Calcicole behaviour of Callisthene fasciculata Mart., an Al‐accumulating species from the Brazilian Cerrado

• Most aluminium (Al)‐accumulating species are found on soils with high Al saturation and low Ca availability (Ca poor). Callisthene fasciculata Mart. (Vochysiaceae), however, is an Al‐accumulating tree restricted to Ca‐rich soils with low Al saturation in the Brazilian Cerrado savanna. Here we tested its calcicole behaviour, and the possible role of organic acids in detoxification of Al during the early stages of plant development.
• We assessed growth, dry mass, nutrients, Al and organic acids in seedlings grown for 50 days on two contrasting Cerrado soils; one with high Ca concentrations and low Al saturation and the other with low Ca availability and high Al saturation.
• Relative to plants on Ca‐rich soil, plants on Ca‐poor soil had necrotic spots and bronzing of leaves. Roots and shoots contained reduced concentrations of P and Cu, but higher concentrations of Fe, Al and citrate. Despite lower concentrations in the soil, Ca and Mg increased in shoots. Shoot concentrations of oxalate were also higher.
• We confirmed C. fasciculata as an Al‐accumulating species with calcicole behaviour. The increased concentrations of organic acids in plants with higher Al accumulation suggest that high availability of soluble Al does not prevent occurrence of this species on soils with high Al saturation. Instead, the absence of C. fasciculata from Ca‐poor soils is probably due to imbalances in tissue Fe, Cu and Zn imposed by this soil type.

     

Redifferentiation of leaflet tissues during midrib gall development in Copaifera langsdorffii (Fabaceae)

The tree Copaifera langsdorffii is a superhost for galling herbivores. This plant species has great morphogenetic potential, and responds differently to the stimuli of more than 20 gall-inducing insects. Among these, an undescribed species of Cecidomyiidae induces a midrib gall in which a radial cecidogenetic field is generated and the leaflet tissues redifferentiate. Our objectives were to assess the amplitude of this cecidogenetic field, in which the leaflet tissues were influenced by the feeding action of the cecidomyiid; how the final gall shape was generated; and if tissue redifferentiation conferred any adaptive value on the galling herbivore. Leaflet morphogenesis followed the pattern described in the literature for simple leaves, resulting in a mesophytic arrangement. Tissue redifferentiation due to gall formation revealed that in a midrib gall, abaxial epidermal cells divided to enlarge the gall; spongy parenchyma cells originated the storage tissue, secretory structures, and vascular bundles; palisade parenchyma cells became homogeneous; and adaxial epidermis originated the nutritive tissue. Cell elongation, a necessary step towards cell redifferentiation, is triggered by an increase in water transport to the gall site and vacuole pressure due to neoformed xylem bundles. The generation of the final shape of the midrib gall involved repetitive histological steps in response to the amplitude of the cecidogenetic field. The largest impact of the cecidomyiid feeding action occurred in gall tissues redifferentiated from protoderm and adaxial ground meristem, which provided advantages to the gall maker of the C. langsdorffii midrib gall in terms of nutritional value, microenvironment, and protection against natural enemies.     

龙苍沟国家森林公园7种花楸属植物的叶解剖特征及其环境适应性

采用石蜡切片法对四川省龙苍沟国家森林公园内7种花楸属（Sorbus）植物的叶解剖特征进行研究,探究其结构特征与生境的相关性。结果显示：7种植物的叶片均为典型的背腹叶;叶片厚度介于108.16~208.21 μm,种间差异极显著（P<0.01）;上表皮厚度均大于下表皮厚度,且复叶物种的下表皮细胞均有乳突;栅栏组织由1~2层细胞构成,仅多对西康花楸（S. prattii var. aestivalis）的栅海比（栅栏组织与海绵组织的厚度比）为1.93,其余6种植物的栅海比均小于1;中脉维管束均呈心型,为典型的外韧型维管束,种间中脉突起度存在极显著差异（P<0.01）。各解剖结构中,上、下表皮可塑性最大,在生境中具有较强的潜在适应能力;中脉可塑性最小,整体结构较为稳定。栅栏组织、海绵组织和中脉组织是7种植物中种间差异最大的解剖结构。叶解剖结构与生境因子的相关性分析表明,栅栏组织厚度、栅海比和紧密度与年降水量、最暖季降水和海拔正相关（P<0.05）,与季节性温差负相关（P<0.05）;中脉直径和突起度与季节性温差呈正相关（P<0.01）,与年降水量、最暖季降水和海拔正相关负相关（P<0.05）。叶解剖结构性状的适应性变化,体现了7种花楸属植物在龙苍沟国家森林公园的生存策略。     

