Genetic Diversity and Population Structure of Cucumber (Cucumis sativus L.)

Knowing the extent and structure of genetic variation in germplasm collections is essential for the conservation and utilization of biodiversity in cultivated plants. Cucumber is the fourth most important vegetable crop worldwide and is a model system for other Cucurbitaceae, a family that also includes melon, watermelon, pumpkin and squash. Previous isozyme studies revealed a low genetic diversity in cucumber, but detailed insights into the crop''s genetic structure and diversity are largely missing. We have fingerprinted 3,342 accessions from the Chinese, Dutch and U.S. cucumber collections with 23 highly polymorphic Simple Sequence Repeat (SSR) markers evenly distributed in the genome. The data reveal three distinct populations, largely corresponding to three geographic regions. Population 1 corresponds to germplasm from China, except for the unique semi-wild landraces found in Xishuangbanna in Southwest China and East Asia; population 2 to Europe, America, and Central and West Asia; and population 3 to India and Xishuangbanna. Admixtures were also detected, reflecting hybridization and migration events between the populations. The genetic background of the Indian germplasm is heterogeneous, indicating that the Indian cucumbers maintain a large proportion of the genetic diversity and that only a small fraction was introduced to other parts of the world. Subsequently, we defined a core collection consisting of 115 accessions and capturing over 77% of the SSR alleles. Insight into the genetic structure of cucumber will help developing appropriate conservation strategies and provides a basis for population-level genome sequencing in cucumber.     

The Growth and Development of Maize (Zea mays L.) at Five Temperatures

The objectives of this work were to measure growth and developmentrates over a range of temperatures and to identify processeswhich may limit vegetative yield of maize (Zea mays L.). Twosingle cross Corn Belt Dent maize hybrids were grown from sowingin a diurnal temperature regime of 16/6 °C day/night andin constant temperature environments of 16, 20, 24 and 28 °C.The 16/6 °C environment was close to the minimum for sustainedgrowth and 28 °C was near the optimum. Entire plants wereharvested at stages with 4, 6, 7 and 8 mature leaves in alltemperature treatments except 20 °C in which the final twoharvests were carried out at 9 and 10 mature leaves. Mean totalleaf number varied between 19.5 and 16.0 with the maximum occurringat 16/6 °C. Although harvests were carried out at comparableleaf numbers, and hence at similar developmental stages, thetime interval between sowing and harvest decreased considerablyas temperatures increased. The relative rates of dry weight and leaf area accumulationwith time increased with a Q₁₀ of 2.4 between 16 and 28 °C,while leaf appearance rate increased with a Q₁₀ of 2.9 overthe same range; both rates were highest at 28 °C. Althoughdry matter partitioning to the shoots increased with temperature,the area of individual leaves varied in a systematic patternwhich resulted in maximum leaf area, leaf area duration andconsequently dry weight being realized at 20 °C for anygiven stage of development. Zea mays, corn, low temperature stress, temperature response, growth, development     

Structure and Development of the Olfactory Organ in the Garfish Belone belone (L.) (Teleostei,Atheriniformes)

Theisen, B., Breucker, H., Zeiske, E., Melinkat, R. 1980. Structure and development of the olfactory organ in the garfish Belone belone (L.) (Teleostei, Atheriniformes). (Institute of Comparative Anatomy, University of Copenhagen, Denmark; Anatomisches Institut, Universität Hamburg, and Zoologisches Institut und Zoologisches Museum, Universität Hamburg, Federal Republic of Germany.) — Acta zool. (Stockh.) 61(3): 161–170. The structure and development of the olfactory organ in the garfish Belone belone (L.) were studied by light and electron microscopy (SEM and TEM). The olfactory organ has the shape of an open groove with a protruding papilla. In embryos and early juveniles the groove is smooth and is provided with a continuous sensory epithelium. During ontogenesis the papilla develops and the composition of the epithelium is changed as areas of nonsensory epithelium appear and eventually separate the sensory epithelium into islets. In adults the sensory epithelium consists of supporting, basal, and two types of receptor cells, ciliated and microvillous. In juveniles also ciliated nonsensory cells are present. This difference can be correlated with differing locomotory habits of adults and juveniles. The receptor cilia show a 9 + 0 microtubular pattern while the nonsensory cilia have the general 9 + 2 pattern. Deviating dendritic endings were found and are considered an indication of ongoing cell dynamics.     

