IAWA Journal, Vol. 26 (1), 2005: 69-77

THE OF AND ITS RESINOUS HEARTWOOD

Luis Garcia Esteban1, Peter Gasson2, Jose Maria Climent3, Paloma de Palacios 1 & Antonio Guindeo 1

SUMMARY

Pinus canariensis (Canary Island or Piteh Pine) forms natural for­ ests on the islands ofTenerife and . The heartwood has an extra­ ordinarily high eontent, and this paper provides an anatomical deseription ofthe wood as weIl as an interpretation ofthe faetors relating to this resinifieation. Pinus canariensis possesses many subsidiary parenehyma eells surround­ ing the axial resin eanals. Similarly, the pereentage of rays is high, whieh means there are many parenehyma eells eapable of aeeumulating large amounts of stareh, whieh in turn ean be used for the synthesis of the piteh extraetives, primarily terpenoids and polyphenols. The presenee of sub­ sidiary parenehyma eells and the high pereentage of rays are a major eontributor to the heartwood of Pinus canariensis being rieh in extrae­ tives. Key words: Pinus canariensis, , pine forest, resinous heart­ wood.

INTRODUCTION

Pinus canariensis C.Smith oeeurs naturally on the highest islands of the arehipelago, , , La Gomera, EI Hierro and La Palma, but it is not found in or Fuerteventura. The speeies oeeupies a total area of 66,700 ha, with 30,000 ha in Tenerife, 23,000 ha in La Palma, 11,000 ha in Gran Canaria and 2,700 ha in EI Hierro. The species is found from sites at sea level to nearly 2400 m. The present-day eondi­ tions of the eastern islands do not allow for the establishment of pine forests, although arehaeologieal sites have been loeated in Fuerteventura (Maehado Yanes 1995) and many of the plaee names on the island of Lanzarote bear witness to the former presenee of the Canary Island pine in these islands.

1) Escuela Tecniea Superior de Ingenieros de Montes, Universidad Politecnica de Madrid, De­ partamento de Ingenierfa Forestal, Ciitedra de Tecnologfa de la Madera, Ciudad Universitaria, E-28040 Madrid, [E-mail: [email protected]]. 2) Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom. 3) Escuela Teenica Superior de Ingenieros de Montes, Universidad Politecnica de Madrid, De­ partamento de Silvopascicultura, Catedra de Anatomfa y Fisiologfa Vegetal, Ciudad Universi­ taria, E-28040 Madrid, Spain.

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Although it occupies a limited and very specific natural area in comparison with other species, Pinus canariensis has a broad genetic base due to its to the diverse ecological conditions of the islands (Climent 1995). Four areas of provenance and five sub-regions have been established for this species (Climent et al. 1996). There is a wide variety of opinion on the absence of true pine forests on the island ofLa Gomera. For some (Ceballos & Ortufio 1951; Rivas-Martinez 1987), the altitude of the island is not sufficient to allow a dry montane forest. For others (Ferreras & Arozena 1987), the presence of relic examples in el Garabato and in the Imada and Agando rock formations is significant. However, the possible existence of a former pi ne forest at some stage in the past should not be discounted. In many of the genus Pinus the resin content of the heartwood is much greater than that of the sapwood. Species such as Pinus rigida, P. merkusii, P. ponderosa and P. caribaea have heartwood with high resin content, for which reason they are given the name of pitch pine in commerce. The Canary Island pine is a c1ear example of this group of , although the small amount of wood placed on the market means that it is virtually unknown outside the Islands. The first complete description of the wood of Pinus canariensis was made by Najera and was inc1uded in Ceballos & Ortufio (1951). Greguss (1955) inc1udes abrief description ofthe xylem ofthe Canary Island pine, and Peraza (1964) provides an ex­ haustive description of this wood. In 1967 he enlarged this description. Garcia Esteban and Guindeo (1988) revised these works and expanded the description. Climent (1995) did an exhaustive study of the genetic and environmental aspects of the resinification of the Canary Island pine, inc1uding a full anatomical description of the axial paren­ chyma sheath that surrounds the resin canals, which Wiedenhoeft and Miller (2002) term subsidiary parenchyma cells. Lastly, Garcia Esteban et al. (2002) presented a new description with features that had not been considered previously.