Aluminium tolerance in plants and the complexing role of organic acids

The aluminium cation Al(3+) is toxic to many plants at micromolar concentrations. A range of plant species has evolved mechanisms that enable them to grow on acid soils where toxic concentrations of Al(3+) can limit plant growth. Organic acids play a central role in these aluminium tolerance mechanisms. Some plants detoxify aluminium in the rhizosphere by releasing organic acids that chelate aluminium. In at least two species, wheat and maize, the transport of organic acid anions out of the root cells is mediated by aluminium-activated anion channels in the plasma membrane. Other plants, including species that accumulate aluminium in their leaves, detoxify aluminium internally by forming complexes with organic acids.     

Al-hyperaccumulator Vochysiaceae from the Brazilian Cerrado store aluminum in their chloroplasts without apparent damage

We investigated the pattern of aluminum (Al) accumulation in leaf tissues of native hyperaccumulator Vochysiaceae species Qualea grandiflora,Callisthene major, and Vochysia pyramidalis, from the Brazilian Cerrado. Non-accumulator Sclerolobium paniculatum was used as a control species. We expected a strong compartmentalization of Al in non-active leaf cell compartments such as cell walls and vacuoles in Al-accumulating species and the absence of Al in critical metabolic sites such as the chloroplasts. Plant leaves were harvested in the field and cut in small segments for histological analysis; hematoxylin dye was used for Al localization in tissues. Results of soil analysis of the three sites and the concentration of Al in leaves indicated that there is no direct relationship between Al availability in soils and Al hyperaccumulation among the Vochysiaceae species evaluated. The cross-sections of leaf tissues showed hematoxylin color in the palisade and spongy parenchyma cells (chloroplast) of Q. grandiflora and C. major. The vascular system of Q. grandiflora was not colored, but some cells from the xylem region of C. major were stained. In contrast, the adaxial and abaxial epidermal cells of V. pyramidalis were colored by hematoxylin, as were some cells from the vascular bundle, but color formation was not observed in the cells of palisade parenchyma. Al was not detected in leaves of S. paniculatum. We concluded that, although hyperaccumulation of Al is a common trait in the Vochysiaceae family, the processes of storage and detoxification in leaf tissues differ among the species. Two of the three hyperaccumulator species use chloroplasts as a sink for Al, with no apparent signs of toxicity. Therefore, the physiological role of Al in plant tissues remains to be elucidated.     

Leaf anatomy of Gluta (L.) Ding Hou (Anacardiaceae)

An anatomical study of the leaves of 21 species of Gluta (L.) Ding Hou (Anacardiaceae) reveals two major groups of species which reflect the original groups of Gluta L. and Melanorrhoea Wall., and a smaller group showing intermediate, or an admixture of, characters. The anatomical characters found to be of most use in this respect are: stomatal outline in surface view; stomatal density; glandular trichomes present/absent; glandular trichome body raised/sunken; cuticle striate/not striate; midrib dimensions as seen in transverse section; kind of simple trichomes (trichome-types 1–4); epidermal cell anticlinal wall undulation and whether visible or not on cuticular surface; resin ducts present/absent in medullary parenchyma of midrib. These characters have been used in a key to the species. Some evidence is given that the lacquer covering the leaf surface of some species is produced by the terminal cells of the glandular trichomes.     

Cell type specific expression of a CaMV 35S-GUS gene in transgenic soybean plants

A number of independently derived transgenic soybean plants expressing a chimeric β-glucuronidase (GUS) gene under the control of the 355 CaMV promoter and a nopaline synthase polyadenylation signal were recovered using direct DNA transfer via electric discharge particle acceleration. Expression of GUS in R, plants was localized using thin tissue sections. Many tissue types expressed GUS at various levels. Pericycle cells in root, parenchyma cells in xylem, and phloem tissues of stem and leaf had high levels of enzyme activity. Procambium, phloem, and cortex cells in root, vascular cambium cells in stem, and the majority of cortex cells in leaf midrib, expressed low or no GUS activity. Intermediate levels of GUS activity were detected in leaf mesophyll cells, certain ground tissue cells in stem and leaf midrib, and in trichome and epidermal guard cells. Thus, we conclude that the 35S CaMV promoter is cell-type specific and is developmentally regulated in soybean.     

