琼脂糖印迹法：观察植物表皮细胞的一种简易方法

本文介绍一种获得完整植物器官表皮细胞大小和数目的简易方法：琼脂糖印迹法。该方法根据琼脂糖凝固时具有可塑性的原理,通过对材料固定、包埋、切胶和显微观察等步骤从而获得材料表皮细胞的轮廓。该方法具有简单迅速、图像清晰、观测结果准确且应用广泛等优点,可使统计植物发育过程中细胞数目及大小的工作变得简单易行。     

植物高度木质化叶片表皮细胞制备方法

以凤凰茶(Camellia sinensis)叶片为例,介绍一种获取高度木质化植物叶片表皮细胞的简易方法——叶片燃烧法.该方法根据高度木质化的叶片在燃烧、过水之后,其上下表皮自行分开、细胞透明化,从而获得材料上下表皮细胞的轮廓.该方法具有简单迅速、制片效率高、上下表皮易区分及可靠稳定等优点,非常适用于木质化叶片表皮特征的研究,也可为植物学及生态学的相关研究方法提供参考.     

植物器官大小相关基因研究进展

器官大小是植物形态的一个重要特征,而且具有严格的种属特异性。植物器官大小虽然受到外在的环境因素（如光照、营养等）的影响,但它由内在特有的细胞数目和细胞大小决定。许多通过转录调节、蛋白合成、激素调节或松弛细胞壁等途径作用于植物细胞繁殖和/或细胞扩张的基因已经被鉴定,它们的过表达或缺失表达能促进植物器官大小和加快植物生长。尽管如此,这些基因通过相对独立的途径起作用,在植物中难以阐明一个相对整合的器官大小基因调控网络,这也是该研究领域的亟待需要解决的问题。目前,一些器官大小相关基因已经应用农作物育种,并培育出显著增大的农作物品种,这也证实了利用器官大小基因进行植物品种选育的可行性。因此,通过研究药用植物器官大小的基因,人为地在分子水平上有目的的调控器官的大小和形态,是缓解当前许多药用植物面临的资源紧缺、枯竭濒危困境的可考虑途径之一。     

27种木犀属植物叶表皮微形态特征的研究

利用光学显微镜和扫描电子显微镜观察了27种木犀属植物的叶表皮,测量并统计了气孔器类型、气孔大小、气孔密度、气孔指数及腺点密度等指标,以明确各种的叶表皮细胞形状及垂周壁式样、表皮角质膜、蜡质纹饰及气孔外拱盖的具体特征。结果显示:木犀属植物叶下表皮有气孔器,形状为圆形、椭圆形;气孔器类型多为不规则型,只有总状桂花和狭叶木犀为环列型;气孔器外围角质层有放射状、条状、环状、颗粒状等多种类型;叶表皮细胞形状有无规则形和多边形2种;下表皮腺点的数目远远大于上表皮。研究表明,木犀属植物气孔器和叶表皮细胞特征在种之间差异比较明显,可以作为种间鉴定的重要依据,具有重要的分类学意义。     

披碱草属3组植物叶片解剖特征及其系统关系

采用石蜡切片法对披碱草属中小颖组、宽颖组和长颖组主要代表种的叶片横切面形态学特征进行观察。结果显示:(1)披碱草属3个组植物的叶片均为等面叶,由表皮、叶肉和维管束三部分构成,表现为典型的狐茅型,即表皮细胞形状、大小和排列不均,叶肉无栅栏组织和海绵组织之分,具有双层维管束鞘,周围叶肉细胞呈不规则排列,厚壁组织与表皮相接;但3个组植物在上表皮细胞形状、大小、沟的深浅,以及大型导管数目等叶片横切面特征上存在明显差异。(2)根据3个组植物叶片横切面性状的演化趋势,对各组的演化关系和系统位置分析表明,小颖组最原始,宽颖组较进化,长颖组最高级;小颖组可能直接派生了较进化的宽颖组,并在宽颖组的基础上进而产生了最高级的长颖组;小颖组、宽颖组和长颖组的这一系统关系与利用外部形态特征所获得的演化趋势基本一致。     

