The vessel elements and hemicelluloses as the most plastic structural components of the brazilwood ontogeny (Caesalpinia echinata Lam.) medium morphotype

Abstract

For this work we hypothesize the existence of proportional increase in the thickness of the mesophyll cells and dimensions of the fiber cells of stem and the content of the cell wall polymers (cellulose, hemicelluloses and lignin) with the ontogeny of brazilwood. We also postulate that the capacity of this heliophile in inhabit lower stratum of forest densely shaded until the canopy highly illuminated is due to high plasticity of specific leaf area and stomatal density. Juvenile individuals stood out for higher specific leaf area, lower stomatal density, size of vessel elements and lignin contents as much in leaf and in stem. Young individuals presented, in general, intermediate values. The adult individuals, whose crowns reached the canopy, stood out for greater thickening of the spongy parenchyma, stomatal density, water content and hemicelluloses and lignins of leaf and stem. The cellulose content of the leaf and stem did not vary between different stages of ontogeny. From all the structural variables, the dimensions of the vessel elements and the proportion of hemicelluloses of leaves showed greater plasticity. Qualitative analysis of the cell wall suggested that the hemicelluloses are the type xylan with the possibility of presence of xyloglucan. Differently than what was hypothesized, we concluded that the capacity of Caesalpinia echinata Lam. in inhabit lower stratum of forest densely shaded until the canopy highly illuminated is due to high plasticity of density and diameter vessel and hemicelluloses of leaves and not specific leaf area and stomatal density.