Crossing experiments in Allium L. section Cepa

VAN RAAMSDONK, L. W. D., WIETSMA, W. A. & DE VRIES, J. N., 1992. Crossing experiments in Allium L. section Cepa . A full diallel was carried out with six diploid species of Allium section Cepa and A. roylei of section Rhizirideum , High isolation barriers were found between the related species A. cepa and A. oschaninii , between A. oschaninii and A. vavilovii , and between A. galanthum and A. pskemense . On the contrary, the species A. cepa and A. roylei , belonging to different sections, show only slight isolation barriers. The Wallace effect, which is the development of internal isolation barriers as such, is likely to have taken place in the evolution of A. oschaninii and A. vavilovii , and possibly also between A. galanthum and A. pskemense .     

The Effect of Oxygen on Endogenous Cytokinin Levels and Germination of Leucadendron daphnoides Seed

The soybean callus assay was used to study the effect of high oxygen tensions on the cytokinin levels of Leucadendron daphnoides Meisn. seed, where dormancy is apparently due to the restricting effect of the seed coat on oxygen diffusion to the embryo. High oxygen tensions led to a six-fold increase in germination compared to seed incubated in air and resulted in significant increases in butanol soluble cytokinins prior to visible germination. It is suggested that the primary effect of oxygen is to increase the rate of respiration and thus, to provide the energy required for the synthesis of butanol soluble cytokinins which leads to cotyledon expansion and subsequent radicle elongation. Present indications are that untreated seeds remain dormant due to low concentrations of butanol soluble cytokinins in their embryos.     

Introgression explains incongruence between nuclear and chloroplast DNA-based phylogenies in Allium section Cepa

Phylogenetic relationships between species of Allium section Cepa and A. rqylei (section Rhizirideum) have been inferred from nuclear DNA variation (RAPDs; nDNA dataset) and from morphological, pollen epidermis texture, chromosomal and chemical variation (supranuclear dataset). These sets were complemented with data, taken from the literature, on cpDNA variation and crossability. The trees produced with the supranuclear, nDNA and cpDNA datasets were compared by using the topology of the most parsimonious tree of one dataset as the constraint for the construction of a most parsimonious tree of another dataset. The accuracy of the trees were evaluated by calculating several Consistency and Incongruence Indices. The constrained tree of supranuclear-nDNA datasets showed the highest index values. The tree topologies of the supranuclear and cpDNA datasets were the least similar. The cpDNA tree and crossability dendrograms were identical. The most important difference between the nDNA-supranuclear trees and the cpDNA-crossability trees pertains to the position of Allium roylei , which is much closer to the clade A. cepa/A. vavilovii in the cpDNA tree than in the nDNA tree. This difference is considered to be the result of chloroplast capture from one species to another after an introgression event. A shorter distance between species inferred from a cpDNA tree than from a nDNA or comparable tree might be indicative for the level of crossability.     

Inadvertent gene silencing of argininosuccinate synthase (bcass1) in Botrytis cinerea by the pLOB1 vector system

For several years, researchers working on the plant pathogen Botrytis cinerea and a number of other related fungi have routinely used the pLOB1 vector system, based on hygromycin resistance, under the control of the Aspergillus nidulans oliC promoter and what was reported to be the β‐tubulin (tubA) terminator. Recently, it has been demonstrated that this vector contains a 446‐bp portion of the B. cinerea argininosuccinate synthase gene (bcass1) rather than the tubA terminator. As argininosuccinate synthase is essential for the production of l ‐arginine, inadvertent gene silencing of bcass1 may result in partial l ‐arginine auxotrophy and, indeed, may lead to altered phenotypes in planta. In this article, we report our findings relating to possible problems arising from this incorrect plasmid construction. As an absolute baseline, gene disruption of bcass1 was carried out and generated a strict auxotroph, unable to grow without exogenous arginine supplementation. The knockout displayed an alteration in host range in planta, showing a reduction in pathogenicity on strawberries, French bean leaves and tomatoes, but maintained wild‐type growth on grape, which is in accordance with the reported arginine availability in such tissues. Deliberate gene silencing of bcass1 mirrored these effects, with strongly silenced lines showing reduced virulence. The degree of silencing as seen by partial auxotrophy was correlated with an observed reduction in virulence. We also showed that inadvertent silencing of bcass1 is possible when using the pLOB1 vector or derivatives thereof. Partial arginine auxotrophy and concomitant reductions in virulence were triggered in approximately 6% of transformants obtained when expressing enhanced green fluorescent protein, luciferase, monomeric red fluorescent protein or β‐glucuronidase using the pLOB1‐based expression system, which inadvertently contains 446 bp of the bcass1 coding sequence. We recommend the testing of transformants obtained using this vector system for arginine auxotrophy in order to provide assurance that any observed effects on the development or virulence are a result of the desired genetic alteration rather than accidental bcass1 silencing.     

Distributions of Ephemeroptera, Plecoptera, and Trichoptera of three maritime catchments differing in pH

1. Two broad-scale environmental influences affecting species of Ephemeroptera, Trichoptera and Plecoptera inhabiting riffle habitat of three study catchments in New Brunswick and Nova Scotia were stream size-temperature-related variables and acidity-related variables. 2. Species richness was most affected by acidity in tributaries of intermediate size <0.001<0.1m³s^?1). 3. Of the three insect orders investigated, mayfly species richness was affected most by acidity, and stonefly species richness affected least by this factor. 4. Zoogeographical isolation of the Nova Scotian catchments resulted in absence of some species of low general abundance, but these species had little influence on the site classification by TWINSPAN analysis. 5. Predaceous stoneflies were collected in greater numbers from circumneutral sites and predaceous caddisflies in greater numbers from the Nova Scotian sites. 6. Although the Nova Scotian catchments have probably been historically acidic, due to high concentrations of organic acids, pH currently limits the distributions of many indigenous invertebrate species. These species may be vulnerable to the more recent, additional, anthropogenic acidification of these catchments.     

Sterilization by Means of Hydrochloric Acid Vapour

As heat sterilization of glass bottles often results in breakage and of most plastic containers in deformation, we investigated a rapid low-temperature sterilization method as an alternative. Vapour evolving from hydrochloric acid was chosen because it does not leave toxic residues which might contaminate food packed in treated containers. Vapour evolving from 0.25 ml of 31% (w/w) hydrochloric acid reduced the number of viable spores of aerobic and anaerobic bacteria in bottles (300 ml) by a factor of at least 2500 and that from 0.01 ml of 37% (w/w) hydrochloric acid reduced the number of mould spores by a factor of over 40 000 within 5 min at 20°C.