Induced DNA Damage Measured by the Comet Assay in 10 Weed Species

For most plant species growing in polluted areas no mutagenicity assays are available. We have studied the possibility of using the alkaline protocol of the Comet assay as a method for detecting induced DNA damage in wildly growing weeds. The monofuctional alkylating agent ethyl methanesulphonate (EMS) was applied on leaves of 10 weed species (ordered according to the diameter of the nuclei): Arabidopsis thaliana, Convolvulus arvensis, Bellis perennis, Urtica dioica, Lamium album, Chenopodium rubrum, Plantago media, Poa annua, Taraxacum officinale, and Agropyron repens. With increasing concentrations of EMS (2 to 10 mM) the DNA damage, expressed by the averaged median tail moment values, significantly increased in nuclei of all weeds studied. Using the Head Extent parameter of the Komet version 3.1, we have measured the diameter size of the nuclei of the 10 weed species either immediately after the isolation of the nuclei or after 20 or 45 min of treatment with alkaline buffer (pH > 13). According to the increase of the diameter of the nuclei (including the formed halo) resulting from the to alkaline buffer treatment, electrophoretic conditions (unwinding and electrophoresis time) for the Comet assay can be selected for the individual weed species.     

SCGE法检测敌敌畏对大鳞副泥鳅DNA损伤的研究

目的 采用SCGE技术检测敌敌畏对大鳞副泥鳅DNA的损伤效应.方法 设置敌敌畏0.64 μg/L、1.28μg./L、1.92μg/L、2.56μg/L、3.20μg/L 5个浓度组和一个空白对照组(15尾大鳞副泥鳅/组),通过单细胞凝胶电泳技术(scGE)研究各浓度敌敌畏处理组在分别处理l d、2 d、3 d后对大鳞...     

Manganese dynamics in the rhizosphere and Mn uptake by different crops evaluated by a mechanistic model

Understanding of the mechanisms of Mn supply from the soil and uptake by the plants can be improved by using simulation models that are based on basic principles. For this, a pot culture experiment was conducted with a sandy clay loam soil to measure Mn uptake by summer wheat (Triticum aestivum L. cv. Planet), maize (Zea mays L. cv. Pirat) and sugar beet (Beta vulgaris L. cv. Orbis) and to simulate Mn dynamics in the rhizosphere by means of a mechanistic model. Seeds of three crops were sown in pots containing 2.9 kg soil in a controlled growth chamber. Root and shoot weight, Mn content of plants, root length and root radius were determined 8 (13 days in case of sugar beet) and 20 days after germination. Soil and plant parameters were determined to run nutrient uptake model calculations. Manganese content of the shoot varied from 25 mg kg^-1 for sugar beet to 34 mg kg^-1 for maize. Sugar beet had the lowest root length/shoot weight ratio but the highest relative shoot growth rate, resulting in the highest shoot demand on the root. This is reflected by the Mn influx which was 0.9 × 10^-7, 1.7 × 10^-7 and 2.5 × 10^-7 nmol cm^-1 s^-1 for wheat, maize and sugar beet, respectively. Nutrient uptake model calculations predicted similar influx values. Initial Mn concentration of 0.2 μM in the soil solution decreased to only 0.16 μM for wheat, 0.13 μM for maize and 0.11 μM for sugar beet at the root surface. This shows that manganese transport to the root was not a limiting step. This was confirmed by the fact that an assumed 20 times increase in maximum influx (I_max) increased the calculated Mn influx by 3.7 times. Sensitivity analysis demonstrated that for controlling Mn uptake the initial soil solution concentration (C _Li), the root radius (r₀), I_max and the Michaelis constant (K _m) were the most sensitive factors in the listed order. This revised version was published online in August 2006 with corrections to the Cover Date.     