利用洋葱鳞叶表皮细胞观察植物细胞结构实验的改进

以洋葱表皮细胞为研究材料,通过中性红液泡染色和质壁分离实验相结合,将能更清晰地观察到细胞壁,细胞质膜,细胞质,液泡膜,液泡,细胞核,核仁等结构,达到光学显微镜下观察植物细胞基本结构的教学目的。改进后的实验大大提高了利用洋葱表皮细胞观察植物细胞结构实验的教学效果,同时可以通过观察不同部位液泡体积变化,了解植物细胞的动态发育,使学生掌握了更多的知识点。     

24种鳞毛蕨科植物叶表皮形态特征的研究

该研究利用光学显微镜对鳞毛蕨科24种植物的叶表皮形态特征进行观察。结果表明:(1)24种鳞毛蕨科植物的上表皮细胞形状为长条形或不规则形,垂周壁为深波状或浅波状,下表皮细胞均为无规则形,垂周壁均为深波状;上表皮细胞长宽比在1.5~5.7之间,下表皮细胞长宽比在2.2~3.9之间。(2)在24种鳞毛蕨科植物中共观察到8种气孔器类型,分别为不等细胞型、无规则四细胞型、极细胞型、腋下细胞型、横列型、无规则型、聚腋下细胞型和聚合极细胞型,每种植物具有2~8种气孔器类型,气孔均为下生型,多为椭圆形;气孔的长宽比在1.2~1.8之间,气孔密度在17.4~86.0个/mm~2之间,气孔指数为8.60%~37.4%。(3)通过对24种鳞毛蕨科植物的观察可将其上表皮细胞形状、垂周壁形状、上表皮细胞长宽比、主要气孔器类型及衍生类型等作为叶表皮形态特征的分类依据。(4)根据叶表皮形态特征可将24种鳞毛蕨科植物分为2类:即耳蕨类和鳞毛蕨类。该研究在一定程度上支持秦仁昌分类系统对鳞毛蕨科的划分,为鳞毛蕨科植物的系统分类及演化研究提供基础资料。     

北京7种鬼针草属植物果实微形态特征及其系统学意义

采用扫描电镜方法对北京地区鬼针草属植物7个种的果实微形态特征进行了观察、比较。结果表明:(1)7种鬼针草属植物瘦果的果体形状、表面棱的数目、芒刺(冠毛)数目及其上倒刺数目和生长位置等特征可以作为鉴定各种的重要形态学依据。(2)根据果皮在扫描电镜下表面纹饰类型及表皮细胞形状等特征,可将7种鬼针草分为两类:一类果皮表面为典型的网纹纹饰,表皮细胞呈不规则多边形,细胞界限明显;另一类果皮表面为条状网纹或纵条纹纹饰,表皮细胞呈长圆形或长条形,细胞界限不明显。由于7个种的果皮表面纹饰有着明显的差异和各自的特点,并与根据叶形、地理分布及分子等证据得出的系统亲缘关系结果基本相符,表明这一特征可能具有一定的系统学意义。     

新疆委陵菜属不同花柱组植物叶表皮微形态结构的研究

利用光学显微镜和扫描电子显微镜,观察了新疆委陵菜属5组不同花柱组10种4变种植物叶表皮的微形态特征,测量统计叶表皮毛的类型、表皮细胞的形状及大小、气孔器的分布及类型、气孔的形状、大小、密度及指数、气孔外拱盖形态及其纹饰等指标。结果显示:新疆委陵菜属10种4变种植物叶的下表皮均有气孔器的分布,形状为长椭圆形、椭圆形、宽椭圆形和近圆形;气孔器的类型多为无规则四细胞型、无规则型、围绕型和辐射型;表皮毛的类型为针状毛、带状柔毛和腺毛;表皮细胞的形状分为不规则形和多边形2种类型。研究表明,新疆委陵菜属植物表皮毛特征、叶片表皮细胞的形状、垂周壁式样、气孔器的形状类型、气孔密度指数及外围蜡质纹饰等存在差异,对属以下等级的划分有重要价值,可作为物种分类及鉴别的依据,同时也为本属一些分类群间的系统关系的探讨提供佐证。     

