position and development of differentiated lateral buds in

Plant Prod. Sci. 18(4): 435―442 (2015)

Received 2 March 2015. Accepted 28 April 2015. Corresponding author: S. Nakamura ([email protected], fax +81-22-245-1278). This research was supported in part by a Grant-in-Aid for Scientific Research (No. 20405017) from the Ministry of Education, Culture, Sports, Science and Technology, Japan and by a grant for research abroad from Miyagi University, Japan.Abbreviations: OSB; sucker bud with one sucker bud, LSB; large sucker bud with two sucker buds, rbL n; the n-th (counted relatively, basipetally) leaf, rbS n; the position of sucker bud that differentiated inside of rbL n, SSB; small sucker bud with two sucker buds.

Position and Development of Differentiated Lateral Buds in Sago Palm (Metroxylon sagu Rottb.)

Keita Nabeya1, Satoshi Nakamura2 and Yusuke Goto1

(1Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan;2School of Food, Agricultural and Environmental Sciences, Miyagi University, Sendai 982-0215, Japan)

Abstract: During sago palm cultivation, many suckers appear from the mother stem as it grows. Some suckers are thinned out, but the rest are left to grow to be harvested several years later after harvesting of the mother stem (trunk). Proper management of the suckers from the mother stem is important to obtain successive sago trunks from a single transplantation. Nevertheless, little scientific knowledge exists about the sucker growth, even the development of its primordium. Our objective is to clarify the differentiation position and the development of the sago palm lateral bud, which is the sucker bud. Results show that in sago palm, the sucker bud differentiates inside of the connate part of the leaf petiole, which is opposite to the axil side. Swelling of tissue is first visible inside of the third leaf from the growth point (rbL 3). Sucker bud initiation is visible at almost all leaf positions lower than rbL 5. Furthermore, at each leaf position, one or two (rarely three) buds are observed. Differentiated buds usually elongate exponentially. Some develop more than two times on average. These sucker buds differentiate inside of the connate part of the thin leaf petiole, which split toward the base gradually as new leaves emerge. The differentiation position of the sucker buds and the thin leaf petiole are expected to be related closely to the further growth of the large sucker buds.

Key words: Bud development, Differentiation position, Lateral bud, Metroxylon sagu Rottb., Sago palm, Sucker bud.

Sago palms (Metroxylon sagu Rottb.), which accumulate large amounts of starch in the trunk, can grow on humid peat soil. They are therefore important as a starch crop, mainly for use as an industrial raw material. Large-scale production at plantations has just begun in Indonesia. An adequate cultivation technique must be developed for future expansion of production.

Sago palm trunks are first harvested ten and several years after transplantation. Many branches, called ‘suckers’, appear from the mother stem during growth. Some of these suckers are thinned out (sucker control), whereas the rest are left to grow to be harvested several years after harvesting of the mother trunk (Nabeya et al., 2013). Consequently, for sago palm cultivation, proper management of the suckers from the transplanted sago plant is important to obtain successive sago trunks from a single transplantation.

For crop cultivation, understanding the developmental behavior of the branch is extremely important to improve crop production. Katayama (1951) reported the relation

between the emerging leaves and appearing tillers in rice. Based on that relation, the differentiation and development of rice tillers have been studied (Sekiya, 1958, 1977; Nishikawa and Hanada, 1959). Organization of the relation between leaf emergence and tiller development of rice contributed to the analysis of growth and the theoretical proof of cultivation techniques (Goto, 2003). However, for sago palm, data related to sucker growth and the development of lateral bud primordium are lacking. The lateral bud of sago palm, the sucker bud, differentiates on the side opposite to the axil, different from many plants (Goto et al., 1998), but details of the position and the ratio of differentiated sucker buds have not been clarified. Sucker bud development and the relation between sucker bud development and leaf emergence have not been elucidated. Development of cultivation techniques such as sucker control requires accumulation of basic knowledge about sucker buds. The present study clarified differentiation of the position and the development of differentiated sucker buds.

