大葱(Allium fistulo sum L.)雄性可育系的减数分裂期的小孢子母细胞及四分体,有厚度不均的胼胝质壁。成熟花粉为二胞花粉,生殖细胞长,具PAS正反应的细胞壁。绒毡层兼有腺质及周缘质团型特点。自小孢子期始,绒毡层细胞的细胞质内含有黄...大葱(Allium fistulo sum L.)雄性可育系的减数分裂期的小孢子母细胞及四分体,有厚度不均的胼胝质壁。成熟花粉为二胞花粉,生殖细胞长,具PAS正反应的细胞壁。绒毡层兼有腺质及周缘质团型特点。自小孢子期始,绒毡层细胞的细胞质内含有黄色油脂颗粒或团块,在二胞花粉中期,绒毡层退化。不育系的小孢子母细胞的减数分裂正常,花粉败育发生在具液泡的小孢子期。败育Ⅰ型的小孢子原生质体收缩,并逐渐解体,同时在细胞质中积累油滴,存留于空花粉中。绒毡层细胞,在小孢子及小孢子败育初期,与可育系者相似,唯含油脂颗粒或团块比可育系者少,个别花药的绒毡层细胞含小液泡特多。小孢子败育后期,绒毡层细胞显示出:(1)细胞扁化,原生质体解体退化中;(2)细胞体积扩大,原生质体收缩;(3)绒毡层破毁,中层扩大。败育Ⅱ型的小孢子细胞质先于细胞核解体。两种败育类型的花药,其药室内壁细胞均具发达的条纹加厚壁。本观察难以说明绒毡层与花粉败育的因果关系。展开更多
The primary role of the gonadal steroid hormones in mammals is to regulate reproduction and related behaviors; however, both androgens and estrogens are also integrally involved in mediating higher brain function and ...The primary role of the gonadal steroid hormones in mammals is to regulate reproduction and related behaviors; however, both androgens and estrogens are also integrally involved in mediating higher brain function and processes including cognition, neural development, and neural plasticity. In particular, a number of studies show that estradiol modulates dendritic spine growth and synapse density （synaptic plasticity） in the hippocampus of females, and that increased estradiol levels are generally associated with improvements on a variety of learning and memory tasks. While the majority of research has focused on the beneficial effects of estradiol in females, much less attention has been given to testosterone and its effects on learning and memory in males. Similar to estradiol titers in females, testosterone titers in males decline with age, albeit more gradually, and this decline has been correlated with impairment of certain cognitive tasks. Moreover, studies involving both humans and animals indicate that testosterone and its metabolites can augment responding on certain behavioral tasks, depending on the subject＇s current hormonal state, the response required, and the stimuli involved （e.g., those involving spatial or nonspatial stimuli）. While the exact mechanisms by which testosterone exerts its effects on learning and memory are not fully understood, recent findings suggest that testosterone modulates learning and memory in males through an interaction with the cholinergic system. The overall objective of this review is to discuss studies investigating the role of the gonadal hormones in mediating learning and memory processes in male mammals [Current Zoology 57 （4）： 543-558, 2011].展开更多
文摘大葱(Allium fistulo sum L.)雄性可育系的减数分裂期的小孢子母细胞及四分体,有厚度不均的胼胝质壁。成熟花粉为二胞花粉,生殖细胞长,具PAS正反应的细胞壁。绒毡层兼有腺质及周缘质团型特点。自小孢子期始,绒毡层细胞的细胞质内含有黄色油脂颗粒或团块,在二胞花粉中期,绒毡层退化。不育系的小孢子母细胞的减数分裂正常,花粉败育发生在具液泡的小孢子期。败育Ⅰ型的小孢子原生质体收缩,并逐渐解体,同时在细胞质中积累油滴,存留于空花粉中。绒毡层细胞,在小孢子及小孢子败育初期,与可育系者相似,唯含油脂颗粒或团块比可育系者少,个别花药的绒毡层细胞含小液泡特多。小孢子败育后期,绒毡层细胞显示出:(1)细胞扁化,原生质体解体退化中;(2)细胞体积扩大,原生质体收缩;(3)绒毡层破毁,中层扩大。败育Ⅱ型的小孢子细胞质先于细胞核解体。两种败育类型的花药,其药室内壁细胞均具发达的条纹加厚壁。本观察难以说明绒毡层与花粉败育的因果关系。
文摘The primary role of the gonadal steroid hormones in mammals is to regulate reproduction and related behaviors; however, both androgens and estrogens are also integrally involved in mediating higher brain function and processes including cognition, neural development, and neural plasticity. In particular, a number of studies show that estradiol modulates dendritic spine growth and synapse density （synaptic plasticity） in the hippocampus of females, and that increased estradiol levels are generally associated with improvements on a variety of learning and memory tasks. While the majority of research has focused on the beneficial effects of estradiol in females, much less attention has been given to testosterone and its effects on learning and memory in males. Similar to estradiol titers in females, testosterone titers in males decline with age, albeit more gradually, and this decline has been correlated with impairment of certain cognitive tasks. Moreover, studies involving both humans and animals indicate that testosterone and its metabolites can augment responding on certain behavioral tasks, depending on the subject＇s current hormonal state, the response required, and the stimuli involved （e.g., those involving spatial or nonspatial stimuli）. While the exact mechanisms by which testosterone exerts its effects on learning and memory are not fully understood, recent findings suggest that testosterone modulates learning and memory in males through an interaction with the cholinergic system. The overall objective of this review is to discuss studies investigating the role of the gonadal hormones in mediating learning and memory processes in male mammals [Current Zoology 57 （4）： 543-558, 2011].
