樟树研究进展与展望

樟树是我国亚热带地区常绿阔叶林的优势树种,具有重要的生态与经济价值。然而,由于人类提取芳香油而对樟树资源造成了极大破坏,因此目前亟待加强樟树的规模化造林与经营管理。介绍了樟树近年来在良种选育、扦插组培快繁、天然活性成分、逆境生理响应、人工林动态、病虫害防治等方面的研究进展,并提出了未来的研究展望,旨在为进一步提高樟树的林分质量和生态经济效益提供理论参考。     

A stress response pathway regulates DNA damage through β2-adrenoreceptors and β-arrestin-1

The human mind and body respond to stress, a state of perceived threat to homeostasis, by activating the sympathetic nervous system and secreting the catecholamines adrenaline and noradrenaline in the 'fight-or-flight' response. The stress response is generally transient because its accompanying effects (for example, immunosuppression, growth inhibition and enhanced catabolism) can be harmful in the long term. When chronic, the stress response can be associated with disease symptoms such as peptic ulcers or cardiovascular disorders, and epidemiological studies strongly indicate that chronic stress leads to DNA damage. This stress-induced DNA damage may promote ageing, tumorigenesis, neuropsychiatric conditions and miscarriages. However, the mechanisms by which these DNA-damage events occur in response to stress are unknown. The stress hormone adrenaline stimulates β(2)-adrenoreceptors that are expressed throughout the body, including in germline cells and zygotic embryos. Activated β(2)-adrenoreceptors promote Gs-protein-dependent activation of protein kinase A (PKA), followed by the recruitment of β-arrestins, which desensitize G-protein signalling and function as signal transducers in their own right. Here we elucidate a molecular mechanism by which β-adrenergic catecholamines, acting through both Gs-PKA and β-arrestin-mediated signalling pathways, trigger DNA damage and suppress p53 levels respectively, thus synergistically leading to the accumulation of DNA damage. In mice and in human cell lines, β-arrestin-1 (ARRB1), activated via β(2)-adrenoreceptors, facilitates AKT-mediated activation of MDM2 and also promotes MDM2 binding to, and degradation of, p53, by acting as a molecular scaffold. Catecholamine-induced DNA damage is abrogated in Arrb1-knockout (Arrb1(-/-)) mice, which show preserved p53 levels in both the thymus, an organ that responds prominently to acute or chronic stress, and in the testes, in which paternal stress may affect the offspring's genome. Our results highlight the emerging role of ARRB1 as an E3-ligase adaptor in the nucleus, and reveal how DNA damage may accumulate in response to chronic stress.     

Interaction between the vestibulo-ocular and the oculomotor systems]

Optomotor nystagmic activity has been elicited in the "encéphale isolé" cat during repetitive electric stimulation of selective oculomotor regions of the frontal cortex and superior colliculus. These regions were nystagmogenic only when facilitated by a cortical arousal or a vestibular activation.     

Assessment of Mars Exploration Rover landing site predictions

Comprehensive analyses of remote sensing data during the three-year effort to select the Mars Exploration Rover landing sites at Gusev crater and at Meridiani Planum correctly predicted the atmospheric density profile during entry and descent and the safe and trafficable surfaces explored by the two rovers. The Gusev crater site was correctly predicted to be a low-relief surface that was less rocky than the Viking landing sites but comparably dusty. A dark, low-albedo, flat plain composed of basaltic sand and haematite with very few rocks was expected and found at Meridiani Planum. These results argue that future efforts to select safe landing sites based on existing and acquired remote sensing data will be successful. In contrast, geological interpretations of the sites based on remote sensing data were less certain and less successful, which emphasizes the inherent ambiguities in understanding surface geology from remotely sensed data and the uncertainty in predicting exactly what materials will be available for study at a landing site.     

Normal maturation involves systematic changes in binocular visual connections in Xenopus laevis

Systematic changes in neuronal connections have been observed during the development of many vertebrate neuronal systems. These changes have usually involved a refinement from an initial exuberance of connections or a response to some experimental perturbation. Here we report on a system of neuronal connections, which, during a protracted developmental period, undergo ordered changes in response to normally occurring changes in functional requirements. In the frog Xenopus laevis, interocular alignment changes markedly during late larval and post-metamorphic life, producing a progressive enlargement of the binocular portion of the visual field. An intertectal system links the two mid-brain optic tecta and is concerned with the neural representation of binocular visual space. In the adult animal, connections in this system link corresponding points (points receiving information from one locus of binocular visual space) on the two tecta. Changes in eye position with development, however, change the set of corresponding points. Therefore, if the intertectal connections link corresponding tectal points throughout development, they must undergo an ordered change with time. We present electrophysiological evidence that the intertectal connections do, indeed, undergo such changes in response to changes in eye alignment, and that the changes are major.