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991.
Chromosome doubling was induced in vitro in a diploid hybrid of Rosa rugosa Thunb. using oryzalin as the spindle inhibitor. Nodal sections, 2 mm long, were exposed to 2.5 or 5 μM oryzalin and 10 mm
nodal sections were exposed to 5 μM oryzalin for 0 (controls), 6, 12, 24 and 48 h. The ploidy of the emergent shoots was determined
by flow cytometry. The frequency of tetraploid and mixoploid leaves that developed from 2 mm nodal sections exposed to 5 μM
oryzalin peaked at 12 h exposure, when 35% of the leaves were tetraploid, but fell after longer exposures. Fewer tetraploid
and mixoploid leaves were found when 2 mm nodes were exposed to 2.5 μM oryzalin for 6 and 12 h, indicating that it took longer
for a spindle inhibiting concentration of oryzalin to build up in the meristem. However, the frequencies of tetraploid and
mixoploid leaves continued to rise after 12 h and were highest at 48 h, when 44% were tetraploid. In treatments with 5 μM
oryzalin, the frequencies of tetraploid and mixoploid leaves were lower, at equivalent exposure times, in 10 mm nodes than
2 mm nodes. This suggests that oryzalin diffused to the meristem mainly via the cut surfaces and that access via the epidermis
and cuticle was impeded. 相似文献
992.
Plant Growth Regulators and Induction of Leaf Senescence in Nitrogen-Deprived Wheat Plants 总被引:1,自引:0,他引:1
M. Victoria Criado Irma N. Roberts Mariela Echeverria Atilio J. Barneix 《Journal of Plant Growth Regulation》2007,26(4):301-307
The sequence of events and the signals that regulate the remobilization of nitrogen (N) reserves during senescence induced
by N starvation were studied in leaf 3, the last fully expanded leaf, in 17-day-old wheat (Triticum aestivum L.) plants. The first event observed was a rapid decrease in the isopentenyl adenosine (iPA) concentration during the first
24 h of N starvation. No differences in t-zeatin riboside and dihydrozeatin riboside concentrations were observed until the
end of the assay. During the following 6 days, a decrease in soluble amino acids, chlorophyll, and protein, as well as an
increase in soluble sugar concentration and endoproteolytic activity, could be observed. At day 3 of the experiment, the abscisic
acid (ABA) concentration in the leaves of N-deprived plants started to increase. After 6 days of N deprivation there was a
rise in oxidative stress, as indicated by the increase in malondialdehyde concentration, as well as a decrease in the activities
of antioxidant enzymes catalase and ascorbate peroxidase. To analyze interactions with leaf development, the first, second,
third, and fourth leaves were studied. iPA concentration decreased in all the leaf stages, including leaf 4, which was not
fully expanded. A linear correlation between iPA and protein concentration was determined. These results suggest that the
sharp fall in iPA could be the earliest event that induces protein degradation during the development of senescence induced
by N deficiency, and that only later is ABA accumulated and oxidative stress developed. 相似文献
993.
Roberts PD 《Journal of computational neuroscience》2007,22(3):283-296
Dynamics of spike-timing dependent synaptic plasticity are analyzed for excitatory and inhibitory synapses onto cerebellar
Purkinje cells. The purpose of this study is to place theoretical constraints on candidate synaptic learning rules that determine
the changes in synaptic efficacy due to pairing complex spikes with presynaptic spikes in parallel fibers and inhibitory interneurons.
Constraints are derived for the timing between complex spikes and presynaptic spikes, constraints that result from the stability
of the learning dynamics of the learning rule. Potential instabilities in the parallel fiber synaptic learning rule are found
to be stabilized by synaptic plasticity at inhibitory synapses if the inhibitory learning rules are stable, and conditions
for stability of inhibitory plasticity are given. Combining excitatory with inhibitory plasticity provides a mechanism for
minimizing the overall synaptic input. Stable learning rules are shown to be able to sculpt simple-spike patterns by regulating
the excitability of neurons in the inferior olive that give rise to climbing fibers. 相似文献
994.
Baumann K Perez-Rodriguez M Bradley D Venail J Bailey P Jin H Koes R Roberts K Martin C 《Development (Cambridge, England)》2007,134(9):1691-1701
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Brian S. Roberts Andrew A. Hardigan Marie K. Kirby Meredith B. Fitz-Gerald C.?Mel Wilcox Robert P. Kimberly Richard M. Myers 《Nucleic acids research》2015,43(21):e145
Highly abundant microRNAs (miRNAs) in small RNA sequencing libraries make it difficult to obtain efficient measurements of more lowly expressed species. We present a new method that allows for the selective blocking of specific, abundant miRNAs during preparation of sequencing libraries. This technique is specific with little off-target effects and has no impact on the reproducibility of the measurement of non-targeted species. In human plasma samples, we demonstrate that blocking of highly abundant hsa-miR-16–5p leads to improved detection of lowly expressed miRNAs and more precise measurement of differential expression overall. Furthermore, we establish the ability to target a second abundant miRNA and to multiplex the blocking of two miRNAs simultaneously. For small RNA sequencing, this technique could fill a similar role as do ribosomal or globin removal technologies in messenger RNA sequencing. 相似文献
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K. Kendall A. D. Roberts 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1661)
Adhesion molecules, often thought to be acting by a ‘lock and key’ mechanism, have been thought to control the adhesion of cells. While there is no doubt that a coating of adhesion molecules such as fibronectin on a surface affects cell adhesion, this paper aims to show that such surface contamination is only one factor in the equation. Starting from the baseline idea that van der Waals force is a ubiquitous attraction between all molecules, and thereby must contribute to cell adhesion, it is clear that effects from geometry, elasticity and surface molecules must all add on to the basic cell attractive force. These effects of geometry, elasticity and surface molecules are analysed. The adhesion force measured between macroscopic polymer spheres was found to be strongest when the surfaces were absolutely smooth and clean, with no projecting protruberances. Values of the measured surface energy were then about 35 mJ m−2, as expected for van der Waals attractions between the non-polar molecules. Surface projections such as abrasion roughness or dust reduced the molecular adhesion substantially. Water cut the measured surface energy to 3.4 mJ m−2. Surface active molecules lowered the adhesion still further to less than 0.3 mJ m−2. These observations do not support the lock and key concept. 相似文献