Detection of complex vascular system in bamboo node by X-ray μCT imaging technique

8/10/2019 Detection of complex vascular system in bamboo node by X-ray CT imaging technique

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00

110.1515/hf-20130080 Hotzforschung 2014; 68(2): 223- 227

Short

Note

Guanyun Peng*, Zehui Jiang,

Xing e Liu*,

Benhua Fei,

Shumin

Yang, Daochun Qin,

Haiqing

Ren,

an u

and Honglan Xie

Detection

of

complex vascular

system

in

bamboo

node

by

X ray

CT

imaging technique

Abstract: Bamboo is

one

of the world s fastest growing

plants. They reach a final heigh t

of 15 40

m during a period

of

40-120 days. The full height

is

reached by intercalary

growth

of each

node. However,

it

is very difficult to detect

the complex vascular system in a bamboo

node

using tra

ditional methods. X-ray

computed

microtomography (.

CT)

is

a noninvasive novel approach to the three-dimensional

3D)

visualization

and

quantification of biological

struc

tures. In the present article,

CT has

been applied to pro

vide insights into the internal structure

of

bamboo node,

where three branches are connected. The picture obtained

could hardly be obtained by any other means. The bamboo

nodal

characteristics of three transverse

and

axial sections

are presented. The complex

3D

network of vascular bun

dles

has been

directly obtained for the first time.

Keywords:

3D

network

of

vascular systems,

bamboo

node,

vascular

system, X-ray

computed

microtomography

CT)

*Corresponding authors: Guanyun Peng, Shanghai Institute of

Appli ed Physics, Chinese Academy of Sciences, Shanghai 201204,

China; and International Center for Bamboo and Rattan, Beijing

100102, China, e-mail: [email protected]; and Xing e Liu,

International Center for Bamboo and Rattan, Beijing 100102, China,

e-mail: [email protected]

Zehui Jiang, Benhua Fei, Shum n Yang, Daochun Qin and an Yu:

International Center for Bamboo and Rattan, Beijing 100102, China

Haiqing Ren: Research Institute

of

Wood Industry, Chinese Academy

of

Forestry, Beijing 100091, China

Honglan Xie: Shanghai Insti

tute

of Applied Physics, Chinese

Academy

of

Sciences, Shanghai 201204, China

ntroduction

Bamboo

is

one

of

the most

important

forest resources

(Peng

et

al. 2013). Bamboos belong to

the

subfamily

Bambusoideae

of

the family Gramineae. More than 1250

species,

under 75

genera, are known worldwide,

which

are

mainly distributed in th e tropical

and

subtropical zones

and

partly in the temperate

and

frigid zones. Bamboo

is

the

fastest-growing woody plant

and

matures

in

4- 8 years

(Jiang 2007). S ince the 1980s, the significance of bamboo

cultivation

and

utilization is increasingly being rec

ognized, mainly due to the

rapid

reduction of tropical

forests especially

in

China, India,

and

some

of the

South

east

Asian countries. Recent research

papers

show the

increased

and

permanent

interest

on bamboo

concerning

its chemical composition

and

utilization

Kim

et

al. 2008;

Lee

et

al.

2011; Sun et

al.

2011;

Qu

et

al. 2012; Vena

et

al.

2013; Wu

et

al. 2013), its fungal degradation Kim

et

al.

2011; Schmidt

et

al. 2011), the mechanical properties

of

single bamboo fibers (Yang

et

al. 2009; Yu

et

al. 2011),

and

its physical properties (Tsubaki

and

Nakano 2010).

The anatomy of

bamboo

is

the

scientific basis for

understanding

its properties

and

its optimal economic

utilization. Thus, there are also plenty

of

reports on the

anatomy

of

bamboo, which focused mainly on the

mor

phological

and

physiological characteristics

of bamboo

culm, which comprises internodes

and

nodes (Liese

1998). The anatomical structure

of

the internodes is better

investigated than

that of

the nodes.