　436 Plant Production Science Vol.18, 2015

Materials and Methods

Suckers with a stem diameter mean and SD of 55.5 ± 13.6 mm were collected from two sago gardens in Mukah, Sarawak, Malaysia. We used 37 suckers derived from the spineless type of sago palm, which is widely cultivated in Sarawak.

To investigate the differentiation of sucker buds, we removed the expanding leaves, the spear leaf which was the emerging and unexpanded leaf and the unemerged leaves formed inside of the spear leaf carefully up to the growth point. Then, we designated the leaf position as follows. In the hood-like leaf primordium covering the growth point, the youngest leaf primordium, with tip of hood-like leaf beyond the tip of growth point, was designated L 1 and next lower leaves L 2, L 3, and so on, basipetally. However, this leaf position represents the relative position, not the absolute position. Accordingly, L 1 is referred to as the rbL 1 (relative basipetally Leaf 1) followed by rbL 2, rbL 3, and so on.

We regard the position of sucker bud that differentiated inside of rbL n, outside of rbL n -1, as rbS n. On the leaf position of all leaves attached to the investigated suckers, we checked for sucker buds using a stereomicroscope. For the size of sucker bud, the length from the base to the tip and the width of the part which is the widest near the base were measured.

In sago palm, since a leaf sheath, which is the lower part of the petiole, wraps around the stem, a part of the leaf sheath attached to the stem appears to be a node like a ring after removal of the leaf sheath (Fig. 1a). Therefore, considering the part of leaf attached to be a circle, we

measured the diameter of the part of leaf attached to the stem in the circle.

To analyze the position at which the sucker bud was attached in detail, we determined the position at which the sucker bud was attached from the designated reference points. At the connate part of leaf petiole, the vascular bundle travels from petiole to the base, the two bundles fuse into one near the base (Fig. 1a). This part is also the part that is gradually split as new leaves emerge and stem

Fig.　1.　Connate part at both edges of leaf petiole. (a): The connate part of leaf petiole. (b): Sucker removed connate part of leaf petiole presented in (a). The triangle denotes the reference point. Two sucker buds differentiated inside of the connate part of leaf petiole and near the reference point. The blue and red arrows indicate the sucker bud developed in a position positive and negative to the reference point, respectively.

a) b)

Fig 1 Connate part at both edges of leaf petiole (a): The connate part of leaf petiole (b): SuckerFig. 1. Connate part at both edges of leaf petiole. (a): The connate part of leaf petiole. (b): Sucker removed connate part of leaf petiole presented in (a). The triangle denotes the reference point. Two sucker buds differentiated inside of the connate part of leaf petiole and near the reference point. The blue and the red arrows indicate the sucker bud developed in a position positive and negative to the reference point, respectively.

Fig. 1. (color printing)Reduction rate = 100 %Nabeya et al.10

Fig.　2.　Cross section of the sucker with clockwise leaf arrangement. Leaves arrange clockwise from an old leaf (rbL n) toward younger leaves (rbL n -1, rbL n -2, ...).

rbL n-2

rbL n-1

rbL n

rbL n-3

Fig. 2. Cross section of the sucker with clockwise leaf arrangement. Leaves arrange clockwise from an old leaf (rbL n) toward younger leaves (rbL n-1, rbL n-2, ･･･).

Fig. 2.Reduction rate = 67 %Nabeya et al.11

437　Nabeya et al.――Position and Development of Differentiated Lateral Buds in Sago Palm

enlarges. Assuming this leaf is rbL n, the position, where the fused vascular bundle attaches to the node, was designated as the reference point of rbL n. The position at which the buds of rbS n attached on the circumference of rbL n is shown by the central angle between the reference point and the position of rbS n. When the sucker bud is located on the right side of the reference point as viewed from the front, the position of attachment of the bud is shown by a positive angle, and when it is located on the left side, it is shown by a negative angle (Fig. 1b).

Sago palm has a phyllotaxis of 4/13 (Jong, 1991) and the leaves are arranged clockwise (Fig. 2) or counterclockwise from an old leaf (rbL n) toward younger leaves (rbL n -1, rbL n -2, ...) from the top view. Therefore, we c lass i f ied into two groups , c lockwise and counterclockwise of leaf arrangement, and analyzed the relationship between the leaf arrangement and the attached position of sucker bud.