大麦亚族3属植物的叶片解剖特征及其系统关系

采用石蜡切片法对大麦亚族中新麦草属、芒麦草属和三柄麦属主要代表种的叶片横切面形态学特征进行观察。结果显示:(1)大麦亚族3属植物的叶片均为等面叶,由表皮、叶肉和维管束三部分构成,表现为典型的狐茅型,即下表皮细胞形状、大小和排列均匀,上表皮细胞形状、大小和排列不均,叶肉无栅栏组织和海绵组织之分,具有双层维管束鞘,周围叶肉细胞呈不规则排列,厚壁组织与表皮相接;但3属植物在上表皮的凹凸程度,下表皮细胞壁的厚薄,叶肉组织中部束间厚,大小型维管束的数目、中肋维管束横径等叶片横切面特征上存在明显差异。(2)根据3属植物叶片横切面性状的演化趋势,对各属的演化关系和系统位置分析表明,新麦草属最原始,芒麦草属较进化,三柄麦属最高级;新麦草属可能直接派生了较进化的芒麦草属,并在芒麦草属的基础上进而产生了最高级的三柄麦属;新麦草属、芒麦草属和三柄麦属的这一系统关系与利用外部形态特征所获得的演化趋势基本一致。     

Cell number counts - The fw2.2 and CNR genes and implications for controlling plant fruit and organ size

Two key determinants of plant and organ size are cell number and cell size, and altering either one may affect the plant organ size, but cell number control often plays a predominant role in natural populations. Domesticated crops usually have larger fruit and harvested organ sizes than wild progenitors. Crop yields have increased significantly by breeding, often via heterosis, which is associated with increased plant and organ size primarily achieved by cell number increases. A small class of genes is now known that control plant and organ sizes though cell number or cell size. The fw2.2 gene was found to control a major QTL for tomato fruit size by negatively affecting cell numbers. Orthologs to these fw2.2 genes underlie QTLs for fruit sizes in other species, and their expression can be negatively correlated with increased cell number. In maize decreased or increased expression of the fw2.2 ortholog ZmCNR1, increases or decreases cell number, respectively, thereby affecting maize organ size throughout the plant and thus also whole plant size. Therefore, these genes should now be considered as more general regulators of plant cell number and organ size. The exact molecular function of these transmembrane domain proteins remains unknown, as does any clear relationship to the cell cycle. Because these genes control organ sizes in diverse plants and important crop species, and because they can affect whole plant size, interest arose into how effects of such genes could parallel agronomic crop improvements, in particular that by heterosis, as it also affects cell number. In joining these subjects here in discussion we speculate on how single gene cell number regulation and heterosis may cooperate in crop improvement.     

SOME EFFECTS OF NITROGEN NUTRITION ON THE MORPHOLOGY AND ANATOMY OF MARROW-STEM KALE

Marrow-stem kale plants grown on plots receiving frequent additions of sulphate of ammonia showed a 40% increase in length of internode and a 25% increase in number of nodes per plant, and the leaf size was increased by between 50 and 70% over plants in plots receiving no N fertilizer. Leaves of kale continue to increase in area until they turn yellow, and the high N leaves showed a greater rate of increase in area at every stage in the life of the leaf.
Various features of leaf structure, such as stomatal index, and thickness of palisade and mesophyll, were unaffected by N treatment. The size of the epidermal cells of the leaves was very variable, and although the high N leaves showed a 12% increase in area per epidermal cell over the low N leaves, this difference is not statistically significant. The increased area of the high N leaves can therefore be attributed mainly to increased cell division during the life of the leaf. Only a very slight increase in rate of cell division is necessary to produce the observed effect.
The greater leaf area of the high N plants can be attributed mainly to increased size of individual leaves, but there was also a significantly greater number of living functional leaves per plant on the high N plants; at 23 weeks from sowing the high N plants had an average of 13.4 living leaves, while the low N plants had only 11.7 living leaves per plant.
There was an appreciable degree of N succulence in the high N kale leaves, which showed a 2% greater moisture content than the low N leaves.
A seasonal drift in epidermal cell size, palisade thickness, and total leaf thickness, is shown to be fully significant, statistically. Marked variations in stomatal frequency are barely significant at the 5% level.     