Accumulation of reactive oxygen species in arbuscular mycorrhizal roots

We investigated the accumulation of reactive oxygen species (ROS) in arbuscular mycorrhizal (AM) roots from Medicago truncatula, Zea mays and Nicotiana tabacum using three independent staining techniques. Colonized root cortical cells and the symbiotic fungal partner were observed to be involved in the production of ROS. Extraradical hyphae and spores from Glomus intraradices accumulated small levels of ROS within their cell wall and produced ROS within the cytoplasm in response to stress. Within AM roots, we observed a certain correlation of arbuscular senescence and H₂O₂ accumulation after staining by diaminobenzidine (DAB) and a more general accumulation of ROS close to fungal structures when using dihydrorhodamine 123 (DHR 123) for staining. According to electron microscopical analysis of AM roots from Z. mays after staining by CeCl₃, intracellular accumulation of H₂O₂ was observed in the plant cytoplasm close to intact and collapsing fungal structures, whereas intercellular H₂O₂ was located on the surface of fungal hyphae. These characteristics of ROS accumulation in AM roots suggest similarities to ROS accumulation during the senescence of legume root nodules.     

重金属诱导拟南芥原生质体DNA损伤的单细胞凝胶电泳检测

以拟南芥原生质体为实验体系,研究不同浓度的3种重金属离子对拟南芥原生质体的毒性和DNA损伤的差异。结果表明,用1-5mmol·L^-1的Zn^2＋、Cd^2＋和Cu^2＋分别处理的拟南芥原生质体,2小时内活力逐渐下降,并表现出明显的浓度依赖性：与相同浓度的Cd^2＋和Cu^2＋相比,Zn^2＋对拟南芥原生质体活力的影响程度较小,表现出较低的毒性。单细胞凝胶电泳检测发现,用0．1-0．8mmol·L^-1的Zn^2＋、Cd^2＋和Cu^2＋分别处理拟南芥原生质体30分钟,以OTM值表示的原生质体DNA损伤量随重金属离子浓度的增加而递增：相同浓度（0．5mmol·L^-1）的3种重金属离子相比,Zn^2＋对原生质体的遗传毒性明显低于Cu^2＋和Cd^2＋。综合原生质体活力和DNA损伤的单细胞凝胶电泳检测结果,发现ZnO^2＋对拟南芥原生质体的遗传毒性较低,而CdO^2＋和Cu^2＋的遗传毒性较高。本研究建立的拟南芥原生质体实验体系,结合运用单细胞凝胶电泳技术,能够快速、灵敏地检测重金属对植物细胞的遗传毒性。     

Evaluation of DNA damage and mutagenicity induced by lead in tobacco plants

Tobacco (Nicotiana tabacum L. var. xanthi) seedlings were treated with aqueous solutions of lead nitrate (Pb²⁺) at concentrations ranging from 0.4 mM to 2.4 mM for 24 h and from 25 μM to 200 μM for 7 days. The DNA damage measured by the comet assay was high in the root nuclei, but in the leaf nuclei a slight but significant increase in DNA damage could be demonstrated only after a 7-day treatment with 200 μM Pb²⁺. In tobacco plants growing for 6 weeks in soil polluted with Pb²⁺ severe toxic effects, expressed by the decrease in leaf area, and a slight but significant increase in DNA damage were observed. The tobacco plants with increased levels of DNA damage were severely injured and showed stunted growth, distorted leaves and brown root tips. The frequency of somatic mutations in tobacco plants growing in the Pb²⁺-polluted soil did not significantly increase. Analytical studies by inductively coupled plasma optical emission spectrometry demonstrate that after a 24-h treatment of tobacco with 2.4 mM Pb²⁺, the accumulation of the heavy metal is 40-fold higher in the roots than in the above-ground biomass. Low Pb²⁺ accumulation in the above-ground parts may explain the lower levels or the absence of Pb²⁺-induced DNA damage in leaves.     