Results

In the investigated suckers, the leaf position of a spear leaf ranged from rbL 6 to rbL 9. About 80% of them were rbL 7 or rbL 8. The diameter of the part of leaf attached on each leaf position is shown in Fig. 3. The diameter increased exponentially at a lower leaf position. The diameter of the part of a spear leaf attached ranged from 6.7 to 18.5 mm, an average of 10.6 mm.

1.　The initiation position and ratio of sucker budIn sago palm, sucker bud differentiated near the

reference point which is inside of the connate part of leaf petiole (Fig. 1b). This position was on the side opposite the axil across the center of the stem. There was no sucker bud on each leaf position in rbL 1 and rbL 2, and the sign of differentiation was not visible. However, in rbL 3, the swelling of tissue was visible in 13.6% of investigated suckers. In this study, the swelling of tissue was regarded as the initiation of sucker bud. The diagram of the differentiation position of sucker bud at the initiation stage is presented in Fig. 4. Since the tip of hood-like leaf primordium was beyond the tip of growth point, this leaf primordium was assumed rbL 1 (Fig. 4a). The swelling of tissue inside rbL 4 was visible in 77.3% of investigated suckers (Fig. 4b). The initiation of sucker bud inside rbL 5 was visible in all investigated suckers, and the sucker bud was visible at almost all leaf positions after rbL 5. Additionally, multiple buds were observed at each leaf position. At leaf positions lower than rbL 6, where the number of differentiated bud was definitely identified, the rate at which one, two and three sucker buds differentiated at each leaf position was 30.1, 68.1, and 1.8% respectively (Fig. 5).

Fig.　3.　Diameter of the part of leaf attached on each leaf position. ×, ○ and ● denote the diameter of the part of the unemerged leaves, the spear leaf and the expanding leaves, respectively. n = 22.

120

mm

)

y = 0.06 x 2.65

120

60

90

60

90

er o

f at

tach

ed p

art(

m y

R2 = 0.94

0

30

0 5 10 150 5 10 150

30

Leaf position (rbL)

Dia

met

e

Fig. 3. Diameter of the part of leaf attached on each leaf position. ×, ○and ● denote the diameter of the part of the unemerged leaves, the spear leaf and the expanding leaves, respectively. n = 22.


Fig.　4.　Diagram of the differentiation position and initiation of sucker bud. (a): Growth point and leaf primordium. This diagram presents the top of sucker with counterclockwise leaf arrangement. Leaves were removed until rbL 3. Boxed area denotes differentiation position of rbS 4. (b): Enlarged view of the differentiation position of rbS 4.

a) Growth point b)

rbL 2rbL 1

rbS 4

Fig. 4. Diagram of the differentiation position and initiation of sucker bud. (a): Growth point and leaf primordium. This diagram presents the top of sucker with counterclockwise leaf arrangement.

Leaf attached part of rbL 3

Leaf attached part of rbL 4rbS 5

rbS 4

p g p p gLeaves were removed until rbL 3. Boxed area denotes the differentiation position of rbS 4. (b): Enlarged view of the differentiation position of rbS 4.



2.　The development of sucker budFig. 6a and 6b show diagrams of the development of

one sucker bud and two sucker buds differentiated, at each leaf position, respectively. The diagrams of rbS 5 in Fig. 6a and 6b are those of sucker bud developed from the swelling of rbS 4 shown in Fig. 4b. In Fig. 6a, the swelling increased, and the top became slightly hollow, while, in Fig. 6b, the development of new organization was visible on both sides of the swelling. The diagram of rbS 6 in Fig. 6a shows the hollow of top part and the organization on both sides of the swelling is more developed in Fig. 6b. In the diagrams of rbS 7 the sucker buds have already begun to elongate.

