Trabeculae and Al-accumulation in the wood cells of Melastomataceae species from Brazilian savanna

Family Melastomataceae is an important component of the Brazilian Cerrado flora, inhabiting different environments from those with well-drained soils to swamp soil sites. Several members of this family are recognized as aluminum (Al)-accumulating. We studied the wood anatomy of six species of Melastomataceae (Miconia albicans (Sw.) Triana, M. fallax DC., M. chamissois Naudin, M. ligustroides (DC.) Naudin, Microlepis oleaefolia (DC.) Triana, Rhynchanthera dichotoma DC.), growing in different environments of Cerrado, exploring the occurrence of trabeculae and Al-accumulation sites. We processed the material following the usual techniques in wood anatomy and histochemistry. We used a chrome azurol-S spot-test in fresh material to detect Al-accumulation. The common features were diffuse porosity, vessel elements with simple perforation plates and vestured pits, abundant parenchyma-like fiber bands and septate fibers, axial parenchyma scanty to vasicentric, and heterocellular rays. The presence of trabeculae in vessel elements, septa in parenchyma cells, and aluminum in the G-layer of the gelatinous fiber walls, in the septa of fibers, in cambial initials and derivatives cell walls, and in the vacuole of ray cells are recorded for the first time for Melastomataceae. The results of this study indicate an additional role for gelatinous fibers in Al-accumulation, and offer a new perspective on Al-compartmentalization in the wood cells from Cerrado species.

ANATOMICAL CHARACTERIZATION OF TENSION WOOD IN Hevea brasiliensis (Willd. ex A. Juss.) Mull. Arg.

ABSTRACT Tension wood is an important anatomical structure for its participation in the orientation of the trunk and the architecture of the branches as a function of structural reinforcement. However, its presence in large amounts significantly affects the technological properties of wood, just as in the rubber tree. Nevertheless, there is still demand for information about the origin, distribution and structural features in this species. Thus, this study aims to characterize the cellular structures in tension and opposite wood in Hevea brasiliensis (rubber tree), as well as its radial and longitudinal distribution. Discs at the base and the middle of the commercial logs were collected from three trees in a commercial plantation located in Tabapoã - SP. Tangential diameter of vessels, fiber length (gelatinous and non-gelatinous fibers), microfibril angle and proportionality of cellular elements (vessels, axial parenchyma, ray, gelatinous fibers and non-gelatinous fibers) were measured, and influence of gelatinous fiber presence in vessel diameter was observed. Gelatinous fibers were observed in the two types of wood and in the two trunk heights. Both types of wood were distinguished by gelatinous fiber length and the proportion of axial parenchyma. The tension wood in mid-trunk was the most different, with long gelatinous fibers and less abundant, larger vessel diameter and vessel proportion. Moreover, smaller vessel diameter was observed in the regions with a high proportion of gelatinous fibers, suggesting that the plant invests more support than in liquid transport.

GROWTH STRAINS AND RELATED WOOD STRUCTURES IN THE LEANING TRUNKS AND BRANCHES OF TROCHODENDRON ARALIOIDES - A VESSEL-LESS DICOTYLEDON

Leaning trunks and branches of Trochodendron aralioides Sieb. & Zucc., a primitive vessel-less dicotyledon, show increased radial growth and gelatinous fibers on the upper side similar to the features found in dicotyledons with vessels. The patterns of peripheral longitudinal growth strain are variable among trees but similar at different heights within the same leaning trunk. Growth strains on the lower side of the trunks are very small but they are relatively large on the lower side of the branches. Growth stress in the branches is partly affected by the gravitational bending stress, which would be exerted mostly on the lower side. Large spring back strains of branches are associated with large surface strains. Both the microfibril angle (MFA) and the percentage area of gelatinous fiber show positive relationships with the measured strains. The MFA of the S2 wall layer in tracheids in the opposite wood is 24.6 ± 2.2°, whereas the MFA of gelatinous layer in the tension wood is only 14.2 ± 2.7°. The difference of MFA between the gelatinous fibers and the opposite wood is one of the factors accounting for the large contracting force for reorientation.