SOME FUNCTIONS IN DANDELION FLOWER HEAD AND SEED HEAD

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1 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 PAPER REF: 5431 SOME FUNCTIONS IN DANDELION FLOWER HEAD AND SEED HEAD Seiichi Sudo 1(*), Maki Sato 2 1 Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, Yurihonjo, Japan 2 Graduate School of Systems Science and Technology, Akita Prefectural University, Yurihonjo, Japan (*) sudo@akita-pu.ac.jp ABSTRACT This paper describes some mechanical functions in a dandelion flower head and seed head. Opening and closing movements in a dandelion flower head were observed. Petal surface cells exhibit shape change through the opening and closing movements of the flower head. Microscopic observations of petal surface of dandelion flower were performed with confocal laser scanning microscope. Furthermore, droplet collision tests on the seeds head were also conducted to examine the mechanical function of dandelion pappus with high-speed video camera system. These experimental results clarified some superior functions of a plant from the engineering standpoint. Keywords: biomechanics, dandelion, microscopic observation, petal surface cells. INTRODUCTION In the development of bio-engineering and material science, the study on various functions of plants is of fundamental interest and importance with respect to a variety of applications. Therefore, extensive investigations on the mechanical properties of a great many plants have been conducted (Niklas et al., 2006). For examples, the relationships between environmental stresses and plant mechanical traits were reviewed (Read & Stokes, 2006). The investigation of the mechanical design and properties of the leaf covering aspects of its structure and failure was reported (King & Vincent, 1996). The unfolding of a leaf with a straight central vein and symmetrically arranged parallel lateral veins was described, and numerical models with different angles between main and secondary veins were made to simulate the unfolding (Kobayashi et al., 1998). In spite of many investigations on plant biomechanics, there still remains a wide unexplored domain. Research data on morphological characteristics and mechanical properties of plants are scanty, and there are many points which must be clarified. This paper is concerned with the morphological characteristics of petal surface cells in a dandelion flower and the mechanical properties of dandelion pappus. Cell shapes of the petal surface were measured with the confocal laser scanning microscope. Furthermore, water drop collision tests on the seed head were conducted with high-speed video camera system. The results of a series of experiments showed some superior mechanical functions of dandelion. EXPERIMENTAL APPARATUS AND PROCEDURES Usually, the flower heads of dandelion are open in the daytime, and closed at night. Microscopic observations of petal surface of dandelion flower were performed through the opening and closing movements of the flower head. In the observation experiment, the color -863-

2 Track_K Biomechanical Applications Fig. 1 - Schematic diagram of experimental apparatus for microscope observation Fig. 2 - Block diagram of experimental apparatus for water drop collision test 3D laser scanning microscope (KEYENCE VK-9700) was used. This microscope adopts the 2 way method of a laser light source and the white light source. The laser light source is as semiconductor laser with the wavelength 408 nm. This lasers scanning microscope enables observations of color images with clarity rivalling scanning electron microscopes, and noncontact high-precision 3D measurements. The indication resolving is µm in height, and µm in width. Test dandelion flower heads were collected in the field in Yurihonjo, Japan. The collected flower heads were put in the water container, and kept alive with the point of the flower arrangement. The cut flower heads are also open in the daytime, and closed at night. One piece of petal was set in the observation area in the laser scanning microscope as shown in Fig.1. The dandelion stem was cut to approximately 100 mm length, and water was supplied through the stem from the water container. The petal surface was observed during closing process or opening process in flower head movement. The time variations in surface roughness of the petal were analyzed with the measured data. In this experiment, the sample dandelions were Taraxacum offinale Weber. The microscopic observation experiments were performed under the condition of the room temperature

