北极的春季:迁徙鸟类抵达的生物学

一旦鸟类抵达北极区,迁徙鸟类必须调整其生理和行为以适应不可预知的雪盖、天气、食物资源和天敌胁迫。换言之,他们必须抵抗环境干扰(压力)以便尽早迁徙到苔原上的巢区并建立领域。然后,一旦外界环境有利时,它们就立即开始繁殖。这些鸟类的繁殖有一部分是利用低雪盖区域的微生境以及雪融较快的苔原斑块(特别是在柳树Salix sp．附近)。在北极地区,地面温度在日照若干小时后急剧上升,同时无脊椎动物开始活动。风速在地面柳枝和生草丛苔原10cm下几乎减弱为零。这些条件结合在一起提供了理想的避难所,对于早春迁徙到此的雀形目鸟类尤其如此。然而,如果环境调节变得更为恶劣,这些鸟类会离开。因为与南方越冬地相比,春季北极区条件具有潜在的严酷性,所以鸟类对于应激时的肾上腺皮质反应有所调整。雄鸟到达北极地区时对于剧烈应激刺激下的肾上腺酮的分泌有所提高,并且伴随着对于负反馈敏感性的下降和肾上腺皮质层细胞对于促肾上腺皮质激素作用反应的变化。同时,肾上腺酮结合蛋白(CBG)的水平也有所提高,以至于肾上腺酮的作用在恶劣的环境条件下得到缓冲。基因组受体水平的调节,尤其是在脑和肝脏中糖皮质类固醇类似受体与肾上腺酮的低亲合性,以及肾上腺酮的非基因组水平的作用,可能是很重要的。换言之,与抵达生物学有关的激素一行为系统是高度可变的[动物学报50(6)：948-960,2004]。     

The Slt2-type MAP kinase Bmp3 of Botrytis cinerea is required for normal saprotrophic growth, conidiation, plant surface sensing and host tissue colonization

Mitogen-activated protein kinases (MAPKs) play important roles in signal transduction and regulation of various aspects of saprotrophic and pathogenic growth in plant pathogenic fungi. We have generated a Botrytis cinerea knock-out mutant in the bmp3 gene encoding a homologue of the yeast Slt2 cell wall integrity MAPK. The Δ bmp3 mutant showed reduced vegetative growth on various media, strongly impaired conidiation and loss of sclerotia formation. Growth retardation of the mutant was enhanced in media with low osmolarity, whereas nearly wild-type growth rates were observed under high osmolarity conditions. The Δ bmp3 mutant did not show increased susceptibility to cell wall damage induced by glucanase, Calcofluor White or Nikkomycin Z, but was more susceptible to the oxidizing agent paraquat and the phenylpyrrole fungicide fludioxonil. Δ bmp3 conidia showed normal germination and germ tube growth on agar, but excessive germ tube elongation on hard surfaces and reduced penetration efficiency, indicating a defect in surface sensing. After penetration, development of necrotic lesions induced by the Δ bmp3 mutant was retarded. All these defects were restored by genetic complementation of the mutant with the wild-type bmp3 gene.