The relation between fine root density and proximity of stems in closed Douglas-fir plantations on homogenous sandy soils: implications for sampling design

Studies have been carried out in two fully stocked, fast growing Douglas-fir plantations of the Dutch ACIFORN project in three consecutive years, to obtain information on fine root densities (Olsthoorn 1991). For the present paper, data collected in early summer 1987 were used to study the relation of fine root density and proximity to the nearest tree or the dominant tree. A large number of samples (37 in one site and 55 in another) was collected in a small plot (10 × 11 m). Two distances were measured at each sampling point: the distance to the nearest tree and the distance to the tree with a dominant crown above that point. There was large variability in fine root density in the samples. Tests with different regression models showed a distinct rooting pattern for one of the two locations. It is concluded that systematic errors in the assessment of fine root density can arise when sampling points are chosen at a constant distance from trees. For Douglas-fir, this systematic error could have been an overestimation of the fine root density by up to 10%. These systematic errors can be avoided easily, using a stratified random design or a random sampling design. When trees are spaced irregularly, a grid sampling design is also appropriate. This revised version was published online in June 2006 with corrections to the Cover Date.     

An Experimental and Theoretical Study on the Novel Tetraphosphorus Triselenide Boron Triiodide (P<Subscript>4</Subscript>Se<Subscript>3</Subscript>)·(BI<Subscript>3</Subscript>) Adduct

Tetraphosphorus triselenide boron triiodide (P₄Se₃)·(BI₃) has been prepared. The product formed has been characterized by Raman and IR spectroscopy. Vibrational assignments for the normal modes of this Lewis acid-base adduct have been made on the basis of comparison between theoretically obtained and experimentally observed Raman and IR data. The geometries of several possible tetraphosphorus triselenide boron triiodide (P₄Se₃)·(BI₃) adducts have been calculated. The bonding and electron transfer from the tetraphosphorus triselenide P₄Se₃ unit to the Lewis acid BI₃ has been investigated by applying NBO analysis.     

Regulatory sequences of Arabidopsis drive reporter gene expression in nematode feeding structures.

In the quest for plant regulatory sequences capable of driving nematode-triggered effector gene expression in feeding structures, we show that promoter tagging is a valuable tool. A large collection of transgenic Arabidopsis plants was generated. They were transformed with a beta-glucuronidase gene functioning as a promoter tag. Three T-DNA constructs, pGV1047, p delta gusBin19, and pMOG553, were used. Early responses to nematode invasion were of primary interest. Six lines exhibiting beta-glucuronidase activity in syncytia induced by the beet cyst nematode were studied. Reporter gene activation was also identified in galls induced by root knot and ectoparasitic nematodes. Time-course studies revealed that all six tags were differentially activated during the development of the feeding structure. T-DNA-flanking regions responsible for the observed responses after nematode infection were isolated and characterized for promoter activity.     

Biological activity of organometallic bismuth compounds

Summary The chemical aspects of organometallic bismuth(Ill) compounds are discussed with respect to the stability of the metal-carbon bond, their low dipole moments, and the limited solubility of these complexes in hydrophilic solvents. A new Bi heterocycle, which is of potential interest in terms of stability and solution behaviour, was shown to exist as an intermediate under the conditions in the mass spectrometer.Although generally bismuth organic compounds are extremely toxic, in the 1970s they became important as biocides and this is still being investigated. They have also been discussed as irritation causing chemical warfare agents. While their application in chemotherapy never became very widespread because antibiotics were discovered, in the last few years the antitumor activity of some derivatives has been reported.Abbreviations BE bond energy - IC inhibition concentration - MIC minimal inhibition concentration - electronegativity (Allred and Rochow) - X halogen, pseudohalogen=F, Cl, Br, CN - Me CH₃ - Et C₂H₅ - Bu C₄H₉ - Ph C₆H₅ - Ac CH₃COO - MS mass spectrometry     

Development of broad virus resistance in non‐transgenic cucumber using CRISPR/Cas9 technology

