Search Results - (Author, Cooperation:P. Nel)

2012-08-04

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Belgium ; *Biological Evolution ; *Fossils ; History, Ancient ; Insects/*anatomy & histology/classification ; Phylogeny ; Wings, Animal

2013-10-18

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Biodiversity ; Biological Evolution ; Ecosystem ; *Fossils ; Insects/anatomy & histology/*classification/genetics ; *Phylogeny ; Species Specificity

1365-3180

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

A total of 74 independently run bioassays with soil incorporated metsulfuron-methyl from 12 different laboratories was analysed by a logistic dose-response curve to assess the precision of regression parameters and relate ED50 to soil properties. The potency in terms of ED50 of metsulfuron-methyl in Brassica rapa L., which was used by all laboratories, varied between 0.05 and 3.9 g a.i. ha-1. ED50 was negatively correlated with pH and positively correlated with organic matter. The majority of laboratories had ED50 within the interval 0.1-1.0 g a.i. ha-1. At one laboratory using three test species, the most sensitive species was Beta vulgaris L. followed by Brassica rapa L. and Lepidium sativum L. The coefficients of variation were smallest for the ED50 and ED90 response levels and largest for the ED10. The slope of the response curves had considerably lower coefficients of variation than the EDs. The results are discussed in relation to a previous collaborative bioassay study. Finally it is suggested that standardization of bioassays with herbicides could be achieved in the same way as standardization of chemical analyses.

Electronic Resource

1432-2242

Springer Online Journal Archives 1860-2000

Biology

Summary Five regions of the maize genome were tested for their response to endogenous factors influencing recombination. These included heterochromatic B chromosomes and abnormal chromosome 10 as well as the sex in which recombination occurred. The frequency of recombination in the proximal A 2-Bt and Bt-Pr segments of chromosome 5 was increased in the presence of B chromosomes, with the male meiocytes showing a greater response than the female meiocytes. In addition, experiments involving 0, 1, 2 and 4 B's revealed a dosage effect of B chromosomes on crossing over in chromosome 5. Recombination in the proximal Wx-Gl 15 interval of chromosome 9 was found to be slightly higher than normal in male flowers when two B chromosomes were present. This increase was accompanied by a decrease in the adjacent Sh-Wx segment. Crossing over in the distal C-Sh segment and in the C-Sh-Wx-Gl 15 regions of female flowers was unaffected by B's. Comparisons of plants heterozygous for abnormal chromosome 10 (K10 k10) and homozygous for the standard chromosome 10 (k10 k10) showed that abnormal 10 greatly enhances crossing over in the A 2-Bt and Bt-Pr segments of chromosome 5. In contrast to the finding with B's, the effect is greater in female than in male sporocytes. K10 showed no significant effect on recombination in the C-Sh-Wx-Gl 15 region of chromosome 9 except in male sporocytes, where there was a slight increase in the Sh-Wx region of 0 B K10 k10 plants and a possible interaction with B chromosomes to raise the level of recombination between Wx and Gl 15. The fact that the regions adjacent to the centromere of chromosome 9 show little or no response to the presence of K10 indicates that the proximal heterochromatin of this chromosome differs qualitatively from that of other maize chromosomes. This conclusion is supported by a comparison of the effects of B chromosomes, K10 and sex on crossing over in chromosomes 5 and 9.

Electronic Resource

1432-0878

Ciliogenesis ; Respiratory epithelium ; Deuterosomes ; Fibrous granules ; Nasal cavity ; Rabbit (New Zealand White), embryos

Springer Online Journal Archives 1860-2000

Biology

Medicine

Summary Previous studies have shown that ciliogenesis in the epithelial cells of various species exhibits similarities as well as differences. In an attempt to establish whether this process is identical in epithelial cells of a single species, early stages of centriole formation not previously described were encountered. Ciliogenesis was investigated in the respiratory epithelium of the nasal cavity of 18 to 23-day-old rabbit embryos. The appearance of groups of deuterosomes and fibrous granules is followed by the radial formation of procentrioles around the deuterosomes and parent centrioles. The majority of the procentrioles, forming acentriolarly, occur in pairs, with their distal ends facing each other, between the deuterosomes. Subsequent growth of these procentrioles between deuterosomes in a group results in separating the deuterosomes from one another. The deuterosomes, however, still remain interconnected by means of the growing procentrioles. Accordingly, long chains and networks consisting of the above-mentioned structures are formed. After the procentrioles have attained a certain length, the chains and networks split into separate deuterosome-procentriole complexes. During these earlier stages of ciliogenesis fibrous granules are present, however, their function is yet to be determined.