Loss or retention of chloroplast DNA in maize seedlings is affected by both light and genotype

We examined the chloroplast DNA (cpDNA) from plastids obtained from wild type maize (Zea mays L.) seedlings grown under different light conditions and from photosynthetic mutants grown under white light. The cpDNA was evaluated by real-time quantitative PCR, quantitative DNA fluorescence, and blot-hybridization following pulsed-field gel electrophoresis. The amount of DNA per plastid in light-grown seedlings declines greatly from stalk to leaf blade during proplastid-to-chloroplast development, and this decline is due to cpDNA degradation. In contrast, during proplastid-to-etioplast development in the dark, the cpDNA levels increase from the stalk to the blade. Our results suggest that DNA replication continues in the etioplasts of the upper regions of the stalk and in the leaves. The cpDNA level decreases rapidly, however, after dark-grown seedlings are transferred to light and the etioplasts develop into photosynthetically active chloroplasts. Light, therefore, triggers the degradation of DNA in maize chloroplasts. The cpDNA is retained in the leaf blade of seedlings grown under red, but not blue light. We suggest that light signaling pathways are involved in mediating cpDNA levels, and that red light promotes replication and inhibits degradation and blue light promotes degradation. For five of nine photosynthetic mutants, cpDNA levels in expanded leaves are higher than in wild type, indicating that nuclear genotype can affect the loss or retention of cpDNA.     

小麦Ven型胞质雄性不育植株与可育植株花药蛋白质组差异研究

普通小麦具有偏凸山羊草（Ae. ventricosa）细胞质的不育系为Ven型胞质雄性不育系（Ven cytoplasmic male sterility, Ven CMS）,是粘类小麦CMS的一种类型。该研究对小麦Ven型雄性不育系冀5418A及其同型保持系冀5419B的单核期和二核期的花药进行差异蛋白质组学分析,探讨小麦质核互作雄性不育的分子机制。通过双向电泳分离花药蛋白,基质辅助激光解析飞行时间串联质谱（MALDI TOF TOF）对差异表达蛋白进行质谱鉴定,利用生物信息学进行差异表达蛋白鉴定和功能注释分析。结果表明,在分子量19.0～100.0 kD、等电点4～7线性范围内,共检测到约2 000个蛋白点。2个时期共检测到差异蛋白98个,其中两个时期差异表达变化一致的蛋白点56个;数据库搜索获得鉴定的蛋白点41个,其中18个蛋白的表达量在冀5418A 中显著下调,23个在冀5418B 中明显下调。在不育系和可育系中均有参与能量代谢、活性氧代谢、核糖体合成、花粉物质合成的差异蛋白。GO分析预测差异蛋白生物学过程多涉及电子传递和能量代谢、核糖体代谢、活性氧代谢等,细胞组成主要是在膜区域和线粒体,分子功能主要是DNA和RNA结合功能和水解酶等。KEGG分析表明,较多蛋白分布于碳水化合物代谢、活性氧代谢和蛋白组装和折叠途径。推测不育系冀5418A 的雄性不育性除了涉及能量代谢、活性氧清除过程,核糖体蛋白、伴侣蛋白等也有重要作用,雄性不育性可能还与蛋白质加工、物质合成过程的紊乱有关。     

Tagging genomic sequences that direct transgene expression by activation of a promoter trap in plants

As part of a gene tagging strategy to study the developmental regulation of patterns of plant gene expression, a promoterlessuidA (gus A) gene, encoding the -glucuronidase (GUS) reporter, was introduced into populations of tobacco,Arbidopsis and potato byAgrobacterium-mediated gene transfer. The objective was to generate random functional fusions following integration of thegusA gene downstream of native gene promoters. We describe here a detailed analysis of levels and patterns ofgusA activation in diverse organs and cell types in those populations.gusA activation occurred at high frequency in all three species, and unique patterns of fusion gene expression were found in each transgenic line. The frequency ofgusA activation was differentially blased in different organs in the three species. Fusion gene activity was identified in a wide range of cell types in all organs studied, and expression patterns were stably transmissible to the T₂ and T₃ progeny. Developmentally-regulated and environmentally-inducible expression ofgusA is described for one transgenic line. Phenotypic variants were detected in the transgenic population. These results demonstrate the potential of T-DNA insertion as a means of creating functional tags of genes expressed in a wide spectrum of cell types, and the value of the approach as a complement to standard T-DNA insertional mutagenesis and transposon tagging for developmental studies is discussed.     

