Carbohydrates of tropical species as modulators of ecophysiological processes and ...
Abstract
There are periods when plants temporarily lose their capacity to maintain their own autotrophy, i.e. when the photosynthetic system becomes temporarily non operational (dormancy for example). Those periods can be considered as the weakest links of the life cycle of plants, since they become totally dependent on their reserves in order to restart growth when environmental conditions are favorable. Plants store reserves of organic compounds (carbohydrates and lipids mainly for carbon and energy resource), and proteins (for nitrogen), which are mobilised during specific periods and under straight metabolic control. Thus, the energetic needs and at the same time carbon are provided as raw material for restarting of growth. The latter demands high quantities of carbon mainly for processes as respiration, cell division and elongation. The main storage carbohydrates' in plants can be divided into intracellular and extracellular reserves. Those accumulated within the cells can be found in the vacuole (fructans, sucrose and raffinose series) or into the cytoplasm (starch) and those stored in the extracellular space are composed of polysaccharides such as hemicelluloses and pectin's. Each type of polysaccharide used as a reserve corresponds to one or more strategies of surviving, including water imbibition and defence. In this way, it is possible that the maintenance of biodiversity in tropical environments presents a relatively high dependence on the period of accumulation and mobilization of reserves. It is therefore important to study these phenomena in detail if one wishes to understand how biodiversity can be maintained or used in a sustainable fashion. On this basis, the present proposition intends to study the biosynthesis and degradation of some of the main storage carbohydrates from plants native to Cerrado (a savanna-like vegetation) and the Tropical Forest. The physiological and cytochemical consequences for the following growth and development will be studied concomitantly. We expect these results to contribute towards a strong scientific basis for the conservation and recuperation of those ecosystems (Cerrado and Tropical Forest) consistently being degraded. We also expect the results to provide means for the sustainable use of the biodiversity. (AU)