The length and the width of sucker buds from rbS 6 to rbS 13 are shown in Fig. 7a and 7b, respectively. The vertical axis of the figures is logarithmic scale. Thus, both length and width increased exponentially. At the leaf position lower than rbS 11, some sucker buds developed markedly in length and width (Fig. 8). The size of all sucker buds from rbS 11 to rbS 13 were 13.0 ± 8.7 mm in length and 1.9 ± 1.7 mm in width on average. The large sucker buds were

about 7.0% of all sucker buds from rbS 11 to rbS 13, and the length and the width near the base were 28.7 ± 10.8 mm and 5.5 ± 2.0 mm on average, respectively. They were 2 times the average size. Additionally, such sucker buds were enlarged generally around its base, and it was easy to distinguish the large sucker buds from other sucker buds.

Fig.　5.　Three sucker buds differentiated. The arrow indicates the sucker buds. The triangle denotes the reference point. Bar = 10 mm.

Fig. 5. Three sucker buds differentiated. The arrow indicates the sucker buds. The triangle denotes the reference point. Bar = 10 mm.


Fig.　7.　Size of sucker bud on each leaf position. (a): The length of sucker bud. (b): The width of sucker bud at the base. ○ denotes sucker bud developing greatly. n = 23.

100100

y = 0 01 e0 61 x

a)

0 1

1

1010

1

0 1

y = 0.01 e0.61 x

R2 = 0.82

Leng

th(m

m)

0.01

0.1

4 6 8 10 12 14

0.1

0.01

10

0 14 0 20 x

b)10

11

y = 0.14 e0.20 x

R2 = 0.51

Wid

th(m

m)

Fi 7 Si f k b d h l f iti ( ) Th l th f k

0.14 6 8 10 12 14

Sucker position (rbS)

0.14 6 8 10 12 14

Fig. 7. Size of sucker bud on each leaf position. (a): The length of sucker bud. (b): The width of sucker bud at the base. ○ denotes sucker bud developing greatly. n = 23.


Fig.　6.　Diagram of development of sucker bud. The development of one sucker bud (a), and two sucker buds (b) on each leaf position, respectively. Bar = 1 mm.

i): One sucker bud ii): Two sucker buds

rbS 5

rbS 6

rbS 7

Fig. 6. Diagram of development of sucker bud. The development of one sucker bud (i), and two sucker buds (ii) on each leaf position, respectively. Bar = 1mm.


a): b):


4.　The attached position of sucker bud to the reference pointFig. 11 shows the position at which the sucker buds

attached to the reference point on the leaf position of a spear leaf and each expanding leaf where vascular bundles developed and the reference point was visible. In this figure, the circumference of attached part of leaves was arranged concentrically and the position of the reference point was on a straight line. The black circles show the position at which the sucker buds were attached; they were distributed in a fan-shaped from inside to outside in a concentric circle. Fig. 12 shows the frequency distribution of the attached position. The sucker buds were distributed from –40.5º to 37.9º to the reference point. Most of the sucker buds were distributed from –5º to 5º, near the reference point, and about 90% of them were distributed from –25º to 25º.

5.　The relationship between the leaf arrangement and the attached position of sucker budTo analyze the relationship between the leaf

arrangement and the position at which the sucker buds attached to the reference point, we categorized the sucker buds as follows. When one sucker bud differentiated, it was designated OSB. When two sucker buds differentiated, the large bud and small bud were designated LSB and SSB, respectively, since the two buds were usually different in size. The case of three buds differentiated was excluded from analysis because such a case was rare. Fig. 13 shows the positions at which the sucker buds were attached presented in Fig. 11, with classification of crosswise property, the clockwise or the counterclockwise leaf arrangement sucker. The attached positions were generally one-side toward positive or negative direction from the reference point in clockwise or counterclockwise leaf arrangement suckers, respectively. Fig. 14 shows the frequency distribution of the positions at which OSB, LSB and SSB were attached. Most of the sucker buds were distributed from –15º to 25º in the

By contrast, some sucker buds with only an increase in length not width were also observed from rbS 11 to rbS 13. Most of these sucker buds elongated meanderingly (Fig. 9).