The distribution and phylogeny of aluminium accumulating plants in the Ericales

The distribution of aluminium (Al) accumulation in the Ericales is surveyed, based on semi-quantitative tests of 114 species and literature data. Al accumulation mainly characterises the families Diapensiaceae, Pentaphylacaceae, Symplocaceae, Ternstroemiaceae, and Theaceae. Al accumulation is consistently present or absent in most families examined, but the character appears to be more variable in a few taxa (e.g., Lecythidaceae, Myrsinaceae). Although the interfamilial relationships within the Ericales require further research, the ability to accumulate high levels of Al appears to show considerable taxonomic significance. While the majority of Al accumulating Ericales includes woody, tropical plants, the feature is remarkably present in several herbaceous Diapensiaceae, which have a distribution in cold to temperate areas. The association of different mycorrhizae types with plant roots is suggested to play a role in the exclusion of high Al levels from the shoot.     

Use of SIMS microscopy and electron probe X-ray microanalysis to study the subcellular localization of aluminium in Vicia faba roots cells.

Received January 4, 1999; Accepted March 25, 1999 Secondary ion mass spectrometry (SIMS), electron probe X-ray microanalysis (EPMA) and transmission electron microscopy (TEM) were used to study the tissular distribution and subcellular localization of aluminium (Al) precipitate in roots of Viciafaba. The broad bean plant, grown in nitrate solution with 193 microM Al3+ at pH 4.8, for 15 days showed Al deposits in the roots. Al accumulation was not detected in the stems nor in the leaves. Al was found mainly localized on the root's surfaces and within the cell walls of the cortical cells. Al signal was not detected in the vascular tissues. Two weeks exposure to Al caused ultrastructural changes in cortical cells and sometimes a complete disruption of these cells. Deposition of Al in form of insoluble complexes associated with phosphorus, appeared as electron opaque materials in the vacuoles of disrupted cortex cells and in the intercellular inclusions. The leaves turned yellowish at the end of 15 days exposure. The use of electron microprobe, to investigate the same tissues as the ones investigated by SIMS, provided complementary results on aluminium allocation.     

Physiological aspects of aluminium tolerance associated with the long arm of chromosome 2D of the wheat (Triticum aestivum L.) genome

Aluminum (Al) uptake in roots of wheat nearisogenic lines having differing tolerances to aluminium toxicity was studied using roots and root segments immersed in a nutrient solution at a controlled pH and temperature. At low Al concentrations a mechanism preventing root tips from accumulating too much Al was observed in an Al-tolerant isoline and a BH1146 euploid. This mechanism was more efficient when divalent cations of calcium or magnesium were present in the nutrient medium. Al accumulation steadily increased in root tips of the Al-sensitive wheat isoline during all 24 h of incubation, and the presence of divalent cations in the medium even increased Al concentration in root tissue. However, at higher Al concentrations in the medium the mechanism preventing the root tips of Al-tolerant genotypes from accumulating too much Al was not observed, and in effect Al concentration in root tips of both Al-tolerant and Al-sensitive isolines increased. It is concluded that genetical factors are located on the long arm of chromosome 2D from the BH1146 euploid that control the mechanism preventing root apical meristems from accumulating too much Al at low Al concentrations in the medium. However, there must be other genetical factors also located on this chromosome segment that control Al detoxication in root tips of Al-tolerant lines at higher external Al concentrations.     

Damage on 'Hass' avocado leaves, webbing and nesting behaviour of Oligonychus perseae (Acari: Tetranychidae)

The damage of Oligonychus perseae Tuttle, Baker and Abbatiello on 'Hass' avocado trees occurs mainly on the underside of the leaves along the midrib, main veins and leaf depressions. The lower epidermal, spongy parenchyma and palisade parenchyma cells of the leaf tissues are destroyed. Large necrotic areas on the underside of the leaves result from feeding when high population levels occur. Feeding and reproduction takes place in 'nests' of silken webbing, which also provide protection from some predator mites and other natural enemies. Oligonychus perseae shows a modification of the earlier defined life-type web nest (WN-c). The greatest number of nests built by a female was 12.17 at 20°C and the greatest number of eggs per female per nest was 5.20 at 25°C.     

