A novel shrunken endosperm mutant of barley |
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Authors: | Alan H Sclulman Hannu Ahokas |
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Institution: | Univ. of Helsinki, Inst. of Biotechnology, Karvaamokuja 3, SF-00380 Helsinki, Finland;Univ. of Helsinki. Dept of Genetics, Arkadiankatu 7, SF-00100 Helsinki, Finland |
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Abstract: | Although mutations affecting several enzymes of the starch synthetic pathway in developing cereal endosperm have been isolated, none has a major effect on soluble starch synthase We report a new recessive shrunken endosperm mutant in barley ( Hordeum vulgare L. cv. Bomi-like), shx , which has 25% of normal starch content. We have assayed the activity of sucrose synthase (EC 2.4.1.13), ADP and UDP-glucose pyrophosphorylases (EC 2.7.7.27 and 2.7.7.9), branching enzyme (EC.2.4.1.18), and granule-bound and soluble starch synthase (EC 2.4.1.21) in shx. Sucrose synthase activity is reduced by 49% and UDP-glucose pyrrphosphorylase is 80% of the normal level. Branching enzyme and starch-bound starch synthase activities are normal, but ADP-glucose pyrophosphorylase activity is reduced by 72%. The soluble starch synthase that is primer-independent in the presence of sodium citrate shows 14% of normal activity in shx. whereas the primer-dependent form is unaffected. This lower starch synthase activity in shx cannot be explained by inhibition, substrate destruction or lack of primer. Although several starch-synthetic enzymes are affected, it is suggested that the primer independent from of soluble starch synthase may be the primary-site of the mutation in shx. |
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Keywords: | ADP-glucose pyrophosphorylase barley branching enzyme Hordeum vulgare mutant shrunken endosperm starch synthase starch synthesis sucrose synthase UDP-glucose pyrophosphorylase |
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