Nitrogen in shoot litter,root litter and root exudates from nitrogen-fixingAlnus incana

Summary A pot experiment withAlnus incana (L.) Moench growing in sand was set up to compare the amounts of nitrogen released from plants shoot litter with that released below ground as root litter and/or root exudation. No nitrogen fixation by free-living microorganisms was found in the sand and the increased nitrogen content of the plant + soil system was therefore due to nitrogen fixation byFrankia in the alder root-nodules. Most of the nitrogen released from the plants was in the nitrogen-rich leaf and other shoot litter. Only small amounts of nitrogen were found in the drainage water from the pots and were recorded as increased nitrogen content of the sand.     

The effects of antibiotics on hemolytic behavior of red cells

Human blood was sheared between rotating polyethylene disks and plasma hemoglobin measured at intervals to produce kinetic hemolysis curves (KHC), plotted as free hemoglobin concentration vs time. The KHC produced by blood samples incubated in the presence of penicillin, streptomycin, gentamicin, and amikacin lie always below those for control samples, indicating a reduction in hemolysis; this reduction was greater as the drug concentration was increased. Explanations in terms of alterations in red cell structure were sought by several characterization tests of amikacin-loaded blood samples. Drug-localization studies demonstrated that significant fractions of the total dosage were associated with the red-cell membrane. Resistive pulse spectroscopy was used to show how amikacin affected cell size, deformability, and osmotic fragility; results were sensitive to storage age of the blood. In all cases, the effect of shearing was to reduce cell size, deformability, and osmotic fragility. Mechanisms for hemolytic protection by drugs are proposed.     

Comparative study of methods for the quantification of fungal spores at the leaf surfaces ofPopulus xeuramericana

Summary The removal of fungal spores, urediniospores ofMelampsora medusae and conidia ofPestalozzia sp., from the leaf surfaces ofPopulus xeuramericana (Dode) Guinier cv. I-488 was assessed using three cultural techniques conventionally employed in phylloplane studies. The method of removal and the original density of spore deposition, but not the interaction of these factors, were significant determinants of variability in spore removal. Irrespective of the original density of deposition, the leaf print method was the most, and the leaf washing technique the least, efficient means of spore removal from the leaf surface. Factors which could contribute to this difference in efficiency are discussed.     

Pressure chamber measurements using two wheat leaves

Summary The most widely used technique of leaf water potential measurements is with the Scholander pressure chamber. Representative leaf water potential values require many determinations on individual leaves and this can be time consuming in large fields or experiments with multiple treatments. This paper describes a method of obtaining a mean value more rapidly, by using two leaves in the pressure chamber at the same time, but recording the end point of each leaf separately.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

Quantity and quality of seston in an impounded and a free-flowing river in Virginia,U.S.A.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.     

Variation in cellular ribulose-1,5-bisphosphate-carboxylase content in leaves of Triticum genotypes at three levels of ploidy

Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 1.1.39) (RuBPCase) was quantified using polyacrylamide-gel electrophoresis in whole 9-d-old first leaves of 14 genotypes of Triticum, and cellular RuBPCase levels calculated. Diploids, tetraploids and hexaploids were analysed and it was confirmed that the RuBPCase level per cell is closely related to ploidy in wheat. Inter-genotypic variation in RuBPCase levels per cell and per leaf were surveyed. It was found that the interactions between leaf size, cell size and RuBPCase levels result in small variations in RuBPCase levels per unit leaf area between genotypes.Abbreviation RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase     

The cellular parameters of leaf development in tobacco: a clonal analysis

The cellular parameters of leaf development in tobacco (Nicotiana tabacum L.) have been characterized using clonal analysis, an approach that provides unequivocal evidence of cell lineage. Our results indicate that the tobacco leaf arises from a group of around 100 cells in the shoot apical meristem. Each of these cells contributes to a unique longitudinal section of the axis and transverse section of the lamina. This pattern of cell lincage indicates that primordial cells contribute more or less equally to the growth of the axis, in contrast to the more traditional view of leaf development in which the leaf is pictured as arising from a group of apical initials. Clones induced prior to the initiation of the lamina demonstrate that the subepidermal layer of the lamina arises from at least six files of cells. Submarginal cells usually divide with their spindles parallel to the margin, and therefore contribute relatively little to the transverse expansion of the lamina. During the expansion of the lamina the orientation and frequency of cell division are highly regulated, as is the duration of meristematic growth. Initially, cell division is polarized so as to produce lineages that are at an oblique angle to the midrib; later cell division is in alternating perpendicular planes. The distribution of clones generated by irradiation at various stages of development indicates that cell division ceases at the tip of the leaf when the leaf is about one tenth its final size, and then ceases in progressively more basal regions of the lamina. Variation in the mutation frequency within the lamina reflects variation in the frequency of mitosis. Prior to the mergence of the leaf the frequency of mutation is maximal near the tip of the leaf and extremely low at its base; after emergence, the frequency of mutation increases at the base of the leaf. In any given region of the lamina the frequency of mutation is highest in interveinal regions, and is relatively low near the margin. Thus, both the orientation and frequency of cell division at the leaf margin indicate that this region plays a minor role in the growth of the lamina.Abbreviation MF mutation frequency     

Loading and translocation of assimilate in the fine veins of sunflower leaves

Abstract The time course of loading and transport of assimilate in sunflower leaves was examined by pulse labelling with ¹⁴CO₂, followed by freeze drying or freeze substitution, and dry autoradiography at both low and high resolution. The five classes of veins, V1-V5 (V5 being smallest), show a division of function: V5 and V4 are engaged in loading and short distance transport; V3 to V1, in long distance translocation. The first high concentration of ¹⁴C is found in two or three phloem parenchyma cells (intermediary cells) of V5 and V4 veins. The sieve elements of V5 and V4 veins do not show comparable concentrations of ¹⁴C at any time. Recently assimilated ¹⁴C is transported by the intermediary cells for distances of about 0.5 mm to the V3 veins. In V3 to V1 veins translocation is in the sieve tubes. Transport in V5 and V4 veins is in two directions, that in V3 to V1, in one direction towards the petiole. The high concentration of ¹⁴C formed in the intermediary cells does not increase further as the assimilate moves to the sieve tubes of the V3 veins, and so is probably the origin of the gradient that drives translocation.     

大鼠中脑导水管壁及周围灰质在针刺镇痛时的~3H-5-羟色胺含量变化

本研究用~3H-5-羟色胺作示踪,由大鼠侧脑室注入后用冰冻微观放射自显影和组织固定微观放射自显影平行探讨了针刺镇痛时中脑导水管壁及周围灰质部位5-羟色胺的含量定位变化。研究结果发现,当电针达到镇痛时,在中脑导水管壁及周围灰质部位~3H-5-羟色胺的放射自显影象都呈明显增高,这表明在针刺镇痛条件下,~3H-5-羟色胺可迅速被中脑导水管壁及周围灰质部位摄取和储存,从而提示上述部位与针刺镇痛作用有密切关系。