IAWA Journal, Vol. 27 (3), 2006: 281–297 ON THE ORIGIN OF INTERCELLULAR CANALS IN THE SECONDARY XYLEM OF SELECTED MELIACEAE SPECIES* Oliver Dünisch1,2 & Pieter Baas3 SUMMARY The anatomy, frequency, and origin of intercellular canals in the xylem of ten Meliaceae species (Carapa guianensis Aubl., Carapa procera DC., Cedrela odorata L., Cedrela fissilis Vell., Entandrophragma cilindricum Sprague, Entandrophragma utile Sprague, Khaya ivorensis A. Chev., Khaya senegalensis (Desr.) A. Juss., Swietenia macrophylla King, Swietenia mahagoni (L.) Jacq.) were investigated using 327 samples from institutional wood collections, 398 plantation grown trees, and 43 pot cultivated plants. Tangential bands of intercellular canals and single canals were found in the xylem of all ten species. Staining of microtome sections indicated that the chemical composition of the secretion is similar to that of “wound-gums”. Studying the origin of the intercellular canals along the stem axis, it became obvious that the formation of the canals can be induced by wounding of the primary meristems (in particular by insect attacks of Hypsipyla spp., wounding of root tips) and by wounding of the cambium (formation of 43–100% of the intercellular canals). In fast growing trees of Carapa spp., Entandrophragma utile, and Khaya ivorensis, planted at an experimental site near Manaus, Brazil, numerous canals were found which were not induced by wounding of the meristems. In these trees an out of phase sequence of xylem cell development and high growth stresses were observed, which are hypothesised to be a fur- ther trigger for the traumatic formation of intercellular canals. Key words: Traumatic canals, mechanical injury, meristem, xylem cell de- velopment, growth stresses. INTRODUCTION Most studies on structure and formation of canals in wood have concentrated on resin canals in gymnosperms. In gymnosperms resin canals are classified into two groups, namely, non-traumatic and traumatic resin canals (Richter et al. 2004). The formation of non-traumatic resin canals is considered to be under genetic control (Werker & 1) Institute of Applied Botany, University of Hamburg, Ohnhorststr. 18, D-22609 Hamburg, Germany. 2) Institute for Wood Biology and Wood Preservation, Federal Research Centre for Forestry and For- est Products, Leuschnerstr. 91, D-21031 Hamburg, Germany. – Corresponding address [E-mail: [email protected]]. 3) Nationaal Herbarium Nederland, Leiden University branch, P.O. Box 9514, 2300 RA Leiden, The Netherlands. *) Dedicated to Prof. Dr. J. Bauch on the occasion of his 70th birthday. Downloaded from Brill.com10/01/2021 03:45:57AM via free access 282 IAWA Journal, Vol. 27 (3), 2006 Dünisch & Baas — Intercellular canals in Meliaceae 283 Fahn 1969), while the formation of traumatic resin canals is induced by exogenous factors, in particular by wounding (Lenely & Moore 1977; Fahn et al. 1979) and other environmental stressors (Wimmer & Grabner 1997). In contrast, information on the structure, the distribution, and factors influencing the formation of intercellular canals in the wood of dicotyledonous trees is very fragmen- tary, although in some dicotyledonous species intercellular canals are so frequent that they are important diagnostic features for wood identification (e.g., Dipterocarpaceae, Gottwald & Parameswaran 1966; Gottwald 1980; Wheeler et al. 1989). Intercellular canals are frequent in the Meliaceae (Record 1926; Wagenführ 2000; Dünisch et al. 2002a), but there is no standard term for them (terms used have been: resin ducts, gum ducts, traumatic resin canals and others). Because there are many high quality timber species within the Meliaceae (mahogany group), special attention has been given to the occurrence of intercellular canals with regard to wood quality and utilisation (e.g., Gottwald 1961; Wagenführ & Steiger 1963). Information on factors influencing the formation of these intercellular canals is rare. The first anatomical descriptions of intercellular canals in Meliaceae wood are in the pioneering works of Moeller (1876), Janssonius (1908), and Groom (1926). These studies indicated that the secretion in the canals is of a “wound-gum type” and that the “distances between suc- cessive intercellular canals or arcs is uneven and the formation is not periodic” (Groom 1926); yet these authors stated that the origin of this secretory tissue is unknown. Other publications considered intercellular canals in the xylem of Meliaceae species to be traumatic (Normand & Sallenave 1958; Normand & Paquis 1976). We studied the structure, frequency, and origin of the intercellular canals in the xylem of ten selected Meliaceae species (five genera). Special attention was given to 1) the impact of wounding, 2) the development and differentiation of xylem cells during the formation of the intercellular canals, and 3) growth stresses and their possible effect on the formation of intercellular canals. MATERIAL AND METHODS Selected species and plant material Ten tree species from five genera of the family Meliaceae were selected: Carapa guianensis Aubl., Carapa procera DC., Cedrela odorata L., Cedrela fissilis Vell., Entandrophragma cilindricum Sprague, Entandrophragma utile Sprague, Khaya ivorensis A. Chev., Khaya senegalensis (Desr.) A. Juss., Swietenia macrophylla King, and Swietenia mahagoni (L.) Jacq. The occurrence of intercellular canals in the sec- ondary xylem of all ten species is documented in the literature (Richter & Dallwitz 2000; Wheeler et al. [www.insidewood.lib.ncsu.edu/search]). 