Role of trichome ofPteris vittata L. in arsenic hyperaccumulation

Environmental scanning electron microscope (ESEM) fitted with an energy dispersive X-ray microanalyzer (EDX) was used to investigate the surface micromorphology and arsenic (As) micro-distribution in Chinese brake (Pteris vittata L.). It was found that amounts of trichome, which possessed multicellular structure with the average length of 160 μm and with an average diameter of 28 μm, existed in the frond ofP. vittata, and the density of trichome on the pinnate axial surface was higher than that on the petiole. Visible X-ray peak of As was recorded in the epidermal cell and trichome. The relative weight of As in the pinnate trichome, which contained the highest concentration of As among all tissues of the plant, was 2.4 and 3.9 times as much as that in the epidermal and mesophyllous cells, respectively. The As concentrations in the basal and stalk cells of the same trichome were higher than that in its cap cell. This is the first time to report that the trichome ofP. vittata plays an important role in arsenic hyperaccumulation. The finding from the present study implies that much attention should be paid to the role of the trichome in understanding the hyperaccumulation and detoxicity of As in the hyperaccumulator and improving the ability of As accumulation.     

Role of trichome of Pteris vittata L. in arsenic hyperaccu-mulation

Heavy metal pollution of soils, caused by various anthropogenic sources, is a major environmental problem. Due to its cost-effectiveness and environ-mental friendliness, phytoremediation of arsenic-con- taminated soils has attracted more and more attention. An arsenic (As) hyperaccumulator, Chinese brake (Pteris vittata L.) was discovered by Chen et al. in China[1]. The field phytoremediation in Chenzhou City, Hunan Province has been successfully carried out by Chen et al. since 2000[2,3].…     

Origin and evolution of the unusual leaf epidermis of Caryodaphnopsis (Lauraceae)

We studied leaf epidermal anatomy of Caryodaphnopsis Airy Shaw, a genus disjunct between tropical Asia and tropical America, using light microscope and scanning electron microscope. We sampled 10 species of Caryodaphnopsis and 52 species of other Lauraceous genera. Our observations suggest that this genus possesses a unique lower leaf epidermis. Compared with other leaves of Lauraceae, this genus has an additional layer covering the lower leaf epidermis and the stomatal apparatus. The additional layer is either closed or poriferous/reticulate. The outer periclinal walls of the lower leaf epidermis protrude outside forming hollow domes or columns, and the distal endings of these domes or columns are expanded and fused, which forms the additional covering layer. Three different types are recognized in the genus: (1) the middle portion of the protuberances is not contracted and the distal endings are free or adnate to each other, with only limited space between the two layers; (2) the middle portion is slightly contracted in the outer part, the distal endings are fused, with more space between the two layers; (3) the middle portion is conspicuously contracted and elongated into columns, the distal endings are fused and it is roomy between the two layers. The structure of the leaf lower epidermis is reconstructed and illustrated for the first time. This unusual leaf lower epidermis of Caryodaphnopsis is derived in Lauraceae and is an autapomorphic character. Outward protrusions of the outer periclinal walls forming papillate protuberances surrounding the stomatal apparatus are also found in a few other genera including Neocinnamomum, a genus closely related to Caryodaphnopsis, but the distal endings of these protrusions are not expanded and connected. We hypothesize that the periclinal wall of the lower leaf epidermis has been gradually modified in Lauraceae, from a smooth pattern in most genera, to papillate pattern (e.g. Neocinnamomum), and to the double layered lower leaf epidermis in Caryodaphnopsis. The origin and evolution of this unique lower epidermis might have been related to the climatic cooling and aridification since the late Eocene.     

Seed treatment with growth regulators and crop productivity. I. 2,4-D as an inducer of salinity-tolerance in wheat (Triticum aestivum L.)

