RESUMO
Every plant organ contains tens of different cell types, each with a specialized function. These functions are intrinsically associated with specific metabolic flux distributions that permit the synthesis of the ATP, reducing equivalents and biosynthetic precursors demanded by the cell. Investigating such cell-type-specific metabolism is complicated by the mosaic of different cells within each tissue combined with the relative scarcity of certain types. However, techniques for the isolation of specific cells, their analysis in situ by microscopy, or modeling of their function in silico have permitted insight into cell-type-specific metabolism. In this review we present some of the methods used in the analysis of cell-type-specific metabolism before describing what we know about metabolism in several cell types that have been studied in depth; (i) leaf source and sink cells; (ii) glandular trichomes that are capable of rapid synthesis of specialized metabolites; (iii) guard cells that must accumulate large quantities of the osmolytes needed for stomatal opening; (iv) cells of seeds involved in storage of reserves; and (v) the mesophyll and bundle sheath cells of C4 plants that participate in a CO2 concentrating cycle. Metabolism is discussed in terms of its principal features, connection to cell function and what factors affect the flux distribution. Demand for precursors and energy, availability of substrates and suppression of deleterious processes are identified as key factors in shaping cell-type-specific metabolism.
Assuntos
Fotossíntese , Folhas de Planta , Folhas de Planta/metabolismoRESUMO
Plants, as biological systems, are organized and regulated by a complex network of interactions from the genetic to the morphological level and suffer substantial influence from the environment. Reductionist approaches have been widely used in plant biology but have failed to reveal the mechanisms by which plants can growth under adverse conditions. It seems likely, therefore, that to understand the complexity of plant metabolic responses it is necessary to adopt non-reductionist approaches such as those from systems biology. Although such approaches seem methodologically complex to perform and difficult to interpret, they have been successfully applied in both metabolic and gene expression networks in a wide range of microorganisms and more recently in plants. Given the advance of techniques that allow complex analysis of plant cells, high quantities of data are currently generated and are available for in silico analysis and mathematical modeling. It is increasingly recognized, therefore, that the use of different methods such as graph analysis and dynamic network modeling are needed to better understand this abundance of information. However, before these practical advances, one of the main challenges currently in plant biology is to change the paradigm from the classical reductionism to the systemic level, which requires not only scientific but also educational changes.