One step antibiotic disk method for obtaining axenic cultures of multicellular marine algae

A simple and rapid method for obtaining axenic plant material has been devised where antibiotic-containing paper disks are applied to nutrient agarose or agar plates upon which small pieces of plant have been spread. By applying multiple disks to the agarose plate, susceptibility to a large number of antibiotics can be tested simultaneously. Clear zones are produced around those disks where contaminating bacteria are susceptible. Plant pieces are then removed from the clear zones and separately tested for sterility to identify the axenic pieces. The method has been successfully applied to multicellular marine algae (e.g.Enteromorpha, Porphyra, laminaria, Gracilaria andAgardhiella). Pieces fromAgardhiella plants survive better on nutrient medium solidified with agarose when -naphthaleneacetic acid and zeatin are present in the medium.     

Involvement of auxin and a homeodomain-leucine zipper I gene in rhizoid development of the moss Physcomitrella patens

Differentiation of epidermal cells is important for plants because they are in direct contact with the environment. Rhizoids are multicellular filaments that develop from the epidermis in a wide range of plants, including pteridophytes, bryophytes, and green algae; they have similar functions to root hairs in vascular plants in that they support the plant body and are involved in water and nutrient absorption. In this study, we examined mechanisms underlying rhizoid development in the moss, Physcomitrella patens, which is the only land plant in which high-frequency gene targeting is possible. We found that rhizoid development can be split into two processes: determination and differentiation. Two types of rhizoids with distinct developmental patterns (basal and mid-stem rhizoids) were recognized. The development of basal rhizoids from epidermal cells was induced by exogenous auxin, while that of mid-stem rhizoids required an unknown factor in addition to exogenous auxin. Once an epidermal cell had acquired a rhizoid initial cell fate, expression of the homeodomain-leucine zipper I gene Pphb7 was induced. Analysis of Pphb7 disruptant lines showed that Pphb7 affects the induction of pigmentation and the increase in the number and size of chloroplasts, but not the position or number of rhizoids. This is the first report on the involvement of a homeodomain-leucine zipper I gene in epidermal cell differentiation.     

Myosin Vb Mediated Plasma Membrane Homeostasis Regulates Peridermal Cell Size and Maintains Tissue Homeostasis in the Zebrafish Epidermis

The epidermis is a stratified epithelium, which forms a barrier to maintain the internal milieu in metazoans. Being the outermost tissue, growth of the epidermis has to be strictly coordinated with the growth of the embryo. The key parameters that determine tissue growth are cell number and cell size. So far, it has remained unclear how the size of epidermal cells is maintained and whether it contributes towards epidermal homeostasis. We have used genetic analysis in combination with cellular imaging to show that zebrafish goosepimples/myosin Vb regulates plasma membrane homeostasis and is involved in maintenance of cell size in the periderm, the outermost epidermal layer. The decrease in peridermal cell size in Myosin Vb deficient embryos is compensated by an increase in cell number whereas decrease in cell number results in the expansion of peridermal cells, which requires myosin Vb (myoVb) function. Inhibition of cell proliferation as well as cell size expansion results in increased lethality in larval stages suggesting that this two-way compensatory mechanism is essential for growing larvae. Our analyses unravel the importance of Myosin Vb dependent cell size regulation in epidermal homeostasis and demonstrate that the epidermis has the ability to maintain a dynamic balance between cell size and cell number.     

