IAWA Bulletin n.s., Vol. 13 (4),1992: 403-410 VARIATION IN FIBRE WALL STRUCTURE IN BAMBOO by R.J. Murphy and K.L. Alvin Timber Technology Research Group, Department of Biology, Imperial College of Science, Technology & Medicine, London SW7 2AZ, U.K. Summary The degree of polylamellation in the fibre these authors, lignification proceeds in a clear cell walls of the bamboo Phyllostachys viri­ pattern related to the growth and maturation deglaucescens has been investigated. The ex­ of the culm and is completed at the end of the tent of polylamellation was found to be influ­ first full growing season. They also noted the enced by position of the vascular bundle in presence of polylamellate fibres at this stage. the culm wall, in certain positions by age of However, Fujii (1985) has reported that ligni­ the culm and, most strikingly, with position fication of the fibre walls continued in the sec- J~ within the vascular bundle. The number of ond growth year and Fujii and Kawase et al. wall lamellae was variable but tended to be (1986) have reported that further deposition greatest in fibres adjacent to either vascular of wall layers occurred in the second and third elements or ground tissue at the periphery of years of growth. Alvin and Murphy (1988), the fibre bundles. A similar pattern of varia­ working with Sinobambusa tootsik, also tion in fibre walliamellation was also observed found evidence for fibre wall thickening con­ in two other species of bamboo. The character­ tinuing after the first growing season, proba­ istic pattern of fibre walliamellation probably bly until at least the third year with lignifica­ influences mechanical properties and warrants tion continuing as the new wall material was further investigation. laid down. They reported that the walls of Key words: Bamboo, fibres, cell walls, poly­ mature fibres mostly showed some stratifica­ lamellation, mechanical properties, Phyllo­ tion and that there was considerable variation stachys virideglaucescens. in lignin content of different fibres and of different layers in individual fibres. Good evi­ Introduction dence that fibres in different parts of the culm A polylamellate structure of the fibre walls wall vary significantly in structure has been in bamboos has been reported by a number of obtained by Murphy et al. (1991) in a study authors (i.e., Parameswaran & Liese 1975, of the development of soft-rot decay in Sino­ 1976; Fujii 1985; Itoh 1990). In their investi­ bambusa tootsik. gation of the fine structure of the fibre wall, We report here the results of a study of the Parameswaran and Liese (1976), working fibres in young and mature culms of Phyllo­ with seven different bamboo species, report­ stachys virideglaucescens (Carr.) A.C. Riv. ed the occurrence of two kinds of fibres: Subsidiary observations have been made on thick-walled polylamellate ones with up to material of Sinobambusa tootsik (Makino) eighteen alternating broad and narrow lamel­ Makino ex Nakai and Sinoarundinariajalcata lae and non-Iamellate ones which, by impli­ (Nees) Chao, using material from our previ­ cation, were thinner walled. The polylamellate ous studies. fibres, it was stated, were especially abun­ dant in the outer part of the culm wall nearest to the epidermis. Material and Methods Lignification of fibres has been studied Two culms of Phyllostachys viridegiau­ by Itoh and Shimaji (1981) and Itoh (1990) cescens were cut in August from specimens working with Phyllostachys sp. According to in outdoor cultivation at the Royal Botanic Downloaded from Brill.com09/24/2021 06:38:04AM via free access 404 IAWA Bulletin n.s., Vol. 13 (4),1992 Fig. 1. Part of wall of younger culm in TS, phloroglucinol-stained, showing heavy lignification in the outermost zone and close to the vascular tissues. - Fig. 2. Part of older culm in TS seen in polarized light. - Fig. 3. Bundle from zone 2 of younger culm. - Fig. 4. Comparable bundle of older culm. - Scale bar of 1 = 1 mm; scale bars of 2-4 = 100 J.lm. Downloaded from Brill.com09/24/2021 06:38:04AM via free access Murphy & Alvin - Fibre walls in Bamboo 405 Gardens, Kew. One culm was in its first year have only a low lignin content. This contrasts of growth, the other was estimated to be 3-5 with the older culm in which all the fibres are years old. Material from internode 6 was fixed extremely thick walled and lignified, although in formalin-acetic acid-alcohol and transferred the degree of lignification of different fibres to 50% alcohol for storage. Transverse and and of different layers of the wall in some longitudinal sections, 20-25 J,lm thick were individual fibres is variable (Figs. 4, 11). A cut on a Reichert sliding microtome and stained character of this species is the presence of an either in safranin and alcian blue and perma­ island of parenchyma in some of