Physiological Roles of Brassinosteroids in Early Growth of <Emphasis Type="Italic">Arabidopsis:</Emphasis> Brassinosteroids Have a Synergistic Relationship with Gibberellin as well as Auxin in Light-Grown Hypocotyl Elongation |
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Authors: | Kiwamu?Tanaka Yasushi?Nakamura Tadao?Asami Shigeo?Yoshida Tomoaki?Matsuo Email author" target="_blank">Shigehisa?OkamotoEmail author |
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Institution: | (1) Department of Agricultural Science, Kagoshima University, Kagoshima 890-0065, Japan;(2) Department of Food Science and Nutritional Health, Kyoto Prefectural University, Sakyo-ku, Kyoto 606-8522, Japan;(3) The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan;(4) Department of Biochemical Science and Technology, Kagoshima University, Kagoshima 890-0065, Japan |
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Abstract: | We examined the physiological effects of brassinosteroids (BRs) on early growth of Arabidopsis. Brassinazole (Brz), a BR biosynthesis inhibitor, was used to elucidate the significance of endogenous BRs. It inhibited growth of roots, hypocotyls, and cotyledonous leaf blades dose-dependently and independent of light conditions. This fact suggests that endogenous BRs are necessary for normal growth of individual organs of Arabidopsis in both photomorphogenetic and skotomorphogenetic programs. Exogenous brassinolide (BL) promoted hypocotyl elongation remarkably in light-grown seedlings. Cytological observation disclosed that BL-induced hypocotyl elongation was achieved through cell enlargement rather than cell division. Furthermore, a serial experiment with hormone inhibitors showed that BL induced hypocotyl elongation not through gibberellin and auxin actions. However, a synergistic relationship of BL with gibberellin A3 (GA3) and indole-3-acetic acid (IAA) was observed on elongation growth in light-grown hypocotyls, even though gibberellins have been reported to be additive to BR action in other plants. Taken together, our results show that BRs play an important role in the juvenile growth of Arabidopsis; moreover, BRs act on light-grown hypocotyl elongation independent of, but cooperatively with, gibberellins and auxin. |
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Keywords: | Brassinosteroids Arabidopsis Hormonal interaction Auxin Gibberellins Brassinazole |
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