IAWA Journal, Vol. 20 (1),1999: 79-83

NUCLEATED WOOD FIBRES IN SOME MEMBERS OF COMBRETACEAE by Kishore S. Rajput & K. S. Rao

Department of Botany, Faculty of Science, M.S. University of Baroda, Vadodara - 390 002, India

SUMMARY

The wood fibres retain their living protoplast in eleven species of five genera of the Combretaceae. Among the species studied, those of Ano• geissus and Terminalia are trees while those of Calycopteris, Combretum and Quisqualis are large scandent shrubs. Living fibres with oval to oblong or fusiform shaped nuclei were found among all the species but their occurrence is more persistent in trees than in scandent species. The fibres are septate, thick-walled with narrow lumen and possess slit• like simple pits. In Combretum ovalifolium prismatic crystals frequently co-occur with the nucleus in the same compartment of the fibres. The possible significance of living fibres is discussed. Key words: Nucleated fibres, Anogeissus, Calycopteris, Combretum, Quisqualis, Terminalia.

INTRODUCTION

Fibres are the principal mechanical or supporting cells; strength and several other properties of hardwoods largely depend on their size and morphology. They are elon• gated sclerenchymatous cells mostly with lignified walls and narrow lumina and usu• ally considered to be dead. However, fibres sometimes retain their living protoplast even after their secondary walls have been laid down (Bailey 1953). Since Bailey's report, living fibres have also been reported in many shrubs and subshrubs belonging to many families (Fahn & Amon 1963; Fahn & Leshem 1963; Wolkinger 1970; Bamber & Fukazawa 1985) as well as in some species of Ephedra (Esau 1965). Wood anatomy of Combretaceae has been studied in detail (Metcalfe & Chalk 1950; Van Vliet 1979), but no mention about the presence of nuclei in xylem fibres was made by these authors. Living xylem fibres have previously been listed for Combretaceae (Carlquist 1988) on account of literature records of septate fibres. The present paper reports the occurrence of nucleated fibres in some members of Com• bretaceae.

MATERIALS AND METHODS

Wood samples measuring about 60 by 20 mm and deep enough to contain 4-5 years growth increment were excised from the main stems of Anogeissus latifolia, A. sericea, Calycopteris floribunda, Combretum coccineum, C. extensum, C. ovalifolium, Quis-

Downloaded from Brill.com09/28/2021 06:29:11PM via free access 80 IAWA Journal, Vol. 20 (1), 1999 qualis indica, Terminalia arjuna, T. bellerica, T. chebula, and T. tomentosa growing at the M. S. University Campus, Baroda. Anogeissus and Terminalis are medium-sized to tall trees reaching 12-20 m in height, while Calycopteris, Combretum and Quisqualis are large scandent shrubs. For each species five plants and from each plant four blocks were excised with the help of chisel, hammer and grafting knife. The blocks were immediately fixed in FAA (Berlyn & Miksche 1976). Tangential and radiallongitudi• nal sections 12-15 J.Ul1 thick were prepared using a sliding microtome and stained with safranin-fast green for general studies. Some of the sections were also treated with 12KI for starch localisation and with 4% acetocarmine to stain nuclei.

RESULTS

In all the species the wood fibres are thick-walled and have narrow lumina. Their shape and size varies, some of them are straight and spindle-shaped while others have undulated walls. Rarely branched fibres are also observed in the species. Each fibre is divided into 2 or 3 compartments by very thin septa. Accumulation of starch is a common feature in all the species studied (Fig. 1A) while prismatic crystals are ob• served only in fibres of Combretum ovalifolium. The length of the fibres varies from species to species and found to be largest (1930 J.Ul1) in Anogeissus latifolia and short• est (817 J.Ul1) in Quisqualis indica. Their lumen diameter is relatively larger in Com• bretum coccineum (16.4 J.Ul1) than in Terminalia chebula (7.4 J.Ul1). Fibre wall thick• ness also differs among the species. It is greatest in Combretum coccineum (7.7 J.Ul1) and least in Calycopterisfloribunda (3.7 J.Ul1). Pits on the walls are simple and confined to radial walls. Their aperture is slit-like and forms a narrow angle with the axis of the fibre. Distribution of nucleated fibres differs in trees and scandent species. In the former they are not common and are observed only in the two outermost growth rings. In the latter they are common and found in all the growth rings. The nuclei are more or less similar in shape, i.e., oval to oblong or elongated and fusiform (Fig. lA-F) but their size differs in the different species (Table 1). Their length including sharp points is maximal (21.6 J.Ul1) in Terminalia chebula and minimal (7.3 J.Ul1) in Anogeissus latifolia, but the width does not show significant variation (Table 1). As aforementioned, the fibres are septate and each of its compartments possesses a single nucleus. In Com-

Table 1. Dimensional details of nucleus in the wood fibres of Anogeissus, Calycopteris, Combretum, Quisqualis and Terminalia.

