Clonal analysis of epidermal patterning during maize leaf development

In plants, specialized epidermal cells are arranged in semiordered patterns. In grasses such as maize, stomata and other specialized cell types differentiate in linear patterns within the leaf epidermis. A variety of mechanisms have been proposed to direct patterns of epidermal cell differentiation. One class of models proposes that patterns of cellular differentiation depend on the lineage relationships among epidermal cells. Another class of models proposes that epidermal patterning depends on positional information rather than lineage relationships. In the dicot epidermis, cell lineage is an important factor in the patterning of stomata, but not trichomes. In this study, the role of cell lineage in the linear patterning of stomata and bulliform cells in the maize leaf epidermis is investigated. Clones of epidermal cells in juvenile leaves were marked by excision of dSpm from gl15-m and in adult leaves by excision of Ds2 from bz2-m. These clones were analyzed in relation to patterns of stomata and bulliform cells, testing specific predictions of clonal origin hypotheses for the patterning of these cell types. We found that the great majority of clones analyzed failed to satisfy these predictions. Our results clearly show that lineage does not account for the linear patterning of stomata and bulliform cells, implying that positional information must direct the differentiation patterns of these cell types in maize.     

植物表皮毛研究进展

表皮毛是大多数植物地上部分表皮组织所延伸出来的一种特化的毛状结构附属物。表皮毛在植物表皮层和环境间构筑了一道天然的物理屏障, 不但对植物的生长发育具有重要意义, 而且还具有非常高的应用价值和经济价值。近几年, 研究者从不同植物中不断克隆出新的表皮毛发育相关基因, 在揭示植物调控表皮毛生长发育的分子机制方面取得很大进展。该文综述了植物表皮毛的最新研究进展, 并展望了植物表皮毛的研究方向及应用开发价值。     

Cell growth and differentiation in Arabidopsis epidermal cells

Plant epidermal cells are morphologically diverse, differing in size, shape, and function. Their unique morphologies reflect the integral function each cell performs in the organ to which it belongs. Cell morphogenesis involves multiple cellular processes acting in concert to create specialized shapes. The Arabidopsis epidermis contains numerous cell types greatly differing in shape, size, and function. Work on three types of epidermal cells, namely trichomes, root hairs, and pavement cells, has made significant progress towards understanding how plant cells reach their final morphology. These three cell types have highly distinct morphologies and each has become a model cell for the study of morphological processes. A growing body of knowledge is creating a picture of how endoreduplication, cytoskeletal dynamics, vesicle transport, and small GTPase signalling, work in concert to create specialized shapes. Similar mechanisms that determine cell shape and polarity are shared between these cell types, while certain mechanisms remain specific to each.     

Specialized structures in the leaf epidermis of basal angiosperms: morphology, distribution, and homology

The morphology of specialized structures in the leaf epidermis of 32 species of basal (ANITA: Amborella, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileyaceae) angiosperms, representing all seven families and 11 of 14 genera, was investigated using light and scanning electron microscopy. Distribution, density, and size of structures were also measured, and character evolution was analyzed. Hydropotes are a synapomorphy of Nymphaeales and ethereal oil cells are a synapomorphy of Austrobaileyales, but uniseriate nonglandular trichomes appear to have arisen independently several times. Specialized structures are frequently characterized by adjacent epidermal cells that have striking similarities in their form and arrangement (i.e., architecture) to subsidiary cells of certain types of stomatal complexes. Additionally, forms intermediate to oil cells and stomata, to trichomes and stomata, and to hydropotes and oil cells are present in some taxa. Thus, all of these specialized structures and their adjacent epidermal cells form complexes that may be homologous with, and evolutionarily derived from stomatal complexes, and the specialized structure, or portion thereof, may be homologous to the stoma or guard mother cell. Improved knowledge of the morphology and evolution of these structures in the earliest branching extant angiosperm lineages has a bearing on many diverse areas of botany.     

Protein profiling of epidermal bladder cells from the halophyte Mesembryanthemum crystallinum

Plant epidermal trichomes are as varied in morphology as they are in function. In the halophyte Mesembryanthemum crystallinum, specialized trichomes called epidermal bladder cells (EBC) line the surface of leaves and stems, and increase dramatically in size and volume upon plant salt-treatment. These cells have been proposed to have roles in plant defense and UV protection, but primarily in sodium sequestration and as water reservoirs. To gain further understanding into the roles of EBC, a cell-type-specific proteomics approach was taken in which precision single-cell sampling of cell sap from individual EBC was combined with shotgun peptide sequencing (LC-MS/MS). Identified proteins showed diverse biological functions and cellular locations, with a high representation of proteins involved in H(+) -transport, carbohydrate metabolism, and photosynthesis. The proteome of EBC provides insight into the roles of these cells in ion and water homeostasis and raises the possibility that they are photosynthetically active and functioning in Crassulacean acid metabolism.     