The paper investigates how the apoplastic route of ion transfer is affected by the outermost cortex cell layers of a primary root. Staining of hand-made cross sections with aniline blue in combination with berberine sulfate demonstrated the presence of casparian bands in the endo- and exodermis, potentially being responsible for hindering apoplastic ion movement. The use of the apoplastic dye Evan's Blue allowed viewing under a light microscope of potential sites of uncontrolled solute entry into the apoplast of the root cortex which mainly consisted of injured rhizodermis and/or exodermis cells. The distribution of the dye after staining was highly comparable to EDX analyses on freeze-dried cryosectioned roots. Here, we used Rb+ as a tracer for K+ in a short-time application on selected regions of intact roots from intact plants. After subsequent quench-freezing with liquid propane the distribution of K+ and Rb+ in cell walls was detected on freeze-dried cryosections by their specific X-rays resulting from the incident electrons in a SEM. All such attempts led to a single conclusion, namely, that the walls of the two outermost living cell sheaths of the cortex largely restrict passive solute movements into the apoplast. The ring of turgescent living rhizodermis cells in the root tip region forms the first barrier. With increasing distance to the root tip, in the course of their maturation resp. degradation, this particular function of the rhizodermis cells is replaced by the hypodermis resp. exodermis. Furthermore, the restriction of apoplastic ion flow by the outermost cortex cell layers is rather effective but not complete. Thus, the solute transfer into the stele is mainly restricted by the casparian bands of the endodermis. The overall conclusion is that the resistances of the rhizodermis and exodermis are additive to the endodermis in their role of regulating the apoplastic solute movement across roots. This revised version was published online in August 2006 with corrections to the Cover Date.     

The distribution of lead in duckweed (Lemna minor L.) root tip

While considerable information on lead distribution in the cells of terrestrial plants has been collected, little is known about lead localization in the cells of the aquatic plant. Lemna minor L. (duckweed) roots were examined using X-ray microanalysis. After 1-h treatment with lead, its concentration was the highest in small vacuoles. After 6 and 12 h, the lead content of cell walls gradually increased. The changes of lead level between vacuoles and cell walls may result from redistribution of this metal from symplast to cell walls or it may reflect increased apoplastic transport. Lead was not found in the ground cytoplasm of any variants of the experiments. This fact and presence of lead in small vesicles suggests that endocytosis may play the role in lead uptake in Lemna.     

毛竹害螨的损失估测和防治指标

采用均匀分布、典型整群抽样调查法对福建省南平市延平区毛竹林毛竹害螨为害进行调查。结果表明,毛竹害螨为害对毛竹竹杆重量和出笋量都有一定的影响,使得竹林蓄积量下降,出笋量大大下降。建立了毛竹害螨对毛竹竹杆重量和出笋量损失的估测模型,并以此推导出了相应的经济危害允许水平和防治指标。     

Accumulation,localisation, and toxic effects of cadmium in the liverwort Lunularia cruciata

Summary. Accumulation, tissue and intracellular localisation, and toxic effects of cadmium were investigated in the liverwort Lunularia cruciata. The results of analyses carried out by atomic absorption spectrometry on single plants showed that the cadmium accumulation was dose- and time-dependent. Cadmium localisation was assessed by X-ray scanning electron microscopy microanalysis in gemmalings and in the different tissues of the thallus and by X-ray transmission electron microscopy microanalysis at the cellular level. The metal preferentially accumulated in the hyaline parenchyma and at the base of the gemma cups. Inside the cell, cadmium accumulated in the vacuoles and the cell wall. Metal accumulation was accompanied by a concomitant increase in sulphur content within the vacuoles of stressed cells. Gel-permeation chromatography showed that most of the cadmium was associated with a low-molecular-mass fraction eluting at a ratio of elution volume to void volume corresponding to that of phytochelatins. The excess of sulphur deposited in the vacuoles may well have been caused by the stress-induced synthesis of phytochelatins. At the ultrastructural level, sublethal concentrations of cadmium caused alterations of the fine structure of the cells, inducing marked alterations of the chloroplast structure. Cadmium also induced a dose-dependent inhibition of apical thallus growth and gemma germination.Correspondence and reprints: Department of Plant Biology, University Federico 11, via Foria 223, 80132 Naples, Italy.     

Dynamics of lead accumulation in mycorrhizal and non-mycorrhizal Norway spruce (Picea abies (L.) Karst.)

