The control of leaf development

The formation of a leaf is a basic aspect of plant development. This review provides an overview of our present understanding of the process from initiation to the final form of the leaf. Molecular genetic and cell biology approaches have yielded significant advances in this area, adding not only to our knowledge of leaf development but also to fundamental principles in plant biology. These principles will be highlighted, as well as areas where our understanding is still incomplete, in particular the problem of coordinating the multifaceted steps involved in the generation of the leaf structure.     

Leaf miners: The hidden herbivores

Leaf mining is a form of endophagous herbivory in which insect larvae live and feed within leaf tissue. In this review we discuss aspects of leaf miner ecology, and the current evidence for three hypotheses relating to the evolution of this feeding guild. We also present a summary of the literature coverage relating to these herbivores, which have been relatively poorly studied compared with insects that feed externally such as sap suckers and leaf chewers. The majority of published studies concern leaf miners from the northern hemisphere, with a general focus on those species considered to be agricultural, forestry or horticultural pests. In a more detailed case study, we examine aspects of leaf miner ecology of Australian species. At least 114 species have been recorded as leaf miners in Australia in four orders: Coleoptera, Lepidoptera, Diptera and Hymenoptera. Lepidoptera and Diptera are the most speciose orders of Australian leaf miners; Hymenoptera are represented by a single endemic genus and half of all coleopteran miners are species introduced for biological control. Both the known number of leaf‐mining species in Australia and the known number of hosts have increased in recent years following new targeted surveys. Leaf miners in Australia occur in many habitats and feed on a wide variety of host plants in at least 60 families although most individual species are monophagous. Although much of the research on leaf miners in Australia has focused on species that are commercially important pests or biological control agents, studies on fundamental aspects of leaf miner ecology are increasing. We identify a number of research questions aimed at better understanding the ecology of leaf miners in Australia and elsewhere.     

Development of leaves and shoot apex protection in Metrodorea and related species (Rutaceae)

Most members of Sapindales are characterized by compound leaves, but several genera also (or only) produce simple or unifoliolate leaves. A few genera may bear stipules or pseudostipules. Little is known about the morphological structure and morphogenesis of these types of leaves in Sapindales, but this information is required for comparative and evolutionary studies. Metrodorea is a Neotropical genus of Rutaceae, comprising species presenting compound and unifoliolate leaves, plus heterophylly, together with an intriguing bud‐protecting structure at the leaf base. The aims of the present study are: (1) to examine leaf morphogenesis in Metrodorea and in closely related species (four Esenbeckia spp., Helietta apiculata and Raulinoa echinata); and (2) to improve our understanding of the morphological evolution of leaves in Metrodorea and Rutaceae. Our data show that the hood‐shaped structure at the base of the leaf in Metrodorea, usually interpreted as a sheath, is, in fact, a pair of united stipules, a synapomorphy of the genus. In the species studied, it is possible to recognize two main types of unifoliolate leaf: early unifoliolate leaves and late unifoliolate leaves. We also found that the number of leaflets in the studied species is dependent on the late or early determination of the leaf primordium, and that loss of leaflets may have been favoured by the restriction of space available for development within the cavity formed by the pair of united stipules. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 267–282.     

植物叶片形态的生态功能、地理分布与成因

叶片是植物与环境进行水气交换的重要场所, 形态多变。叶片形态可直接影响植物的生理生化过程, 反映植物的资源获取策略。该文以叶片大小、叶形、叶缘特征(有无叶齿)和叶型(单、复叶)等形态性状为例, 总结了当前叶片形态的研究进展, 分析了叶形态性状的生态功能, 综述叶片形态的地理分布, 探讨叶片形态性状变化的驱动因素及其对生态系统功能的影响。现有研究主要聚焦于局域尺度的特定类群, 关注叶大小、叶缘具齿性以及叶型的地理分布与生态成因, 发现叶片的形态发育受基因调控, 叶形态性状与其他性状相互权衡, 其空间变异受气温和降水量共同驱动。以叶大小为代表的叶片形态性状影响水分和养分循环, 能够反映气候变化下的群落响应, 也可用于预测生态系统初级生产力。今后应结合新方法获得覆盖度高且区域无偏的数据, 探索叶形态在长时间尺度上的适应性进化, 研究叶形态特征及其对生态系统功能影响的尺度推绎。该文有助于从叶片的角度认识植物对环境变化的响应, 以性状为桥梁将个体适合度、群落动态与生态系统功能联系起来, 能够加深对植物群落生态学和功能生物地理学等相关领域研究进展的了解。     