拟南芥表皮毛发育的分子机制

拟南芥（Arabidopsis thaliana）表皮毛是存在于地上部分表皮组织的一种特化的、典型的单细胞结构。近几年,对其发育的分子调控机制的研究取得了很大进展,已克隆出大量的控制表皮毛不同发育阶段的基因,通过对这些基因的功能解析揭示出表皮毛发育及生长调节的内在分子机制。该文对拟南芥表皮毛发育的最新研究进展进行综述,并展望了关于表皮毛的研究方向及潜在的应用价值。     

Epidermal structure and development of stomata in vegetative and floral organs ofHybanthus enneaspermus (Linn.)F. Muell

The present paper deals with the epidermal structure and ontogeny of stomata in vegetative and floral organs ofHybanthus enneaspermus. The epidermal cells are either polygonal or elongated with straight, sinuous or arched thick anticlinal walls. The surface of the cuticle shows parallel striations radiating from the guard cells or hair bases. Unicellular and uniseriate bicellular trichomes with verrucose margins have been observed on all organs. The mature stomata are anisocytic, paracytic, anomocytic and transitional between anisocytic and paracytic. The ontogeny of anisocytic and paracytic stomata is syndetocheilic or mesogenous, anomocytic is haplocheilic or perigenous, while that of the transitional type is mesoperigenous. Four types of stomata have been observed on all the vegetative and floral organs and their ontogeny from organ to organ of this plant is constant. Stoma with a single guard cell is the result of disintegration of one of the guard cells before or after pore formation. Contiguous stomata are also occasionally noticed.     

拟南芥表皮毛发育的分子机制

拟南芥(Arabidopsis thaliana)表皮毛是存在于地上部分表皮组织的一种特化的、典型的单细胞结构。近几年, 对其发育的分子调控机制的研究取得了很大进展, 已克隆出大量的控制表皮毛不同发育阶段的基因, 通过对这些基因的功能解析揭示出表皮毛发育及生长调节的内在分子机制。该文对拟南芥表皮毛发育的最新研究进展进行综述, 并展望了关于表皮毛的研究方向及潜在的应用价值。     

Leaf surface development and the plant fossil record: stomatal patterning in Bennettitales

Stomata play a critical ecological role as an interface between the plant and its environment. Although the guard‐cell pair is highly conserved in land plants, the development and patterning of surrounding epidermal cells follow predictable pathways in different taxa that are increasingly well understood following recent advances in the developmental genetics of the plant epidermis in model taxa. Similarly, other aspects of leaf development and evolution are benefiting from a molecular–genetic approach. Applying this understanding to extinct taxa known only from fossils requires use of extensive comparative morphological data to infer ‘fossil fingerprints’ of developmental evolution (a ‘palaeo‐evo‐devo’ perspective). The seed‐plant order Bennettitales, which flourished through the Mesozoic but became extinct in the Late Cretaceous, displayed a consistent and highly unusual combination of epidermal traits, despite their diverse leaf morphology. Based on morphological evidence (including possession of flower‐like structures), bennettites are widely inferred to be closely related to angiosperms and hence inform our understanding of early angiosperm evolution. Fossil bennettites – even purely vegetative material – can be readily identified by a combination of epidermal features, including distinctive cuticular guard‐cell thickenings, lobed abaxial epidermal cells (‘puzzle cells’), transverse orientation of stomata perpendicular to the leaf axis, and a pair of lateral subsidiary cells adjacent to each guard‐cell pair (termed paracytic stomata). Here, we review these traits and compare them with analogous features in living taxa, aiming to identify homologous – and hence phylogenetically informative – character states and to increase understanding of developmental mechanisms in land plants. We propose a range of models addressing different aspects of the bennettite epidermis. The lobed abaxial epidermal cells indicate adaxial–abaxial leaf polarity and associated differentiated mesophyll that could have optimised photosynthesis. The typical transverse orientation of the stomata probably resulted from leaf expansion similar to that of a broad‐leaved monocot such as Lapageria, but radically different from that of broad‐leafed eudicots such as Arabidopsis. Finally, the developmental origin of the paired lateral subsidiary cells – whether they are mesogene cells derived from the same cell lineage as the guard‐mother cell, as in some eudicots, or perigene cells derived from an adjacent cell lineage, as in grasses – represents an unusually lineage‐specific and well‐characterised developmental trait. We identify a close similarity between the paracytic stomata of Bennettitales and the ‘living fossil’ Gnetum, strongly indicating that (as in Gnetum) the pair of lateral subsidiary cells of bennettites are both mesogene cells. Together, these features allow us to infer development in this diverse and relatively derived lineage that co‐existed with the earliest recognisable angiosperms, and suggest that the use of these characters in phylogeny reconstruction requires revision.     