MATERIAL AND METHODS

The material used for this study was collected in the natural forests ofTenerife and La PaIrna. In order to locate the natural forests the Mapa Forestal de Espafia (Ceballos 1966) and the Atlas Cartograficos de los Pinares Canarios (DeI Arco et al. 1992; Perez de Paz et al. 1994) were used. The sampIe sites were chosen by using the Estudio Ecol6gico deI Pi no Canario (Blanco et al. 1989). The specimens collected in Tenerife covered the three provenance subregions of the island, and in La Palma specimens could only be taken from the northem subregion. Eleven were cut, six in Tenerife and five in La PaIrna. The microscopic preparations were made following the usual methods of softening, sectioning, staining, and mounting. For the observation of starch content in the parenchyma cells Lugol 's solution was used, prepared following the method of Johansen (1940). The lipids and contained in the lumen of the tracheids were identified with Sudan IV dye using the method of Jensen (1962). The tannins were identified by being immersed in an aqueous solution of potassium dichrornate for 15 minutes (Locquin & Langeron 1985).

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WOOD ANATOMICAL DESCRIPTION

Growth rings dearly defined, with a relatively gradual change from earlywood to late-wood. Axial tracheids without spiral thickenings. The axial tracheids ofthe early­ wood are of irregular shape, with rounded edges and intercellular spaces (Fig. la). These intercellular spaces also occur in non-compression wood. The axial tracheids of the latewood are hexagonal or square in cross seetion. These intercellular spaces also occur in non-compression wood. In the resinous heartwood, all the axial tracheids have the lumen occupied by translucent substances of a caramel colour and of terpenic nature, which react positively with Sudan IV and cupric acetate. These deposits appear abruptly either in the sapwood ring dosest to the heartwood or in the two dosest rings. The average radial diameterofthe axial tracheids ofthe earlywood is 51 f-lm (37-58 f-lm) (12.1)*) and in the latewood it is 37 f-lm (24-43 f-lm) (6.4). The average tangential diameter of the axial tracheids is 49 f-lm (45-51 f-lm) (4.1). The axial resin canals appear in the transition wood or latewood and very rarely in the earlywood. Their average tangential diameter is 221 f-lm (168-293 f-lm) (8.3) (Method A in IAWAComrnittee 2004), with a density ofO.25 to 0.60 canals permrn2. The latewood was impregnated with resin earlier and with greater intensity than the earlywood. The epithelial cells that surround the canals are thin-walled and are surrounded by a very extensive group of subsidiary parenchyma cells which in some cases number as many as 65 cells (normally around 35, Fig. 2). The appearance of the subsidiary tissue is on occasion aliform, and when two contiguous canals are in proxirnity it may be conftuent. The further away we are from the epithelial cells, the greater the degree of lignification of the secondary walls of the subsidiary parenchyma cells. Groups of subsidiary cells in trans verse section can frequently be found, and even diffuse groups of parenchyma cells between the axial tracheids, which can be confused with 'normal' diffuse paren­ chyma, although after making contiguous transverse cuts above or below these cells it appeared that all of the parenchyma cells are continuous with the subsidiary tissue of the axial resin canals (Fig. 1b). The subsidiary parenchyma cells comrnunicate with the adja­ cent axial tracheids through semi-bordered pits, which are smaller than those of the cross fields in the ray-tracheid contacts. The epithelial cells in the initial stages are turgid, completely covering the canal intemally, with starch grains being very evident in the subsidiary parenchyma cells and less so in the epithelial cells. Lipids, detected by Sudan IV staining, are also present in the epithelial cells. Once the has reached the age of ten years, the epithelial cells in the newly-formed wood become disorganised and appear squashed against the walls of the subsidiary tissue of the resin canal, apparently due to the excess of resin in the interior of the canal (Climent 1995). In the subsidiary parenchyma cells there is a pro­ cess of substitution of the grains of starch by substances of a more intense colour, usually reddish-brown, with a base of stilbenes and ftavonoids, sometimes with tannic properties. At the end of the maturation process of the resin canals in the pitch wood, the canals are totally blocked by solid res in. All the rings near the resinous heartwood show this condition.