3 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 Fig. 3 - Microscopic optical ptical image of dandelion petal surface at 2:41 Fig. 4 - Three-dimensional dimensional description of dandelion petal surface at 2:41 In this paper, drop collision tests on the seed were also conducted to examine the resistance to rain drop collision. A schematic chematic diagram of the experimental apparatus is shown in Fig.2. Droplets were dropped from the burette. The impact velocity of the droplet was varied by the change of fall height. Targets were dandelion seed heads or seed. The seed head and seed were bonded to the heavy stand with an adhesive. The drop collision phenomena were recorded with the high-speed speed video camera system at 9000 frames per second, and the series of frames were analyzed by the personal computer. SHAPE CHANGE OF SURFACE CELL IN OPENING PROCESS Cells are the fundamental structural and functional units of living organisms. The growth of plant tissues is the result of two essential processes,, that is, the expansive growth of existing cells and the creation of near cells by mitosis.. In plants, the rapid growth is related to the division and enlargement of cells produced during the init initial ial phase. In this paper, the petal surface of live dandelion flower was observed with the color 3D laser scanning microscope. An example of the results is shown in Fig.3. Fig.3 shows an optical image of dandelion petal surface at 2:41 in Japan Standard tandard Ti Time. The observation area is µm µ µm in Fig.3. A large number of longitudinal domains are recognized. Each domain corresponds to Fig. 5 - Microscopic optical ptical image of dandelion petal surface at 7:58 58 Fig. 6 - Three-dimensional dimensional description of dandelion petal surface at 7:

4 Track_K Biomechanical Applications one surface cell of the dandelion petal. The surface cells make longwise array structure in petal direction. Fig.4 shows the three three-dimensional description of shape measurement for the petal surface. Fig.4 corresponds to exactly the same area in Fig.3. Various colors show the topographical map on the petal. It can be seen from Fig.4 that the petal surface is not a flat plane. A large number of longitudinal mountains are recognized in the observation area on the petal surface. Each mountain in Fig.4 corresponds to one surface cell. The size of each cell is about 10 µm in width, 100 µ µm in length, and 19 µm m in height in Fig.4. These cell shapes change little by little with time. The change of these cell shapes was observed for approximately five hours. Fig.5 shows the optical image of the same petal surface as Fig.3. The observation time in Fig.5 is 7:58 in Japan Standard Time. It can be seen on comparing Fig.5 and Fig.3 that each cell thickens with time. Fig.6 shows the three-dimensional three description of shape measurement for the petal surface which corresponds to Fig.5. The mountain of each cell becomes higher. This fact shows the enlargement of existing cells. Cell enlargement can result in substa substantial ntial growth of the tissue. In general, plant cells have a cellulose wall outside the cell membrane, large permanent vacuoles, nucleus, and chloroplasts. The enlargement ement of cells depends, in part, on the stretching capacity of the cell wall. The cell wall is the rigid outer layer that surrounds each plant cell. Cell walls are composed primarily of cellulose that can be flexible. Cellulose is an important structural component of cell wall, Fig. 7 - Microscopic optical images of one surface cell during opening process Fig. 8 - Color display of the surface cell in height and it is a complex carbohydrate molecule. Pressure exerted from inside the cell causes the cell wall to stretch and expand. In plant cell, the increase in size is described as follows (Ortega, 2010); -866-

5 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 dv w Vdt = L (σ Π P ) T where (dv w /Vdt) is the relativee rate of change in water volume, V is the volume, t is the time, L is the membrane relative hydraulic conductance (L=L p A/V), L p is the membrane hydraulic conductivity, A is the membrane area, σ is the solute reflection coefficient, Π is the osmotic pressure difference across the membrane ( Π=Π Ι Π Ε ), P is the turgor pressure, and T is the relative rate of change in water volume lost via transpiration (T= dv T /Vdt). The relative rate of change in volume of the cell wall chamber, dv cwc /Vdt, is described as follows (Ortega, 2010); dv Vdt cwc = φ( P P ) + 1 dp ε dt where φ is the irreversible extensibility of the wall, P c is the critical turgor pressure, and ε is the volumetric elastic modulus. The rate of change of turgor pressure, dp/dt, is described as follows (Ortega, 2010); dp = ε [ L( σ Π P) φ( P Pc ) T ] (3) dt c (1) (2) (a) Measured line (b) Measurement results Fig.9 Results of surface shape measurement of the cell -867-