327 samples from wood collections (Table 1), stem and branch samples of 398 plantation grown trees (age: 4 years; Table 2) and of 43 pot cultivated plants (age: 2 years; Table 3) were examined. Samples from wood collections — Wood samples and samples from slide collections of the selected species were available from the collections of the National Herbarium of the Netherlands (Leiden - Lw / Utrecht - Uw), of the Federal Research Centre for Forestry and Forest Products, Hamburg, Germany (RBHw), and of the Federal Uni- Downloaded from Brill.com10/01/2021 03:45:57AM via free access 282 IAWA Journal, Vol. 27 (3), 2006 Dünisch & Baas — Intercellular canals in Meliaceae 283 Table 1. Number of wood samples from the wood collections of the National Herbarium of the Netherlands (Leiden/Utrecht), the Federal Research Centre for Forestry and Forest Products, Hamburg, Germany, and the Federal University of Paraná State, Curitiba, Brazil examined for this study. Number and portion (%) of samples with intercellular canals. Frequency (number per cm2 cross section area) of canals (local or in tangential bands) in the wood samples. Values followed by different letters differ significantly between species atp < 0.05 (Fisherʼs F-test). Species No. of samples No. of samples Frequency of inter- with intercellular cellular canals canals (%) (no. cm-2) Carapa guianensis 53 30 (57) 0.0160 a Carapa procera 43 26 (60) 0.0225 b Cedrela odorata 69 18 (26) 0.0180 a Cedrela fissilis 30 12 (40) 0.0143 c Entandrophragma cilindricum 23 6 (26) 0.0092 d Entandrophragma utile 23 5 (22) 0.0125 c Khaya ivorensis 16 15 (94) 0.0375 e Khaya senegalensis 10 6 (60) 0.0371 e Swietenia macrophylla 28 5 (18) 0.0090 d Swietenia mahagoni 32 8 (25) 0.0060 f versity of Paraná State, Curitiba, Brazil. As far as possible the samples were cross- checked for duplication within and between the collections. For the statistical analyses on the occurrence of intercellular canals only one of duplicated samples was included. Plantation grown trees — Trees from 4-year-old plantations located in the region of Manaus, Amazonas (03° 08' S, 59° 52' W; Carapa guianensis, Carapa procera, Cedrela odorata, Khaya ivorensis, Khaya senegalensis, Swietenia macrophylla, Swietenia mahagoni), in the region of Santarem, Para (02° 52' S, 54° 45' W; Entan- drophragma cilindricum, Entandrophragma utile), and in the region of Ponta Grossa, Paraná, Brazil (25° 15' S, 50° 45' W; Cedrela fissilis) were selected. The Manaus site (tropical) is located at approximately 30–50 m above sea level with an annual precipitation of about 2500 mm (min. 110 mm [August], max. 295 mm [February] per month), a mean air temperature of 26.4 °C, and a mean air humidity of 87%. The soil is a poor oxisol (FAO-UNESCO 1990) with a low cation exchange capacity (Schroth et al. 2000). Edaphic factors of the Santarem region (30 m above sea level) correspond to the Manaus region, but the soil of the plantation near Santarem is more fertile than that in the plantation near Manaus (Dünisch et al. 2002b). In addition, the drier period is more distinct on the Santarem site than on the Manaus site. The subtropical site near Ponta Grossa is located 870 m above sea level. The annual precipitation is about 1570 mm and the mean air temperature is 19.1 °C. July and August are the driest and coldest months of the year with a monthly precipitation of about 70 mm and a mean air temperature of about 14 °C. The soil is of the cambisol type (EMBRAPA-SNLS 1984). The plantations near Manaus and Santarem /Belterra were installed at the research stations of the Brazilian Federal Research Centre EMBRAPA, while the plantation near Downloaded from Brill.com10/01/2021 03:45:57AM via free access 284 IAWA Journal, Vol. 27 (3), 2006 Dünisch & Baas — Intercellular canals in Meliaceae 285 Ponta Grossa was installed by private owners (Fazenda Bitumirim). All species were planted in open plots (spacing: 3 × 3 m) of 12 to 100 trees each (Bauch et al. 1999; experiment 1). In addition Carapa guianensis and Khaya ivorensis were planted in a line enrichment of a secondary vegetation and in a mixed agroforestry plantation, re- spectively (Dünisch 2001; Schroth & Sinclair 2003; experiment 2). In these plantations the growth rate of the trees was reduced compared to trees grown in open plantations (Table 2). For the study on the occurrence and on the origin of intercellular canals, 4-year-old trees of the plantations were completely harvested by excavation (Fig. 1). The trees were divided into segments of 1 m length. After that each root/shoot segment was cut in the longitudinal direction into 2 parts (radial cut, Fig.