Genome editing in plants has been boosted tremendously by the development of CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) technology. This powerful tool allows substantial improvement in plant traits in addition to those provided by classical breeding. Here, we demonstrate the development of virus resistance in cucumber (Cucumis sativus L.) using Cas9/subgenomic RNA (sgRNA) technology to disrupt the function of the recessive eIF4E (eukaryotic translation initiation factor 4E) gene. Cas9/sgRNA constructs were targeted to the N′ and C′ termini of the eIF4E gene. Small deletions and single nucleotide polymorphisms (SNPs) were observed in the eIF4E gene targeted sites of transformed T1 generation cucumber plants, but not in putative off‐target sites. Non‐transgenic heterozygous eif4e mutant plants were selected for the production of non‐transgenic homozygous T3 generation plants. Homozygous T3 progeny following Cas9/sgRNA that had been targeted to both eif4e sites exhibited immunity to Cucumber vein yellowing virus (Ipomovirus) infection and resistance to the potyviruses Zucchini yellow mosaic virus and Papaya ring spot mosaic virus‐W. In contrast, heterozygous mutant and non‐mutant plants were highly susceptible to these viruses. For the first time, virus resistance has been developed in cucumber, non‐transgenically, not visibly affecting plant development and without long‐term backcrossing, via a new technology that can be expected to be applicable to a wide range of crop plants.     

Tomato facultative parthenocarpy results from SlAGAMOUS‐LIKE 6 loss of function

The extreme sensitivity of the microsporogenesis process to moderately high or low temperatures is a major hindrance for tomato (Solanum lycopersicum) sexual reproduction and hence year‐round cropping. Consequently, breeding for parthenocarpy, namely, fertilization‐independent fruit set, is considered a valuable goal especially for maintaining sustainable agriculture in the face of global warming. A mutant capable of setting high‐quality seedless (parthenocarpic) fruit was found following a screen of EMS‐mutagenized tomato population for yielding under heat stress. Next‐generation sequencing followed by marker‐assisted mapping and CRISPR/Cas9 gene knockout confirmed that a mutation in SlAGAMOUS‐LIKE 6 (SlAGL6) was responsible for the parthenocarpic phenotype. The mutant is capable of fruit production under heat stress conditions that severely hamper fertilization‐dependent fruit set. Different from other tomato recessive monogenic mutants for parthenocarpy, Slagl6 mutations impose no homeotic changes, the seedless fruits are of normal weight and shape, pollen viability is unaffected, and sexual reproduction capacity is maintained, thus making Slagl6 an attractive gene for facultative parthenocarpy. The characteristics of the analysed mutant combined with the gene's mode of expression imply SlAGL6 as a key regulator of the transition between the state of ‘ovary arrest’ imposed towards anthesis and the fertilization‐triggered fruit set.     

Biodiversity of Dutch forest ecosystems as affected by receding groundwater levels and atmospheric deposition

Forests in the Netherlands are heavily under stress. Recent surveys suggest that about one-third of the forest area in the Netherlands is affected by desiccation. Generally, plant species of moist situations decline, whereas drought tolerant species tend to increase. Besides desiccation, adverse ecological effects of acidification and nitrogen deposition also occur. Their combined action is held responsible for, among others, the decline of oligotrophic vascular plants, lichens and mycorrhizal fungi. At the same time, N-demanding species increase, which is partly caused by nitrogen deposition, and is partly a secondary effect of desiccation through aeration and concomitant mineralization. Nutrient balance of trees is disrupted. Effects on animals also occur: small snails in forest on acid soil decrease, causing Ca deficiency in birds. Measures to reduce these impacts include restoration of the former hydrology, liming, fertilization and removal of N-saturated littler layers.     

Differential gene expression in nematode-induced feeding structures of transgenic plants harbouring promoter—gusA fusion constructs

Sedentary plant-parasitic nematodes are able to induce specialized feeding structures in the root system of their host plants by triggering a series of dramatic cellular responses. These changes presumably are accompanied by a reprogramming of gene expression. To monitor such changes, a variety of promoter— gus A fusion constructs were introduced into Arabidopsis and tobacco. Transgenic plants were analysed histochemically for GUS activity in the nematode feeding structures after infection with either Heterodera schachtii or Meloidogyne incognita . Promoters of the Cauliflower Mosaic Virus 35S gene, the bacterial nopaline synthase, rooting loci ( rol ) and T- cyt genes and the plant-derived phenylalanine ammonia-lyase I gene, which are highly active in non-infected roots, were all downregulated in the feeding structures as indicated by the strong decrease of GUS activity inside these structures. Less stringent down-regulation was observed with chimeric gus A fusion constructs harbouring truncated rol B and rol C promoter sequences. Similar observations were made with transgenic Arabidopsis lines that carried randomly integrated promoterless gus A constructs to identify regulatory sequences in the plant genome. Most of the lines that were selected for expression in the root vascular cylinder demonstrated local down-regulation in feeding structures after infection with H. schachtii . The reverse pattern of GUS activity, a blue feeding structure amidst unstained root cells, was also found in several lines. However, GUS activity that was entirely specific for the feeding structures was not observed. Our data show that the expression of a large number of genes is influenced during the development of the nematode feeding structures.