University of Fribourg

About: University of Fribourg is a education organization based out in Fribourg, Freiburg, Switzerland. It is known for research contribution in the topics: Population & Glacier. The organization has 6040 authors who have published 14975 publications receiving 542500 citations. The organization is also known as: UNIFR & Universität Freiburg.

Differences in Effects of Pyrrolizidine Alkaloids on Five Generalist Insect Herbivore Species

Abstract: The evolution of the diversity in plant secondary compounds is often thought to be driven by insect herbivores, although there is little empirical evidence for this assumption. To investigate whether generalist insect herbivores could play a role in the evolution of the diversity of related compounds, we examined if (1) related compounds differ in their effects on generalists, (2) there is a synergistic effect among compounds, and (3) effects of related compounds differed among insect species. The effects of pyrrolizidine alkaloids (PAs) were tested on five generalist insect herbivore species of several genera using artificial diets or neutral substrates to which PAs were added. We found evidence that structurally related PAs differed in their effects to the thrips Frankliniella occidentalis, the aphid Myzus persicae, and the locust Locusta migratoria. The individual PAs had no effect on Spodoptera exigua and Mamestra brassicae caterpillars. For S. exigua, we found indications for synergistic deterrent effects of PAs in PA mixtures. The relative effects of PAs differed between insect species. The PA senkirkine had the strongest effect on the thrips, but had no effect at all on the aphids. Our results show that generalist herbivores could potentially play a role in the evolution and maintenance of the diversity of PAs.

Cerebello-cortical linkage in the monkey as revealed by transcellular labeling with the lectin wheat germ agglutinin conjugated to the marker horseradish peroxidase

Abstract: 1. The possibility of a cerebellar linkage, via the thalamus with medial area 6 of the cerebral cortex was further explored in the present experiments (cf. preceding companion paper). 2. It was found that HRP conjugated to the lectin wheat germ agglutinin injected into motor cortical areas was transported beyond the thalamus to the contralateral intracerebellar nuclei when the survival time was 4–7 days. 3. It is suggested that the labeling in the deep cerebellar nuclei occurred via the thalamic relay where cerebellofugal fibre terminals had taken up the marker substance released by corticothalamic fibre terminals or by the retrogradely labeled thalamic perikarya. 4. In general, transcellular labeling of perikarya was weaker than retrograde labeling in the thalamic cells. Some of the nuclear zones in the cerebellum showed relatively dense granulations of the reaction product; in other zones only cells with few granules were seen, and large parts of the nuclei were not labeled at all. 5. The topography of secondary labeling in the cerebellar nuclei depended on the cortical injection sites. In all cases, most labeling was found in the contralateral dentate nucleus. The interposed nucleus received a fair amount of heavy labeling only in the precentral arm and face cases. Very little labeling was seen in the fastigial nucleus and in the cerebellar nuclei ipsilateral to the cortical injections. A somatotopic organization of secondary labeling was noted in the precentral cases with the face being represented caudally, the hindlimb rostrally and the arm between the face and the hindlimb representation. This is in agreement with previous anatomical and electrophysiological investigations. 6. These observations thus lend support to the conclusion that the SMA receives a transthalamic input not only from the basal ganglia but also from the cerebellum, especially from its lateral, neocerebellar portion.

Plant development regulated by cytokinin sinks

Abstract: Morphogenetic signals control the patterning of multicellular organisms. Cytokinins are mobile signals that are perceived by subsets of plant cells. We found that the responses to cytokinin signaling during Arabidopsis development are constrained by the transporter PURINE PERMEASE 14 (PUP14). In our experiments, the expression of PUP14 was inversely correlated to the cytokinin signaling readout. Loss of PUP14 function allowed ectopic cytokinin signaling accompanied by aberrant morphogenesis in embryos, roots, and the shoot apical meristem. PUP14 protein localized to the plasma membrane and imported bioactive cytokinins, thus depleting apoplastic cytokinin pools and inhibiting perception by plasma membrane–localized cytokinin sensors to create a sink for active ligands. We propose that the spatiotemporal cytokinin sink patterns established by PUP14 determine the cytokinin signaling landscape that shapes the morphogenesis of land plants.