油樟油细胞和粘液细胞发育的超微结构

利用超薄切片法和透射电镜研究油樟油细胞和粘液细胞发育过程。依据油细胞3层细胞壁的发育将其分为4个阶段。阶段1：仅有初生纤维素壁层，又可分为原始细胞和细胞液泡化二时期。质体内具白色小泡和黑色嗜饿滴，细胞质中有黑色或灰色的嗜饿物质，以及嗜饿物质与液泡的融合。阶段2：栓质化壁层的形成。片层状的栓质叠加在初生纤维素壁内侧。阶段3：内纤维素壁层的形成。较厚而结构松散的内纤维素壁层逐步形成，并叠加在栓质化壁层的内侧，大液泡成为充满嗜饿油脂的油囊。阶段4：油细胞成熟及细胞质解体。杯形构造由内纤维素壁层向细胞腔内突起形成，油囊由液泡包被连接到杯形构造中。解体的细胞质变得电子不透明或呈杂乱状态。粘液细胞发育方式有两种：一种是由内纤维素形成以后的油细胞发育而来，其细胞质中不断产生以同心圆或螺旋线方式排列的多膜结构，并充满整个细胞腔，最后多膜结构解体而成为丝状或颗粒状的粘液；另一种是由已完全成熟的油细胞发育而来，其油囊中的油呈不均匀的状态，并产生局部降解点，逐步扩大，最后油完全降解成颗粒成或丝状的粘液。     

Additions of maize root mucilage to soil changed the structure of the bacterial community

The organic compounds released from roots (rhizodeposits) stimulate the growth of the rhizosphere microbial community. They may be responsible for the differences in the structure of the microbial communities commonly observed between the rhizosphere and the bulk soil. Rhizodeposits consists of a broad range of compounds including root mucilage. The aim of this study was to investigate if additions of maize root mucilage, at a rate of 70 μg C g⁻¹ day⁻¹ for 15 days, to an agricultural soil could affect the structure of the bacterial community. Mucilage additions moderately increased microbial C (+23% increase relative to control), which suggests that the turnover rate of microorganisms consuming this substrate was high. Consistent with this, the number of cultivable bacteria was enhanced by +450%. Catabolic (Biolog^® GN2) and 16S-23S intergenic spacer fingerprints exhibited significant differences between control and mucilage treatments. These data indicate that mucilage can affect both the metabolic and genetic structure of the bacterial community as shown by a greater catabolic potential for carbohydrates. We concluded that mucilage is likely to significantly contribute to differences in the structure of the bacterial communities present in the rhizosphere compared to the bulk soil.     

假野菰粘液挥发性成分的GC-MS分析

[目的]分析假野菰花萼筒与花冠筒之间粘液的挥发性成分,为假野菰的综合开发利用提供参考。[方法]用GC-MS技术对假野菰粘液的挥发性成分进行了分析。[结果]在假野菰粘液的挥发性成分中鉴定出2种化学成分,分别为2-（2-丁氧基乙氧基）乙醇和正丁基甲基亚砜。[结论]假野菰粘液的挥发性成分可作为某些药物和精细化学品的原料,但挥发性成分并非假野菰粘液的主要成分,今后研究应侧重于假野菰粘液的多糖类物质。     

Structure and Function of the Root Cap

The root cap (RC) is a multilayered dome of spindle-shaped parenchyma cells that overlies the growing root tip. It is present in the roots of almost all crop species. This paper briefly reviews some topics on the structure and function of the RC in the major crop species such as maize and rice. Special attention is placed on its contribution to the root system formation, that is, the elongation and growth direction of axile roots. The cells produced in the RC meristem are pushed forward as new cells form beneath them, and eventually the cells on the periphery of the RC fall off. The life cycle of RC cells of maize has been studied extensively and ranges from one to seven days. Approximately 4,000 to 21,000 cells are present in a complete maize RC, and 1,400 to 3,200 sloughed cells can be found in the rhizosphere soil per day per root. These cells, called root border cells (RBCs), mix with RC mucilage and play important roles for the root growth in soil. The RBC-mucilage complex effectively reduces the resistance roots experience during penetration into field soil, about 30–40% of the resistance being reduced by the presence of RC alone. The RC is also a tissue integral to gravitropism, and is known to determine the direction of root growth. The size of amyloplasts and coumellae in RCs has a strong influence on determining the growth angle of axile roots. The function of the individual regions of the RC and how the RC tissues and cells are formed should be studied further to advance our understanding regarding the critical roles of the RC in crop root growth.     

喜马拉雅紫茉莉瘦果粘液对种子低温萌发的保护

以采自西藏林芝的喜玛拉雅紫茉莉(Mirabilis himalaica)瘦果为材料,了解瘦果结构组成、淀粉颗粒对瘦果TTC活性检测的影响,及不同吸胀时间瘦果抵抗低温胁迫的效果,以揭示瘦果分泌粘液在萌发过程中的低温保护作用.结果表明:瘦果由果皮、种皮、胚和淀粉颗粒组成,淀粉影响了TTC检测细胞活性的准确性,并发现成熟瘦果有分泌粘液的特性;瘦果发芽的适温为15℃;TTC法检测瘦果细胞活力显示,吸胀72 h是研究低温胁迫对喜马拉雅紫茉莉瘦果萌发影响的较适宜时间;吸胀72 h的瘦果低温胁迫处理后再进行萌发试验,-5℃和-10℃处理的瘦果在发芽进程中后期有粘液瘦果发芽率比去掉粘液瘦果的发芽率高8.3%左右.     