北方地区藤本类忍冬叶表皮结构及其生态适应性比较研究

利用光镜和扫描电镜观察了8种在北京地区引种栽培成功的藤本类忍冬的叶表皮形态,观察指标包括气孔器、表皮毛、表皮细胞特征等.结合其在北京的栽培状况,发现叶片表皮形态和解剖结构与生态适应性之间有很强的相关性.自然分布广、适应性强的种在叶表皮形态上表现出气孔密度大、表皮细胞小、被毛或叶革质等特征.金银花、红白忍冬、淡红忍冬是8种忍冬中适应性最强的,具有推广应用价值.本研究为藤本类忍冬在北方地区推广应用提供了理论基础.     

Integrating signals in stomatal development

Stomata are specialized epidermal structures that control the exchange of water and carbon dioxide between the plant and the atmosphere. The classical developmental mechanisms that define cell fate and tissue patterning - cell lineage, cell-cell interactions and signals from a distance - are employed to make stomata and to define their density and distribution within the epidermis. Recent work has shown that two genes that are involved in stomatal pattern may encode components of a classical cell-surface-receptor-mediated signaling cascade. Additional work has suggested that signals from the overlying cuticle and the underlying mesophyll also influence stomatal pattern. These findings highlight the need for models that explain how the signals that regulate stomatal development are integrated and how they act to regulate cell polarity, the cell cycle and, ultimately, cell fate.     

Endoreplication Controls Cell Fate Maintenance

Cell-fate specification is typically thought to precede and determine cell-cycle regulation during differentiation. Here we show that endoreplication, also known as endoreduplication, a specialized cell-cycle variant often associated with cell differentiation but also frequently occurring in malignant cells, plays a role in maintaining cell fate. For our study we have used Arabidopsis trichomes as a model system and have manipulated endoreplication levels via mutants of cell-cycle regulators and overexpression of cell-cycle inhibitors under a trichome-specific promoter. Strikingly, a reduction of endoreplication resulted in reduced trichome numbers and caused trichomes to lose their identity. Live observations of young Arabidopsis leaves revealed that dedifferentiating trichomes re-entered mitosis and were re-integrated into the epidermal pavement-cell layer, acquiring the typical characteristics of the surrounding epidermal cells. Conversely, when we promoted endoreplication in glabrous patterning mutants, trichome fate could be restored, demonstrating that endoreplication is an important determinant of cell identity. Our data lead to a new model of cell-fate control and tissue integrity during development by revealing a cell-fate quality control system at the tissue level.     

SCD1 is required for cytokinesis and polarized cell expansion in Arabidopsis thaliana [corrected

In the leaf epidermis, guard mother cells undergo a stereotyped symmetric division to form the guard cells of stomata. We have identified a temperature-sensitive Arabidopsis mutant, stomatal cytokinesis-defective 1-1 (scd1-1), which affects this specialized division. At the non-permissive temperature, 22 degrees C, defective scd1-1 guard cells are binucleate, and the formation of their ventral cell walls is incomplete. Cytokinesis was also disrupted in other types of epidermal cells such as pavement cells. Further phenotypic analysis of scd1-1 indicated a role for SCD1 in seedling growth, root elongation and flower morphogenesis. More severe scd1 T-DNA insertion alleles (scd1-2 and scd1-3) markedly affect polar cell expansion, most notably in trichomes and root hairs. SCD1 is a unique gene in Arabidopsis that encodes a protein related to animal proteins that regulate intracellular protein transport and/or mitogen-activated protein kinase signaling pathways. Consistent with a role for SCD1 in membrane trafficking, secretory vesicles were found to accumulate in cytokinesis-defective scd1 cells. In addition the scd1 mutant phenotype was enhanced by low doses of inhibitors of cell plate consolidation and vesicle secretion. We propose that SCD1 functions in polarized vesicle trafficking during plant cytokinesis and cell expansion.     

Einfluss von Chlorcholinchlorid und Ethrel auf Zellteilung und Zellstreckung bei Primärblättern von Weizenkeimpflanzen

Both chlorcholinchloride and ethrel are used as growth retardants in cereal cultivation. Wheat seedlings were cultivated in nutrient solutions containing 10^-3M CCC, CEPA or 5 × 10^-4M CCC and CEPA, respectively. The epidermis of full-grown primary leaves was analysed. CCC relatively equally decreases the length of leaves and long epidermal cells, whereas CEPA mainly inhibits cell division. Leaf growth is always a little more inhibited than the number of stomata and trichomes is reduced by CCC or CEPA. This results in an increased frequency of stomata and trichomes by about 14 to 16 per cent. This means that retardants can strongly influence the length of leaves and the length or number of long epidermal cells but, due to the mechanism of programmed determination, the frequency of stomata and trichomes is kept constant within relatively narrow limits. Furthermore it can be concluded that long epidermal cells function as pace-makers in the growth of leaves of monocotyledonous plants.      