3.　The differentiation position of two sucker budsIn the sucker buds growing to more than 1 mm in

length, when two sucker buds differentiated, the differentiation position of two buds was located at a distance. The distance between two buds was 17 mm at rbS 16 (Fig. 8), and 13 mm at rbS 15 (Fig. 9). However, at rbS 7 the distance between two buds was less than 1 mm (Fig. 6b). To clarify the relationship of the position of two sucker buds, we examined the central angle subtended by the differentiation positions of two buds at each leaf position (Fig. 10). The central angle from rbS 5 to rbS 15 was 24.9 ± 7.3º on average. Approximated by a straight line, y-intercept was 26.3º and the line was almost parallel to x-axis, indicating that the distance between two sucker buds tend to be more apart from each other at a lower leaf position.

Fig.　8.　A sucker bud greatly developed. Sucker bud (A) differentiated at the reference point and developed markedly. Sucker bud (B) differentiated at position B’ and elongated thinly. The triangle denotes the reference point. Bar = 10 mm.

B

A

B’

Fig. 8. A sucker bud greatly developed. Sucker bud (A) differentiated at the reference point and developed markedly. Sucker bud (B) differentiated at position B’ and elongated thinly. The triangle denotes the reference point. Bar = 10 mm.


Fig.　9.　Sucker buds elongated meanderingly. Sucker bud (A) and (B) differentiated at position A’ and B’, respectively. The triangle denotes the reference point. Bar = 10 mm.

B A

Fig. 9. Sucker buds elongated meanderingly. Sucker bud (A) and (B) differentiated at position A’ and B’, respectively. The triangle denotes the reference point. Bar = 10 mm.

B’ A’


Fig.　10.　Central angle subtended by the positions the two buds attached. n = 21.

6060) y = -0.17 x + 26.31

20

40

20

40

gle

of su

cker

bud

s(°

R2 = 0.004

0

20

4 6 8 10 12 14 164 6 8 10 12 16

Leaf position (rbL)

140

20

Cen

tral a

ng

Fig. 10. Central angle subtended by the positions of the two buds attached. n = 21.



clockwise leaf arrangement sucker, from –25º to 15º in the counterclockwise leaf arrangement sucker. LSB buds were distributed near the reference point, OSB buds were distributed slightly distant from the reference point and SSB were distributed at a greater distance in both suckers, though there was difference in right and left.

Discussion

In sago palm, the lateral bud which is called the sucker bud, differentiates inside of the connate part of leaf petiole. This position is the side opposite to the axil. Fisher and Dransfield (1979) reported that the lateral bud of an Arecaceae, Daemonorops spp. and Korthalsia rigida differentiated on the side opposite to the axil, and named it leaf-opposed bud.

At a leaf position lower than rbL 6, almost all sucker buds were visible. This result was different from the report by Goto et al. (1998). At each leaf position lower than rbL 6, the rate of two sucker buds and three sucker buds was 68.1 and 1.8%, respectively. The presence of multiple vegetative buds differentiated in a leaf position has been reported in Plectocomia elongata (Fisher and Dransfield, 1979). In P. elongata, one to ten vegetative buds appear as small swellings in a node, and become multiple branches. By contrast, in sago palm, a small swelling occurred (Fig. 4b), then, it differentiated into two sucker buds (Fig. 6b). So far, we have not observed sago palm with both sucker buds developing and appearing from a leaf position.

When two sucker buds differentiated, the two buds were at a distance, which tended to become longer at a lower leaf position. However, the central angle subtended by two buds was constant at 25º from rbS 5 onward (Fig. 6), regardless of the leaf position (Fig. 10), indicating that the relative positional relation of two buds at the circumference of attached part was not changed by leaf position. Therefore, the increase of the distance between two buds was attributed to the enlarging of stem and the length of stem circumference with lower leaf position.

Fig.　12.　The frequency distribution of position at which the sucker bud is attached. The dashed line ( ) shows the position of the reference point. n = 37.

3030

10

20

10

20

Freq

uenc

y(%

)

01 2 3 4 5 6 7 8 9

0-5 5-15 15-25 25-35 35-45 45

F

Attached position of sucker bud to the reference point (°)

Fig. 12. The frequency distribution of position at which the sucker bud isattached. The dashed line ( ) shows the position of the reference point. n= 37.