Twelve-week-old seedlings of Norway spruce (Picea abies (L.) Karst), non-mycorrhizal or mycorrhizal with Laccaria laccata, Paxillus involutus or Pisolithus tinctorius were exposed to 5 M Pb for either 32 or 42 days in a quartz sand-nutrient solution system. Ultrathin sections of mycorrhizal and non-mycorrhizal short roots were examined by X-ray microanalysis. After 42 days Pb treatment, the Pb content of the cortex cell walls was lower in the non-mycorrhizal short roots and in the P. involutus mycorrhizae than in the mycorrhizae of L. laccata or P. tinctorius. The Pb content of the cell walls of the hyphal mantle was higher in P. involutus than in L. laccata or P. tinctorius. The short term experiment over 32 days showed that the Pb content of the cortex cell walls strongly increased during the first 16 days in the non-mycorrhizal roots and the L. laccata mycorrhizae, whereas it increased more slowly in the P. involutus mycorrhizae. After 32 days Pb treatment, the Pb content in the cortex cell walls in the P. involutus mycorrhizae was similar to that in the non-mycorrhizal roots. P. involutus also decreased Pb translocation from the roots to the stems. Mycorrhizal infection was not affected by Pb but with P. involutus, the amount of extramatrical mycelium was reduced by 50% on day 32 compared to day 16. The extramatrical mycelium of L. laccata was not reduced by Pb. It is concluded that ectomycorrhizal fungi differ in their effect on Pb accumulation in the roots of Norway spruce. The binding capacity of the extramatrical mycelium seems to be an important factor.     

Silica deposition in relation to ageing of leaf tissues in Sasa veitchii (Carriere) Rehder (Poaceae: Bambusoideae)

BACKGROUND AND AIMS: Silica deposition is one of the important characteristics of plants in the family Poaceae. There have been many investigations into the distribution, deposition and physiological functions of silica in this family. Two hypotheses on silica deposition have been proposed based on these studies. First, that silica deposition occurs passively as a result of water uptake by plants, and second, that silica deposition is controlled positively by plants. To test these two apparently contradictory hypotheses, silica deposition in relation to the ageing of leaf tissues in Sasa veitchii was investigated. METHODS: Tissues were examined using a light microscope and a scanning electron microscope equipped with an energy dispersive X-ray microanalyser. KEY RESULTS: The deposition process differed depending on cell type. In mesophyll tissue, fusoid cells deposited large amounts of silica depending on leaf age after maturation, while chlorenchyma cells deposited little. In epidermal tissue, comprised of eight cell types, only silica cells deposited large amounts of silica during the leaf's developmental process and none after maturation. Bulliform cells, micro-hairs and prickle hairs deposited silica densely and continuously after leaf maturation. Cork cells, guard cells, long cells and subsidiary cells deposited silica at low levels. CONCLUSIONS: The significance of these observations is discussed in relation to the two hypotheses proposed for silica deposition in Poaceae. The results of the present study clearly indicate that both hypotheses are compatible with each other dependent on cell types.     

Ultrastructural investigations and EDX-analyses of Al-treated oat (Avena sativa) roots

Seedlings of Avena sativa were precultivated hydroponically at pH 4.1 and subsequently treated with solutions containing 0 or 400 µM Al. Electron microscopic and X-ray microanalytic (EDXA) investigations were carried out on root tips after 1 to 10 days of treatment. Root growth and mitotic activity decreased rapidly upon application of Al. The meristematic tissues of Al-treated roots showed enhanced vacuolation. The cells, however, remained intact after a longer period of Al-treatment and no alterations in ultrastructure (for example of the nucleus) were visible. The EDX analyses of bulk frozen hydrated tissues showed that Al was predominantly localised in the walls of the outermost cortex cells. One day after onset of Al-stress no intracellular Al was detectable. Even after 10 days with continuous Al-stress, only small amounts of the absorbed Al were localised within the cells. These results suggest that the plasma membrane is a very effective barrier for Al in oats. It is improbable that impairments of cytoplasmatic functions are primary effects of Al-intoxication.     

燕山山脉野生欧李群体叶表皮微形态特征研究

利用扫描电子显微镜对同一生境条件下自然生长的燕山山脉野生欧李实生群体（含嫁接类型）叶片表面微形态特征进行观测。结果表明：欧李叶表皮细胞形态存在两种类型,一类是上下表皮细胞向下凹陷相互连接形成蜂窝状,另一类是上下表皮细胞向上隆起近圆形,且上表皮细胞均具条纹状的角质层;叶片上表皮仅有表皮毛而无气孔分布,叶片下表皮仅有气孔分布;气孔突出于表皮细胞,属无规则型,气孔平均长度8.22±1.30 μm,宽度2.55±0.65 μm,大小21.64±8.60μm²,密度836.23±197.16 个/mm²;欧李群体中不同株系间、叶表皮细胞形态不同类别间气孔特征变异程度较大,可作为欧李优异种质选育和抗干旱胁迫研究的指标之一。     

