植物的顶端优势现象

植物主茎顶芽生长能抑制侧芽生长的现象称为顶端优势。它是植物器官相关性的一种表现。经常看到有些向日葵的顶端优势很强,它们的顶端只长出一个大花盘来。它们的顶端一旦被除去或受病虫害侵染后死亡,上面的一个或几个侧芽就代替顶芽的地位而长出一个或几个小花盘来。     

“顶端优势”原理在生产实践中的应用与思考

<正>在新课标人教版高中生物必修3第三章《植物的激素调节》中,以顶端优势为例,说明植物激素之一——生长素对植物生长有两重性——既能促进生长,又能抑制生长。典型体现在植物的"顶端优势"上。顶芽产生生长素由于极性运输从而造成侧芽生长素积累,结果导致顶芽生长快,侧芽生长受到抑制。这在农业生产上对一些农作     

树木是怎样渡过严寒冬季的

秋季来临时,树木大都停止生长,脱去树叶,进入休眠,在形态上形成或加强保护组织（如芽鳞、木栓层等）,以适应冬季的低温环境。然而,仅凭以上的变化,树木是很难逃脱冰冻伤害的,它们是怎样渡过严寒的冬季的呢？笔者想从以下两个方面予以解释。１树木可以利用深过冷现...     

正交设计法在变叶木组织培养中的应用

以琴叶变叶木（Codiaeum variegatum vra.pictum)的当年生或二年生茎段诱导顶芽、侧芽萌发,以其形成的小绿叶为外植体,利用正交设计法考察四种不同激素对其叶片愈伤组织诱导的影响,结果表明：6-BA对愈伤组织的诱导是必需的,生根培养以1/2MS NAAO.5mg/1 IBAO.1MG/l最好。     

赤霉素对日本落叶松幼苗顶芽生长的影响

日本落叶松(Larix japonicus)为华北和东北地区主要造林树种之一。但在次年春季幼苗移栽后,幼苗出现干尖现象,即顶芽和一些侧芽干枯,干尖长1～4厘米,严重的仅剩下基部几个侧芽,群众称之为“干梢”。顶芽死亡率达90％,直接影响苗木的生长和上山育林。为解决这一问题,我们在抚顺矿务局林场后腰分场苗圃从不同角度进行了一系列试验。本文是关于赤霉素试验(1969～1972)的初步结果。     

金桔嫩枝侧芽的培养

植物名称:金桔(Fortunella margarita)。材料类别:结果植株上嫩枝的侧芽。培养条件:生长培养基为H+0.1ppmIBA+1—2ppmBA;长根培养基为H+0.2-0.5ppmIBA,每升补加蔗糖3％。培养温度15—30℃,每日光照10—12小时,光强500—10001x。生长与分化情况:切取侧芽,接种于生长培养基上,一星期后,可见到侧芽萌动,一个月后,形成2—5个丛生芽,芽长有0.1—0.8厘米。将幼芽     

顶端优势的克服与抽枝宝的应用

从事农林业生产实践的人都知道,具有顶芽的枝条伸长时,其下侧的芽受到抑制并长期处于“休眠”状态,若剪掉枝条的顶端之后,留在该枝条上的侧芽就会很容易地前发,这种现象就叫做“顶端优势”。最近的研究表明,侧芽的受抑或萌发,同时受到来自顶芽的生长素与来自根系的细胞分裂素的制约。基于这样的原理,我们可以局部地对受到顶芽抑制的侧芽施加某些激素,以改变芽体的内部激素的平衡,有选择性地促使某些芽萌发抽枝。这也正是近年来开发与推广高效植物休眠芽萌发促进剂——抽枝宝的理论根据。抽枝宝为油脂状膏剂,其主要活性成分为细胞…     

问题解答

问:在中学《植物学》课本中提到“茎背光的一面得到的生长素较多,因而这一面的细胞伸长得快”;在讲到顶芽和侧芽的关系时又提到“顶芽产生的生长素向下运输,使侧芽含生长素较多,因而就抑制了侧芽的生长”,这两段话应该怎样理解?答:这是因为:不同浓度的生长素(IAA)可使不同的器官有不同的反应。研究指出:10~(-10) M 生长素促进根的生长,对芽和茎的伸长仅有很少的反应;10~(-8) M 时抑制根的生长,却     

问：蒜薹和葱白是茎吗？

问：蒜薹和葱白是茎吗？答：蒜的茎严重退化，成为一个扁平的盘状地下茎即鳞茎盘，这是蒜瓣着生的地方，在食用蒜时人们常将这个鳞茎盘弃之不食。茎的顶芽发育成较长的花梗，这就是蒜薹，而蒜瓣则是在茎的周围环生的几个或十几个肥厚肉质的侧芽。它们与外面包围着的叶子即...     

被子植物合子的一些休眠表现

受精的卵细胞称为合子。胚的发育是从合子开始的。合子形成以后,通常要经过一个或长或短的“休眠”期才进行分裂,因此胚的开始发育一般较胚乳晚。合子“休眠”期的长短因植物种类不同而异,一般在数小时至几天不等,例如橡胶草传粉后大约4小时初生胚乳核分裂,5小时后合子跟着分裂;水稻在传粉后3小时初生胚乳核分裂,6小时后合子分裂;棉花传粉后24小时才可看到初生胚乳核分裂,而合子分裂要迟至传粉后的第3天。竟有少数植物合子“休眠”期很长,据记载秋水仙在秋季受精后,不久就有多数的胚核形成,而合子在整个冬季的4-5个月期间停留在休眠状态。合子的“休眠”期间发生许多显著的变化:①在电子显微镜下观察到有的植物如荠菜,卵     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.