干旱区叶片形态特征与植物响应和适应的关系

叶片形态是指示植物适应特定环境的重要指标。由于植物叶片形态不仅对时空环境变化具有极强的敏感性和可塑性, 而且能够通过叶片形态的调整调节自身的生存适应能力, 所以叶片形态学研究一直是植物生理及植物生态学研究中的热点。该文在总结前人叶片形态学研究成果的基础上, 探索建立了简单的叶片形态指标分类体系; 结合物质能量交换的物理学原理, 回顾总结了叶片表观形态变化与叶片物质能量交换之间的相关关系; 应用叶片形态影响物质能量交换的物理学原理, 重点分析了干旱区植物叶片表观形态对低水分环境、高辐射(或高温)的响应与适应特征; 最后, 在回顾分析的基础上, 对叶片形态研究中存在的几个问题进行了讨论。     

干旱区植物叶片大小对叶表面蒸腾及叶温的影响

利用热及物质交换原理, 并结合前人研究成果, 在单叶尺度上建立了简单的叶温和水气蒸腾模型。模型通过预设值驱动, 预设值参照干旱区环境及植物叶片特征设置。模拟结果显示: 随气孔阻力的增加, 叶片蒸腾速率降低, 叶温升高; 同一环境下, 具有低辐射吸收率的叶片蒸腾速率和叶温更低, 并且气孔阻力越大, 这种差异越明显。另外, 叶片宽度及风速是影响叶片蒸腾及叶温的重要因子。干旱地区植物生长季节, 风速小于0.1 m·s ^-1、气孔阻力接近1000 s·m ^-1时, 降低叶片宽度不仅有利于降低叶片温度, 而且能够降低叶片蒸腾速率, 从而实现保持水分, 增强植物适应高温、干旱的能力。     

植物叶片性状对气候变化的响应研究进展

叶片性状反映了植物对环境的高度适应能力及其在复杂生境下的自我调控能力。叶片性状如何响应和适应气候变化是植物适应性研究的重点内容。该文系统综述了叶片大小、比叶质量、叶片氮含量、碳同位素等指标对气候变化响应的最新研究结果。不同叶片性状对气候变化的响应结果存在差异,所指示的生态学含义也有所不同。单一叶片性状不能全面地反映植物对气候变化的响应;不同尺度的研究(如环境的修饰或筛选作用的研究)还存在很多不确定性。高寒地区的研究工作相对缺乏。该文有助于理解植物与气候之间的相互关系、植物对气候变化的响应与适应对策,对了解植物演化、预测植物在未来气候变化条件下的变化特征具有一定意义。     

Evolution of leaf form correlates with tropical-temperate transitions in Viburnum (Adoxaceae)

Strong latitudinal patterns in leaf form are well documented in floristic comparisons and palaeobotanical studies. However, there is little agreement about their functional significance; in fact, it is still unknown to what degree these patterns were generated by repeated evolutionary adaptation. We analysed leaf form in the woody angiosperm clade Viburnum (Adoxaceae) and document evolutionarily correlated shifts in leafing habit, leaf margin morphology, leaf shape and climate. Multiple independent shifts between tropical and temperate forest habitats have repeatedly been accompanied by a change between evergreen, elliptical leaves with entire margins and deciduous, more rounded leaves with toothed or lobed margins. These consistent shifts in Viburnum support repeated evolutionary adaptation as a major determinant of the global correlation between leaf form and mean annual temperature. Our results provide a new theoretical grounding for the inference of past climates using fossil leaf assemblages.     

Genetic control of early stages of leaf development

The results of studies of genetic regulation of the early leaf morphogenesis, demarcation of the future primordium and transition of cells to determination, have been reviewed. The genetic systems of control of these developmental stages were shown to be conservative and hypotheses of possible mechanisms underlying the evolution of leaf morphology on their basis have been considered.     

