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IAWA Journal, Vol. 24 (1), 2003: 87–95 TRANSPIERCING IN WOOD CELLS by Agnes Elisete Luchi Instituto de Botânica, Seção de Anatomia e Morfologia, Caixa Postal 4005, CEP 01061-970, São Paulo-SP, Brazil [E-mail: [email protected]] SUMMARY This paper discusses the nature of ‘transpierced’ elements in wood. In Croton urucurana and Alchornea triplinervia, different stages of development have been studied. These have provided the possibility of understanding the origin of ‘tranpiercing regions’ from the dissolution of the central core of the trabecula that has pierced the cell from one wall to the opposite one. Key words: Transpiercing region, transpierced fibre, transpierced parenchyma cell, Croton urucurana, Alchornea triplinervia, Euphorbiaceae, trabeculae. INTRODUCTION While studying trabeculae and related structures in the wood of Araucaria angustifolia, Gomes et al. (1988) observed what they considered at that time to be an anomalous feature, which they named ‘transpierced tracheids’. To understand the origin and nature of the holes in the cell walls, the authors also studied Austrocedrus chilensis, Fitzroya cupressoides, Podocarpus salignus, P. lam- bertii, Taiwania cryptomerioides, and Torreya taxifolia. Their observations indicated that this structural ‘abnormality’ was associated with the presence of abundant, variously- shaped trabeculae, and they suggested that the ‘piercing’ could possibly be formed either through dissolution of the central core of a wide trabeculae, or through the concurrent development of matching piercing lateral protuberances of two neighbouring tracheids. However, when studying the hardwood species Cabralea glaberrima (Meliaceae) they found a transpierced fibre and transpierced axial contact-parenchyma cells, but no trabeculae. Luchi and Mazzoni-Viveiros (1988) observed the same feature in fibres and axial parenchyma cells of Alchornea triplinervia (Euphorbiaceae). Luchi (1990) found it also in Tapirira marchandii (Anacardiaceae), Tibouchina candolleana (Melastomataceae), Inga sessilis (Leguminosae), Aegiphila sellowiana (Verbenaceae), and in Vochysia tucanorum (Vochysiaceae). Earlier, Woodworth (1934, 1935) had observed this feature in fibre-tracheids of many Passiflora species, and named them ‘perforated fibre-tracheids’. Zhong et al. (1992) observed holes in fibre walls and axial parenchyma cell walls of some genera of Ulmaceae. However, they considered them to be ‘simple perfora- tions’. Downloaded from Brill.com10/04/2021 07:53:03PM via free access 88 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 89 Dias-Leme and Angyalossy-Alfonso (1998) recorded this feature in Alchornea triplinervia, A. sidifolia, Croton floribundus, Sapium glandulatum and Sebastiania serrata (Euphorbiaceae), naming them ‘intrusive cavities’. Angyalossy-Alfonso (1998) used this same name when observing this structure in three Cycadaceae species. The present study suggests that a possible origin of the ‘transpiercing’ in the elements can be inferred from already completely developed cells, and proposes the preserva- tion of this very adequate denomination, adding the use of the term ‘transpiercing region’. MATERIAL AND METHODS Samples SPw 1091, 1385, 1458, 1459, 1460, 1472, 1474, and 1850 were taken from stem and root of adult trees of Croton urucurana Baill. from two areas of gallery forest at Estação Ecológica de Moji-Guaçu do Instituto Florestal, São Paulo State, Brazil. The sample SPw 687 was taken from the stem of an adult tree of Alchornea triplinervia (Spreng.) Müll. Arg. from a gallery forest at Serra do Cipó, Santana do Riacho, Minas Gerais State, Brazil. Stem samples were collected at breast height (1.30 m) and root samples at a depth of 30 cm below the soil surface. Macerations were prepared with Franklin’s solution, modified according to Berlyn & Miksche (1976), and stained with safranin. Sections, 15 to 20 µm thick, were prepared according to the usual technique (Johansen 1940; Sass 1951), stained with safranin or fast green and mounted in permanent slides with synthetic ‘Permount’ medium. In macerated material, many flattened cells tend to assume a similar position under the microscope usually showing the cavities studied here. This cell view is called here ‘frontal view’, in opposition to the ‘side’ or ‘lateral view’, which exhibits the channels. In order to get good side views of the cells and their channels, the cover slips were moved carefully and patiently until the cells were appropriately positioned. RESULTS The transpiercing regions were observed in fibres (Fig. 1, 3–17, 23, 24) and in axial parenchyma cells (Fig. 19, 20, 21) of both stem and roots of Croton urucurana, as well as in the stem of Alchornea triplinervia (Fig. 2, 18, 22, 25). A great number of morphologically intermediate structures between trabeculae and transpiercing holes were found among fully developed cells. These transpiercing regions are of different sizes and in spite of the larger ones being more easily seen, the smaller ones may give a better idea