دانلود رایگان مقاله انگلیسی کلانشیم: بافت مکانیکی متنوع و تطبیق پذیر با دیواره سلولی پویا و فعال به همراه ترجمه فارسی
|عنوان فارسی مقاله:||کلانشیم: بافت مکانیکی متنوع و تطبیق پذیر با دیواره سلولی پویا و فعال|
|عنوان انگلیسی مقاله:||Collenchyma: a versatile mechanical tissue with dynamic cell walls|
|رشته های مرتبط:||زیست شناسی، علوم سلولی و مولکولی، علوم گیاهی، میکروبیولوژی، فیزیولوژی گیاهی|
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Background Collenchyma has remained in the shadow of commercially exploited mechanical tissues such as wood and fibres, and therefore has received little attention since it was first described. However, collenchyma is highly dynamic, especially compared with sclerenchyma. It is the main supporting tissue of growing organs with walls thickening during and after elongation. In older organs, collenchyma may become more rigid due to changes in cell wall composition or may undergo sclerification through lignification of newly deposited cell wall material. While much is known about the systematic and organographic distribution of collenchyma, there is rather less information regarding the molecular architecture and properties of its cell walls. Scope and conclusions This review summarizes several aspects that have not previously been extensively discussed including the origin of the term ‘collenchyma’ and the history of its typology. As the cell walls of collenchyma largely determine the dynamic characteristics of this tissue, I summarize the current state of knowledge regarding their structure and molecular composition. Unfortunately, to date, detailed studies specifically focusing on collenchyma cell walls have not been undertaken. However, generating a more detailed understanding of the structural and compositional modifications associated with the transition from plastic to elastic collenchyma cell wall properties is likely to provide significant insights into how specific configurations of cell wall polymers result in specific functional properties. This approach, focusing on architecture and functional properties, is likely to provide improved clarity on the controversial definition of collenchyma.
Key words: Collenchyma, histology, plant anatomy, mechanical tissue, plant cell wall, primary and secondary cell walls, plant biomechanics.
The emergence of mechanical tissues was a key innovation in the evolution of land plants and a prerequisite for the appearance of large terrestrial species. By the middle Devonian, many plant species developed a hypodermal sterome consisting of heavily thickened sclerenchyma cells (Rowe and Speck, 2004). Biomechanical investigations indicated that the sterome significantly contributed to the stiffness of stems and allowed them to reach great heights and evolve diverse branched architectures compared with plants with turgor-based support systems (Rowe and Speck, 2004). While sclerenchyma tissues confer rigidity and tensile and shear strength to many plant organs (Niklas, 1992; Jarvis, 2007), their properties are incapable of supporting growing plant organs which undergo extensive turgor-driven elongation. Indeed, sclerified tissues generally consist of dead cells with non-extensible rigid cell walls which are unable to undergo mitotic divisions. In small slowly growing plant organs, turgor pressure generated in parenchyma cells may provide sufficient support, but many plant stems grow fast and are fragile, and therefore they cannot fully rely on turgor pressure for support. Partly because they are nonsclerified and only minimally lignified, young plant tissues are preferentially selected by grazing animals and plant bugs. For this reason, supporting tissues in these regions should not be terminally differentiated but capable of undergoing wound healing or tissue regeneration. Moreover, as secondary growth increases the diameter of stems, the ability to transdifferentiate and initiate periderm formation is an additional advantage. Finally, young above-ground organs are photosynthetic and the reinforcing tissues should ideally be as translucent as possible to enable light to reach the chloroplasts in tissues deeper in the plant. To meet most of the above-mentioned requirements, and to provide support without preventing cell elongation, many plants – eudicotyledons in particular – develop collenchyma: a mechanical tissue composed of elongated cells with thick flexible and translucent cell walls and with protoplasts capable of resuming meristematic activity. In this review, I describe the remarkable origin of the term ‘collenchyma’ and discuss some of the controversies associated with the description of this tissue. In contrast to scleri- fied mechanical tissues such as wood and fibres, which are economically important raw materials, collenchyma tissues have received little attention. Consequently, a clear definition of collenchyma has never been given. It is not surprising that this has resulted in some confusion with respect to its designation in certain cases. However, it needs to be highlighted that one of the factors that makes collenchyma so unique is also the reason why it is difficult to define: the dynamic nature of its cell walls.