*) 51IAm (37-58IAm) (12.1) = average value (minimum value - maximum value) (standard devi­ ation).

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Fig. 1-4. Pinus canariensis. - 1: Transverse sec ti on showing intercellular spaces throughout the wood (a) and subsidiary cells (b) of an axial resin canal not visible in this seetion. - 2: Sub­ sidiary cells associated with the axial resin canal. - 3: Starch grains in ray parenchyma cells. - 4: Cross-field pits pinoid. - Scale bars for 1 = 150 f.tm; for 2 = 200 f.tm; for 3 & 4 = 25 f.tm.

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Fig. 5 & 6. Pinus canariensis. - 5: Dentate ray tracheids. - 6: Biseriate and opposite bordered pits with crassulae on the radial wall of the axial tracheids. - Scale bars far 5 = 25 !lffi; for 6 = 150 !lffi.

The height of the uniseriate rays varies from 2 to 32 cells and their average value is 9 cells (5.46). The number of rays per mm2 is 17 (16.2-19.5) (1.2); the number of ray tracheids per mrn2 is 35 (27.2-54.1) (4.3); and the number of ray parenchyma cells per mm2 is 76 (61.3-97.1) (4.3). The presence of radial resin canals gives rise to the typical appearance of fusiform multiseriate rays, with an average diameter of 36 llm (24-48 llm) (6.3). Bordered pits on the tangential wall of the axial tracheids were not observed either in early- or latewood. The rays are heterogeneous with an average percentage of parenchyma cells in rela­ tion to the number of cells of the ray of 70% (58-81 %) and an average percentage of ray tracheids of 30% (19-41 %). The cells ofthe ray parenchyma are generally thick-walled, the horizontal walls are pitted and the end walls are smooth. The ray cells have a high content of starch grains, which can have a diameter ofup to 20 llm (Fig. 3). On the boundary ofthe sapwood and the heartwood the starch grains transform into reddish-brown substances, in particular in the latewood, of the same nature as those of the subsidiary parenchyma cells of the resin canals, but in a much more abrupt manner than in the latter. In the pitch wood, although some isolated cells can be observed where the transformation has not been completed, starch grains have virtually disappeared.

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The cross-field pits are of the pinoid type, generally 1 or 2 per field, although there can be as many as 4 (Fig. 4). Their greatest diagonal diameter has an average value of 18 Jlm (13-22 Jlm) (2.5). The ray tracheids are located both in the marginal position as weil as in the interior of the ray. Their walls show irregular thickenings without marked dentations, although some dentations can be found sporadically (Fig. 5). The bordered pits ofthese tracheids have an average diameter of 11 Jlm (10-11 Jlm) (0.8). The bordered pits on the radial wall of the axial tracheids are normally uniseriate, and occasionally biseriate, and in both cases crassulae are present, although not in all the tracheids (Fig. 6). The average pit diameter is 24 Jlm (21-26 Jlm) (1.5).

