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(Lycopersicon Esculentum) and Mung Bean (Vigna Radiata) Seedlings

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(Lycopersicon Esculentum) and Mung Bean (Vigna Radiata) Seedlings Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29, pp. Th_5-Th_10, 2014 Topics The Effect of Clinorotation to the Growth of Tomato (Lycopersicon esculentum) and Mung Bean (Vigna radiata) Seedlings (9mm) ) ) By Leonita SWANDJAJA1 , Rizkita Rachmi ESYANTI1 , KHAIRURRIJAL2), Fenny M. DWIVANY 1) and Chunaeni LATIEF 3) K(5mm) RR 1)School of Life Sciences and Technology, Institut Teknologi Bandung, Bandung, West Java, Indonesia 2)Physics Department of Mathematics and Natural Sciences, Institut Teknologi Bandung, Bandung, West Java, Indonesia 3)Laboratory of Atmospheric Technology, National Institute of Aeronautics and Space, Bandung, West Java, Indonesia 㸦Received June 24th, 2013㸧 Plant growth and development are affected by abiotic factors such as light, temperature, water and gravity. Gravity ensures primary shoot grows upward towards sunlight to optimize photosynthesis, while the primary root grows downward into the soil to find water and mineral supply. Plants with impaired gravity response are poorly fit for survival in nature, since the roots may not be able to absorb the nutrient and the shoot may not be able to track sunlight.In the first study, the tomato seedlings on agar medium were treated on clinostat in light and dark condition. In dark, the tomato seedlings on the clinostat responded by bending their shoot and coiled their root. In the light condition, the shoot bending and root coiling were reduced significantly compare to the plants grew in the dark after seven days in clinorotation, which might indicate that phototropic response was stronger than gravitropic response in tomato seedlings. The mung bean on hanging mesh was tested on clinostat without light. Under this condition, instead of coiling, the root grew staight to the wet rockwool. The condition might indicate that mung bean seedling has stronger hidrotropic response compare to gravitropic response, as moisture gradient may trigger statolith degradation in columella cells. Key Words: Microgravity, 3D Clinostat, Gravitropism, Tomato, Mung Bean 1. Introduction gravity, the statolith mass concentrated at the distal part of the statocytes, following the vector of gravity. The experiment Plant growth and development are affected by several proposed that clinorotation disrupted root cap cells structure. abiotic factors such as light, temperature and water quantity. The constant rotation of clinostat caused the cell wall in the However, nearly upon germination, another physical factor columella cells deteriorated, and so reduced the amount of called gravity, affected the growth of root and shoot to orient visible amyloplasts. Several results also showed that the seedling correctly in space for the survival of the newly sedimentation of amyloplasts affected auxin movement. developed seedling. One of the most important mechanisms Until recently, the complex signal transduction cascade that for the survival of the germinating seedling is the growth of regulates the differential cell elongation induced by the root, which guarantees the young plant a rapid supply of gravitropic and phototropic remains unclear. A general model water and minerals. On the other hand, the shoot grows of root/shoot gravitropic and phototropic response is based on upward to tract sunlight. Since plants have evolved growing the model of the asymmetric redistribution of auxin that under the constant stimulus of gravity, its presence is one of causes a differential cellular elongation on opposite flanks of the most important requirements for their growth and spatial 1) the central elongation zone. The hypothesis was proposed by orientation . Studies on the effects of a weightlessness and 6) Cholodny–Went . The downward bending of roots and the hypergravity environment on plants have focused mainly on upward bending of shoots in multicellular plants to response investigations of the gravitropic response 2). gravity is the result from induction of unequal redistribution of In higher plants, the gravity detector called statolith, are auxin within the elongation zone, which is correlated with an believed to be sedimentation of amyloplast in the cells called accumulation of elevated auxin levels along the lower side. In statocyte3). Amyloplast displacement in statocyte is sufficient roots, high concentration of auxin inhibits cell growth and to promote organ-tip curvature4). However, signal transduction elongation, thus a downward curvature is the consequence. In of amyloplast sedimentation into a physiological signal in the contrast, the upward bending in shoots is induced due to the statocyte is not fully understood. growing stimulation effect of auxin, resulting in an