IAWA Journal, Vol. 28 (3), 2007: 315-324 COMPARATIVE ANATOMY OF THE BARK OF STEMS, ROOTS AND XYLOPODIA OF BROSIMUM GAUDICHAUDII (MORACEAE) Dario Palhares, Jose Elias de Paula, Luiz Alfredo Rodrigues Pereira and Concei~ao Eneida dos Santos Silveira Department of Botany, University of Brasilia, Darcy Ribeiro Campus, 70919-970, Brasilia-DF, Brazil Correspondence: C. E. S. Silveira [E-mail: [email protected]] SUMMARY Brosimum gaudichaudii Trec. occurs in the Atlantic and Amazon for­ ests, and is the only species of Brosimum commonly found in Cerrado vegetation. It is of pharmaceutical interest due to the large accumulation of furocoumarins such as psoralens in the bark of roots and xylopodia. This work describes the bark anatomy of sterns, roots, and xylopodia. Although the external bark morphology of stern and subterranean system are different, anatomically they are similar, with both having wavy and fused rays at the outer region of the phloem and a gradual transition be­ tween pervious (non-collapsed) and collapsed phloem. Tbe stern and bark periderms have three to seven layers of cells. The bark of younger stern regions is different from the bark of older parts of the stern. Younger stern parts have higher abundance of laticifers in the phloem, and gelatinous fibers arranged in bundles. Compared with the younger regions, older sterns have fewer laticifers and the gelatinous fibers are scattered in the phloem. The root and the xylopodium bark are structurally similar to each other, with a higher abundance of laticifers than sterns. Starch was found in the roots, but not in sterns. Key words: Moraceae, Brosimum gaudichaudii, bark anatomy, stern, root, xylopodium. INTRODUCTION Even though Brosimum gaudichaudii is found in the Amazon and Atlantic forests (Santos & Kinoshita 2003), it is the only occurring species of the genus Brosimum in Brazilian Cerrado (Berg 1972), which is a savanna type formation (Mistry 2000). This species has a xylopodium, a woody tuberosity capable of resprouting (Rizzini & Heringer 1961; Appezzato-da-GI6ria & Estelita 2000). The aerial portion of the plant is not fire resistant, probably because of the thin bark, which is unable to confer a proper protection. As a consequence, the growth habit of mature plants varies from sub-shrub to tree. Brosimum gaudichaudii trees only occur in places where fire is not frequent (Ribeiro et al. 1985). Latex is abundant in the bark of the subterranean system. In sterns, latex is only abundant in the bark and pith of young sterns and branches. Latex is scarce in both bark and pith of older stern parts and not present in B. gaudichaudii wood (Palhares et al. 2006). Downloaded from Brill.com09/27/2021 08:10:48AM via free access 316 IAWA Journal, Vol. 28 (3), 2007 Brosimum gaudichaudii has been largely exploited by the pharmaceutical industry because of the large accumulation of psoralens in the bark of its subterranean system (Monteiro et al. 2002). Psoralens are furocoumarins with photo-mutagenic and photo­ chemotherapeutic properties used in the treatment of auto-immune skin disorders. While sterns, leaves, flowers, and fruits have only trace amounts of these compounds, the concentration of psoralens in the roots may represent up to 3% of the dry weight (Pires 2004). As the psoralens active principle is primarily found in the subterranean system of B. gaudichaudii, we have carried out an anatomical characterization of the bark of stern, root and xylopodium. The purpose of this study is to prepare a list of characteristics that may help to separate stern and subterranean system barks in the plant material indis­ criminately collected in the field. Also, this study makes a contribution to the knowledge of the genus Brosimum; most Brosimum species are found in wet forests and B. gaudi­ chaudii is the only species commonly found in the Cerrado. MATERIAL AND METHODS Five mature plants of shrubby and arboreal size were collected in Cerrado areas of Brasilia. Voucher specimens were deposited in the herbarium of the Vniversity of Brasilia (VB) underregistration numbers VB 12050, VB 12051, VB 12052, VB 13190 and VB 13191. Stern sampIes were obtained at a height of 20 cm, from sterns with a circumference ranging from 5 to 45 cm. The tap roots were 1.5 to 2 m deep with a cir­ cumference of 10 to 15 cm in the middle section where the sampIes were taken. The xylopodia had a circumference varying from 10 to 115 cm, and a length varying from 15 to 25 cm. More details on the extemal morphology of the studied material can be found in Palhares et ai. (2006) and Palhares & Silveira (2007). Transverse, radial and tangential bark sections (20-30!