DISCUSSION

The lack of references to the presence of the aliform subsidiary parenchyma cells found around the axial resin canals could be attributed to the loss of this subsidiary tissue during the sectioning process, and ac counts for the fact that the measurements shown in the previous descriptions give a larger diameter to the canals (350 Jlm) than those obtained in the present biometrie study (221 Jlm). Only the photographs in Najera(1951) clearly show the subsidiary parenchyma tissue of the resin canals, but the author does not establish any differences between the subsidiary cells and the epithelial cells. La Pasha and Wheeler (1990) note a similar structure in the resin canals of Pinus taeda, but no references have been found to indicate that the heartwood of this species is particularly resinous (Mirov 1967; Farjon 1984; Vidakovic 1991). Baas et al. (1986) describe subsidiary parenchyrna cells around the resin canals in Pinus longaeva and note an abundant resin content in the axial tracheids and in the ray cells of the heartwood. Although the abundance of resin canals (from 0.25 to 0.60 canals per mm2) is greater than in other pines, this is not sufficient to explain the large amount of resin in the resin­ ous heartwood of this species. In fact, when heartwood formation occurs in this wood, the epithelial cells have already lost their nuclei and became disorganised several years previously. In , Pardos (1976) showed that only the epithelial cells of the first rings ofthe sapwood were able to proliferate. Therefore, the resin ofthe resin canals is preformed inside the lumen of the canal and is liberated towards the tracheids when the tracheids have lost their water conducting function. However, it is possible that the radial resin canals, considered to have little to do with resinification, help to increase the volume of resin due to their connection with the living cells of the sapwood. The fact that the radial resin canals are interconnected with the axial resin canals, forming a three-dimensional network (La Pasha & Wheeler 1990), does not account for the resinification of this wood either. Only a metabolie route such as that described by Hillis (1987) for the impregnation by resin of the axial tracheids of Pinus radiata after the application of Paraquat, through the cross fields from the ray parenchyma cells, can explain resinification of this type. Yamada (1992) also highlights this circumstance, attributing to the resin canals the first stage in response to a fungus attack, as the resin is preformed, but at a later stage it is the ray parenchyma cells which are responsible for completing the impregnation.

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The most significant episodes in the fonnation of the heartwood are: aspiration of the bordered pits (Liese & Bauch 1967); death ofthe parenchyma cells ofthe rays, which corresponds to the most important cytological change, after a process of increasing lignification (Balatinez & Kennedy 1967; Fenge11970; Nobuchi & Harada 1985); and the transfonnation of the starch (Yamamoto 1982) and impregnation of substances. The microscopic observation of the sampies of Pinus canariensis analysed has shown that the starch present in the transition zone disappears completely in the heartwood in order to give rise to different impregnation substances. In all of the descriptions, with the exception of the one made by Greguss (1955), the extraordinary abundance of starch is shown. Its presence is not only limited to the rays, but also to the subsidiary parenchyma cells that surround the axial resin canals. This abundance is obvious in the transition zone between the sapwood and the heart­ wood, and affects two or three rings. In the transition zone many authors have defined an area with a high level of biological activity responsible for the principal processes of heartwood formation (Frey-Wyssling & Bosshard 1959; Bamber & Fukazawa 1985). Climent (1995) shows the larger percentage of rays in Pinus canariensis in relation to other , wh ich occupy up to 10% of the volume, as opposed to 6% in Pinus strobus (Panshin & DeZeeuw 1980),5% in Larix (Cote et al. 1966),5-7% in Coniferae (Wi1son & White 1986) and 9% in Pinus spp. (Koch 1972). This high ray volume implies a higher number of metabolically active cells capab1e of synthesising a larger amount of products, thereby providing some explanation for the high content of extractives in the Canary Island pine in relation to other species. In the same way, other characteristics of this species such as its ability to grow stump shoots and epiconnics, and even to survive after trunk gird1ing, are probably related to the ability to store and synthesise the compounds in the xylem, as shown in the results on other species by Kramer and Kozlowski (1979). Finally, the fact that the latewood is impregnated earlier and more intensely was also seen in the wood of Pinus radiata (Campbell et al. 1965; Lloyd 1978) and is ex­ plained both by the greater amount of resin canals in the latewood and by the fact that the bordered pits remain unaspirated in this area (Hillis 1987).

ACKNOWLEDGEMENTS

We are grateful to Prof. Pieter Baas and an anonymous referee for critical reading of the manuscript and valuable suggestions; and to all the staff of the Servicio de Medio Ambiente of the islands of Tenerife and La Palma.

