Boron Nutrition of Cultured Tobacco BY-2 Cells
Boron (B) is one of the essential microelements for higher plants and its deficiency is one of the major constraints to crop production in many parts of the world (Shorrocks 1997). In B-deficient plants, the development and elongation of terminal buds and
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1 Introduction Boron (B) is one of the essential microelements for higher plants and its deficiency is one of the major constraints to crop production in many parts of the world (Shorrocks 1997). In B-deficient plants, the development and elongation of terminal buds and youngest leaves and root tips are inhibited. Internodes become shorter, giving the plants a bushy or rosette appearance. Reproductive growth is more sensitive to B deficiency and failure in pollination, abscission of reproductive organs or falling of young fruits are typical symptoms of deficiency (Marschner 1995). However, the mechanism by which B influences these processes is not known yet. In the case of intact plants, deprivation of B stops root elongation, however, it is difficult to separate the B-affected cells from the bulk of cells. Cultured cells offer several advantages over intact plants for the research into the role of B. Firstly, a B-free culture medium is easily prepared. Secondly, the experimental results can be interpreted more clearly, because cultured cells are not differentiated. A requirement for boron by cultured plant cells has been reported in the case of rice (Ohira et al. 1975), carrot (Durst and Loomis 1984; Goldbach 1985) and cabbage (Bowen and Robbins 1988). The authors have been studying the physiological function of B in cultured tobacco BY-2 cells, because tobacco BY-2 cells propagate quickly and do not aggregate heavily. The authors found that deprivation of B brings about cell wall swelling and in those cell walls, the pectic polysaccharide chains are not cross-linked due to B deficiency. Based on the examination, the authors presented a tentative conclusion that B cross-links pectic polysaccharide chains and organizes the pectic network properly. In this chapter, the authors summarize research on the function of B in the cell wall using tobacco BY-2 cells and report their latest data of the response of tobacco BY-2 cells to B deficiency.
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Plant Nutrition Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, 606-8502, Kyoto, Japan, e-mail: [email protected]
Biotechnology in Agriculture and Forestry, Vol. 53 Tobacco BY-2 Cells (ed. by T. Nagata, S. Hasezawa, and D. Inzé) © Springer-Verlag Berlin Heidelberg 2004
Boron Nutrition of Cultured Tobacco BY-2 Cells
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2 Intracellular Localization of Boron in Tobacco BY-2 Cells Since the essential role of B was first demonstrated in intact broad bean (Vicia faba) by Warington (1923), many researchers have tried to identify the primary function of B in higher plants. Parr and Loughman (1983) summarized the postulated functions of B such that it works in (1) sugar transport, (2) cell wall synthesis, (3) lignification, (4) cell wall structure, (5) carbohydrate metabolism, (6) RNA metabolism, (7) respiration, (8) indole acetic acid metabolism, (9) phenol metabolism, and (10) membranes. However, abnormalities observed under B deficiency do not always indicate the direct involvement of B in those processes, as the changes may be seco
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