of their origin. Fig. 1–7. Transpiercing and trabeculae. – 1: Croton urucurana, tangential longitudinal section (TLS). – 2: Alchornea triplinervia, macerated wood. Note the mark (*) made by the transpiercing region of the neighbouring fibre. — 3–7: Trabeculae in Croton urucurana, macerated wood. – 3: frontal view (arrow); 4: side view (arrow); 5: frontal view (arrow); 6 & 7: side view (arrows). Note the alteration shown by the junction of a trabecula to a fibre wall. — Scale bars = 20 µm for Fig. 1 & 7; 50 µm for Fig. 2–6. Downloaded from Brill.com10/04/2021 07:53:03PM via free access 88 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 89 Downloaded from Brill.com10/04/2021 07:53:03PM via free access 90 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 91 Downloaded from Brill.com10/04/2021 07:53:03PM via free access 90 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 91 Figure 3 (arrow) shows a little mark, representing the frontal view of a small trabecula. This mark is a result of the linkage of the trabeculae to the fibre wall, as seen in the side view shown in Figure 4. There is no alteration of the wall structure. This is the first stage of the origin of that which I propose to call the ‘transpiercing’ region. Another fibre (Fig. 5 arrow) shows (frontal view) the junction of a trabecula to a fibre wall; a small wall alteration can be seen in side view in Figures 6 and 7, like a cone facing towards the exterior wall (arrows). It appears as if the trabecula becomes short- ened and pulls the fibre walls inwards. A similar situation can be observed in Figures 8 and 9 (arrow); however, here the trabecula is dilated and forms a transpiercing ‘channel’ visible in the light microscope. In another case a hole denoting the presence of the channel can be easily seen in frontal view (Fig. 10). In this stage the transpiercing channel is short and wide. The channel shortening seems to continue until it changes from a channel into a ‘transpiercing region’ (Fig. 10, 11). When the cavities are greater (Fig. 10, 13), it is no longer possible to distinguish any trabeculae in side view (Fig. 11, 12, 14). In these cases it is some- times possible to observe outgrowths of the juxtaposed fibres to the inside of the transpiercing regions (Fig. 12, 14, 17). The normal trabeculae as well as those showing different degrees of alteration, and the lateral intrusive growth of the juxtaposed fibres (Fig. 17), can be found both in macerations (Fig. 15) and in radial sections (Fig. 16, 17). The transpiercing region can be found also in axial parenchyma cells, in frontal view of macerated cells (Fig. 18, 22), and in tangential sections (Fig. 19). The radial sections exhibit the same trabeculae variations as seen in fibres (Fig. 20, 21). These parenchymatic cells show, indeed, the same intrusive outgrowth when juxtaposed to the cavities (Fig. 22). ← Fig. 8–14. Trabeculae in Croton urucurana, macerated wood. – 8: frontal view; 9: side view (arrow). – 10 & 11: same transpiercing region; 10: frontal view; 11: side view, note the thickening in the central region, corresponding to the inside wall thickening of the transpiercing region (arrow). – 12: side view of another transpiercing region showing the intrusive growth of the wall of a neighbouring fibre (arrow). – 13 & 14: larger transpiercing region; 13: frontal view; note the lateralization of the transpiercing region in the fibre; 14: side view showing the wall of a neighbouring fibre growing into the transpiercing region (arrow). — Scale bars = 20 µm for Fig. 8–11, 13 & 14; 50 µm for Fig. 12. →→ Fig. 15–22. Trabeculae in different grades of dilatation and transpiercing regions. – 15: real trabecula (arrow) in macerated tissue of Croton urucurana; 16: dilatation grade of a trabecula that becomes a ‘transpiercing channel’, longitudinal radial section in Croton urucurana; 17: a very large grade of dilatation formed by a large transpiercing region in the wall of a neighbouring (arrow). – 18–22. transpiercing regions in axial parenchyma cells; 18: frontal view (*) of macerated tissue in Alchornea triplinervia; 19: frontal view in longitudinal tangential section of Croton urucurana (arrow); 20: the arrow shows a transpiercing channel, in longitudinal radial section of Croton urucurana, like that observed in fibres; 21: an advanced grade in the formation of the transpiercing region, in Croton urucurana, that does not show the transpiercing channel; 22: macerated tissue of Alchornea triplinervia showing a transpiercing region (*) and the intrusive growth of a wall from a neighbouring axial parenchyma cell (arrow). — Scale bars = 50 µm for Fig. 15, 20 & 21; 20 µm for Fig. 16–19 & 22. Downloaded from Brill.com10/04/2021 07:53:03PM via free access 92 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 93 Downloaded from Brill.com10/04/2021 07:53:03PM via free access 92 IAWA Journal, Vol. 24 (1), 2003 Luchi — Transpiercing wood cells 93 Laterally positioned transpiercing regions that cause lateral openings both in fibres (Fig.

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