Denaturing gradient gel electrophoresis identifies genomic DNA polymorphism with high frequency in maize

Summary We have used denaturing gradient gel electrophoresis (DGGE) to identify genomic DNA polymorphism in maize (Zea mays L.). DGGE probes detect polymorphism in maize at a frequency comparable to the incidence of restriction fragment length polymorphism (RFLP). Probes identifying polymorphism were mapped to maize chromosome arms by utilizing DGGE and maize lines carrying B-A chromosomal translocations. The methods for library construction, probe screening, and genome analysis, described here for maize, can also be applied to the genomic analysis of other organisms.     

High-resolution mapping of repetitive DNA by in situ hybridization: molecular and chromosomal features of prominent dispersed and discretely localized DNA families from the wild beet species Beta procumbens

Members of three prominent DNA families of Beta procumbens have been isolated as Sau3A repeats. Two families consisting of repeats of about 158 bp and 312 bp are organized as satellite DNAs (Sau3A satellites I and II), whereas the third family with a repeat length of 202 bp is interspersed throughout the genome. Multi-colour fluorescence in situ hybridization was used for physical mapping of the DNA families, and has shown that these tandemly organized families occur in large heterochromatic and DAPI positive blocks. The Sau3A satellite I hybridized exclusively around or near the centromeres of 10, 11 or 12 chromosomes. The Sau3A satellite family I showed high intraspecific variability and high-resolution physical mapping was performed on pachytene chromosomes using differentially labelled repeats. The physical order of satellite subfamily arrays along a chromosome was visualized and provided evidence that large arrays of plant satellite repeats are not contiguous and consist of distinct subfamily domains. Re-hybridization of a heterologous rRNA probe to mitotic metaphase chromosomes revealed that the 18S-5.8S-25S rRNA genes are located at subterminal position on one chromosome pair missing repeat clusters of the Sau3A satellite family I. It is known that arrays of Sau3A satellite I repeats are tightly linked to a nematode (Heterodera schachtii) resistance gene and our results show that the gene might be located close to the centromere. Large arrays of the Sau3A satellite II were found in centromeric regions of 16 chromosomes and, in addition, a considerable interspersion of repeats over all chromosomes was observed. The family of interspersed 202 bp repeats is uniformly distributed over all chromosomes and largely excluded from the rRNA gene cluster but shows local amplification in some regions. Southern hybridization has shown that all three families are specific for genomes of the section Procumbentes of the genus Beta.     

Ecological genetics of host plant exploitation in the green peach aphid, Myzus persicae

The ecological consequences of genetic variability in host plant exploitation of Myzus persicae (Hemiptera, Aphididae) were studied in several agro-ecosystems, differing in crop plant heterogeneity. An analysis of aphid populations sampled from sugar beet, potatoes, and lettuce revealed changes in the frequency distribution of aphid clones according to their respective host plant adaptations. The spatial unit of differentiation was below an average field size of 3–5 hectares and a differentiation could be found in the centre of potato and sugar beet fields but not at the edge of the fields. On a temporal scale, the differentiation of populations is transitory even on a large-scale basis of highly specialized cropping areas. The ecological parameters of differentiation are discussed with special reference to agro-ecosystems and integrated pest management. Increasing the genetic heterogeneity of crop fields may help to reduce population outbreaks.

