteolysis (autolysis) and subunit dissociation, both of which could release constraints on the core by breaking the link between the anchor helix and the small subunit to allow the active site to form. By measuring the rate of autolysis at different sites in calpain, we show that while the anchor helix is one of the first targets to be cut, this occurs in the same time-frame as several potentially inactivating cleavages in Domain III. Thus autolytic activation would overlap with inactivation. We also show that the small subunit does not dissociate from the large subunit, but is proteolyzed to a 40-45k heterodimer of Domains IV and VI. It is likely that this autolysis-generated heterodimer has previously been misidentified as the small subunit homodimer produced by subunit dissociation. We propose a model for m-calpain activation that does not involve either autolysis or subunit dissociation. 相似文献
Decades of breakthroughs resulting from cross feeding of microbiological research and technological innovation have promoted Listeria monocytogenes to the rank of model microorganism to study host–pathogen interactions. The extraordinary capacity of this bacterium to interfere with a vast array of host cellular processes uncovered new concepts in microbiology, cell biology and infection biology. Here, we review technological advances that revealed how bacteria and host interact in space and time at the molecular, cellular, tissue and whole body scales, ultimately revolutionising our understanding of Listeria pathogenesis. With the current bloom of multidisciplinary integrative approaches, Listeria entered a new microbiology era. 相似文献
The relative increase with elevated CO2 of canopy CO2 uptake rate (A), derived from continuous measurements during the day, was examined in full-cover vegetative Lolium perenne canopies after 17 days of regrowth. The stands were grown at ambient (358±50 mol mol-1) and increased (626±50 mol mol-1) CO2 concentration in sunlit growth chambers. Over the entire range of temperature and light conditions (which were strongly coupled and increased simultaneously), A was on average twice as large in high compared to ambient CO2. This response (called M=A in high CO2/A in ambient CO2) could not be explained by changes in canopy conductance for CO2 diffusion (GC). In spite of interaction and strong coupling between temperature and light intensity, there was evidence that temperature rather than light determined M. Further, high CO2 treatment was found to alleviate the afternoon depression in A observed in ambient CO2. A temperature optimum shift or/and a larger carbohydrate sink capacity through altered root/shoot ratio are proposed in explanation.Abbreviations A
CO2 uptake rate
- C350
ambient CO2 treatment
- C600
elevated CO2 treatment
- E
canopy evapotranspiration rate
- GC
canopy conductance for CO2 diffusion
- M
high CO2 modification factor 相似文献
Summary From an area of 60 sq. km in East-Flanders (Belgium), two sets of stereoscopic aerial photographs were taken. After selection of 13 soil types, 58 grasslands (mainly permanent ones) were localized. Data on species composition (S1 taxa) were quantitatively sampled with a double meter.Density values were obtained from both emulsions and using three filters. Using the densitometric varishles (extended to 22) or taxa variabies. Minimum Variance Clustering (MVC) and Principal Component Analysis (PCA) were applied. The recognition of different grasslandtypes and their relative position in both new sample point spaces was discussed as well as their relation to soil type. The results obtained by both Canonical Analyses (CCA and CVA) were examined and where necessary compared to the searce applications in vegetation ecology.Finally, the possible reasons for the meagre results were briefly discussed.Nomenelature follows De Langhe e.a. (1973). 相似文献