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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 perforations’.

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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.

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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.

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Laterally positioned transpiercing regions that cause lateral openings both in fibres (Fig. 23, 24) and in axial parenchyma cells, in frontal (Fig. 25) and lateral views, also occur, and can best be observed in macerations

Fig. 23–25. Incomplete transpiercing regions in Croton urucurana and Alchornea triplinervia. – 23: frontal view, note the extreme lateralization of the transpiercing region with an incomplete wall on one side (arrow); 24: side view, note the wall interruption (arrows); 25: axial parenchyma cell in frontal view, note the extreme lateralization of the transpiercing region with an incomplete wall (arrow). — Scale bars = 40 µm.

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DISCUSSION An intergrading series has been demonstrated here from slender ‘ordinary’ trabeculae into the ‘piercing’ holes. It is empting to interpret this as a developmental series. The great number of intermediate morphological structures in fully differentiated cells suggests that the beginning of the formation of the transpiercing is independent of the cell age. Because of this, the piercing process can be interrupted when the cells stop growing, resulting in all intermediate stages found among the adult cells. It seems that the piercing holes are formed through the dilatation of trabeculae. Some trabeculae, characteristically thin structures, are dilated and hollow, crossing the cell wall to wall (Fig. 7, 9, 11) and are, therefore, associated with transpierced cells. The presence of the transpiercing regions in a cell enables the growth of the walls of the neighbouring cells into the space of the cavities (Fig. 12, 14, 17), shaping protuberances similar in outline to the cavities (Fig. 2 asterisk). The dissolution of the central core of a trabecula may be the origin of such structures, as suggested for the first time by Gomes et al. (1988). However, the piercings have originated not only from the wide trabeculae, as Gomes et al. (1988) suggested, but also from the narrow ones due to the growth of the transpierced cells which produce larger or smaller cavities (transpiercing holes), depending on the establishment of the trabeculae at different stages of the cellular growth. Therefore, the term ‘simple perforation’ is inappropriate because it does not imply the occurrence of perforations in both opposite walls. Furthermore the term ‘intrusive cavities’ gives no indication of a channel that crosses the entire cell. Indeed, the term ‘transpierced’ of Gomes et al. (1988) gives us the real idea of the discussed structure; however, since Gomes et al. wrote about ‘transpierced cells’, giving no name for the observed structure, I propose the use of the term ‘transpiercing region’ for this feature since this term has already been used by Luchi and Mazzoni-Viveiros (1988) in Por- tuguese. Dias-Leme and Angyalossy-Alfonso (1998) found what they called a ‘concavity’ in intrusive fibres of some species of Euphorbiaceae, includingCroton floribundus, sug- gesting for it an origin by means of apical forking and posterior fusion of the separated apices. The same structures were observed here, and their development is explained better and more easily as incompletely formed transpiercing regions. I believe that they are formed by the development of eccentrically positioned trabeculae (Fig. 5, arrow), of which the growth leads to eccentric channels that reach only one side of the cell (Fig. 13) and, in a more advanced stage, give origin to bag-like cavities, like those observed in the fibres of Croton urucurana (Fig. 23) and parenchyma cells of Alchornea triplinervia (Fig. 25).

REFERENCES

Angyalossy-Alfonso, V. 1998. Cycadaceae: traqueíde com cavidade. Resúmen del Congresso Latinoamericano de Botánica, VII, Ciudad de México, México. Berlyn, G.P. & J.P. Miksche. 1976. Botanical microtechnique and cytochemistry. The Iowa University Press, Iowa. Dias-Leme, C.L. & V. Angyalossy-Alfonso. 1998. Intrusive cavities in Euphorbiaceae fibre walls. IAWA J. 19: 279–283.

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Gomes, A.V., L.L. Teixeira, G.B. Muniz & A. Bohren. 1988. Transpierced tracheids, trabeculae and other unusual features in Gymnosperm wood. Conferência Global da Divisão 5 – Produtos Florestais. International Union of Forestry Research Organizations IUFRO. Johansen, D.A. 1940. Plant microtechnique. McGraw-Hill Book Co., New York, London. Luchi, A.E. 1990. Estudo anatômico do lenho em espécies de mata ciliar da Serra do Cipó (MG). Dissertação de Mestrado, Instituto de Biociências. Universidade de São Paulo, São Paulo. Luchi, A.E. & S.C. Mazzoni-Viveiros. 1988. Regiões de transpasse em elementos celulares de lenho de Alchornea triplinervia (Spreng.) Müll.Arg. (Euphorbiaceae). VII Congresso da Sociedade de Botânica de São Paulo. Livro de Resumos, Rio Claro. Sass, J.E. 1951. Botanical Microtechnique. The Iowa State College, Iowa.

Woodworth, R.H. 1934. Perforated fiber-tracheids in the passion flowers. Science 16: 449 – 450. Woodworth, R.H. 1935. Fibriform vessel members in the Passifloraceae. Trop. Woods 41: 8–18. Zhong, Y., P. Baas & E.A. Wheeler. 1992. Wood anatomy of trees and shrubs from China. IV. Ulmaceae. IAWA Bull. n.s. 13: 419– 453.

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