Electronic Resource

1871-4528

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Zusammenfassung An der Universität von Pretoria wurden mit der Kartoffelstorte Up-to-Date Versuche durch-geführt, um den Zusammenhang zwischen dem Gibberellinniveau und der Auslösung der Knollenbildung zu untersuchen. In nicht induktiven Photoperioden erfolgte eine Knollenbildung, wenn die junge Blätter und die meristematischen Spitzen entfernt wurden. In diesen Pflanzen konnte die Knollenbildung durch Anwendung von Gibberellinsäure gehemmt werden. Die sich entwickelnden Blätter schienen unter Langtagbedingungen eine Substanz, wahrscheinlich Gibberellin, zu entwickeln, welche die Knollenbildung verzögerte. Beigabe von CCC zum Wurzelnährboden führte zum fast gleichen Grad der Knollenbildung, wie wenn die Pflanzen durch kurze Tageslängen zur Knollenbildung angeregt wurden. Diese Wirkung des CCC wurde durch Anwendung von Gibberellinsäure zu den jungen Blättern nahezu ganz aufgehoben. Verwendung von Gibberellinsäure zu Pflanzen, die unter Kurztagbedingungen zur Knollenbildung angeregt wurden, hatte auch eine nachteilige Wirkung auf die Knollenbildung. Wenn GA und CCC gleichzeitig angewendet wurden, hing die Reaktion von den jeweiligen Konzentrationen der angewendeten Mittel ab (siehe Tabelle 1 und Abb. 1). Es wird vorausgesetzt, dass Knollenbildung normalerweise durch hoch wirksame Gibberellin niveaux verhindert wird und dass eine Knollenbildung erfolgt, sobald das Gibberellinniveau auf ein kritisches Mass herabgesetzt wird. Wenn eine spezifisch knollenbildende Substanz mit im spiele ist, dann ist sie auch in nicht induzierten Kartoffelpflanzen vorhanden. Umweltbedingungen können das Gleichgewicht zwischen den Gibberellinen und den endogenen Hemmern (und wahrscheinlich andern Wachstumssubstanzen) beeinflussen, indem sie ihr Niveau oder ihre Aktivität beeinträchtigen. Ein deutlicher Beweis für die wahrscheinliche Rolle des Gibberellins im Knollenbildungsprozess wird in Abb. 2 dargestellt.

Résumé Des espériences ont été exécutées à l'Université de Pretoria, sur le cultivar Up-to-Date, dans le but d'étudier la relation entre le niveau de gibberelline et l'initiation des tubercules. La tubérisation était réalisée en photopériodes non-inductives alors que les jeunes feuilles et les sommets méristématiques de tiges sont enlevés. On pouvait inhiber la tubérisation dans ces plantes par application d'acide giberrellique. Les feuilles en développement semblaient produire une substance dans des conditions de jours longs, probablement la gibberelline, qui retardait la tubérisation. L'application de CCC au système radiculaire provoquait un degré presque identique de tubérisation que lorsque l'induction était provoquée par par de courtes photopériodes. Cet effet du CCC est presque complètement annihilé par l'application d'acide gibberellique aux jeunes feuilles. L'application d'acide gibberellique aux plantes à tubérisation induite par de courtes photopériodes a également un effet opposé à la tubérisation. Lorsqu'on applique simultanément GA et CCC, la réaction dépend des con-(voir tableau 1 et fig. 1). Il est admis que la tubérisation est normalement inhibée par de hauts niveaux de gibberelline active et que la tubérisation se déclenche aussitôt que le niveau gibberellique est abaissé en-dessous d'un seuil critique. Si une substance spécifique formatrice de tubercules est impliquée, elle est également présente dans les plantes de pomme de terre non induites. Les conditions de milieu peuvent influencer l'équilibre entre les gibberellines et les inhibiteurs endogènes (et probablement d'autres substances de croissance) en agissant sur le niveau ou l'activité de quelquesuns d'entr'eux. La fig. 2 apporte quelque preuve du rôle probable de la gibberelline dans le processus de tubérisation.

Summary Experiments were conducted with the cultivar Up-to-date to study the relationship between gibberellin level and tuber initiation. Tuberization resulted in case of all treatments which led to a decrease in the endogenous gibberellin level. This observation is also applicable to most of the results published by other research workers. It is postulated that a balance between gibberellins and other endogenous growth substances (especially inhibitors) controls the tuberization process, and that tuber initiation results as soon as the gibberellin content decreases beneath a threshold level.

Electronic Resource

0362-2525

Life and Medical Sciences ; Cell & Developmental Biology

Wiley InterScience Backfile Collection 1832-2000

Biology

Medicine

General ultrastructural properties of the atrioventricular valve and the endo- and myocardium of the tigerfish Hydrocynus forskahlii add further information to our knowledge of fish heart morphology. Small pieces of tissue from the heart of H. forskhalii were immersion-fixed in 3% glutaraldehyde in Sörensen's phosphate buffer. Samples were postfixed in 1% osmium tetroxide and processed for transmission electron microscopy using standard techniques. The atrioventricular valve consists of dense collagen and fibroblasts lying between two layers of squamous endothelial cells. The ventricular endothelium consists of squamous cells with large nuclei protruding into the lumen of the ventricle. These cells lie on a basal lamina which overlies loose collagen in the subendothelial space. The ventricular myocardium is built up of distinctive nucleated fibres. Mitochondria, ribosomes, and glycogen are abundant in the sarcoplasm. Less conspicuous intercalated discs with no typical, steplike pattern are found between the myocardial cells. The Z lines as well as the I and A bands are clearly visible. The M lines are prominent, but the most important feature is the N line which is found on either side of the Z line in the lateral parts of the I band. The current research clearly underlines the fact that cardiac ultrastructure presents considerable diversity in different fish species.

9 Ill.

Electronic Resource