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71.
Optical replicas of leaf surfaces were made for characterizingthe lens properties of individual epidermal cells. Using a dentallatex, moulds were made of leaf surfaces and subsequently usedto produce agarose replicas. The replicas focused light in amanner similar to intact epidermal cells and it was possibleto measure both focal lengths and intensifications within leafreplicas of Thermopsis montana, Mahonia repens, and Smilacinastellata which had epidermal cells of different diameter. Focallengths ranged from 74130 µm which indicated thatlight was concentrated within the underlying photosynthetictissues of these leaves. Focal intensifications were measuredsensiometrically and were 1.5 for T. montana and 2-6 for theother species. These values compare favourably with calculatedfocal lengths and measurements taken from isolated epidermallayers. The results indicate that the epidermis can concentratelight within the leaf to amounts well in excess of ambient light.Furthermore, the replicas faithfully reproduced fine anatomicaldetails from a wide variety of leaves and they provide a non-destructiveway to reproduce surface characteristics for anatomical andphysiological studies. 相似文献
72.
Localization of sucrose synthase in soybean root nodules 总被引:7,自引:2,他引:5
73.
74.
Terrestrial crabs are physiologically rather similar to theiraquatic relatives, despite their markedly different access towater and ions. They have high evaporation rates and void vitalsalts in isosmotic urine. Some of them manage to have fairlymiserly water and ion budgets, but others succeed despite profligacy.There is no single solution to the challenges of terrestriallife; each pairing of animal and environment must be seen asa system in which a unique suite of behaviors compensates forlimited physiological prowess. By exploiting temporal and spatialvariability of available microhabitats, each species assemblesa "composite habitat" in which it can balance the "debit" sidesof its water and ion budgets with the requisite "credits." 相似文献
75.
Martingale-based residuals for survival models 总被引:27,自引:0,他引:27
76.
Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium 总被引:11,自引:1,他引:10
RUFTY THOMAS W. Jr; JACKSON WILLIAM A.; RAPER C. DAVID Jr. 《Journal of experimental botany》1982,33(6):1122-1137
Experiments were conducted to investigate the effect of concentrationof NH4+ in nutrient solution on root assimilation of NO3and to determine whether the NH4+NO3 interaction wasmodified in the presence of K+. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2and varying concentrations of (NH4)2SO4 in the absence or presenceof 0.15 mM K2SO4. The accelerated phase of NO3 uptakeappeared most sensitive to restriction by additions of 0.15mM (NH4)2SO4. In the absence of K+, the restriction increasedonly slightly even when solution (NH4)2SO4, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH4+in the tissue from about 7.0 to 35 µmol g1 fr.wt. of root. Increasing concentrations of solution NH4+ progressivelyinhibited net K+ uptake. At the highest solution NH4+ concentrations,there was an initial net efflux of K+ and no net influx occurredduring the treatment period. The severity of the NH4)SO4 restrictionof NO3 uptake was moderated considerably in the presenceof K+ as long as a net influx of K+ occurred. However, net influxof K+ was not associated with alteration of NH4+ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO3 uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH4+ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH4+. Several mechanisms were postulatedto account for the moderating influence of K+. In all experiments,root NO3 reduction was restricted by the presence ofambient NH4+. The quantitative decreases in reduction tendedto be less than decreases in NO3 uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded. 相似文献
77.
Scanning electron microscopy was used in conjunction with normal microbiological procedures to evaluate the stomacher as a means of recovering bacteria from chicken skin. Stomaching removed most bacteria from the skin and viable counts of skin micro-organisms obtained by this method were not significantly different from those obtained by blending. The stomacher represents a useful alternative to blending techniques commonly used to assess contamination of poultry carcasses. 相似文献
78.
Scanning Electron Microscopy of Microorganisms on Chicken Skin 总被引:1,自引:1,他引:0
1. Scanning electron microscopy was used to examine microorganisms in situ on chicken skin. They developed in a layer of material on the surface of the skin. The observations explain the relative ineffectiveness of carcass cleaning procedures and the increased recovery of microorganisms by destructive compared with non-destructive sampling techniques. 相似文献
79.
O. H. D. MAKUNGA I. PEARMAN S. M. THOMAS G. N. THORNE 《The Annals of applied biology》1978,88(3):429-437
In 2 years the distribution of radioactivity recovered in entire shoots of field-grown winter wheat was determined at various times after exposing the top two leaves (flag leaf or second leaf) to 14CO2 for 30 s. In 1976 when 14C was supplied to either leaf 14 days before anthesis, 30% was in the ear at anthesis. Less than 5% was in the leaf exposed to I4CO2. The remainder was equally divided between the stem above and below the flag-leaf node when the flag leaf had been exposed, and was mainly in the lower part of the stem when the second leaf had been exposed. By maturity the proportion in the stem had decreased; 20% of the total activity was in the grain and 30% was still in the ear structures. When 14C was supplied 10 days after anthesis, the proportion in the ear 24 h later ranged from 42 to 69% of that in the whole shoot when the flag leaf was exposed, and from 6 to 28% when the second leaf was exposed. At maturity these proportions increased to 92 and 85% when the 14C had been supplied to flag leaves and second leaves respectively. When 14C was supplied 25 days after anthesis to either flag leaves or second leaves, more than 90% of the activity was in the mature ears. Less than 5% of the 14C remaining at maturity from any treatment was still in the leaf exposed to 14CO2. Between 2 and 6% of 14C supplied after anthesis was in the non-grain parts of the ear. The proportion of the 14C in the ear was greatest for the semi-dwarf varieties Maris Fundin and Hobbit, less for Maris Huntsman, and least for Cappelle-Desprez. These varietal differences were large 24 h after exposure to 14CO2, especially in 1976. They were small and rarely significant at maturity. Nitrogen fertiliser up to 210 kg N ha-1 had negligible effects on the distribution of 14C, although it greatly increased growth and yield, especially in 1975. 相似文献
80.