REFERENCES

Baas, P., R. Schmid & B. 1. van Heuven. 1986. Wood anatomy of Pinus longaeva (Bristelcone pine) and the sustained length-on-age increase of its tracheids. IAWA Bull. 7 n.s.: 221-228. Balatinez, J.1. & R.w. Kennedy. 1967. Maturation ofray parenchyma cells in pine. For. Prod. J. 17 (10): 5-64. Bamber, R.K. & K. Fukazawa. 1985. Sapwood and heartwood: a review. For. Abstr. 46 (9): 567-580.

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Blanco, A., M. Castroviejo, J. L. Frai!e, J. M. Gandullo, L. A. Muiioz & O. Sanchez Palomares. 1989. Estudio ecol6gico dei Pino canario. ICONA, Serie Tecnica no. 6. Madrid. 199 pp. Campbell, J. R., E. P. Swan & J. W. Wilson. 1965. Comparison of wood and growth zone resinous extractives in Douglas fir. Pulp Paper Mag. Can. 66: 248-252. Ceballos, L. 1966. Mapa Forestal de Espaiia 1:400.000. Direcei6n General de Montes, Caza y Pesca Fluvial, Madrid. Ceballos, L. & F. Ortuiio. 1951. Vegetaei6n y flora forestal de las Canarias Oceidentales. MO de Agricultura, Direcei6n General de Montes, Caza y Pesca fluvia!. IFIE. Madrid. 465 pp. Climent, J. M. 1995. Aspectos geneticos y ambientales dei enteamiento dei pino canario. Estudio anat6mica y dendrometrico. Tesis doctoral, Madrid. 191 pp. Climent, J. M., L. Gi! & M. De Tuero. 1996. Regiones de procedeneia de Pinus canariensis Chr. Sm. ex DC. ICONA. Madrid. 49 pp. Cöte, WA., A.c. Day, B.W Simson & T.E. Timei!. 1966. Studies on larch arabinogalactan. I. The distribution of arabinogalactan in larch wood. Holzforschung 20: 178-192. Dei Arco, M., M.J. Perez, P.L. Rodrfguez, M. Salas M. & W Wi!dpret. 1992. Atlas cartografico de los pinares de Canarias: La Gomera y EI Hierro. Dir. Gra!. De Medio Ambiente y Con­ servaei6n de la Naturaleza, Gobiemo de Canarias, Sta. Cruz de Tenerife. 90 pp. Farjon, A. 1984. Drawings and descriptions of the genus Pinus. Brill & Backhuys Pub!., Leiden. 220 pp. Fengel, D. 1970. Ultrastructural changes during ageing ofwood cells. Wood Sci. Techn. 4: 176- 188. Ferreras, C. & M.E. Arozena. 1987. Gufa ffsica de Espaiia, 2. Los bosques. Alianza Editorial, Madrid. 394 pp. Frey-Wyssling,A. & H.H. Bosshard. 1959. Cytology ofthe ray cells in sapwood and heartwood. Holzforschung 13: 129-137. Garcfa Esteban, L. & A. Guindeo. 1988. Anatomfa e identificaei6n de las maderas de confferas espaiiolas. AiTiM, Madrid. 142 pp. Garcfa Esteban, L., P. de Palaeios, A. Guindeo, Ly. Garcfa Esteban, I. Lazaro, L. Gonzalez, Y. Rodrfguez, F. Garcfa, I. Bobadilla & A. Carnacho. 2002. Anatornfa e identificaci6n de maderas de confferas a nivel de especie. FUCOVASA y Edieiones Mundi-Prensa, Madrid. 421 pp. Greguss, P. 1955. Identification of living on the basis of xylotomy Akademiai Kiad6, Budapest. 263 pp. Hillis, W E. 1987. Chernical aspects of the heartwood formation. Wood Sci. & Techn. 2: 241- 259. IAWA Committee. 2004. List of microscopic features for softwood identification. IAWA 1. 25: 1-70. Jensen, W A. 1962. Botanical histochemistry, prineiples and practice. San Franeisco. 408 pp. Johansen, D.A. 1940. microtechnique. New York. 523 pp. Koch, P. 1972. Utilisation ofthe southem pines. US Dep. Agri. For. Servo Agric. Hand. 420, vol 11: 1476-1493. Kramer, P.J & T. T. Kozlowski. 1979. Physiology of woody . Academic Press, New York, San Francisco, London. 811 pp. La Pasha, C. A. & E. A. Wheeler. 1990. Resin canals in Pinus taeda. IAWA. Bull. n.s. 11: 227- 238. Liese, W & 1. Bauch. 1967. On the closure ofbordered pits in conifers. Wood Sci. & Techn. 1: 1-13. Lloyd, 1. A. 1978. Distribution of extractives in Pinus radiata earlywood and latewood. New Zea;. J. For. Sei. 8: 288-294. Locquin, M. & M. Langero. 1985. Manual de microscopfa. Barcelona. 373 pp.

