新热带区两种潮虫的生态特征(甲壳纲:等足目)

对体型大小不同的两种陆生等足类动物进行形态特征和行为特征研究,探讨环境变化对其繁殖特征和种群结构的影响。自2004年5月至2005年4月,在巴西Parque Estadual de Itapua进行野外采样,其中每月采集12个凋落物和土壤样品,实验室手拣法收集等足类,共获得2540只,同时进行个体性别鉴定与测量。结果表明,Atlantoscia floridana平均密度为114只Pm2,Balloniscus glaber平均密度为133只Pm2。A.floridana雌性个体全年可育,B.glaber雌性个体只在早春至初夏时段可育,其中春季这两种动物雌性可育个体数量高。2005年夏季干旱,该气候因子对两种动物种群影响存在差异,其中干旱使A.floridana种群减少,而B.glaber种群基本保持稳定,两种动物间形态结构不同是上述差异的主要原因,尤其是B.glaber,特殊的体型和腹肢肺的存在使其更能忍耐干燥。此外,B.glaber可能也依赖行为策略适应环境,例如挖掘活动,在不利气候条件下挖掘活动能够增加年轻个体生存的机会,也可能对成年个体起到保护作用。对于A.floridana来说,它具有连续繁殖、性成熟时间短和高雌性生育比率的特征,这些策略是对其幼体死亡率高的一种反应     

Structure of plasma membrane in radicles from cotton seeds

Summary Cortical cells in the apical region of excised radicles from cotton (Gossypium hirsutum L. var. M-8) seeds of differing moisture content (6, 12, or 16%) were examined in thin sections of vapor-fixed tissue and in freeze-etched replicas of unfixed tissue with transmission electron microscopy (TEM). The structure of the plasma membrane, as revealed in chemically-fixed tissue, had the tripartite feature characteristic of unit membranes. Regions of the plasma membrane appearing as discontinuities or breaks were shown by stereo tilting to represent an optical artifact caused by image superposition of curved regions of the plasma membrane contained within the thickness of a thin section. In freeze-etched preparations two complementary-type images of the plasma membrane were consistently observed. The asymmetric distribution of membrane-associated particles (MAPS) in the P and E fracture faces suggests that the structure of plasma membranes in cells of dry seeds resembles that of plasma membranes in germinating seeds. The physiological significance of these findings is that leaching of ions and small molecules during seed imbibition does not appear to involve passage through disorganized membranes in the radicle.