upward curvature6). The characteristic of unequal polar auxin movement induced by gravity in the early growth stages of The modulation of the statolith of clover seedlings in etiolated Pisum sativum epicotyls has been studied7). The normal gravity and microgravity simulated by a clinostat has results suggested that gravity was indeed important for 5) been reported before . The results suggested that in normal inducing asymmetrical accumulation of auxin during the Copyright© 2014 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. Th_5 Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29 (2014) negative gravitropic response of the epicotyls. significant asymmetry found in other tissues17), supported the Auxin regulates cell division, elongation and differentiation. research done much earlier by Went6). Therefore, it plays critical role in plant growth and For this experiment, microgravity condition was simulated 8) development . While regulating cell division and elongation, on 3D clinostat. The verification for the clinostat was done by auxin is basipetally transported into and out of the cell by growing tomato (Lycopersicon esculentum) seeds and the protein transporter. The influx and efflux of the auxin is effect of clinorotation on plant growth was observed in mung believed to be involved in many physiological responses, bean (Vigna radiata) growth. Both experiments were then including phototropism and gravitropism. Auxin bioassay in verified by auxin concentration analysis and statolith position curved Coleus stem showed uneven auxin distribution. The observation. convex side of the stem had less auxin than the concave side9). Harrison and Pickard observed auxin asymmetry in tomato 2. Materials and Methods hypocotyl10). The results suggested that the upper part of tomato hypocotyl had higher auxin level at the curvature site The 3D clinostat (Fig. 1) was made in Institut Teknologi compare to the lower side. The ratio became larger as it was Bandung. The verification was conducted by observing nearing the curvature point. This result suggested that the tomato seeds growth on the 3D clinostat in comparison to curvature could only happen if the ratio of the auxin level is ground control. large enough. Aside from gravitropism, plant seedlings also respond to water and light. The response is known respectively as hydroptopism and phototropism11,12). Hydrotropism is caused by moisture differential, while phototropism is caused by the light, mainly the sunlight. Under natural situations, all these abiotic stimuli interact with each other and with gravity to control plant growth, explaining a concise description of such interactions in an evaluation of gravitropism13). It was proposed that the root growth orientation, both on ground and under microgravity condition, was probably controlled by hydrotropic response in the absence or reduction of gravity. Whilst sedimentation of amyloplasts affects auxin distribution in columella cells during gravitropic response, it Fig. 1. Three dimensional (3D) clinostat made for microgravity also influences hydrotropic response. Research in radish root simulation. showed that moisture differential led to amyloplasts degradation, though it was formed again once the root reached 2.1 Seeds and seedlings preparation agar medium. Water stress also reduced gravitropic response For clinostat verification, the tomato seeds were sterilized 14) in radish root without reduction in elongation growth . with 15% of chlorox for 5 minutes, then rinse three times with Wild-type Arabidopsis seedlings treated with inhibitors to sterilized water. The sterilized seeds were then incubated nullify auxin influx, efflux, or response, and their responses to overnight in sterile water. After incubation, the seeds were 15) either gravitropic or hydrotropic stimuli was observed . Their placed on plain agar medium and incubated in dark room until analysis showed that polar auxin transport was needed in the shoots reach 3 cm in height (± 7 days). Half of the gravitropic response, whereas other auxin response played prepared seedlings were placed on 3D-clinostat (8-10 rpm) definite role in giving hydrotropic response. Even though the that simulated microgravity for 2-3 days, the rest were treated mechanism remained unclear, both amyloplasts and auxin as control. All experiments were conducted in light and dark react to gravity and moisture, and give different response at condition. the same time. In the second experiment, mung beans were sterilized by As the seedlings respond to gravitropism and hydrotropism, 70% ethanol for several seconds. The seeds were then rinsed it also responds to phototropism. The relation between root in sterilized water several times to ensure no ethanol left on gravitropism and phototropism in Arabidopsis has been the surface of seeds coat. The seeds were
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