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Machado Yanes, M.C. 1955. Reconstrucci6n de la vegetaci6n lefiosa de la isla de Fuerteven­ tura. Amilisis antracol6gico de la cueva de Villaverde (siglos III-IX). Actas dei Simposio Intemacional Pa1eoambiente Cuatemario en la Peninsula Iberica. Santiago de Compostela, 16-200ctubre 1995: 83. Mirov, N.T. 1967. The genus Pinus. Roland Press C.N. York. 602 pp. Najera, F. 1951. In: L. Ceballos & F. Ortufio. 1951. Vegetaci6n y flora forestal de las Canarias Occidentales. MO de Agricultura, Direcci6n General de Montes, Caza y Pesca fluvial. IFIE. Madrid. 465 pp. Nobuchi, T. & H. Harada. 1985. Ultrastructural changes in parenchyma cells of sugi (Cryptomeria japonica D. Don) associated with heartwood formation. Mokuzai Gakkaishi 31: 965-973. Panshin, A.J. & C. DeZeeuw. 1980. Textbook of wood technology. Ed. 4. McGraw-Hill, New York. 722 pp. Pardos, J. A. 1976. Cultivo in vitro de explantos tornados dei tronco de arboles de Pinus pinaster Ait. Con especial enfasis en el comportamiento de los canales resinfferos dei xilema. Anales INIA, Serie Recursos Naturales 2: 149-168. Peraza, C. 1964. Estudio de las maderas de confferas espafiolas y de la zona Norte de Marruecos. IFIE. No. 83. Madrid. 112 pp. Peraza, C. 1967. Estudio de las principales maderas de Canarias. IFIE. Madrid. 120 pp. Perez de Paz, P., M. dei Arco, O. Rodrfguez, J. Acebes, M. Marrero & W. Wildpret. 1994. Atlas cartografico de los pinares de Canarias III: La Pairna. Dir. Gral. De Medio Ambiente y Con­ servaci6n de la Naturaleza. Gobiemo de Canarias, Sta. Cruz de Tenerife. 160 pp. Rivas-Martfnez, S. 1987. Memoria dei mapa de series de vegetaci6n de Espafia. MO de Agricul­ tura, ICONA. Madrid. 268 pp. Vidakovic, M. 1991. Conifers: morphology and variation. Graf. Zavod Hrvatske, Zagreb. 754 pp. Wiedenhoeft, A. C. & R. B. Miller. 2002. Brief comments on the nomenc1ature of softwood axial resin canals and their associated cells. IAWA J. 23: 299-303. Wilson, K. & D.J.B. White. 1986. The anatomy ofwood. Stobart & Son, London. 309 pp. Yamada, T. 1992. Biochemistry of xylem responses to fungal invasion. In: R. Blan­ chette & A. R. Biggs (eds.), Defense mechanisms of woody plants against fungi: 147-164. Springer-Verlag, Heidelberg, New York. Yamamoto, K. 1982. Yearly and seasonal process of maturation of ray parenchyma cells in Pinus species. Res. Bull. of Experim. For., Hokkaido Univ. 39: 245-296.

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