Epidermal Structure and Stomatal Ontogeny in Some Polygonales and Centrospermae

The epidermal structure and ontogeny of stomata in 19 speciesof Centrospermae and two of Polygonales are described. The cellsof the epidermis are polygonal, isodiametric, or elongated invarious directions and arranged irregularly. The anticlinalepidermal walls are thick, sinuous, straight, or arched. Eleventypes of glandular and eglandular trichomes have been observed.Six types of stomata: anomocytic, paracytic, stomata with asingle subsidiary cell, diacytic, anisocytic, and transitionalbetween diacytic and paracytic, have been noticed in the speciesinvestigated. The ontogeny of anomocytic stomata is haplocheilicor perigenous, while that of the other five types is syndetocheilicor mesogenous. Abnormal stomata with a single guard cell, unequalguard cells, aborted guard cells, and arrested development arecommon. Groups of stomata are also frequent but contiguous stomataare rather rare.     

Stomatal patterning in Tradescantia: an evaluation of the cell lineage theory.

The cell lineage theory, which explains stomatal patterning in monocot leaves as a consequence of orderly divisions, was studied in Tradescantia. Data were collected to test the theory at three levels of organization: the individual stoma; stomata distributed in one dimension, in linear fashion along cell files; and stomata apportioned in two dimensions, across the length and breadth of the leaf. In an attempt to watch the patterning process through regeneration, stomata in all visible stages of development were laser ablated. The results showed that the formation of stomatal initials was highly regular, and measurements of stomatal frequency and spacing showed that pattern was determined near the basal meristem when the stomatal initials arose. Following the origin of initials, the pattern was not readjusted by division of epidermal cells. Stomatal initials were not committed when first present and a small percentage of them arrested. The arrested cells, unlike stomata, were consistently positioned in cell files midway between a developed pair of stomata. At the one-dimensional level of pattern, stomata in longitudinal files were separated by a variable number of epidermal cells and the frequency of these separations was not random. The sequential spacing of stomata also was not random, and stomata separated by single epidermal cells were grouped into more short and long series than expected by chance. The stomatal pattern across the width of the leaf resulted from cell files free of stomata which alternated with cell files containing stomata, but not with a recurring periodicity. Files lacking stomata were found only over longitudinal vascular bundles. Laser ablations of developing stomata did not disrupt the pattern in nearby cells or result in stomatal regeneration. We conclude that the cell lineage theory explains pattern as an individual stomatal initial arises from its immediate precursor and satisfactorily accounts for the minimum spacing of stomata in a cell file, i.e., stoma-epidermal cell-stoma. However, the theory does not explain the collective stomatal pattern along the cell files, at the one-dimensional level of patterning. Nor does the theory account for the for the two-dimensional distribution of stomata in which regions devoid of stomata alternate with regions enriched with stomata, but not in a highly regular nor haphazard manner. We suggest that the grouping of epidermal cells and stomata separated by single epidermal cells in cell files may result from cell lineages at a specific position in the cell cycle as they traverse the zone where stomatal initials form.(ABSTRACT TRUNCATED AT 400 WORDS)     

利用激光扫描共聚焦显微镜研究植物细胞发育形态学变化

通过激光扫描共聚焦显微镜,利用不同种类(波长)的激光研究植物细胞发育形态学变化。结果表明,利用紫外激光(351 nm)扫描可以清楚地观察到拟南芥叶片表皮细胞的形态及其变化,在已分化的叶片表皮上可观察到包括“铺垫”表皮细胞(epidermal pavement cells)、气孔保卫细胞(guard cell)、气孔伴胞(subsidiarycells)、表皮毛细胞(trichomes)和表皮毛的足细胞(socket cells)等多种形态不同的细胞种类;利用蓝光激光(488nm)辅助曙红浅染,可清晰地显示出拟南芥根生长区内部的各种原始细胞,包括静止区(quiescent center)细胞、皮层/内皮层原始细胞(cortex/endodermal initial cell)、表皮/根冠原始细胞(epidermal/root cap initial cell)和中柱/根冠原始细胞(columella/root cap initial cell)等。利用双光子激光(800 nm)连续扫描30 s可以诱发叶绿体产生自发荧光,并可观察到叶绿体在叶肉细胞中的运动轨迹。结果说明激光扫描共聚焦显微镜在植物细胞形态及发育研究上具有独特的功能。