Nodes belong to the basic anatomical character

istics of the Gramineae family. The bamboo

nodes

are

very unique, which distinguish

them

from

other

plants;

moreover, the nodes are species specific. One node

of

a

bamboo

culm usually consists of a

sheath

scar, a nodal

ridge, a diaphragm,

and the intranode

between the

nodal

ridge

and

the

sheath

scar. Bamboo

nodes

play a key role

in

its

rapid

growth. From the technical application

point

of

view, the

nodes

are important for the liquid movement

during

drying

and

preservation

as

well

as

for the physical

and

mechanical properties

of

culm. The function of the

bamboo node and

their structure received more attention

in the last

decades

(Shao

et

al. 2010; Xing

et

al. 2012) . Ding

and

Liese (1995) recorded

SEM

images from serial sect ions

of

the

bamboo node and

reconstructed

the

three-dimen

sional 3D)

image of the

bamboo nodal

region. However,

serial sectioning is not

only

time-consuming but also

can

lead

to artifacts due to the irregular thickness

of

the serial

sections

and manual

stacking

of

the series of images.


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G Peng et al : Detection

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X-ray computed microtomography CT)

has

a high

application potential in

plant

science

as

a noninva

sive

approach

for

3D

visualization, including the

leaf

(Kaminuma

et

al. 2008), stem (Stuppy

et

al. 2003), flowers

(Stuppy

et

al. 2003; Dhondt

et

al. 2010),

seed

(Cloetens

et

al. 2006), fruitage (Mendoza

et

al. 2007), just to

mention

a few. In

t C T

fixing, sectioning,

and

stainingare

not

neces

sary to produce a

3D

digital

map

of a specimen; thus arbi

trarily oriented sections

can

easily

be

visualized. During

the past decade there is a growing number of studies

on

nondestructive investigations using

CT,

including

anatomical details (Steppe et al. 2004; Trtik

et

al. 2007;

Mannes et al. 2010; Mayo et al. 2010), wood shrinkage

(Taylor

et

al. 2013), wood decay (Fuhr

et

al. 2012), defor

mations of wood (Forsberg

et

al. 2008), particle

board

panels (Sackey

and

Smith 2010), etc. For example, Steppe

et

al. (2004) presented the

CT

-derived

3D

image

of

beech

wood

Fagus sylvatica

and

oak

Quercus robur ,

which

clearly illustrated their complex internal vessel network.

In

the

present work,

CT with phase

-contrast imaging

techniques will

be used

for imaging two-dimensional 2D)

transverse

and

axial sections

and

the

3D

microstructure

of

a bamboo node. Phase-contrast imaging techniques

have two key advantages: first, light elements (showing

poor contrast in absorption radiography) can be easily

detected; second, this

method helps

to reduce the radia

tion dose deposited

on

the object

under

investigation. The

aim

of this study is to contribute further to the knowledge

of

bamboo node

anatomy

and

to establish

CT as

routine

methodology, which could contribute a lot for the rapid

observation

and

classification of

the

complex structure

of

nodes in

the versatile realm of bamboos.

Materials and methods

Plants

Bamboo, Pleioblastus

gozadakensis

Nakai, was sampled

from Chi

nese Anji Bamboo Species Garden Zhe jiang Province, China). This

bamboo species are mainly distributed

at

Southeast China, such as

Zhejiang, Jiangxi, and Fujian provinces. Its diameter at breast height

DBH)

is approximately 1cm; height, 3-4 m; age, 3 years. The nodal

area, including 20

mm

below and above a sheath scar, was cut

from

the middle of a mature culm. A sample size of 7

mm

diameter was

used, and the sample was prepared by air-drying.

X ray computed

microtomography

This study was performed

at

Xradia lnc. s Demo Laboratory in Con

cord,

CA, USA.

The instrument used was MicroXCT-200, which is a

high-resolution, non-destructive

3D

X-ray imaging system. The lens

detectors provide superior contrast even for low absorption materi

als. The following parameters were used: 40

kV,

8

W,

100 s per image;

scan interval,

0

-

359

in

0.5

scan steps; view field,

9.3 mm;

each pix

el represents a linear resolution of 6 m. The sample is fixed on the

sample stage while running a tomography. Because of the area of the

bamboo samples, the detector and source are placed at a consider

able distance

to

allow a

fu

ll 360 rotation, which

li

mi

ts the maximum

view

field.

A

9.3

-

mm

vertical span \vas imaged, and the maximum

field

of

view for a 2x ob jective was

12

mm. The high-resolution mode

was applied. Automatic single- and multiple-point tomographies

were made \Vith the Xradia software Recipes; references and tomo

graphies are recorded automatically

for

each point, and 20 and 3D

images were generated.

Results

2

images of the

node

The

nodal

area is

presented

in Figure

la.

