Automorphosis of maize shoots under simulated microgravity on a three-dimensional clinostat |
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Authors: | Takayuki Hoson Seiichiro Kamisaka Ryoichi Yamamoto Masamichi Yamashita Yoshio Masuda |
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Institution: | Dept of Biology, Faculty of Science, Osaka City Univ., Sumiyoshi-ku, Osaka 558, Japan;Tezukayama College, Nara 631, Japan;Institute of Space and Astronautical Science, Sagamihara 229, Japan. |
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Abstract: | Seedlings of maize ( Zea mays L. cv. Golden Cross Bantam T-51) were grown under microgravity conditions simulated by a three-dimensional clinostat. On the clinostat, maize shoots exhibited curvatures in three different portions: (1) the basal transition zone connecting roots and mesocotyls, (2) the coleoptile node located between mesocotyls and coleoptiles, and (3) the elongating region of the coleoptiles. Even non-clinostatted control shoots showed some degree of curvature away from the caryopsis in the transition zone and bending toward the caryopsis in the coleoptile node. Clinostat rotation greatly stimulated these curvatures. Control coleoptiles elongated almost straightly, whereas coleoptiles on the clinostat bent either away from or toward the caryopsis depending on the timing of rotation. The curvature in all three portions became larger with time, both in control and clinostatted seedlings. There was no difference in the osmotic concentration of the cell sap between the convex and the concave halves of any portion. However, in coleoptile nodes and coleoptiles, the faster-expanding convex side exhibited a higher extensibility of the cell wall than the opposite side, and this appears to be a cause of the curvature. Thus, changes in the cell wall metabolism may be involved in automorphosis, which governs the life cycle of plants under a microgravity environment. |
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Keywords: | Automorphosis cell wall extensibility coleoptile gravitropism growth regulation maize mesocotyl simulated microgravity three-dimensional clinostat Zea mays |
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