墨兰试管苗植株的发育解剖学研究

用石蜡切片和扫描电镜对墨兰试管苗植株的生长发育进行了研究。发现幼叶中脉附近的叶肉细胞类似栅栏组织,随着叶片的不断成熟,叶片基部中脉附近的叶肉细胞逐渐变为近圆形或椭圆形,而叶尖部和叶中部中脉附近的叶肉细胞仍似栅栏组织。茎的发育经历了原球茎、根状茎和假鳞茎3个阶段。原球茎的大部分细胞都含有淀粉粒,根状茎的皮层细胞含淀粉粒,而假鳞茎几乎不含淀粉粒。幼根没有髓,皮层细胞含淀粉粒：成熟根具含淀粉粒的髓。出瓶苗上即带有4个芽,一般只有最外侧叶腋的1个花芽和最内侧叶腋的1个叶芽发育。     

The beneficial effect of aluminium and the role of citrate in Al accumulation in Melastoma malabathricum

* Here we investigated the beneficial effect of aluminium (Al) on the development of the Al accumulating plant Melastoma malabathricum. * Seedlings of M. malabathricum were cultivated in a nutrient solution containing 0.5 mM Al and compared with barley (Hordeum vulgare). In addition, roots of M. malabathricum were divided into one part growing in a nutrient solution, and the other part growing in a calcium solution. Al (0.5 mM) was applied to either solution. * Al-induced improvements of the root activity contributed to a growth enhancement in M. malabathricum. Al exposure without nutrients did not increase root growth and Al accumulation in the leaves. The beneficial effect, however, was induced by the combination of Al and nutrients. * We suggest that without nutrients roots are not able to synthesize an adequate amount of citrate that is required for transporting Al to the leaves. High Al levels in the plant tissues and/or an interaction of Al with particular nutrient elements in the apoplast of root cells appear to be essential to exert the beneficial effect of Al.     

Anatomical features, monomer lignin composition and accumulation of phenolics in 1-year-old branches of the Mediterranean Cistus ladanifer L.

Mediterranean shrub species are described as having phenology, habitus , reproductive biology and anatomical alterations in certain tissues, allowing their survival during the dry season and protecting them from herbivory. Anatomical and chemical analyses were conducted in 1-year-old branches of Cistus ladanifer L. in order to investigate the role played by shoot structure in the adaptive strategies of this species in the Mediterranean environment. Results showed that both xylem and pith underwent lignification. Pith parenchyma cells had thickened walls, higher lignin content than xylem and different monomer composition. Xylem presented features aiding safe water transport. A large accumulation of phenolic substances was found in xylem, pith and cortical parenchyma. Observations reported in this paper suggest the occurrence of adaptive strategies in 1-year-old branches of C. ladanifer whose structural features: (1) allow mechanical reinforcement of tissues to withstand drought without suffering permanent damage; (2) favour safety rather than efficiency in water transport; (3) defend the plants from animal predation and pathogens by accumulating phenolics in various tissues, and (4) protect inner tissues against UV-B radiation through deposition of phenolic compounds in cortical layers.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 361–371.     

Genetic adaptation to soil acidification: experimental evidence from four grass species

Anthropogenic acidification has reduced soil pH and released potentially toxic aluminium (Al) ions in many regions. This investigation examines whether increased acidity has caused genetic adaptation to acidic conditions within the grass species Elymus caninus, Poa nemoralis, Deschampsia cespitosa and D. flexuosa. We sampled tussocks (genets) of each species in two regions of southern Sweden, differing in their exposure to acidifying deposition. The tolerance of the genets was tested in a solution experiment with different pH and Al concentrations. Our data suggest that species found at lower pH field locations have a greater tolerance to low pH and high Al levels than species found on less acidic soils. Analysis of variance showed a significant average effect of population and (or) genet in most species; however, we found little evidence of genetic adaptation to acidic conditions at the regional, population and micro-site level. In fact, there was no consistent change in the ranking of populations or genets with varying pH or Al concentration. Based on these results, we hypothesize that phenotypic plasticity rather than genetic adaptation has been favoured as the predominant mechanism to cope with soil acidity in the four grass species.     

Role of phytohormones in aluminium rhizotoxicity

Elevated concentrations of soluble aluminium (Al) reduce root growth in acid soils, but much remains unknown regarding the toxicity of this Al as well as the mechanisms by which plants respond. This review examines changes in phytohormones in Al‐stressed plants. Al often results in a rapid ‘burst’ of ethylene in root apical tissues within 15–30 min, with this regulating an increase in auxin. This production of ethylene and auxin seems to be a component of a plant‐response to toxic Al, resulting in cell wall modification or regulation of organic acid release. There is also evidence of a role of auxin in the expression of Al toxicity itself, with Al decreasing basipetal transport of auxin, thereby potentially decreasing wall loosening as required for elongation. Increasingly, changes in abscisic acid in root apices also seem to be involved in plant‐responses to toxic Al. Changes in cytokinins, gibberellins and jasmonates following exposure to Al are also examined, although little information is available. Finally, although not a phytohormone, concentrations of nitric oxide change rapidly in Al‐exposed tissues. The information presented in this review will assist in focusing future research efforts in examining the importance of phytohormones in plant tissues exposed to toxic levels of Al.     