Plants Length Width Plants Length Width (J.III1) (J.III1) (J.III1) (J.III1)

Anogeissus latifoUs 7.3 ± 1.0 3.2 ± 0.3 Quisqualis indica 9.6 ± 2.7 2.7 ± 0.5 A. sericea 8.9±1.4 3.2 ± 0.5 Terminalia arjuna 9.8±0.1 2.1 ± 0.4 Calycopteris floribunda 7.8 ± 1.0 2.1 ± 0.5 T. bellerica 1O.6± 2.5 2.6 ± 0.6 Combretum coccineum 11.8 ± 1.1 3.2 ± 0.7 T. chebula 21.6 ± 2.7 3.2 ± 0.4 C. extensum 10.6 ± 2.1 3.0 ± 0.7 T. tomentosa 7.6 ± 1.4 2.1 ± 0.5 C. ovalifolium 8.5 ± 2.1 3.3 ± 0.8

Downloaded from Brill.com09/28/2021 06:29:11PM via free access Rajput & Rao - Nucleated fibres in Combretaceae 81

Fig. 1. Parts oflongitudinal sections of wood fibres showing nuclei (arrows). - A: Terminalia bellerica; arrowhead indicates starch grain in fibre lumen. - B: Terminalia arjuna. - C: Terminalia tomentosa. - D: Combretum coccineum. - E: Quisqualis indica. - F: Combretum extensum. - Scale bar = 20 JlIll.

Downloaded from Brill.com09/28/2021 06:29:11PM via free access 82 IAWA Journal, Vol. 20 (1), 1999 bretum ovalifolium, prismatic crystals are also present in the compartments, Nuclei of the fibres remain similar in shape to those of the axial and ray parenchyma cells of the xylem. The parenchyma cells differ from xylem fibres by being broader, shorter and hav• ing thinner walls. They also possess large circular simple pits on both radial and tan• gential walls.

DISCUSSION

Occurrence of wood fibres with living protoplast seems to be not uncommon and is reported in many genera belonging to different families (Fahn & Leshem 1963; Carlquist 1988). In the present study, nucleated fibres are reported in eleven species of five genera belonging to Combretaceae. Our observations indicate that the distri• bution of nucleated fibres vary between tree and scandent species. In tree species living fibres are restricted to the outermost xylem but starch is found in all the four growth rings. In the scandent species they are widespread throughout the stem. Fahn and Leshem (1963) considered that nucleated fibres in subshrubs, shrubs and climb• ers are associated with their diminishing support function, exhibiting transition forms towards parenchyma cells prevailing in the herbaceous plants. Moreover, accumula• tion of starch in nucleated wood fibres also suggests that in addition to mechanical support it also acts as a reservoir of photosynthetic products representing a further functional connection between parenchyma cells and wood fibres. Fibres with living protoplasts are considered to be an adaptive feature (Fahn & Amon 1963) and their main function appears to be storage of starch, which can be used at times of high cambial activity (Metcalfe & Chalk 1983). This appears true in the case of plants in the present investigation. However, the plants show massive flowering and sprouting of new leaves in April-May at the end of the dry season except for Quisqualis. The latter is an ornamental plant bearing leaves and flowers for most of the year which may be due to regular water supply. Furthermore, it has been suggested by Parameswaran and Liese (1969) that the ability to store starch in fibres may compensate for a paucity of storage parenchyma. In all the species of the present study, all the wood fibres are septate and possess a single nucleus in each compartment. Very thin septa in all the species of trees and scandent shrubs indicate that their development may be similar to that described by Parameswaran and Liese (1969).

ACKNOWLEDGEMENT

The authors are thankful to the Council of Scientific and Industrial Research, New Delhi, for financial support.

REFERENCES

Bailey,I.W. 1953. Evolution of tracheary tissues of land plants. Amer. J. Bot. 40: 4-8. Bamber, R.K. & K. Fukazawa. 1985. Sapwood and heartwood: a review. For. Prod. Abstr. 8: 265-278.

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Berlyn, G.P. & J.P. Miksche. 1976. Botanical microtechnique and cytochemistry. Iowa State Univ. Press, Ames, Iowa. Car1quist, S. 1988. Comparative wood anatomy. Springer-Verlag, Berlin. Esau, K. 1965. Vascular differentiation in plants. Holt. Rinehart & Winston Inc., New York. Fahn, A. & N. Amon. 1963. The living wood fibres of Tamarix aphylla and the changes occur- ring in them in transition from sapwood to heartwood. New Phytol. 62: 99-104. Fahn, A. & B. Leshem. 1963. Wood fibres with living protoplasts. New Phytol. 62: 91-98. Metcalfe, C.R. & L. Chalk. 1950. Anatomy of the Dicotyledons. Vol. 2. Oxford Univ. Press, Oxford. Metcalfe, c.R. & L. Chalk. 1983. Anatomy of the Dicotyledons. Ed. 2. Vol. 2. Wood structure and conclusions of the General Introduction. Clarendon Press, Oxford. Parameswaran, N. & W. Liese. 1969. On the formation and fine structure of septate wood fibres of Ribes sanguineum. Wood Sci. Technol. 3: 272-286. Van Vliet, G.J.C.M. 1979. Wood anatomy of the Combretaceae. Blumea 25: 141-223. Wolkinger, F. 1970. Das Vorkommen lebender Holzfasern in Strauchern und Baumen. Phyton 14: 55-67.

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