Fig.　13.　Distinction of the position at which the sucker bud is attached based on the difference of leaf arrangement. The solid lines ( ) show the circumferences of the attached part of leaves. The dashed line ( ) shows the position of the reference point. ×, ○ and ● denote OSB, LSB and SSB, respectively. n = 29.

Clockwise CounterclockwiseClockwise Counterclockwise

Fig. 13. Distinction of the position at which the sucker bud is attached based on the difference of leaf arrangement. The solid lines ( ) show the circumferences of the attached part of leaves. The dashed line ( ) shows the position of the reference point. ×, ○ and ● denote OSB, LSB and SSB, respectively n = 29respectively. n = 29.


Fig.　11.　Position at which the sucker buds attached to the reference point (attached position). The solid lines ( ) show the circumferences of the attached part of leaves. The dashed line ( ) shows the position of the reference point. ● denotes the attached position at each leaf position. n = 37.

Fig. 11. Position at which the sucker buds attached to the reference point ( tt h d iti ) Th lid li ( ) h th i f f th(attached position). The solid lines ( ) show the circumferences of the attached part of leaves. The dashed line ( ) shows the position of the reference point. ● denotes the attached position at each leaf position. n = 37.



When suckers were classified into two leaf arrangements and into OSB, LSB and SSB, the position at which each sucker bud was attached to the reference point showed a similar tendency though there was a difference in the crosswise property of leaf arrangement (Fig. 14). In order to analyze the attached position of sucker bud to the reference point in detail, the difference of crosswise property in leaf arrangement was removed as follows. Based on the frequency distribution presented in Fig. 14, in the sucker with the counterclockwise leaf arrangement, the sign of attached position was reversed, and the frequency distribution of counterclockwise leaf arrangement was unified in the clockwise leaf arrangement. Then, the unified frequency distribution of OSB, LSB, SSB and total buds were approximated by Richard function, and presented in Fig. 15. The peak of frequency distribution of total was 11.5º and it leaned toward the positive direction from the reference point. The peak of OSB, LSB and SSB

were 9.5º, –6.8º and 20.6º, respectively. In case of one sucker bud, the sucker bud develops at the position where the tissue swells as presented in Fig. 6a. Hence, in the sucker with clockwise leaf arrangement, the differentiated

position of sucker bud was considered to be essentially leaned toward positive direction from the reference point. In the case of two sucker buds, sucker buds developed on both sides of the swelling (Fig. 6b). Consequently, it was

Clockwise Counterclockwise

0

5

10

15

1 2 3 4 5 6 7 8 90

5

10

15

1 2 3 4 5 6 7 8 90

10

5

15

0

10

5

15


OSB OSB

1 2 3 4 5 6 7 8 9

0

5

10

15

1 2 3 4 5 6 7 8 9

0

5

10

15

0

10

5

15

Freq

uenc

y(%

)

0

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15LSB LSB

1 2 3 4 5 6 7 8 9

0

5

10

15

1 2 3 4 5 6 7 8 9

0

5

10

15

0

10

5

15

0

10

5

15SSB SSB

Fig. 14. Distinction in the frequency distribution of the position at which the sucker bud is attached based on the difference of leaf arrangement. The solid line ( ) shows the frequency distribution of attached position of sucker bud on the clockwise of counterclockwise leaf arrangement sucker, respectively. , ■ and ■ denote OSB, LSB, SSB, respectively. The dashed line ( ) shows the

1 2 3 4 5 6 7 8 91 2 3 4 5 6 7 8 9

Initiation position to the point (°)

-5 5-15 15-25 25-35 35-45 45 -5 5-15 15-25 25-35 35-45 45

position of the reference point. n = 29.


Fig.　15.　Approximate curves of the frequency distributions. The frequency distribution is shown by unifying counterclockwise leaf arrangement clockwise. The vertical dashed line ( ) shows the position of the reference point.