Preliminary results from a microscopic examination on the effects of aluminium on the root tips of wheat

Root tips from aluminium (Al) tolerant (Waalt) and Al sensitive (Warigal) wheat (Triticum aestivum (L). Thell.) cultivars exposed to low concentrations of Al (10 M) for 10, 24 and 72 hours were examined under the light and electron microscope. After fixing and embedding, longitudinal and transverse thin and ultrathin sections were cut. There was no evidence of Al damage to the root tips of the Al tolerant cultivar under both the light and electron microscope. For the Al sensitive cultivar, Al had no observable effect on the root tips 10 hours after Al addition when examined under the light microscope. When examined under an electron microscope, electron dense globular deposits were observed between the cell wall and cell membrane of the epidermal cells. There was not obvious damage to the cell cytoplasm. Two or 3 days after Al addition, light microscopy showed that the cells in the root tips had become swollen and extensively vacuolated. The tissues appeared disorganised and degenerate, particularly in the epidermis and outer cortical cells. The electron microscope also revealed a thickening of the cell wall. The cell wall was broken down, particularly in the epidermis in the region 4–6 mm from the root tip. The tissue in the meristematic area was largely intact.     

Elemental concentrations in plant tissues as influenced by low pH soils

Summary Soils influenced by acid mine drainage (pH<5.0) are characterized by low concentrations of essential nutrients and increased solubility of heavy metals. The conditions typically reduce plant establishment and growth. However, river birch (Betula nigra L.) is commonly found along low pH streams in southeastern Ohio. The objective of this study was to determine the concentration of Al, Mn, Ca and Mg inB. nigra tissues.The results indicate Al and Mn are accumulating inB. nigra when compared to other species. Within river birch, Al concentrations are highest in roots; Mn concentrations are highest in leaves. There is not a concomitant reduction in Ca and Mg concentrations as suggested by soil levels.     

Characterisation of Ca- and Al-pectate gels by thermal analysis and FT-IR spectroscopy

Thermal analysis (TG-DTA) and FT-IR spectroscopy have been performed on calcium-pectate membranes to investigate their structure and the consequent variation caused by aluminium sorption. Calcium-polygalacturonate (Ca-PG) membranes, model systems of the soil-root interface, were exposed to aluminium solutions at different concentrations (25-800 microM). Three different pHs (3.50, 4.00 and 4.50) were chosen to study the influence of different aluminium species, such as [Al(H2O)6]3+, [Al(OH)(H2O)5]2+ and [Al(OH)2(H2O)(4)]+, on the structure of the Ca-PG membrane. The DTA profiles and FT-IR spectra showed how aluminium sorption induces structural modifications leading to a reorganisation of the chain aggregates and a weakening of the structure. Higher pH, that is, 4.00 and 4.50, and thus hydrolytic aluminium species and related higher calcium content maintain a more regular structure than at pH 3.50. At pH 3.50, both the effect of [Al(H2O)6]3+ and a major calcium release had a greater impact and thus induced a greater weakening of the structure.     

Leaf anatomy of Desmos and Dasymaschalon (Annonaceae) from China in relation to taxonomic significance

Leaf morphology in four species of Desmos and three species of Dasymaschalon was comparatively studied using scanning electron microscopy (SEM) together with epidermal maceration and paraffin methods. The results showed that there were some remarkable foliar anatomical differences between Desmos and Dasymaschalon. In leaves of Desmos, some of the adaxial epidermal cells were enlarged into globose cells each containing one large cluster crystal, while other epidermal cells were normal without any crystal, and in abaxial epidermis each cell contained one smaller cluster crystal. The leaf structure was typically bifacial, and the mesophyll cells were differentiated into palisade tissue and spongy tissue. Oil cells were distributed in the second layer of palisade and the whole spongy tissue, and the number of oil cells per mm leaf width ranged from 4 to 6. The vascular tissue in the midrib was separated into bundles by parenchyma cells. In leaves of Dasymaschalon, all the adaxial epidermal cells contained one cluster crystal, and the crystal size was similar to that of thecrystals in abaxial epidermal cells. The leaf structure was more or less isobilateral. Oil cells were distributed only in the spongy tissue between the two layers of the palisade, and the number of oil cells per mm leaf width ranged from 2 to 3. The vascular tissue in the midrib formed a continuous circle. It is clear that the anatomical differences between Desmos and Dasymaschalon are remarkable, supporting the treatment of Desmos and Dasymaschalon as two independent genera.