The use of mustard (Brassica juncea L.) and gram (Cicer arietinum L.) seedling germination inhibition assay for aflatoxin B1

Seed germination and seedling growth as well as chlorophyll and carotenoid contents of mustard and gram seeds were inhibited or reduced significantly due to the treatment of different concentrations (100, 250, 500, 1000 and 2000 ng/ml) of aflatoxin B₁. The range of inhibition in all the parameters was found to be directly influenced by the concentrations of toxin applied. Mustard and gram seedling germination inhibition assay can be used for aflatoxin B₁.     

The Development of Flower Primordia of Phaseolus vulgaris (L.) Savi.

The first-formed flower primordium on determinate varieties(plants with terminal inflorescences) of Phaseolus vulgarishas been identified and located. Irrespective of the numberof leaves on the main stem, it is formed directly in the axilof the uppermost leaf. The physiological significance of thisis discussed.     

Effect of Seed Damage on Growth and Development in Pea (Pisum sativum L.) and Wheat (Triticum aestivum L.)

The effect of damage to the food storage of the seed on theensuing plant was compared in cultivars of two species differingin seed structure, the Greenfeast pea with cotyledons and theGabo wheat with endosperm. Partial removal of storage tissue slightly retarded growth ratein both species and slowed development rate in wheat. Completeremoval lowered the germination rate, drastically slowed thegrowth rate of the survivors for the first 20 d after sowingand lowered the development rate throughout the life cycle. This treatment doubled the time to flower initiation (20 d later)compared with the control, thus indicating the promotive roleof both cotyledon and endosperm in the progress of the shoottowards the reproductive state. The number of vegetative nodes in the pea was lowered by twonodes whereas it was raised by one in the wheat.     

Isolation and verification of anatoxin-a producing clones of Anabaena flos-aquae (Lyngb.) de Breb. from a eutrophic lake

Abstract We present a technique to isolate and confirm anatoxin-a producing clones (single trichome-isolates) of Anabaena flos-aquae (Lyngb.) de Breb. from blooms of this cyanobacterium. A single trichome is isolated from a field sample and grown in ASM medium. Single trichomes are then isolated from this culture and grown in ASM medium to produce single clone cultures. Mouse bioassay, and thin-layer chromatography (TLC) using purified anatoxin-a as reference is then used to confirm the anatoxin-a producing clones. Using this methodology, Anabaena flos-aquae samples collected during July 1991 from Hebgen Lake, Montana, were found to contain only 8.7% anatoxin-a producing clones. This minor proportion of anatoxin-a producing clones apparently accounts for the anatoxin-a produced by the entire population of A. flos-aquae . Our technique is simple and reproducible. A selected clone of A. flos-aquae that produces anatoxin-a and one that does not produce anatoxin-a were deposited in the UTEX culture collection, University of Texas at Austin.     

Effects of Soil Structure on Pea (Pisum sativum L.) Root Development According to Sowing Date and Cultivar