30Total

Osb30TotalO

10

20

30 Osb

Lsb

Ssb20

30

Freq

uenc

y(%

)

10

OSB

LSB

SSB

0

10

0 1 2 3 4 5 6 7 8 9

Fig 15 Approximate curves of the frequency distributions The

0


10

-5 5-15 15-25 25-35 35-45 45

Fig. 15. Approximate curves of the frequency distributions. Thefrequency distribution is shown by unifying counterclockwise leafarrangement clockwise. The gray dashed line ( ) shows the position ofthe reference point.


Fig.　14.　Distinction in the frequency distribution of the position at which the sucker bud is attached based on the difference of leaf arrangement. The solid line ( ) shows the frequency distribution of attached position of sucker bud on the clockwise of counterclockwise leaf arrangement sucker, respectively.


0

5

10

15

1 2 3 4 5 6 7 8 90

5

10

15

1 2 3 4 5 6 7 8 90

10

5

15

0

10

5

15


OSB OSB

1 2 3 4 5 6 7 8 9

0

5

10

15

1 2 3 4 5 6 7 8 9

0

5

10

15

0

10

5

15

Freq

uenc

y(%

)

0

10

5

15LSB LSB

1 2 3 4 5 6 7 8 9

0

5

10

15

1 2 3 4 5 6 7 8 9

0

5

10

15

0

10

5

15

0

10

5

15SSB SSB

Fig. 14. Distinction in the frequency distribution of the position at which the sucker bud is attached based on the difference of leaf arrangement. The solid line ( ) shows the frequency distribution of attached position of sucker bud on the clockwise of counterclockwise leaf arrangement sucker, respectively. , ■ and ■ denote OSB, LSB, SSB, respectively. The dashed line ( ) shows the

1 2 3 4 5 6 7 8 91 2 3 4 5 6 7 8 9


-5 5-15 15-25 25-35 35-45 45 -5 5-15 15-25 25-35 35-45 45

position of the reference point. n = 29.


, ■ and ■ denote OSB, LSB, SSB, respectively. The dashed line ( ) shows the position of the reference point. n = 29.


considered that the peaks of LSB and SSB were located on the right and left side of the peak of OSB. Furthermore, the central angle subtended by the peaks of LSB and SSB in Fig. 15 was calculated to be 27.4º. This angle was almost the same as the y-intercept presented in Fig. 10 and the average of the central angle subtended by two buds.

Fig. 16 shows the diagram of the leaf arrangement and the differentiated position of sucker bud. The area of the reference point indicated by arrows is the part where leaf petiole connate and the tissue of leaf sheath around this part becomes extremely thinner than in other parts. Moreover, this part is gradually split toward the base as new leaves emerge and expand. These results suggested that it should be easier for sucker buds in this area to develop and enlarge due to lower physical pressure than in other

areas. This characteristic in the area should be closely related to the further growth of the large sucker buds (LSB) attached around the reference point.

Acknowledgements

This research was supported in part by a Grant-in-Aid for Scientific Research (No. 20405017) from the Ministry of Education, Culture, Sports, Science and Technology, Japan and by a grant for research abroad from Miyagi University, Japan. We are also very grateful for the assistance of Mr. Smith and his family in Malaysia.

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Sekiya, F. 1958. Studies on the tillering primordium and tillering bud in rice seedlings. (7) Developmental process of the tillering primordium and tillering bud. Proc. Crop. Sci. Soc. Jpn. 27: 75-76*.

Sekiya, F. 1977. Studies on the tiller primordium and tiller bud in rice seedlings. XII. On the differentiation and growth process of the tiller primordium and tiller bud. Jpn. J. Crop Sci. 46: 474-482*.

　* In Japanese.

Fig.　16.　Diagram of the leaf arrangement and the position at which the sucker bud is attached. The sucker is shown in clockwise leaf arrangement. ■ denotes the range of attached position. ×, ○ and ● denote the peaks of OSB, LSB and SSB, respectively. The arrows indicate the reference points. shows the rachis position estimated extending to the base. ■ denotes the position the leaf is attached.

position and development of differentiated lateral buds in

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