the fibre nently mounted in Euparal or in phlorogluci­ bundles on the protoxylem side in zones nol and temporarily mounted. Observations 2 and 3 (Figs. 2-4, 6). This parenchyma, were made on a Leitz Diaplan microscope which varies in extent from one to some using either ordinary bright-field illumination thirty cells, is very obvious in the younger or polarized light. culm where it resembles the typical ground Fibres as seen in transverse section of the tissue in the same region of the culm, in­ mature culm were classified on the basis of cluding the presence of some very thin-walled the number and position of thin birefringent cells, isodiametric in longitudinal section, layers in the wall as seen under the x 40 ob­ a feature characteristic of bamboo ground jective, using polarised light. The intention of tissue (Liese 1980). In the more mature culm, this investigation was to determine the distri­ however, most of the island cells have be­ bution of fibres having different degrees of come almost as thick walled as the surround­ walliamellation and the technique developed ing fibres and can be distinguished from them was found to be appropriate for distinguish­ in transverse section only by the more abun­ ing different types of fibres on the basis dant pits and the slightly larger lumina (cf. of walilamellation characteristics. Transects Figs. 3, 4). The walls of these cells become across fibre bundles (taken along the mid­ very heavily and uniformly lignified as indi­ radial line through the phloem and protoxylem) cated by deep phloroglucinol staining. The were used to record the number of birefrin­ thin-walled isodiametric cells remain un­ gent layers in each fibre along the line. Ten changed as they do in the ordinary ground vascular bundles in each of four zones of the tissue. culm wall were examined and the results Fibres in the outermost zone in the younger averaged for each zone. Zones (Fig. 1) were culm, where most are already more or less defined as previously (Murphy et al. 1991). mature, show much the same low degree of Since the number of fibres along the transect polylamellation as those in this position in the varied from bundle to bundle, a formula was older culm. Those that have lamellae usually devised to standardise the results by convert­ show only one or two thin layers, seen to be ing all into 10% intervals before averaging birefringent in polarised light, close to the for each zone. Included parenchyma, often lumen. Similarly, the other early maturing present in the fibre bundle on the protoxylem fibres, namely, those lying in close proximity side (see below), was disregarded in this pro­ to the conducting tissues elsewhere in the culm cedure. (zones 2-4), show the same degree of poly­ lamellation and lignification in both younger and older culms. However, the bulk of the Results larger, later maturing fibres lying further away Comparison between the two culms of from the vascular elements are still immature Phyllostachys virideglaucescens differing in in the younger culm and show either no evi­ estimated age by at least 2 years, confirm the dence of polylamellation or else again one or general findings reported by Alvin and Mur­ two thin lamellae close to the lumen (Fig. 6). phy (1988) concerning maturation and varia­ In the older culm, many of these same fibres tion oflignin content. Figures 3 and 5 show a show conspicuous polylamellation, especially vascular bundle from zone 2 of the younger those in the peripheral parts of the bundles culm in which the peripheral fibres are rela­ close to the ground tissue (Fig. 7). Up to 12 tively thin walled and are either unlignified or birefringent layers have been counted. Downloaded from Brill.com09/24/2021 06:38:04AM via free access 406 IAWA Bulletin n.s., Vol. 13 (4),1992 Downloaded from Brill.com09/24/2021 06:38:04AM via free access Murphy & Alvin - Fibre walls in Bamboo 407 Although much intergradation occurs, most almost at right angles to the long axis. Paren­ fibres in the more mature culm fall into one of chyma walls and the primary walls of fibres four structural patterns which may for con­ are also strongly birefringent due to either venience be recognised. These are best ob­ random or again predominantly horizontal served with polarised illumination: microfibril orientation. Figure 2 shows that the fibres in the outermost zone of the culm I. With no lamellae clearly visible, though and those close to the vascular elements in the sometimes with a thin birefringent layer other zones are darker (less birefringent) than adjacent to the lumen (Fig. 8, I). those elsewhere. The fibres in the more peri­ II. With 1-3 thin birefringent layers situated pheral parts of the bundles in the middle and in the inner half of the wall thickness inner zones are the most heterogeneous in (Figs.