6 Track_K Biomechanical Applications Eq. (3) is solved as follows (Ortega, 2010); P (t ) = ( P0 Peq ) exp[ ε (φ + L )t ] + Peq Peq = Lσ Π + φpc T φ+l (4) (5) where P0 is the turgor pressure at t= 0, and Peq is the equilibrium turgor pressure. Plant cell expansive growth obeys the mechanical aspects, Eqs.(1)-(5). (5). Fig.7 shows the time variation of one surface cell in the optical image. The first observation time is defined as t=0 h, Japan Standard Time. It can be seen in Fig.7 that the width of the surface cell waves gradually with increase of the time t. The wavelength of wavy pattern on the cell width is λcell 26 µm. Such change in surface shape means the increase of the cell volume in the state where the cell is surrounded by other cells. ells. Fig.8 shows the color display in height of the surface cell. Red color indicates the higher part, and blue color indicates the lower part. It can be seen from Fig.8 that red domains gradually increase with time progress. The quantitative indication of o such shape change is shown in Fig.9. In Fig.9, (a) shows the measured line for cell cross (a) Microscopic optical images of one surface cell (b) Color display of the surface cell in height Fig Changes in cell shape during closing process sectional shape measurement and (b) shows the measured data for approximately 5 hours. The measured line was defined in the middle of the cell longitudinal length in this case. Time changes in cell cross section are clarified in Fig.9 (b). The highest pointt is 6.65 µm, and the lowest point is 0.24 µm at t=0 =0 h. Therefore, the height difference in the cell shape is ht=0=6.40 µm at t=0 =0 h. Furthermore, the cell width is bt=0=9.38 µm at t=0 =0 h. On the other hand, the height difference is ht=5=8.94 µm, and the cell width is bt=5=12.14 µm at t=5 t h. Therefore we can obtain the value of Eq.(1) by rough calculation during the process; dvw 1 (6) Vdt s This rough value is the relative rate of change in water volume during the opening movement of petal surface in dandelion flower solutess in the cell play a role in controlling the movement -868-

7 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 of water into the cell. The osmotic pressure difference Π in Eq.(1) causes water to move into the cell. The opening movement of dandelion flower head is performed by a little water movement. SHAPE CHANGE OF SURFACE CELL IN CLOSING PROCESS In the same manner, the petal surface of live dandelion flower was observed during the closing movement of flower head. Fig.10 shows the time variation of one surface cell in dandelion petal during the closing movement. In Fig.10, (a) shows the optical images and (b) shows the displays in height of the surface cell. The surface cell contracts and red domains gradually decrease with time progress. Fig.11 shows the result of cell cross-sectional shape measurement. The height difference in the cell shape is h t=0 =6.37 µm at t= =0 h (12:40 in Japan Standard Time), and its cell width is b t=0 =14.90 µm. On the other hand, the height difference is h t=5 =7.58 µm, and the cell width is b t=5 =9.11 µm at t=5 h (17:45 in Japan Standard Time). Therefore, the roughness value of the relative rate of change in water volume during the closing movement of the dandelion flower head can calculate as follows; dv w (7) Vdt s (a) Measured line (b) Measurement results Fig Results of surface shape measurement of the cell -869-

8 Track_K Biomechanical Applications Fig Microstructural patterns observed on the surf surface cells Fig Measured profile along the measured line in Fig.12 (a) Measured line (b (b) Measured profile Fig Measured line and measured profile Negative sign in Eq.(7) indicates water loss from the surface cell. Extreme water loss from the cell may cause collapse of both the membrane and cell wall, that is, it may result in the cell ss death. However, the value of Eq.(7) is moderately suppressed value because the petal is alive during the observation experiment