铝毒胁迫下植物的响应机制

铝(Al)毒胁迫会引起植物一系列的生理生化响应。本文针对Al毒胁迫下植物的不同响应机制展开了综述,分别介绍了根系有机酸的分泌、根表黏胶物质、细胞壁成分的变化及pH和酚类物质的变化与抗Al性的关系,尤其以细胞壁胼胝质的形成为重点给予了详细的论述。最后结合Al毒的研究现状,为未来相关领域的研究提出了自己的一些看法。     

Maize root mucilage decreases adsorption of phosphate on goethite

 This work was carried out to determine the influence of root exudates on phosphorus solubility in the presence of a strong phosphate sorbant. Root mucilage was collected from maize grown under field conditions. Polygalacturonic acid (PGA) was also used as a model of exudates. Adsorption of phosphate by synthetic goethite was measured in the absence of either (1) root mucilage collected from maize in the field, or (2) PGA. The ranking order of the adsorption on goethite was phosphate at low concentration >PGA >mucilage >phosphate at high concentration. Then, competitive adsorption between phosphate ions and PGA or mucilage was studied. Increasing the concentration of PGA or mucilage added to the goethite suspension decreased the amount of phosphate adsorbed on goethite. It is likely that PGA, mucilage and phosphate compete for the same adsorption sites on goethite: the effect of the coating of the mineral by the mucilage is another possible explanation. Received: 18 April 2000     

Method to quantify root border cells in sandy soil

Root border cells are cells that detach from the growing root cap, and serve both physical and biological roles in the rhizosphere. Most work on border cells has been confined to agar, or hydroponic culture, because of the difficulty in separating them from soil particles. We present a new method to separate the root border cells from soil, and quantify border cell numbers in non-sterile sandy loam soil at contrasting matric potentials (−20 and −300 kPa). Recovery rates of 90±1% were achieved using a combination of surfactants, sonication, and centrifugation. Root border cell numbers in the dry soil (1.4×10³ after 24 h) were significantly decreased as compared with those in the wetter soil (1.7×10³ after 24 h). Possible reasons for the decreased release of border cells are discussed.     

低pH和铝毒对荞麦根边缘细胞特性的交互作用研究

采用悬空气培法,研究低pH(3.5、4.5、5.5)和铝毒(0、50、100μmolL-1)及其交互作用对荞麦根长、根边缘细胞活性及其分泌的黏液层厚度的影响。处理12h,Al3+浓度由50μmolL-1增至100μmolL-1时,pH3.5的根伸长量分别降低18.6%和31.9%,pH4.5时分别降低18.9%和26.8%,pH5.5时各降低8.5%。处理24h的根伸长量变化与12h类似。pH降低至3.5时,边缘细胞的活性下降28.6%,黏液层厚度无明显变化。Al3+浓度升高至100μmolL-1时,黏液层增厚64.6%,而边缘细胞活性变化不大。pH3.5与100μmolL-1Al3+的处理,边缘细胞活性最低,黏液层厚度最大,两者间存在极显著的交互作用。可见低pH加剧铝毒发生,外围黏液层产生可以减轻Al3+对边缘细胞的伤害。     

Constitutive expression of Cry proteins in roots and border cells of transgenic cotton

Transgenic cotton plants expressing Cry1Ac and Cry2Ab, from the soil bacterium Bacillus thuringiensis (Bt), provide effective control of certain lepidopteran pests, however, little is known about the proteins below ground expression. We used ELISA to quantify in vitro expression of the Cry1Ac and Cry2Ab proteins in mucilage, root border cells and root tips in five transgenic cultivars of cotton compared to conventional cultivar Sicot 189. Expression of Cry proteins in roots and border cells of the transgenic cotton cultivars was constitutive and at detectable levels, with Cry1Ac and Cry2Ab protein expression ranging from <20 ppb to >100 pbb. To determine if genetically modified cotton demonstrated simple differences in properties of the root, when compared to an elite parental line (cv. Sicot 189), we enumerated border cells on seedling radicles. Border cell counts of 14 cultivars ranged from 0.2 to 1.1 × 10⁴ cells per root tip with an average of 5 × 10³ border cells. Border cell production in the transgenic cultivars was generally similar to that of both donor and elite parents, the exception being the cultivar Sicot 189, which had substantially more border cells than all of its transgenic derivatives. Comparison of border cell number with varietal disease resistance ranking found a limited relationship (r ² = 0.65, n = 7) between border cell numbers and the commercial resistance rank against Fusarium wilt of cotton. The implications of differences in cotton cultivar border cell number and root tip expression of Cry proteins for plant–microbe interactions in the rhizosphere and the soil ecosystem are yet to be resolved.