Silica deposition in abaxial epidermis before the opening of leaf blades of Pleioblastus chino (Poaceae, Bambusoideae)

BACKGROUND AND AIMS Silica deposition is one of the important characteristics of the family Poaceae. The distribution, deposition process and physiology of silica in this family have been extensively investigated. Bamboos among members of Poaceae have leaves with a fairly long life span, and the leaves continuously accumulate silica in their tissues throughout their life, not only during the course of leaf opening, but also after opening. It has been revealed that the silica deposition process in relation to ageing of the bamboo leaf after opening differed depending on the cell types comprising the tissues. However, silica deposition has never been examined during the development and maturation periods of bamboo leaves. Hence, to clarify the silica deposition process in a developmental stage of the bamboo leaf, distribution of silica was observed in the abaxial epidermis before the opening of the leaf blades of Pleioblastus chino. METHODS: Abaxial epidermal tissues of leaves were examined using a scanning electron microscope equipped with an energy dispersive X-ray microanalyser. KEY RESULTS: Among seven cell types comprising the abaxial epidermis, three types of cells, guard cells, prickle hairs and silica cells, deposited silica conspicuously, and another four types, cork cells, long cells, micro hairs and subsidiary cells, deposited only a little silica. Among the former group of cell types, silica cells and guard cells deposited silica over their entire surfaces, while prickle hairs deposited silica only in the point-tips. Silica deposition was detected firstly in prickle hairs, and then in silica cells and guard cells. Only silica cells were assumed to deposit silica conspicuously before leaf opening but not conspicuously after opening. CONCLUSIONS: Cell types in leaf epidermis of bamboo are classified into three groups according to the silica deposition pattern. Silica deposition in silica cells may be positive as a part of the physiological activities of leaves.     

安徽母草属植物花粉形态特征的研究

利用光镜和扫描电子显微镜首次对安徽母草属(Lindernia)六种植物的花粉形态进行了观察研究.结果表明该属花粉粒多为近球形, 具3 沟, 表面光滑.探讨了花粉形态特征的分类学意义,支持属级水平的分类.     

12种十字花科植物花粉形态研究

采用扫描电子显微镜对十字花科8属12种植物的花粉形态特征进行了观察分析.其中8种为首次报道.观察结果表明:4族8属12种十字花科植物花粉形态的一般特征为:花粉粒长球形至超长球形;极面观三裂圆形,少数四裂圆形;外壁纹饰为网状或细网状纹饰;三沟,偶四沟.12种植物的花粉可划分为5种类型:(1)花粉粒长球形,网状纹饰,三沟;(2)花粉粒超长球形,网状纹饰,三沟;(3)花粉粒长球形,细网状纹饰,三沟;(4)花粉粒超长球形,细网状纹饰,三沟;(5)花粉粒长球形,三或四沟,网状纹饰.十字花科花粉形态特征在不同族间、不同属间以及同属不同种间均没有明显规律,在十字花科分类过程中,不宜单独以花粉形态特征作为依据.     

假眼小绿叶蝉触角化感器的扫描电镜观察

扫描电镜观察结果表明,假眼小绿蝉触角上只有一种毛状感器,而且,感器数量和分布在雌雄两性个体间相似。     

凤仙花属两种植物花粉的扫描电镜制样研究

采用腊叶标本花粉直接制样法、烘干法、FAA固定液复原法(酒精梯度脱水、自然干燥)和FAA固定新鲜花药法(脱水、干燥处理同前)四种不同处理方法对凤仙花属(Impatiens L.)植物红纹凤仙花(I.rubro-striata Hook.f.)和长角凤仙花(I.longicornut Y.L.Chen)的花粉进行了制样研究。结果表明:经后两种方法处理的花粉形状不变,且外壁网纹清晰,可获得质量较高的照片,观察时间也不受季节和产地的影响,既可在野外固定保存新鲜花蕾备用,又可利用标本馆现有的腊叶标本花粉经固定液复原后制样观察,操作简便,是进行花粉形态研究的一种较理想的方法。