Tylenchulus graminis n. sp. and T. palustris n. sp. (Tylenchulidae), from Native Flora of Florida,with Notes on T. semipenetrans and T. furcus

Tylenchulus graminis n. sp. and T. palustris n. sp. are described and illustrated from broomsedge (Andropogon virginicus L.) and pop ash (Fraxinus caroliniana Mill.), respectively. T. graminis resembles T. furcus in having a distinct anus, but T. graminis second-stage juveniles (J2) do not have a bifid tail. T. semipenetrans does not have a perceptible anus. The mature female of T. graminis has a mucronate pointed terminus while T. semipenetrans has a smooth and round terminus. T. graminis males have wider stylet knobs and basal bulb and a longer tail than T. semipenetrans males. T. graminis J2 have a longer posterior body portion (without large fat globules) than T. semipenetrans J2. T. palustris resembles T. semipenetrans in having an undetectable anus but differs by the short and conoid mature female postvulval section. The male of T. palustris has larger stylet knobs and basal bulb than those of T. semipenetrans and a bluntly rounded tail terminus, which is tapered in T. semipenetrans. T. palustris differs from T. furcus and T. graminis in having an undetectable anus, by the conoid postvulval section of mature females, by the shorter and rounded tail of males, and the shorter J2 posterior body section without large fat globules. T. graminis and T. palustris are parasites of indigenous flora of Florida.     

Cloning and analysis of a 6.8-kb rDNA intergenic spacer region of the European ash (Fraxinus excelsior L.)

The 6.8-kb rDNA intergenic spacer region of F. excelsior was isolated from a CsCl/actinomycin-D gradient and cloned into pUC18 for further characterization. We observed the presence of subrepeats delimited by HaeIII enzyme sites. These subrepeats were sub-cloned and 11 clones were sequenced. These corresponded to subrepeated elements of either 32 bp or 41 bp that shared a 23-bp common sequence in the 5 end. Within each family of subrepeats, the percentage of common nucleotides was 84.4% for the 5 32-bp subrepeats and 67.4% for the 640-bp subrepeats. Non-repeated HaeIII fragments of 450 bp and 650 bp were also sub-cloned. To compare homology at the IGS region between the rDNA spacers of F. excelsior and the three related species (F. oxyphylla, F. americana, F. ornus), we conducted Southern hybridization analyses using each member of the 32-bp and 40-bp subrepeat families and the unique 450-bp and 650-bp fragments as probes. These analyses indicated that (1) the American ash is more genetically distant from the other three species that the latter are from each other and (2) F. oxyphylla and F. excelsior are more closely related to each other than to F. ornus.     

水曲柳大孢子发生及雌配子体发育的研究

水曲柳（ＦｒａｘｉｎｕｓｍａｎｄｓｈｕｉｃａＲｕｐｒ．）子房为二心皮;二室,中轴胎座,每室内具二个倒生胚珠,薄珠心,单珠被。单个孢原细胞分化于珠心顶端表皮之下,直接发育成为大孢子母细胞,大孢子四分体为直线形,通常为合点端第一大孢子具功能,胆囊发育为蓼型。     

女贞和白蜡树的树皮结构及次生韧皮部发育的季节变化

女贞（ＬｉｇｕｓｔｒｕｍｂｕｃｉｄｕｍＡｉｔ）和白蜡树（ＦｒａｘｉｎｕｓｃｈｉｎｅｎｓｉｓＲｏｘｂ）是白蜡虫的两种主要寄主树。树皮由外向内为周皮,皮层,初生韧皮部的纤维束和次生韧皮部．它们的筛管分子具复筛板或单筛板,具Ｐ－蛋白质和筛管淀粉。伴胞为与筛管分等长的一列或单个细胞。筛管寿命在女贞中最长为一年,在白蜡树中则不超过８个月．形成层活动时间在女贞中是３月中下旬到１１月中旬,在白蜡树中是３月中下旬到１１月下旬．两种树木的木质部和韧皮部在３月中旬已开始分化,木质部和韧皮部分化停止的时间在女贞中分别是１１月中旬和１２月下旬;在白蜡树中分别是９月下旬和１１月下旬．两种树木在冬季都有部分分化的筛管分子,白蜡树中的部分分化的筛管分子于秋季形成,翌年３月中旬成熟,同年９—１０月瓦解。女贞枝条冬季平均保留１７０．２μｍ的具功能韧皮部区;而白蜡树在径向仅保留数列细胞宽的具功能韧皮都区越冬．     

Organization of nuclear ribosomal DNA and species-specific polymorphism in closely related Fraxinus excelsior and F. oxyphylla