The leaf base in palms: structural and functional aspects

Abstract

The study of the palm leaf base has consequences that relate to overall development of the crown and the function of the crown as a whole, especially in relation to wind resistance. Palms provide a supreme example of the phenomenon of “giantism”, which is exhibited by many groups of tropical organisms. The distinctive features of the leaf sheath are related to this process, but palms exhibit such a range of adult sizes and occupy such a diversity of habitats that there is considerable scope for comparative study.     

LEAF SHAPE EVOLUTION IN THE SOUTH AFRICAN GENUS PELARGONIUM L' HÉR. (GERANIACEAE)

Leaf shapes reflect complex assemblages of shape-determining elements, yet evolutionary studies tend to treat leaf shape as a single attribute, for example cordate or linear. As with all complex structures, individual elements of a leaf could theoretically evolve independently and at different rates to the extent permitted by genetic and functional limitations. We examined relative evolutionary lability of shape-determining elements in the highly diverse South African plant genus Pelargonium (Geraniaceae). We used SIMMAP to calculate Bayesian posterior probabilities for ancestral states of leaf-shape characters for major nodes across multiple phylogenetic trees. Trees were derived from a Bayesian analysis of DNA sequence data from four partitions. We found that shape elements differed in rates of character-state transformations across the tree. Leaf base, apex, and overall outline had low rates. Transformations in venation occurred at slightly higher rates and were associated with shifts in venation among major clades. Leaf margin type and overall leaf size showed intermediate rates, whereas high rates were observed in the extent of lamina lobing and functional leaf size. The results indicate that suites of elements characteristic of the recently evolved xerophytic lineage, for example pinnate venation, dissected lamina, and entire margins, were acquired piecemeal over nested levels of the phylogeny.     

Sensitivity of leaf size and shape to climate within Acer rubrum and Quercus kelloggii

* Variation in the size and shape (physiognomy) of leaves has long been correlated to climate, and paleobotanists have used these correlations to reconstruct paleo-climate. Most studies focus on site-level means of largely nonoverlapping species sets. The sensitivity of leaf shape to climate within species is poorly known, which limits our general understanding of leaf-climate relationships and the value of intraspecific patterns for paleoclimate reconstructions. * The leaf physiognomy of two species whose native North American ranges span large climatic gradients (Acer rubrum and Quercus kelloggii) was quantified and correlated to mean annual temperature (MAT). Quercus kelloggii was sampled across a wide elevation range, but A. rubrum was sampled in strictly lowland areas. * Within A. rubrum, leaf shape correlates with MAT in a manner that is largely consistent with previous site-level studies; leaves from cold climates are toothier and more highly dissected. By contrast, Q. kelloggii is largely insensitive to MAT; instead, windy conditions with ample plant-available water may explain the preponderance of small teeth at high elevation sites, independent of MAT. * This study highlights the strong correspondence between leaf form and climate within some species, and demonstrates that intraspecific patterns may contribute useful information towards reconstructing paleoclimate.     

Morphology and morphogenesis of ensiform leaves, syndesmy of shoots and an understanding of the thalloid plant body in species of Apinagia, Mourera and Marathrum (Podostemaceae)

The flattened, irregularly shaped and lobed or dissected leaves of Apinagia riedelii , A. latifolia , A. goejei , Mourera aspera and Marathrum utile (subfamily Podostemoideae) are ensiform in structure. After the typical bifacial inception, further growth of leaves proceeds in the midrib area, i.e. in the median plane of the leaf. The lower leaf zone is characterized by a sheath that orientates 'at the side of the blade', i.e. at the adaxial edge of the sword-like leaf. The ensiform blades are lobed, incised or pinnately dissected with the tips terminated in elongated threads or thin filaments. Leaves of Apinagia riedelii resemble pinnately dissected compound leaves. The dissected structure represents a secondary superimposition of the ensiform shape and a parallel development to compound leaves. It is interpreted as an adaptation to the rapid current, established in the floating shoots of these aquatic plants. The basal portions of main shoots and successive branches are fused due to a retarded separation. Fusion of this kind has been termed a syndesmy. The fused region of shoots is superseded by the fusion of the lower leaf zones of (distichously positioned) adjacent leaves, occurring at their margins. The fused leaf bases form a cavity for the terminal flower bud of each shoot and cover it in the form of a hood. The flower buds are hidden from external view. The meristematic growing zones are thus protected and enclosed within the syndesmic plant body which, in this way, attains the 'thalloid' appearance especially developed in Apinagia goejei and A. latifolia but also present in the other species. The results of this study enable an understanding of the particular appearance of these Podostemoideae as modifications of the typical structures according to the 'principle of variable proportions'.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 47–71.     

