The large bat Helitron DNA transposase forms a compact monomeric assembly that buries and protects its covalently bound 5′-transposon end

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Can transposable element copy number distribution parameters be estimated from natural populations of Drosophila melanogaster?

The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients.     

Systems ecological accounting for wastewater treatment engineering: Method,indicator and application

Wastewater treatment facility is vital for sustainable urban development. In the course of removing contaminants and discharging ready-for-reuse water, wastewater treatment consumes resources and triggers environmental emission during its lifetime. A comprehensive framework to analyze the embodied ecological elements as natural resources and environmental emissions of wastewater treatment is presented in this work. The systems method as a combination of process and input–output analyses is applied and a set of indicators are accordingly devised. Two representative ecological elements, i.e., greenhouse gases emissions and solar emergy of alternative wastewater treatment systems, i.e., a traditional activated sludge wastewater treatment plant and a constructed wetland have been taken into consideration. For each ecological element, five indicators have been calculated and compared to assess the impact on climate change and resources utilizing style of the case systems. The framework raised in this paper is fully supportive for optimal decision-making among different wastewater treatment technologies, and could be transplanted to be applied to systems ecological accounting for other production systems.     

Wound phloem in transition to bundle phloem in primary roots ofPisum sativum L.

Summary 48 hours after interrupting the root stele ofPisum, wound phloem initiated (proximally or distally to the wound) to reconnect the vascular stumps was found to contain some nucleate wound-sieve elements. At the elongating end of an incomplete wound-sieve tube these elements exhibit a sequence of ultrastructural changes as known from protophloem-sieve tubes. Elongation occurs by the addition of newly divided (wound-) sieve-element/companion-cell complexes. In order to dedifferentiate and assume a new specialization formerly quiescent stelar or cortical cells require at least one (mostly more) preliminary division. Companion cells are consequently obligatory sister cells to wound-sieve elements.By reconstruction using serial sections it could be shown that wound-sieve tubes elongate bidirectionally, starting in an early activated procambial cell of the stele. The elongation is directed by the existence of plasmodesmata, preferably when lying in primary pit fields, and by the plane of preceding divisions. Thus, the developing wound-sieve tube can deviate from the damaged bundle and radiate into the cortex as soon as the plane of the preceding divisions is favourable. In the opposite direction, elongating wound-sieve tubes run parallel to pre-existing phloem traces, thus broading their base at the bundle for the deviating part of the wound-sieve tube. Frequently an individual wound-sieve tube is supplemented at the bundle by a further wound-sieve tube which is partly running parallel to it. Both sieve tubes are interlinked with sieve plates by three-poled sieve elements.Ultrastructurally, the developmental changes of nucleate wound-sieve elements follow the known pattern. In spite of its contrasting origin and odd shape a mature wound-sieve element eventually has the same contents as regular sieve elements: sieve-element plastids, mitochondria, stacked ER and small amounts of P-protein within an electronlucent cytoplasm.     

Comparison of genetic behaviour of the transposable element Tam3 at two unlinked pigment loci in Antirrhinum majus

Summary In Antirrhinum majus the transposable element Tam3 has been described at two unlinked loci pallida and nivea, both of which are required for the production of anthocyanin pigment in flowers. In each case the element is inserted in the promoter region and gives a variegated phenotype. We show that the rate of Tam3 excision at both loci is greatly affected by temperature, being approximately 1000-fold higher at 15°C compared with 25°C. Tam3 is also controlled by an unlinked gene Stabiliser, which considerably reduces excision rate. We show that the high degree of sensitivity to temperature and Stabiliser is an intrinsic property of Tam3 which is not shared by an unrelated element, Tam1. The Tam3 insertion at nivea gives rise to a series of alleles which confer reduced pigmentation, novel spatial patterns and changed instability. These are probably a result of imprecise excision and rearrangements of the Tam3 element.     

Ac transposition in transgenic tomato plants

Summary As an initial step towards developing a transposon mutagenesis system in tomato, the maize transposable element Ac was transformed into tomato plants via Agrobacterium tumefaciens. Southern analysis of leaf tissue indicated that in nine out of eleven transgenic plants, Ac excised from the T-DNA and reintegrated into new chromosomal locations. The comparison of Ac banding pattern in different leaves of the same primary transformant provided evidnece for transposition during later stages of transgenic plant development. There was no evidence of Ds mobilization in tomato transformants.     

Altered tissue specificity of the revertant shrunken allele upon Dissociation (Ds) excision is associated with loss of expression and molecular rearrangement at the corresponding non-allelic isozyme locus in maize

Summary Transposable element Activator (Ac) induced wild-type stable revertants, derived from McClintock's Dissociation (Ds) insertion shrunken (sh) mutant sh-m5933, have been examined for sucrose synthases, SS1 and SS2, encoded by the revertant (Sh) locus and the non-allelic gene Sus (previously designated as Ss2), respectively. A structurally normal Sh locus has been previously described in these revertants. Immuno-blot (Western) and Southern hybridization analyses reported here identify one of the nine alleles, Sh-r5, as unique for several features. It showed altered tissue specificity, as the SS1 protein encoded by the Sh-r5 allele was readily detectable in the immature embryo which is otherwise characterized by the Sus expression only. The level of Sh-r5 expression at the protein and enzyme level was marked by endosperm specific SS1 abundance and a significant down-regulation in the embryo similar to the standard Sh and Sus loci in endosperm and embryo, respectively. We infer that tissue specific levels of gene expression among maize Ss genes is significantly determined by trans-regulatory factors present in these two tissues. The Sh-r5 strain also exhibited a complete loss of the Sus expression in all tissues tested in the plant. Lack of any detectable phenotypic abnormality in the Sh-r5 strain due to the loss of SS2 protein indicated that either the SS2 protein is nonessential or that the two SS isozymes are functionally compensatory. Genomic filter hybridizations with the Sus cDNA clone indicated that the Sus locus in the Sh-r5 strain was not deleted and was, in fact, unique among these revertants. Together, these data provide an unusual insight into the regulation and function of the two SS isozymes in the maize plant.     

Molecular cloning of the c2 locus of Zea mays, the gene coding for chalcone synthase

Summary The c2 locus of Zea mays, identified as one of the genes affecting anthocyanin biosynthesis, was cloned using the transposable element En (Spm) as a gene tag. The Spm element present at the c2 locus in the autonomously mutating c2-m1 line was isolated using En1 element specific probes. Sequences flanking the element were identified as c2 locus specific and were used to clone the nonautonomous c2-m2 and wild-type alleles. The cloning and analysis of a cDNA complementary to the c2 locus provided evidence that this gene encodes the enzyme chalcone synthase.     

Lead and cadmium content of Indian flue-cured tobacco

Summary Studies on levels of lead and cadmium of Indian flue-cured tobacco indicated that the leaf contained very low amounts of these heavy metals as compared to tobacco from other countries. Indian tobacco can therefore be adjudged as ‘safe and clean’ and least hazardous to the smoker. Of the two heavy metals, lead content of soils is higher than cadmium. But in the leaf, cadmium content is more than lead indicating that soil cadmium may be more available to tobacco and hence more readily absorbed by the plant than lead.