Sugar-Controlled Ca2+ Uptake and {alpha}-Amylase Secretion in Cultured Cells of Rice (Oryza sativa L.) |
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Authors: | Mitsui, Toshiaki Loboda, Tadeusz Itoh, Akira Ikarashi, Taro |
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Affiliation: | 1 Laboratories of Molecular Life Sciences, Graduate School of Science and Technology, Niigata University Niigata, 950-2181 Japan 2 Department of Applied Biological Chemistry, Faculty of Agriculture, Niigata University Niigata, 950-2181 Japan |
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Abstract: | Sugar starvation-induced synthesis and extracellular liberationof -amylase molecules in suspension-cultured cells of rice (Oryzasativa L.) required Ca2+, although the level of translatable-amylase mRNA was not affected in the presence of Ca2+. Sugardepletion markedly stimulated Ca2+ uptake by rice cells andsucrose supplementation reduced it. Immunohistochemical andelectron probe microanalyzer studies indicated an apparent resemblancebetween the distribution pattern of Ca2+ and that of -amylasemolecules induced in the sugar-depleted cells. Ca2+ uptake wasreduced by sucrose, maltose, fructose, and glucose similarlyat more than 5 mM, but was unaffected by mannitol (88 mM), 6-deoxy-D-glucose(10 mM), and 3-O-methyl-D-glucose (10 mM). Furthermore, an effectiveCa2+ channel blocker, La3+ significantly inhibited the Ca2+uptake and the synthesis and extracellular liberation of -amylasemolecules in the absence of sucrose, while a general P-typeATPase inhibitor, vanadate greatly stimulated both in the presenceof sucrose. We concluded that, by controlling the Ca2+ uptake,metabolic sugars regulate the protein synthesis and posttranslationalsecretory processes of -amylase molecules in rice cells. 4 Invited research fellow of the Japan Society for the Promotionof Science. Present address: Plant Physiology Department, WarsawAgricultural University, Rakowiecka Str. 26/30 02-528 Warsaw,Poland. |
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