RESUMO
Intact starch granules were isolated from leaves of Solanum tuberosum L. (and from Pisum sativum L.), and the patterns of starch-associated proteins were determined by SDS-PAGE. Depending on the pretreatment of the leaves the protein patterns varied: a 160 kDa compound was present in the starch-associated protein fraction when the leaves were darkened and performed net starch degradation. However, following illumination (i.e. during net starch biosynthesis) the 160 kDa protein was recovered almost exclusively in a soluble state. The 160 kDa protein was identified to be the recently described starch-related R1 protein. In in vitro assays recombinant R1 did bind to starch granules isolated from either illuminated or darkened leaves. However, binding to the latter was more effective. It is concluded that, depending upon the metabolic state of the cells, the starch granule surface changes and thereby affects binding of the R1 protein.
Assuntos
Proteínas de Plantas/metabolismo , Amido/metabolismo , Peso Molecular , Pisum sativum/metabolismo , Folhas de Planta , Proteínas de Plantas/química , Ligação Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Solanum tuberosum/metabolismo , Amido/químicaRESUMO
We have cloned a gene involved in starch metabolism that was identified by the ability of its product to bind to potato starch granules. Reduction in the protein level of transgenic potatoes leads to a reduction in the phosphate content of the starch. The complementary result is obtained when the protein is expressed in Escherichia coli, as this leads to an increased phosphate content of the glycogen. It is possible that this protein is responsible for the incorporation of phosphate into starch-like glucans, a process that is not understood at the biochemical level. The reduced phosphate content in potato starch has some secondary effects on its degradability, as the respective plants show a starch excess phenotype in leaves and a reduction in cold-sweetening in tubers.
Assuntos
Temperatura Baixa , Proteínas de Plantas/química , Amido/metabolismo , Sequência de Aminoácidos , Clonagem Molecular , DNA de Plantas/química , DNA de Plantas/genética , Escherichia coli/genética , Engenharia Genética , Glicogênio/química , Dados de Sequência Molecular , Fenótipo , Fosfatos/análise , Folhas de Planta/química , Folhas de Planta/genética , Proteínas de Plantas/genética , Plantas Geneticamente Modificadas , Solanum tuberosum/genética , Amido/análise , Amido/genéticaRESUMO
The proteinase inhibitor II (pin2) gene family exhibits two different modes of expression. It is, on the one hand, constitutively expressed in flowers of potato and tomato plants. and in potato tubers. On the other hand, its expression is induced in the plant foliage by mechanical wounding. To define cis-regulatory elements involved in pin2 promoter activity, deletion analysis of a potato pin2 promoter has been performed in stably and transiently transformed potato and tobacco plants. Two different elements, a quantitative enhancer and a regulatory element, are required for promoter activity. While functional promoter elements required for pin2 activity in tubers and wounded leaves could not be separated, its expression in flowers is mediated by different cis-acting sequences. Induction of pin2 expression in leaves by treatment with the plant growth regulators abscisic acid and jasmonic acid, and the general metabolite sucrose, depends on the presence of the regulatory element involved in expression in tubers and wounded leaves. Thus, pin2 expression in tubers and wounded leaves apparently results from the action of similar hormonal signals on closely linked promoter elements, while a different signal pathway leads to its constitutive expression in flowers.