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Zusammenfassung Die ökologischen Konsequenzen genetischer Variabilität in der Wirtspflanzennutzung von Myzus persicae (Hemiptera, Aphididae) wurden in mehreren Agro-Ökosystemen untersucht, die sich in der Kulturpflanzenheterogenität unterscheiden. Eine Analyse von auf Rüben, Kartoffeln und Salat siedelnden Populationen zeigte eine genetische Differenzierung in Wirtspflanzen-angepaßte Feld-populationen. Die räumliche Einheit solcher Differenzierungen liegt unterhalb einer Feldgröße von 3–5 ha. Eine Differenzierung konnte hier in der Mitte der Felder aber nicht am Rand festgestellt werden. Aus zeitlicher Sicht ist die Differenzierung selbst in großräumigen, spezialisierten Anbaugebieten nur vorübergehend feststellbar. Die ökologischen Parameter der Differenzierung werden besonders in Hinsicht auf die integrierte Schädlingsbekämpfung in Agro-ökosystemen diskutiert. Eine Erhöhung der genetischen Heterogenität von Kulturpflanzenbeständen kann möglicherweise zu einer Verringerung von Blattlaus-Massenvermehrungen beitragen.

     

The Promoter of a Metallothionein-Like Gene from the Tropical Tree Casuarina Glauca is Active in Both Annual Dicotyledonous and Monocotyledonous Plants

A chimeric gene consisting of the -glucuronidase (gusA) reporter gene under the control of the metallothionein-like promoter cgMT1 from the tropical tree Casuarina glauca was introduced into Nicotiana tabacum via Agrobacterium tumefaciens and into Oryza sativa by particle bombardment. The strongest histochemical staining for GUS activity was observed in the root system of the transgenic plants, and especially in lateral roots. In contrast, a relatively low level of reporter gene expression was seen in the aerial tissues and GUS staining was located mainly in the plant vascular system. The average ratio of GUS activity between root and leaf was found to be 13:1 in tobacco and 1.5:1 in rice. The pattern of cgMT1 promoter activity in floral organs was found to be different in tobacco and rice. High levels of gusA gene expression were detected in the ovules, pollen grains and tapetum, whereas in rice PcgMT1 directs expression to the vascular system of the floral organs. These results suggest that PcgMT1 is potentially useful in molecular breeding to express genes of interest whose products are preferentially needed in roots.     

Cultivar variation in the effect of chlorsulfuron in depressing the uptake of copper in wheat

The application of herbicides has induced symptoms of nutrient deficiencies under some circumstances. This glasshouse study examined the effect of chlorsulfuron on the uptake and utilization of copper (Cu) in four cultivars of wheat plants (Triticum aestivum L. cvs. Kulin, Cranbrook, Gamenya and Bodallin) on a Cu-responsive soil. Application of chlorsulfuron depressed the concentration of Cu in wheat plants receiving either inadequate or adequate Cu. In plants with inadequate Cu supply, chlorsulfuron increased the severity of Cu deficiency. Shoot weight was markedly decreased by chlorsulfuron at all levels of Cu, through decreasing the number of tillers and the elongation of leaves. This decreased growth of shoots occurred prior to the effect on Cu concentration in tissues. The retranslocation of Cu in old tissues over time was unaffected by chlorsulfuron. In all wheat cultivars, the decreased growth of shoots were correlated with the concentration of Cu in the youngest fully emerged leaf blade with critical levels of 1.6−1.7 at day 25 and 0.9−1.0 μg g⁻¹ d. wt. at day 60. The application of chlorsulfuron tended to increase the critical level at day 25 but not at day 60. In addition, Kulin seems to be most, and Cranbrook least, sensitive to chlorsulfuron. This sensitivity was associated with the sensitivity of the cultivars to Cu deficiency. It is suggested that chlorsulfuron application induces Cu deficiency in wheat plants mainly due to effects on the uptake of Cu. This revised version was published online in June 2006 with corrections to the Cover Date.     

