THYMIDINE DEGRADATION PRODUCTS IN PLANT TISSUES LABELED WITH TRITIATED THYMIDINE

A study of the metabolic pathways of H³-thymidine utilization in buds of Lilium longiflorum and root tips of Vicia faba was undertaken in order to obtain information that might explain the binding of H³ from H³-thymidine in the cytoplasm of these plants. H³-thymidine was administered for various periods of time, the tissues were fixed and processed in the manner routinely used in preparation for sectioning and autoradiography, and the radioactivity removed in this way from the tissues was determined. It was found that the ethanol/acetic acid fixative contained the major portion of the radioactivity. Analysis of this extract by paper chromatography showed that the radioactivity was distributed among various degradation products of thymidine, principally β-ureidoisobutyric acid and β-aminoisobutyric acid. Time course experiments with Vicia showed that these degradation products rapidly appeared in the tissue during incubation with H³-thymidine, while H³-thymine appeared in the incubation medium. Preliminary studies indicated that Vicia root tips incubated with H³-dihydrothymine for 24 hours would bind a small amount of H³ non-specifically in the cells. It seems unlikely that utilization of degradation products of H³-thymidine is sufficient to explain labeling which is concentrated in the cytoplasm.     

FIXATION OF NEURAL TISSUES FOR ELECTRON MICROSCOPY BY PERFUSION WITH SOLUTIONS OF OSMIUM TETROXIDE

This paper describes in detail a method for obtaining nearly uniform fixation of the nervous system by vascular perfusion with solutions of osmium tetroxide. Criteria are given for evaluating the degree of success achieved in the preservation of all the cellular components of the nervous system. The method permits analysis of the structural relations between cells at the electron microscopic level to an extent that has not been possible heretofore.     

ZONE LINES IN PLANT TISSUES

The black lines of Polyporus squamosus have been found in the wood of elms. Isolations were made from these lines and an account of the development of P. squamosus in artificial culture is given. Particular mention is made of the formation of black plates, or lines as they appear in section, in culture media and of the appearance of abnormal fructifications. Pure cultures of the fungus on sterilized wood blocks have produced black lines in the wood, similar to those occurring in nature.
From a consideration of the structure and formation of the black plates, the suggestion is made that they form the limiting layer or rind of sclerotium-like bodies buried in the attacked wood.
A review is given of sclerotium formation and structure in several species of Polyporus, and analogies are made between these sclerotia and the sclerotium-like body of P. squamosus. It is decided to distinguish the P. squamosus body from these sclerotia by naming it a pseudo-sclerotium, on the criteria previously advanced for Armillaria mellea (8).     

荧光共振能量转移效率的实时定量测量

荧光共振能量转移（FRET）广泛用于研究分子间的距离及其相互作用,与荧光显微镜结合,可定量获取有关生物活体内蛋白质、脂类、DNA和RNA的时空信息。随着绿色荧光蛋白（GFP）的发展,FRET荧光显微镜有可能实时测量活体细胞内分子的动态性质。提出了一种定量测量FRET效率以及供体与受体间距离的简单方法,仅需使用一组滤光片和测量一个比值,利用供体和受体的发射谱肖除光谱间的串扰。该方法简单快速,可实时定量测量FRET的效率和供体与受体间的距离,尤其适用于基于GFP的供体－受体对。     

人体病理组织中细菌L型的电镜观察

对9例细菌L型感染的人体病理组织进行透射电镜观察。结果显示:(1)L型可分布于组织间质或进入吞噬细胞、上皮细胞和癌细胞等细胞胞质;(2)L型具有多形态、大小不等、胞壁缺陷、电子密度低等特点,细胞胞质内的细菌L型尚有A、B两种形态区别;(3)L型在组织中形成了不完全箍缩分裂;(4)宿主细胞超微结构仅出现轻微改变。本结果与文献报道基本一致,提出了透射电镜下病理组织中细菌L型的形态特征及分布;并对L型感染与慢性炎症的关系等问题进行了讨论。     

GROWTH OF EDIBLE CHLOROPHYLLOUS PLANT TISSUES IN VITRO

Hildebrandt, A. C, J. C. Wilmar, H. Johns, and A. J. Riker. (U. Wisconsin, Madison.) Growth of edible chlorophyllous plant tissues in vitro, Amer. Jour. Bot. 50(3): 248–254. Illus. 1963.—Plant callus cultures were attempted from roots, stems, leaves or excised embryos of 32 species of plants on a basal mineral salts–sucrose agar medium (T-medium), on T-medium + coconut milk + α-naphthaleneacetic acid + calcium pantothenate (C-medium) and on C-medium + 2,4-dichlorophenoxyacetic acid (D-medium). Embryos on T- or C-medium generally produced normal plants, while on D-medium, they often produced callus only. Fresh isolates of carrot, endive, lettuce, parsley, red kidney bean, and navy bean gave moderate to excellent callus on C-medium. Parsley and navy bean also produced excellent callus on D-medium. Strains of callus from potato, tomato, grape and rose also grew well on C- or D-medium. In the light, red pigmentation developed on rose, parsley, and grape callus. Chlorophyll formation was inhibited on D-medium, but on C-medium more or less chlorophyll was initiated in callus from carrot, endive, lettuce, pea, potato and certain rose varieties. Chlorophyll formation was also strong in endive callus on T-medium supplemented with casein hydrolysate, i-inositol and NAA. The amount and type of sugar used in C-medium influenced the amount of growth and were critical in relation to chlorophyll formation. Carrot tissues in constant light produced abundant chlorophyll and were still growing on media without added sugar after 6 weeks.     

RAPID CHEMICAL DEHYDRATION OF PLANT MATERIAL FOR LIGHT AND ELECTRON MICROSCOPY WITH 2,2-DIMETHOXYPROPANE AND 2,2-DIETHOXYPROPANE

A rapid and simple procedure was used for chemical dehydration of plant tissue during sample preparation for light and electron microscopy. Chemically fixed tissues were washed with distilled water and then rapidly dehydrated with either 2,2-dimethoxypropane or 2,2-diethoxypropane for 15 minutes. Light microscopic observation of paraffin-embedded tissue or tissue embedded in Spurr's plastic showed excellent preservation. Electron microscopic examination of plastic-embedded tissue showed well maintained ultrastructural morphology. The dehydration procedure was also successfully applied to plant tissue destined for examination in a scanning electron microscope.