9 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 Mass flow of liquid water between cells is causing the opening and closing movements of dandelion flower head. The surface minute irregularities of petals are maintained through all processes in flower head movement. The microrelief structure of plant surfaces causes effective water repellency cy (Barthlotl Neinhuis, 1997). The surface roughness is a function that is important to prevent the water invasion to the plant body. Enough surface roughness of dandelion ion petal is kept after water movement from the cell as shown in Fig.11. FINE STRUCTURE ON CELL SURFACE As was stated previously, the measured profile data of the petal surface showed the existence of the irregularity of µm 100µm formed by surface cells. In this paragraph, more detailed surface roughness was observed and measured. Fig.12 shows the optical image im of petal surface at the higher magnification compared with Fig.3 and Fig.5. In Fig.12, the view area is µm µm. Fig.12 corresponds to the final stage of opening process of flower head movement, and shows the petal condition following the state of Fig.5. The observation time of Fig.12 is 8:05 in Japan Standard Time. Several types of wrinkle pattern on the surface of cells are observed in Fig.12. Basically a large number of wrinkles are perpendicular to the longitudinal direction of the cell cells. s. These wrinkles have a certain constant height and width. Fig.13 shows the measured profile along the measured line in Fig.12. The height of the Fig Water droplet collision on pappus dandelion seed wrinkles is distributed to 0.55µm from 0.18µm. These wrinkles are considered as microfibrils. The majority of plant cells expand anisotropically, and growth anisotropy is determined by the structure of the cell wall (Crowell et al., 2010). In Fig.12, the difference in wrinkle pattern may show the difference rence of the direction in anisotropic cell expansion at each cell. Not only global expansion but also localized expansion of a plant cell has been reported (Mathur, 2004). Furthermore many experimental results indicate that cell wall enlargement may be regulated ulated at many levels (Cosgrove, 2000). Fig.14 shows the measured profile for the whole of cell showed in Fig.12. In Fig.14, (a) shows the measured line along the longitudinal direction, and (b) shows the measured profile along the line. The measured profile profi presents a mountain range shape. The cell surface shows the waviness on the mountain. The waviness spacing is about 10-18µm, 18µm, and the waviness height is about 55-13µm. 13µm. The mountain profile changes little by little during opening and closing process of flo flower head

10 Track_K Biomechanical Applications PAPPUS BEHAVIOR DURING DEROPLET IMPACT In biology, all plants that develop a flower are classified as angiosperms. All flowers are reproductive structures that contain both male and female reproductive pasts. Many flowers are adapted to attract animal pollinators. Seeds are formed when the male reproductive organs produce pollen that contain sperm. After fertilization, seeds develop inside the fruit. In seeds dispersal of dandelion, feathery bristles of the pappus function as a flight organ which enables that seed to be carried by the wind over long distance. In this paper, droplet collision tests on the pappus were conducted. Fig.15 is a sequence of photographs showing the collision of a droplet on the pappus. Drop is touching the feathery bristles in the picture number 2 in Fig.15. In Fig.15, δ t is the time interval between each frame. The drop is collided to the half of bristles in pappus in the picture number 3, and the beak part is changed by the drop collision. In the picture number 4, the drop bends the bristles greatly. In the picture number 5, the drop is cut by the bristles, and the bent bristles begin to be restored to the original state. In the picture number 6, the drop collapses into minute many water particles. In the picture number 9, the bristles are almost restarted to the original state. Fig.16 shows the trajectory of the bristle tip in the orthogonal coordinate system x-z fixed to the camera viewpoint. Firstly the bristle is bent downward, and it is restored to the original state by the Fig Trajectory of bristle tip during droplet collision Fig Damping oscillation in time history of bristle tip -872-