A novel approach to the analysis of the initiation of embryo development in gramineae

An in vivo model system to study the initiation of embryo development is presented. From the so-called Salmon system of wheat (alloplasmic lines with a 1BL-1RS chromosome translocation), three completely isogenic and homozygous lines were produced by selection for uniformity in about 20 selfing/backcross generations as well as between sublines of doubled haploids. The line (aestivum)-Salmon is male fertile and sexual. The lines (caudata)-Salmon and (kotschyi)-Salmon are male sterile and have a parthenogenetic capacity of about 90%. The expression of nuclear-cytoplasmic male sterility is different for the two parthenogenetic lines. The initiation of autonomous embryo development at defined developmental stages of the ovaries and the maximum degree of parthenogenesis are identical in both parthenogenetic lines as proved by the auxin test and progeny analyses. The protein patterns from ovary extracts of the three isogenic lines were identical for more than 200 spots of 2-D polyacrylamide gels, confirming their homogeneity. However, one protein (P 115.1) was found 3 days before and during anthesis only in ovaries of the parthenogenetic lines. It seems to be involved in the initiation of parthenogenesis.     

Genetic variability in host plant adaptation of the green peach aphid, Myzus persicae

The green peach aphid, Myzus persicae (Sulz.), is polyphagous on over 400 plant species in more than 50 families. Phenotypic plasticity of individuals and genetic variability in the population presumably contribute to this polyphagy. The genetic variability in field populations of M. persicae was assessed with respect to their adaptation to sugar beets and potatoes. An analysis of more than 1 000 clones, sampled during 1980, 1981 and 1982 from different host plants in the field, revealed a wide genetic variability in host plant adaptation to sugar beets as well as to potatoes. Both traits seem to be inherited independently from each other and do not correlate with clone-specific host plant preference of apterous adults. The aphid M. persicae can be characterized as a polyphagous insect species with a wide, continuously distributed variability and a broad phenotypic plasticity. A general differentiation of herbivorous species into generalists and specialists tends to ignore the genetic component in the complex of insect-plant relationships.

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Zusammenfassung Die Grüne Pfirsichblattlaus Myzus persicae (Sulz.) lebt polyphag an über 400 Pflanzenarten in mehr als 50 Pflanzenfamilien. Ein breites Nahrungsspektrum einer Art ergibt sich jedoch aus der phänotypischen Plastizität des Individuums oder einer Klonlinie und der genetischen Variabilität der Population. Felpopulationen der Grünen Pfirsichblattlaus wurden auf ihre genetische Variabilität bezüglich der Wirtspflanzenanpassung an Rübe und Kartoffel untersucht. Eine Analyse von mehr als 1 000 Klonen, die über die Jahre 1980, 1981 und 1982 im Rheinland gesammelt wurden, lassen eine breite Variabilität in der Wirtspflanzenanpassung der Population erkennen. Beide Merkmale scheinen unabhängig voneinander vererbt zu werden und zeigen keine Beziehung zum Wirtswahlverhalten adult apterer Läuse der entsprechenden Klone. Die Art M. persicae kann daher charakterisiert werden als eine polyphage Insektenart mit einer breiten genetischen Variabilität und einer grossen phänotypischen Plastizität. Eine generelle Differenzierung von Herbivoren in Generalisten und Spezialisten vernachlässigt die genetische Komponente in der komplexen Beziehung zwischen Insekten un ihren Wirtspflanzen.

     

Comparison of plastid DNA replication in different cells and tissues of the rice plant

In a previous study, we mapped replication origin regions of the plastid DNA around the 3 end of the 23S rRNA gene in rice suspension-cultured cells. Here, we examined initiation of the plastid DNA replication in different rice cells by two-dimensional agarose gel electrophoresis. We show for the first time, to our knowledge, that the replication origin region of the plastid DNA differs among cultured cells, coleoptiles and mature leaves. In addition, digestion of the replication intermediates from the rice cultured cells with mung bean nuclease, a single-strand-specific nuclease, revealed that both two single strands of the double-stranded parental DNA were simultaneously replicated in the origin region. This was further confirmed by two-dimensional agarose gel analysis with single-stranded RNA probes. Thus, the mode of plastid DNA replication presented here differs from the unidirectional replication started by forming displacement loops (D-loops), in which the two D-loops on the opposite strands expand toward each other and only one parental strand serves as a template.     