Cellular Differentiation and Leaf Morphogenesis in Arabdopsis

A focused approach that exploits a single plant species, namely, Arabidopsis thaliana, as a means to understand how leaf cells differentiate and the factors that govern overall leaf morphogenesis has begun to generate a significant body of knowledge in this model plant. Although many studies have concentrated on specific cell types and factors that control their differentiation, some degree of consensus is starting to be reached. However, an understanding of specific mechanisms by which cells differentiate in relation to their position, that appears to be an overriding factor in this process, is not yet in place for cell types in the Arabidopsis leaf. It is clear that perturbations in cellular development within the leaf do not necessarily have a general effect on morphogenesis. Environmental factors, particularly light, have been known to affect leaf cell differentiation and expansion, and endogenous hormones also appear to play an important role, through mechanisms that are beginning to be uncovered. It is likely that continued identification of genes involved in leaf development and their regulation in relation to positional information or other cues will lead to a clearer understanding of the control of differentiation and morphogenesis in the Arabidopsis leaf.     

The Role of Meristematic Activities in the Formation of Leaf Blades

Arabidopsis thaliana (L.) Heynh. Leaf primordia also have their own meristematic regions and meristematic activity is maintained in part of the leaf blade, in some case, even after maturation. Transgenic plants have been generated that have proved to be useful tools in the analysis of the behavior of meristematic regions in leaf blades of A. thaliana. This review, based on our present understanding of molecular mechanisms for the maintenance and development of shoot apical meristems in A. thaliana, summarizes the variations in patterns and functions of meristematic regions in leaf blades focusing, in particular, on the case of indeterminate leaves. Received 5 April 2000/ Accepted in revised form 12 April 2000     

叶发育的遗传调控机理研究进展

叶是植物进行光合作用的主要器官。高等植物叶原基起始于顶端分生组织的周边区,在一系列基因精确调控下,叶原基建立近一远轴、基一顶轴和中．侧轴极性,引导原基细胞朝着特定的方向分裂和分化,最终发育戍一定形态和大小的叶片。近年来分子遗传学研究结果表明,数个转录因子家族基因、小分子RNA和细胞增殖相关因子组成一个复杂的遗传控制网络,调节叶片极性建成过程。此外,复叶的形态建成还受到另外一些转录因子的调控。本文对近年来叶发育遗传调控机理研究的新进展做简要介绍。     

What is the role of cell division in leaf development?

An idea underlying a great deal of research and discussion in plant cell and developmental biology is that the spatial regulation of cell division plays a key role in plant development. In this article, the role of cell division in two aspects of leaf development is analysed: morphogenesis (leaf initiation, growth, and the generation of leaf shape) and histogenesis (the differentiation of leaf cells to form the various cell types that make up a functional leaf). The point of view that emerges from this analysis is that the rate and pattern of cell division is important for leaf development, but does not dictate leaf size, shape, or cell fate.     

Adaxial–abaxial polarity: The developmental basis of leaf shape diversity

Leaves of flowering plants are diverse in shape. Part of this morphological diversity can be attributed to differences in spatiotemporal regulation of polarity in the upper (adaxial) and lower (abaxial) sides of developing leaves. In a leaf primordium, antagonistic interactions between polarity determinants specify the adaxial and abaxial domains in a mutually exclusive manner. The patterning of those domains is critical for leaf morphogenesis. In this review, we first summarize the gene networks regulating adaxial–abaxial polarity in conventional bifacial leaves and then discuss how patterning is modified in different leaf type categories. genesis 52:1–18, 2014. © 2013 The Authors. Genesis Published byWiley Periodicals, Inc.