-Lm thick) were dehydrated in alcohol-xylene series un­ der vacuum, and subsequently double-stained with safranin and malachite green (Johan­ sen 1940). Maceration ofthe bark sampIes was accomplished as described by Franklin (1945). Histochemical tests were carried out to detect stareh, phenolic compounds, lignin and alkaloids (Johansen 1940; Bamber 2001). Anatomical terminology follows the nomenclature as described by Trockenbrodt (1990), Lev-Yadun (1991), Junikka (1994) and Richter et al. (1996). A dissociated bark preparation was used to measure the length /width of 20 intact sieve elements as weIl as the sieve plate angle. The sampIe size was determined by the number of intact cells found in the macerations. The values were used to calculate the average and standard error (SE). RESULTS Stern The general arrangement of Brosimum gaudichaudii bark fits into type 2 in Richter's classification (Richter et ai. 1996), with bark thickness ranging from 0.8 to 3.5 mm. The rays are wavy, funnel-shaped and sometimes fused in the distal part near the cortical zone (Fig. 1-3). The cortical zone is made of a parenchymatous tissue between the phloem and the periderm (Fig. 4). Downloaded from Brill.com09/27/2021 08:10:48AM via free access Palhares et al. - Bark anatomy of Brosimum gaudichaudii 317 There are few differences between the barks of thinner (younger) sterns and thicker (older) sterns. The bark of thinner sterns has remnants of the cortex (Fig. 2 & 4). The secondary phloem has laticifers, as does the cortical zone. However, in all sampies studied laticifers are generally inconspicuous and collapsed (Fig. Ib & 4). Moreover, due to the presence of cortex remnants, it appears that in younger sterns there is a higher abundance of laticifers than older sterns. Bundles of gelatinous fibers are observed in the cortical region of the bark of younger sterns (Fig. la). On the other hand, the bark of thicker sterns does not have cortical remnants (Fig. 3) and the gelatinous fibers are diffusely distributed in the secondary phloem. The outer sieve elements have a higher accumulation of callose than those in more internal regions of the phloem (Fig. 5). In general, sieve elements of B. gaudichaudii stern barks (Fig. 6) are small (138 ± 2 f.tm long, 12.5 ± 0.5 f.tm thick). Sieve plates are oblique, with inclinations ranging from 70° to 80°. The lateral sieve areas are elliptical, and a nacreous wall is frequently observed (Fig. 6 & 7). As mentioned previously, as the phloem parenchyma rays go outward, they become wider (Fig. 3); however, there is no corresponding increase in their height (Fig. 8). Furthermore, besides being perpendicular to the phloem rays (Fig. lb), the laticifers are also found inside the rays, as well as in the axial system of the phloem (Fig. 8). The periderm has three to seven layers of cells. The outer layers easily slough off from the bark (Fig. 9). Phloroglucinol tests (Bamber 2001) revealed the presence of lignified parenchyma cells in the outer region of the barks (Fig. 10 & 11). Phenolic compounds are abundant throughout the bark. Lipids occur in the phellern and crystals of calcium oxalate are occasionally observed in the cortical zone. Starch and alkaloids are absent. Figures 1-5. Anatomical structure of stern bark. - 1: TS of a young stern bark (0.8 mm thick). Note the laticifers (star) in the inner layers of the phloem and a bundle of gelatinous fibers (square) in the cortical zone. Inset a: higher magnification of a gelatinous fiber bundle. Inset b: detail of a collapsed laticifer in the bark (arrowhead). - 2: TS of a stern bark (1.5 mm thick). - 3: TS of bark in older sterns (3.5 mm thick). Note that there is no cortex remnant. - 4: RLS of the young stern bark (1.0 mm thick). The arrowheads indicate the location of laticifers in the cortical zone and phloem based on the differential staining. - 5: Bark stained with aniline blue and observed under fiuorescent light. High accumulation of callose (arrowheads) in the outer sieve tubes. - Sca1e bars = 100 !-Lm. Figures 6-9. Sieve elements, laticifers, and periderm of the bark of young sterns. - 6: Macera­ tion showing sieve elements with ellipticallateral sieve areas and compound sieve plate (arrow­ heads). - 7: Naereous walls (arrowhead) observed in TS. - 8: TLS. Note the presenee of lati­ eifers inside and outside of the ray (arrowheads). - 9: TS of the periderm of the stern bark. Note the outer periderm layers sloughing off (star). - Seale bar in 6 = 3 !-Lm; in 7 = 15 !-Lm; in 8&9=100!-Lm. Downloaded from Brill.com09/27/2021 08:10:48AM via free access 318 IAWA Journal, Val. 28 (3), 2007 Figures 1-5; für the legends, see page 317. Downloaded from Brill.com09/27/2021 08:10:48AM via free access Palhares et al. - Bark anatomy 0/ Brosimum gaudichaudii 319 Figures 6-9; for the 1egends, see page 317. Downloaded from Brill.com09/27/2021 08:10:48AM via free access 320 IAWA Journal, Vol. 28 (3), 2007 Figures 10-13.