Spring peas are known to be very sensitive to compaction, particularly when sowing takes place soon after winter. Winter peas, which are sown in autumn, should present an opportunity to sow the crop in better soil structural conditions than for spring peas, because of more favourable moisture conditions at that time. As environmental conditions have a big influence on root systems, it is important to determine the effects of soil structure on pea root systems for different cultivars and sowing dates. A spring pea cultivar and a winter pea cultivar were both sown at two dates (one in autumn and one in spring) on soils with different plough-layer structures (compacted and uncompacted) at two sites in 2002 and one site in 2003. Soil structure was characterised by bulk density and the percentage of highly compacted zones in the ploughed layer. Root distribution maps were produced every month, from February to maturity. Root development was described in terms of general root dynamics, root elongation rate (RER) in the subsoil, final maximum root depth (Dmax) and root distribution at maturity. Root depth dynamics depended on compaction and its interaction with climatic conditions. The effects of compaction on RER in the subsoil depended on the experimental conditions. Dmax was reduced by 0.10 m by compaction. Compaction also reduced root distribution between 10 and 40% in the ploughed layer only. Pea cultivars differed in sensitivity to soil compaction, with a direct effect on the final depth explored by roots. These results are discussed in terms of their relevance to water and nutrient uptake.     

荚果蕨胚胎发育的研究

利用石蜡切片法研究了荚果蕨（Matteuccia struthiopteris(L.) Todaro）胚胎发育过程。合子第一次分裂,分裂面垂直于原叶体纵轴且平行于颈卵器颈部;第二次分裂面平行于原叶体纵轴且垂直于颈卵器颈部;第三次分裂面同时平行于原叶体纵轴和颈卵器颈部。经多次分裂的球形胚胎,胚胎的外上和外下区域几乎同时分别发育出第一叶顶端细胞和第一根顶端细胞。随着发育的进行,它们分别斜向分裂产生第一叶原基和第一根原基。随后,第一叶原基迅速分裂,突破帽状体形成第一幼叶;而第一根原基的分裂速度稍慢,第一根发育速度稍慢于第一叶。     

马铃薯块茎发育机理及其基因表达

马铃薯（Solanum tuberosum L.)块茎是有块茎马铃薯植物的地下变态器官,它由匍匐茎顶端膨大形成,对于马铃薯块茎形成的生理机制已有许多研究,这些研究表明,块茎发生受许多因素的影响,总体来讲短日 照,较低的温度以及离体条件下培养基较高的蔗糖浓度等有利于块茎形成,同时,块茎形成过程中内源激素亦发生一系列变化,然而,对于块茎形成中相关基因表达,进而调控块茎形成的系统研究目前还较滞后,已有研究显示,块茎形成与膨大涉及到一系列基因的表达与关闭,同时它也与淀粉合成和块茎储藏蛋白基因的表达有关,综述了这一领域现有的研究进展。     

The Histology of Seed Development in Diploid and Tetraploid Raspberries (Rubus idaeus L.)

Ovules of the raspberry, Rubus idaeus L., resembled those ofother Rubus species in being unitegmic, crassinucellate, andanatropous. In one cultivar, ‘M. 69/139’, both eggcell and embryo were inserted slightly laterally to the micropyle.Of the tetraploid forms, 4n M. 69/139 showed a proportion ofembryo sacs with delayed differentiation, and 4n ‘M. Jewel’some with four antipodal cells. Embryo development showed littleuniformity in timing, but followed the Asterad type. Occasional delayed endosperm development seemed to be a varietalpeculiarity of M. 69/139. At maturity, the ergastic materialin healthy endosperms consisted of oil globules and aleurongrains. The hypostase formed a projecting pedestal below theendosperm at 8 days. The inner epidermal layer of the testaappeared specialized, both in the early stages of seed growth,when it is suggested that it functioned as an endodermis, andat maturity, when it appeared to form an osmotic barrier.     

The Development of the Shoot Apex of Agropyron repens (L.)Beauv.

During the phase of growth between the production of one and10 mature leaves the primary shoot apex of Agropyron repensundergoes first an increase and then a decrease in size. Theapical dome was found to attain a maximum size at the six leafstage. The changes are attributable to changes in cell number,mean cell size remaining constant after an initial decrease.The zonation pattern, and particularly the number of tunicalayers, varies with the size of the dome. The apex as a wholeundergoes a greater increase in height than in diameter, withcommensurate changes in the number of leaf primordia presentupon it. Similar changes occur in the tiller but no such obvioustrends were found in the rhizome. In an experiment in whichall axillary buds were excised from the primary shoot it wasfound that the apex continued to increase in size well beyondthe maximum attained by that of an intact plant. On this evidenceit is suggested that the eventual decline of the primary shootand tiller apices is due to an inhibitory effect on the mainshoot by the developing axillary shoots.     

