Ultrastructure and chemistry of the cell wall of gelatinous fibers from native rubber trees

Abstract

During the growth of trees, tension forces act on the trunk and branches in order to maintain their posture. When present, gelatinous fibers are considered responsible for this force, due to the presence of the gelatinous layer (G-layer). The cell wall structure and the chemical characteristics of the gelatinous fibers of Hevea brasiliensis (Willd. ex. A. Juss.) Mull. Arg., from a native forest in Brazil, were studied. For this purpose, scanning electron microscopy, transmission electron microscopy, Wiesner and Mäule histochemical tests, and Fourier transformed infrared microspectroscopy (FT-IR) were carried out. The non-gelatinous fibers presented a typical P + S1 + S2 + S3 configuration, while the gelatinous fibers presented a P + S1 + S2 + G configuration, in which the G-layer presented a lamellar structure. The chemical characterization of the lignified walls in both types of fiber indicated the presence of guaiacyl units in the lignin, however, at low levels. The G-layer did not react to the tests used, indicating the absence of lignin or low lignification. FT-IR analysis detected slightly higher intensities for signals related to G units in the gelatinous fibers than in the non-gelatinous fibers. The S / G ratio indicated G and S lignin units in equal proportions, differently from literature for this species. The lignification process and the structure of the fiber walls present in rubber trees vary depending on the origin of the wood material.