Characteristic of Vascular Bundles and Morphology of Gigantochloa apus (J.A. and J.H. Schulltes) Kurz Culm

MATERIALS AND METHODS

Three culms of bamboo G. apus used in the study were obtained from Sayang Village, Jatinangor Subdistrict, Sumedang Regency, West Java, Indonesia. The bamboos used were two years old. This research was conducted from April, 2017 until February, 2018.

Each bamboo culm was measured in dimensions: Internode length, outer and inner diameter and wall thickness of culm. The measurement results were projected in the drawing sketch to determine the morphology or the shape of bamboo culm. Observation of the distribution and shape of vascular bundles on bamboo culm was conducted by cutting 2 cm length at the middle part of internode. The piece was then slashed at the cross section with a sharp knife. Samples were observed in the distribution and shape of vascular bundles using Nikon SMZ 745T stereos. The observations were displayed on the computer screen and analyzed with NIS Elements v.4.00.00 imaging software.

RESULTS AND DISCUSSION

Morphological characters of G. apus culm: The shape of bamboo culm was basically composed of internodes and separated by a node. Bamboo culm was composed of internodes with varying lengths as shown in Fig. 1. In a bamboo G. apus culm, the internode length increased from the bottom until the 10th and 11th internodes then decreased to the top.

Fig. 1:	Internode length on bamboo culm of G. apus from bottom to top

Fig. 2:	Dimensions of bamboo culm of G. apus: Outer diameter, inner diameter and wall thickness from bottom to top

Fig. 3:	Distribution of vascular bundles from the outer layer to the inner layer on the internode of the bamboo culm of G. apus

The increase in length started again on the 24th internode but did not exceed its maximum length. The minimum and maximum length of bamboo internodes were 19.67 and 45.67 cm, respectively. Internode length variations also occur in other bamboo species such as in Schizostachyum¹⁷, Bambusa striata¹⁸.

The bamboo culm dimensions such as outer and inner diameter and wall thickness indicated variation from bottom to top (Fig. 2). The diameter and wall thickness of the bamboo culm on each internode showed a decrease from bottom to top. The inner diameter dimension of the bamboo increases from the bottom to the middle (9th internode) and then decreased in size to the top. The range of outer diameter, inner diameter and wall thickness of the bamboo culm were 30.08-66.21, 24.85-50.78 and 2.62-13.75 mm, respectively. Usually, the preferred bamboo was one that has a straight bamboo culm and approximately the same diameter at both ends. Based on Fig. 2 bamboo culm of G. apus shape was like cylinder tube starting from the bottom to 9th internode with length of 302.67 cm. If the expected bamboo culm had the same diameter at both ends, the utilized bamboo culm was only about 1/4 part of the total length. Bamboo would be more usefully effective if made into bamboo split.

The bamboo G. apus morphology was not different from the young shoot. When young shoot was split in longitudinal direction, largest cavity diameter was found in the middle part. The growth of bamboo culm did not only occur at the top (apical meristem) but also occurred in its constituent internodes (intercalary meristem) causing the shape of young shoot was not different from the old bamboo culm shape. The diameter of the mature culm also was already determined by the diameter of the young shoot¹. This form was also found in Bambusa vulgaris¹⁹. The morphology of a young shoot was often very characteristic in recognizing a mature bamboo culm.

Distribution and shape of vascular bundles in G. apus culm: Anatomically, vascular bundles and parenchymal base tissue were the main components of bamboo culm. Both of these components played an important role in the properties of bamboo. Vascular bundles were spread unevenly from the outer layer to the inner layer (Fig. 3). The distribution of vascular bundles which expressed the number of vascular bundles per mm² area on each internode bamboo culm showed the same pattern. Vascular bundles on the outer layer were numerous and less frequent to the inner layer. The distance between the vascular bundles got closer with the higher internode position on the bamboo culm (Fig. 3). However, the number of vascular bundles per unit area became less and less because the shape and size was larger from the bottom to the top of bamboo culm. The pattern of distribution of vascular bundles in bamboo culms was illustrated in Fig. 4. The same pattern was found in Bambusa rigida²⁰ and in palm trees^21-23. The distribution of vascular bundles of bamboo G. apus culms as shown in Fig. 4 could be modeled in a non-linear power regression equation. The arrangement of vascular bundles on the cross section of the bamboo culm appeared to form alternate patterns (Fig. 5). In the cross section of bamboo culm, there was a variation in the shape and size of the vascular bundle from the outer layer to the inner layer (Fig. 3). In the outer layer (peripheral zone) the vascular bundles were small and ellipsoid in large numbers. In the middle layer of the bamboo culm, there was a separation of the fiber cap at the top and bottom of the main vascular bundles (type IV) and vascular bundles had only one fiber cap (type III) on the inner layer.

Fig. 4:	Distribution of vascular bundles on bamboo culm of G. apus

Fig. 5:	Macroscopic pattern of alternate arrangement of vascular bundles on cross section of bamboo culm of G. apus

Type of vascular bundles on bamboo G. apus from previous studies showed types III and IV (Fig. 3). In the 1st and 5th internodes, both types could be found in the middle layer, but on the 10th, 15th and 20th internodes only found type III. Variations of vascular bundles were also found in bamboo from China²⁴.

Shapes and sizes (radial and tangential diameters) vascular bundles of bamboo G. apus varied from the outer layer to the inner layers. The tangential diameter of the vascular bundles tended to increase from the outer layer to the inner layer, while in the radial diameter it increased from outer layer to the center and then decreased toward the inner layer. The dimensions of the vascular bundles in the bamboo G. apus culm also decreased from the top to the bottom (Fig. 6a, b).The structure of a young shoot was often very characteristic in recognizing a bamboo species.

Fig. 6(a,b):	Diameter of vascular bundles on the bamboo culm of G. apus in (a) Tangential and (b) Radial directions

CONCLUSION

The morphological characters of the mature culm of G. apus culm was already determined by the morphological characters of the young shoots. The size of vascular bundles towards the middle layer became larger in the bamboo culms and also more widely spread, but longer and smaller towards the outer layer. The type of vascular bundle on the bamboo culm of G. apus were type III and type IV. Type vascular bundles on G. apus depended on the height position of the culm.

SIGNIFICANCE STATEMENT

This study exposes the morphology of culms, size and type of vascular bundles of G. apus which can be used along with its characteristics as reference data in determining the appropriate part of the bamboo culm in accordance with its intentional purposes.

ACKNOWLEDGMENTS

We would like to thank Institut Teknologi Bandung for funding this research through the Research and Community Service and Innovation Program (P3MI) of 2017 with grant number 1257/I1.C02.2/PL/2017.