Cell Number Regulator1 Affects Plant and Organ Size in Maize: Implications for Crop Yield Enhancement and Heterosis

Genes involved in cell number regulation may affect plant growth and organ size and, ultimately, crop yield. The tomato (genus Solanum) fruit weight gene fw2.2, for instance, governs a quantitative trait locus that accounts for 30% of fruit size variation, with increased fruit size chiefly due to increased carpel ovary cell number. To expand investigation of how related genes may impact other crop plant or organ sizes, we identified the maize (Zea mays) gene family of putative fw2.2 orthologs, naming them Cell Number Regulator (CNR) genes. This family represents an ancient eukaryotic family of Cys-rich proteins containing the PLAC8 or DUF614 conserved motif. We focused on native expression and transgene analysis of the two maize members closest to Le-fw2.2, namely, CNR1 and CNR2. We show that CNR1 reduced overall plant size when ectopically overexpressed and that plant and organ size increased when its expression was cosuppressed or silenced. Leaf epidermal cell counts showed that the increased or decreased transgenic plant and organ size was due to changes in cell number, not cell size. CNR2 expression was found to be negatively correlated with tissue growth activity and hybrid seedling vigor. The effects of CNR1 on plant size and cell number are reminiscent of heterosis, which also increases plant size primarily through increased cell number. Regardless of whether CNRs and other cell number–influencing genes directly contribute to, or merely mimic, heterosis, they may aid generation of more vigorous and productive crop plants.     

How have the alpine dwarf plants in Yakushima been miniaturized? A comparative study of two alpine dwarf species in Yakushima, Blechnum niponicum (Blechnaceae) and Lysimachia japonica (Primulaceae)

Many plant species are miniaturized in the alpine region in Yakushima, Japan. To examine how these alpine dwarf plants are different from their related lowland ones of the same species, we analyzed two phylogenetically distinct species cytologically, genetically and morphologically: one is a fern species, Blechnum niponicum, and the other is an angiosperm species, Lysimachia japonica. The analysis shows that the alpine dwarf and the lowland plants in each of these species do not differ in chromosome number or genetic constitution. The organ-level comparison between the alpine dwarf and lowland plants of B. niponicum shows that the fertile leaf size correlates closely with the sterile one. By contrast, the flower size does not correlate with the leaf size in L. japonica. At the cell level, the leaf size of the alpine dwarf plants of B. niponicum consists of a smaller number of epidermal cells than that of the lowland plants of this species. On the other hand, the smaller leaf size of the alpine dwarf plants of L. japonica depends on both the smaller number and the smaller size of the epidermal cells. We conclude that plant dwarfism in Yakushima shows variation at both the organ and cell levels.     

Autonomy of cell proliferation and developmental programs during Arabidopsis aboveground organ morphogenesis

Elaboration of size and shape in multicellular organisms involves coordinated cell division and cell growth. In higher plants, continuity of cell layer structures exists from the shoot apical meristem (SAM), where organ primordia arise, to mature aboveground organs. To unravel the extent of inter-cell layer coordination during SAM and aboveground organ development, cell division in the epidermis was selectively restricted by expressing two cyclin-dependent kinase inhibitor genes, KRP1/ICK1 and KRP4, driven by the L1 layer-specific AtML1 promoter. The transgenes conferred reduced plant size with striking, distorted lateral organ shape. While epidermal cell division was severely inhibited with compensatory cell size enlargement, the underlying mesophyll/cortex layer kept normal cell numbers and resulted in small, packed cells with disrupted cell files. Our results demonstrate the autonomy of cell number checkpoint in the underlying tissues when epidermal cell division is restricted. Finally, the L1 layer-specific expression of both KRP1/ICK1 and KRP4 showed no effects on the structure and function of the SAM, suggesting that the effects of these cyclin-dependent kinase inhibitors are context dependent.