The ribosomal DNA repeat units of two closely related species of the genus Fraxinus, F. excelsior and F. oxyphylla, were characterized. The physical maps were constructed from DNA digested with BamHI, EcoRI, EcoRV and SacI, and hybridized with three heterologous probes. The presence or the absence of an EcoRV restriction site in the 18s RNA gene characterizes two ribosomal DNA unit types found in both species and which coexist in all individuals. A third unit type appeared unique to all individuals of F. oxyphylla. It carries an EcoRI site in the intergenic spacer. Each type of unit displayed length variations. The rDNA unit length of F. excelsior and F. oxyphylla was determined with EcoRV restriction. It varied between 11kb and 14.5kb in F. excelsior and between 11.8kb to 13.8kb in F. oxyphylla. Using SacI restriction, at least ten spacer length variants were observed in F. excelsior, for which a detailed analysis was conducted. Each individual carries 2–4 length variants which vary by a 0.3-kb step multiple. This length variation was assigned to the intergenic spacer. By using the entire rDNA unit of flax as probe in combination with EcoRI restriction, each species can be unambiguously discriminated. The species-specific banding pattern was used to compare trees from a zone of sympatry between the two species. In some cases, a conflicting classification was obtained from morphological analysis and the use of the species-specific rDNA polymorphism. Implications for the genetic management of both species are discussed.     

Osmotic adjustment in Fraxinus excelsior L . : malate and mannitol accumulation in leaves under drought conditions

 In leaves of Fraxinus excelsior L., malate and mannitol were characterized by ¹³C NMR spectroscopy and enzymatic specific assays as the major constituents of a soluble carbon fraction involved in an osmotic adjustment. During a summer drought where predawn leaf water potential of adult trees growing in a mesoxerophilic stand fell to – 4 MPa in August, malate and mannitol leaf contents increased by a factor of 1.8 and 2.2 respectively, compared to control trees growing on a flood plain. This drought stress led to concentrations as high as 280 mM and 600 mM for mannitol and malate, respectively. The effects of gradually developing water deficit were also studied in a semi-controlled environment in 3-year-old seedlings. When predawn leaf water potential reached -6 MPa, leaves displayed a low turgor pressure but stomatal conductance was still measurable. Malate and mannitol were also the main osmoticum involved. After rewatering, gas exchange capacities were largely restored. Altogether, these results show that the strong water-stress tolerance of Fraxinus excelsior is in part related to an accumulation of malate and mannitol. Received: 3 January 1996 / Accepted: 19 March 1996     

The presence of extended phragmosomes containing cytoskeletal elements in fusiform cambial cells ofFraxinus excelsior L.

Summary Fusiform cambial cells of the ash (Fraxinus excelsior L.), which are strongly elongated and vacuolated, contain a phragmosome which traverses the whole length of the cells during preprophase and karyokinesis and which remains present during cytokinesis until it is integrated in cell plate with adjacent cytoplasm.The phragmosome consists of a thin perforated cytoplasmic layer located in the plane of the future cell plate. Otherwise oriented transvacuolar cytoplasmic layers or strands are not present in these cells.The phragmosome contains cytoskeletal elements, namely microtubules and also microfilament bundles both of which are oriented mainly in longitudinal direction.The phragmosomal microtubules are a new category of microtubules associated with cell division; presumably they guide the centrifugally growing cell plate to the parental cell wall site previously marked by the preprophase band of microtubules.     

3个温带阔叶树种根系长期分解速率研究

根系分解对土壤碳固持和养分长期有效性具有重要意义,但目前对根系的长期分解模式仍知之甚少。比较3个温带阔叶树种不同直径根系7 a分解动态,可为生态过程模型提供数据支撑。在帽儿山生态站采用分解袋法对白桦（Betula platyphylla）、春榆（Ulmus davidiana var.japonica）、水曲柳（Fraxinus mandshurica）的5个直径等级（< 1 mm）、（1-2 mm）、（2-5 mm）、（5-10 mm）、（10-20 mm）根系进行了7 a野外分解实验。重复测量方差分析表明：时间、树种、直径与树种交互作用、树种与时间交互作用显著影响根系质量保持率。根系质量保持率随时间呈指数下降趋势,7 a间根系经历早期快速分解和后期慢速分解两个阶段,实验结束时根系仍剩余相当部分的初始质量（24%-56%）。利用Olson指数衰减模型估计各树种根系分解系数发现：白桦根系分解系数与根直径间具有显著的线性正相关关系,水曲柳具有显著对数正相关关系,春榆的关系不显著。3个树种短期分解系数均高估根系分解速率,而且不能完全代表长期分解系数的种内、种间差异。研究结果对理解根系长期分解速率随直径变化模式提供了数据支撑。