11 Proceedings of the 6th International Conference on Mechanics and Materials in Design, Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, July 2015 other route. Furthermore, the bristle overshoots. Fig.17 shows such bristle transients time history (as illation). In Fig.17, z/l p is dimensionless position of the bristle tip, and l p is the length of pappus. The time history of bristle tip in z position shows damping oscillation except for the stage of the droplet collision. If we ignore the initial position of the bristle tip, the oscillation is described in the following from; z γ t = ce cos( ωt + ϕ) (8) l p where c and γ are constants, ω is the angular frequency, and ϕ is the phase at t=0. The time t in Eq.(8) was defined the beginning of the oscillation as t=0. It can be seen from Fig.17 that the period of the bristle oscillation is T n 7.4 ms. This value of the period corresponds to the natural frequency f n =135.1 Hz in the bristle. This value of the natural frequency in the bristle oscillation is related to the Young s modulus in the beam model. Further research is needed with respect to the Young s modulus in the pappus of dandelion seed. The bristle oscillation shows a rapid dumping from large displacement. These facts mean that the dandelion pappus has both extreme flexibility and strength. Such pappus characteristics will be due to the structure of bristle. One bristle in dandelion pappus consists of many fine pipes (Sudo et al., 2008). CONCLUSIONS Some mechanical functions of dandelion flower head and seed were studied experimentally. Petal surface cells were observed with the confocal laser scanning microscope. Furthermore, water droplet collision on the pappus of dandelion seed was examined with the high-speed video camera analysis system. The results obtained are summarized as follows. (1) The dandelion cells make longwise array structure in petal direction. The petal surface is not a flat plane. The size of each cell is about 10µm in width, 100µm in length, and 20µm in height. (2) The dandelion surface cells change in size little by little during opening and closing process of flower head movement. The surface cells increase in size during opening process, and they decrease in size during closing process. (3) The surface minute irregularities of dandelion petals are maintained through all processs in flower head movement. (4) Several types of wrinkle pattern are observed on the surface cells. Basically a large number of wrinkles are perpendicular to the longitudinal direction of the cells. (5) The pappus equipped with dandelion seeds shows the extreme flexibility and strength for water drop collision. REFERENCES [1]-Barthlotl W, Neinhuis C. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta, 1997, 202, p [2]-Cosgrove DJ. Expansive growth of plant cell walls. Plant Physiology and Biochemistry, 2000, 38, p [3]-Crowell EF, Gonneau M, Vernhettes S, Hӧfte H. Regulation of anisotropic cell expansion in higher plants. Comptes Rendus Biologies, 2010, 333, p

12 Track_K Biomechanical Applications [4]-King MJ, Vincent JFV. Static and dynamic fracture properties of the leaf of New Zealand flax Phormium Tenax (Phormiaceae: Monocotyledones). Proceedings of the Royal Society of London, Series B, 1996, 263, p [5]-Kobayashi H, Kresling B, Vincent JFV. The geometry of unfolding tree leaves. Proceedings of the Royal Society of London, Series B, 1998, 265, p [6]-Mathur J. Cell shape development in plants. Trends in Plant Science, 2004, 9, p [7]-Niklas KJ, Spatz HC, Vincent J. Plant biomechanics: an overview and prospectus. American Journal of Botany, 2006, 93, p [8]-Ortega JKE. Plant cell growth in tissue. Plant Physiology, 2010, 154, p [9]-Read J, Stokes A, Plant biomechanics in an ecological context. American Journal of Botany, 2006, 93, p [10]-Sudo S, Matsui N, Tsuyuki K, Yano T. Morphological design of dandelion. Proceedings of the 2008 SEM XI International Congress and Exposition on Experiment and applied Mechanics, 2008, p

Dynamic Behavior of Dandelion Flower Head and Spherical Seed Head

Int. J. Mech. Eng. Autom. Volume 2, Number 1, 2015, pp. 32-39 Received: June 10, 2014; Published: January 25, 2015 International Journal of Mechanical Engineering and Automation Dynamic Behavior of Dandelion