The tomographic

images were reconstructed by enlarging

721

X-ray micro

graphs. The images

of

the cross section in the area of

the three

branches

are shown

in

Figure lb and c, which

reveal

the anatomical

details. In Figure lb,

manyvascular

bundles

are

visible

with

axial connection,

whereas

a few

of them have transverse connections. The arrows repre

sent transverse vascular

bundles

. From the

periphera

l to

the inner zone of the stem the area of the fibers around

the

vascular

bundles gradually

decreases,

whereas

the

opposite is true for

the

vascular

bundles

.

All

vascular

bundles

in the internodes are axial

and

parallel

and do

not have

any

across vascular elements. Cross-connections

are present

in

the

area without pith

cavity. Figure

le

shows the

absence across

vascular

bundles in

the stem

or

in

branch I,

whereas both dispose

of

pith cavities. A few

cross-vascular

bundles in branch

III are

without

a pith

cavity.

The bamboo

nodal

axial section

is

depicted in

Figure

ld

. Here, there

are many

across

vascular bundles

with different characters. For example, between the nodal

ridge

and

the upper edge

of

the diaphragm, there

are

more fibers

around

the vascular bundles

than on

the

dia

phragm. This observation is consistent with

that of

Ding

and

Liese (1995).

3 network of vascular bundles

A

3D

image was

obtained by

adjusting the

opacity and

color scheme. Sections

of

the

bamboo

were cropped

and adjusted

to

show

the dispersion

of

the vascular


3/5

DE

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G. Peng et a

l

: Detection of complex vascular system in bamboo node

5

5

6

9

10

II

12

13

14

re The

scanning area

of

the bamboo node and its

20

images. a)

The

scanning bamboo node. b,

c)

Cross-section images of the

bamboo node: b) the stem and the three branches connected to each other and containing many vascular bundles with axial connection

and a few with transverse connection arrows); c) there are no across vascular bundles in the stem

or

in branch I, both having

pith

cavities,

whereas a few cross-vascular bundles present in branch Il l are

without

a p

it

h cavity. d) Longitudinal section image of bamboo node: the

nodal ridge and t he upper edge of diaphragm around the vascular bundles have more fibers than the diaphragm. l=a rea imaged; 2=sheath

scar; 3=d iaphragm; 4=nodal ridge; 5=vascular bundle; 6=fibers; ?=vascular bundle; 8=fibers; 9=sheath scar; lO=across vascular bundles;

l

l=diap

hragm; 12=upper edge of the diaphragm; 13=nodal ridge; 14=fiber

s.

bundles in the 3D images Figure 2 . In Figure 2a, the

light areas indicate fibers,

nd

the

d rk

ones represent

vascular bundles. After inversion

of

Figure 2a, Figure 2b

b

was obtained, where the light areas represent the vas

cular bundl

es

. The main vascular

bund

les pass directly

tllrough the node, nd t the same time, a number of

201 0 Jll

gure 2 30 images of the fine structure

of

the bamboo node obtained by CT. a) The light areas indicate fibers. b) Inverted 30 volume

dis

persion of vascular bundles of bamboo node; inverted volume represents non nverted volume of a);

ligh

t areas represent vascular

bundles; dark areas represent fibers. As shown in the image, the vascular bundles pass directly through the node, and

at

the same time, a

number of small vascular bundles turn horizontally and twist repeatedly in the upper edge of the diaphragm.


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6

G.

Peng et al.: Detection

of

complex vascular system in bamboo node

DE GRUYTER

small

vascular bundles turn

horizontally

and

twist

repeatedly

in

the upper edge

of

the

diaphragm in

Figure

2b. The axial

and

horizontal

vascular bundles

form a

complex network structure.

iscussion

and conclusions

The complex

structure of

a

bamboo

node is readily visible

on the CT images. The depicted vascular

bundles

con

tribute to

tangential

and

axial transp ortation. The twist

ing contributes a lot to the mechanical properties

such

as high strength which is especially effective

against

cleavage. This

specia

l

structure

of

the

vascular

tissue

of

the nodes

is

essential

for

long

-

and

thin

-

shaped

bamboos,

which

tend

to split. The easily accessible 30 images of the

vascular

bundles

are excellent examples for biomimetic

materials.

The

rapid CT

methodology

has

significant advan

tages compared

with other

methods

of

vascular system

research (Zimmermann and Tomlinson 1966; Fujii

1993)

.

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Detection of complex vascular system in bamboo node by X-ray μCT imaging technique