The effects of handling on flounder (Platichthys flesus L.) and Atlantic salmon (Salmo salar L.)

The effect of 9 min of net confinement on two marine teleost species, the flounder and the Atlantic salmon, was investigated in order to gauge how different species respond to the same stress stimulus. Net confinement in both species induced significant elevations in plasma cortisol, glucose, lactate, osmolality, and monovalent ion levels; the responses to net confinement in salmon were generally of a greater magnitude. In both species, handling induced significant alterations in PFFA levels though there were marked species differences in the qualitative and quantitative aspects of this response. Plasma protein levels were significantly elevated only in the flounders. In general, the two species responded similarly to the net confinement with differences only in the absolute levels and durations of the responses.     

FOULING ON EELGRASS (ZOSTERA MARINA L.)1

The diatom Cocconeis scutellum (Meunier) colonizes the surface of young plants emerging from the mud in the spring and the usually emersed plant tips as they are knocked over and become immersed in the fall to form a virtually unialgal mat. Broken frustules and detritus adhere to form a crust which then becomes colonized nonselectively by a variety of microorganisms. Removal of the crust shows that the original “cobblestone” surface of the eelgrass is obscured with a layer of deformed cells of C. scutellum which appears to be impressed into the epithelium.     

Epidermal Structure in the Ligule of Rice (Oryza sativa L.)

The structure of the abaxial epidermis of the ligule of rice(Oryza sativa L.) as seen in the light and scanning electronmicroscope is described. Long cells, silica cells, cork cells,prickle hairs, microhairs and stomata-like structures were found.Reasons for considering these latter structures to be true stomataare given. Results of an X-ray analysis for silicon are presentedand the distribution of silica discussed in relation to itsfunctional role in the ligule. Oryza sativa L, rice, Gramineae, ligule, epidermis, scanning electron microscopy, X-ray analysis, silica, stomata     

Development and analysis of EST-SSRs for flax (Linum usitatissimum L.)

A set of 146,611 expressed sequence tags (ESTs) were generated from 10 flax cDNA libraries. After assembly, a total of 11,166 contigs and 11,896 singletons were mined for the presence of putative simple sequence repeats (SSRs) and yielded 806 (3.5%) non-redundant sequences which contained 851 putative SSRs. This is equivalent to one EST-SSR per 16.5 kb of sequence. Trinucleotide motifs were the most abundant (76.9%), followed by dinucleotides (13.9%). Tetra-, penta- and hexanucleotide motifs represented <10% of the SSRs identified. A total of 83 SSR motifs were identified. Motif (TTC/GAA)n was the most abundant (10.2%) followed by (CTT/AAG)n (8.7%), (TCT/AGA)n (8.6%), (CT/AG)n (6.7%) and (TC/GA)n (5.3%). A total of 662 primer pairs were designed, of which 610 primer pairs yielded amplicons in a set of 23 flax accessions. Polymorphism between the accessions was found for 248 primer pairs which detected a total of 275 EST-SSR loci. Two to seven alleles were detected per marker. The polymorphism information content value for these markers ranged from 0.08 to 0.82 and averaged 0.35. The 635 alleles detected by the 275 polymorphic EST-SSRs were used to study the genetic relationship of 23 flax accessions. Four major clusters and two singletons were observed. Sub-clusters within the main clusters correlated with the pedigree relationships amongst accessions. The EST-SSRs developed herein represent the first large-scale development of SSR markers in flax. They have potential to be used for the development of genetic and physical maps, quantitative trait loci mapping, genetic diversity studies, association mapping and fingerprinting cultivars for example. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.