Induction of the plastidic starch-phosphorylase gene in potato storage sink tissue

Abstract

The expression of the gene encoding the plastidic enzyme starch phosphorylase (EC 2.4.1.1) varies according to tissue carbohydrate status. Incubation of excised potato (Solanum tuberosum L. cv. D6sir6e) leaves carrying a portion of the stem under a short photoperiod resulted in a drastic accumulation of starch, accompanied by a rapid increase in the level of phosphorylase mRNA and by a similar change in phosphorylase protein level. However, under the same incubation conditions, the transcriptional activity of the phosphorylase promoter in transgenic plants did not change markedly. Therefore, the increased expression of the phosphorylase gene in petioles of stem cuttings is not controlled by the level of initiation of transcription. Phosphorylase mRNA accumulated to a high level in petioles of detached leaves kept under constant light for 24 h, but not in petioles kept in the dark. The effect of light on the accumulation of the mRNA was appreciably reduced if the petioles were incubated in ethylendiaminetetraacetic acid (ED-TA), a treatment known to increase phloem exudation in detached leaves. The inhibition by EDTA could be partially counteracted by the addition of sucrose to the incubation solution. Furthermore, incubation of petioles in darkness in solutions with high levels of sucrose resulted in enhanced expression of the gene. These results suggest that sucrose, the main compound transported by phloem in potato, is involved in the regulation of the starch phosphorylase gene. This also indicates that conditions favouring starch synthesis lead to increased expression of the phosphorylase gene.

Starch Biosynthesis. 3: The Glycogen Precursor Mechanism Using Phosphorylase in the Production of the Precursor Glycogen

“…c) Phosphorylase activity increases with an increase in the activities of ADPGlu pp, SSSs and GBSS as observed by Steup [40], Nakamura and Yuki [48], Sivak [49], Nelson and Pan [50] , and Tsai et al [51]. This correlates with studies which show that an increase in sucrose produces a corresponding increase in the activity of both phosphorylase [52] and ADPGlu pp [53]. Also the greater the activity of sucrose synthase, the greater is the yield of starch [54].…”

Activity and expression of banana starch phosphorylases during fruit development and ripening

“…In its high affinity and specificity for amylopectin, banana phosphorylase I is similar to the cytosolic phosphorylases from other plant tissues (Steup and Schachtele 1981;Mori et al 1991;van Berkel et al 1991;St-Pierre and Brisson 1995;Buchner et al 1996). As the chloroplast envelope membrane is not permeable to highmolecular-weight polysaccharides, there are two possible explanations for phosphorylase I activity: an independent pool of carbohydrates in the cytosol, or a disintegration of the chloroplast envelope during banana ripening, allowing the cytosolic phosphorylase to participate in the starch degradation process.…”

“…spinach leaves (Steup and Scha¨chtele 1981), pea cotyledons (van Berkel et al 1991), potato tubers (Mori et al 1991), potato leaves (St-Pierre and Brisson 1995) and Vicia faba cotyledons (Buchner et al 1996).…”

Mutation of the Plastidial α-Glucan Phosphorylase Gene in Rice Affects the Synthesis and Structure of Starch in the Endosperm

“…Two types of starch phosphorylase (Pho) were observed in the following organs of higher plants: spinach (Spinacia oleracea) leaves (Steup and Schä chtele, 1981), pea (Pisum sativum) cotyledons (van Berkel et al, 1991), potato (Solanum tuberosum) leaves (St-Pierre and Brisson, 1995), fava bean (Vicia faba) cotyledons (Buchner et al, 1996), banana (Musa acuminata) fruits (da Mota et al, 2002), and wheat (Triticum aestivum) endosperm (Schupp and Ziegler, 2004). The two Pho types differ from each other not only in structure and kinetic properties but also in their expression pattern and subcellular localization (Steup, 1990).…”

“…Pho1 enzyme activity and protein levels are coordinated with starch production in potato tuber (Kossmann et al, 1991;St-Pierre and Brisson, 1995), maize (Zea mays) endosperm (Ozbun et al, 1973), and wheat endosperm (Schupp and Ziegler, 2004). The exact role of Pho1 in the biosynthesis of polysaccharides in both photosynthetic and nonphotosynthetic tissues of higher plants is still controversial and a subject of many discussions.…”