Estudos anatômicos, ultraestruturais e topoquímicos do lenho de seringueiras provenientes de floresta natural

Abstract

The reaction wood in the angiosperms is characterized primarily by the presence of gelatinous fibers, which are differentiated fibers with a thick and highly cellulosic inner layer, known as tgelatinous layer. The presence and severity of the reaction wood can be influenced by the gravitational stimulus when the tree has its branches and trunk deviated from its natural axis, as in slopes, action of strong winds, artificial induction, injuries, and others. In the case of rubbertree, it is possible that the latex tapping may influence the cambium activity, leading to the formation of this type of fibers. Therefore, the aim of this work was to study Hevea brasiliensis (Willd. ex A. Juss.) Mull. Arg. trees in order to characterize the wood structure of native trees that have passed through latex exploitation, as well as characterize the chemistry and distribution of lignin, and ultrastructure of the gelatinous fibers cell wall. For this purpose, samples of xylem were collected from rubbertrees at the Fazenda Experimental Catuaba, located in Senador Guiomard - AC (67.62711 W; 10.08433 S). In the anatomical characterization, fiber length (non-gelatinous and gelatinous); total diameter and lume diameter of non-gelatinous fibers; diameter and frequency of vessel elements; width, height and frequency of rays and tissue proportion were evaluated. Differences were observed between the anatomical structure of tapped and untapped trees to the quantitative characteristics. Only gelatinous fiber length; fiber lumen diameter; frequency of rays, and proportion of vessel elements and rays did not show significant statistical differences. The most important observations were the increase of ray width and height in the tapped trees, as well as the greater proportions of gelatinous fibers in the untraped ones. For the observation of the fiber cell wall ultrastructure, scanning electron microscopy (SEM), transmission electron microscopy (TEM) were used, which revealed that the non-gelatinous fibers present the typical configuration P + S1 + S2 + S3, while the gelatinous fibers presented the configuration P + S1 + S2 + G, in wich G layer presented a lamellar structure. The chemical analysis was performed by histochemical tests of Wiesner and Mäule, and Fourier transform infrared microspectroscopy (FT-IR). The staining presented in Wiesner test showed evidence of a lower lignin contente. The gelatinous layer G did not stain, indicating none or insignificant lignification in this portion of the wall. The Mäule test revealed the presence of guaiacil (G) units in the lignin, a result that was aligned with the FT-IR analysis. The spectra showed higher intensities for the bands assigned to G units in the gelatinous fibers than observed in non-gelatinous fibers. The S / G ratio indicated that the lignina G and S units had similar proportions, unlike that found in the literature for this species