Quantitative transient gene expression: Comparison of the promoters for maize polyubiquitin1, rice actin1, maize-derivedEmu andCaMV 35S in cells of barley,maize and tobacco

The particle gun approach was used for the quantification of promoter efficiency in a test system for transient gene expression. β-Glucuronidase was used as reporter gene for determining promotote strength. The variability inherent in this gene transfer system was considerably reduced by calculating a transformation efficiency factor given by the expression of a cotransferred second reporter gene (firefly luciferase). The calibration of β-glucuronidase activity by the transformation efficiency factor caused a lower statistical variance of the values and allowed reliable results to be obtained with a smaller set of repetitions. The CaMV 35S promoter (as a control) and the monocot-specific promoters for maize polyubiquitin1, rice actin 1 and the maize-derivedEmu were characterized and compared with respect to expression strength, as tested under identical conditions in suspension cell cultures of maize, barley and tobacco. Compared to the 35S promoter, the monocot-specific promoters show up to 15-fold higher expression in maize and barley but give only weak expression in tobacco. No expression was found for the rice actin 1 promoter in tobacco. The level of reporter gene expression is influenced by the osmotic potential in the agar medium. For theEmu promoter, the calibrated β-glucuronidase activities remained mearly constant at low sucrose concentrations. Above 8% sucrose, the calibrated activities increased steadily with increasing osmotic conditions, reaching a three-to four-fold higher level at the highest sucrose concentration (32%) as compared to the standard concentration (4% sucrose) in the medium.     

Cytological events induced by the inhibition of polyamine biosynthesis in thin cell layers of tobacco

Summary The proliferative growth of thin cell layers ofNicotiana tabacum cultured on a rhizogenic medium was markedly disturbed when polyamine biosynthesis was inhibited. Treatments with polyamine inhibitors led to cell expansion, accompanied by thinning of the cell wall and inhibition of cell division, and frequent cases of nucleolar extrusion, mainly in the parenchymal layer in contact with the medium. Nucleolar extrusion was not correlated with cell expansion. The highest incidence of nucleolar extrusion occurred when the pathways of putrescine biosynthesis were inhibited and when spermidine synthesis, via S-adenosylmethionine decarboxylase, was blocked. The duration of the growth phase with nuclear amitotic divisions was prolonged in the presence of the inhibitors and root meristem formation delayed. When polyamines were added with the inhibitors, all reactions proceeded as in the controls.Abbreviations CHA cyclohexylamine - DFMA DL--difluoromethyl-arginine - DFMO DL--difluoromethylornithine - LS longitudinal section - MGBG methylglyoxal-bis(guanylhydrazone) - PA polyamine - Pu putrescine - RLS radial longitudinal section - S.E. standard error - Spd spermidine     

Reproduction of Pratylenchus penetrans on Potato and Crops Grown in Rotation with Potato

The relative suitability of potato and crops frequently grown in rotation with potato as hosts for Pratylenchus penetrans was evaluated. Suitability of rye, wheat, corn, oat, sorgho-sudangrass, and potato were compared in pot studies based on ratios of final population : initial population density and densities of nematodes in roots at harvest. Population densities increased more on potato, oat, and corn than on rye, wheat, and sorgho-sudangrass. There were no differences among the four rye cultivars or between the two oat cultivars in host suitability. Population increases were not related to root weight or consistently to nematode densities in roots. Although rye and wheat were equally suitable hosts in pot studies, P. penetrans increased more on wheat than on rye in a field study, indicating that reproduction was reduced or mortality was increased on rye under field conditions.