Starch metabolism in developing embryos of oilseed rape

Abstract

The aim of this work was to characterise the metabolism of starch in developing embryos of oilseed rape (Brassica napus L. cv. Topaz). The accumulation of starch in embryos in siliques which were darkened or had been exposed to the light was similar, suggesting that the starch is synthesised from imported sucrose rather than via photosynthesis in the embryo. Starch content and the activities of plastidial enzymes required for synthesis of starch from glucose 6-phosphate (Glc6P) both peaked during the early-mid stage of cotyledon development (i.e. during the early part of oil accumulation) and then declined. The mature embryo contained almost no starch. The starch-degrading enzymes a-(EC 3.2.1.1) and b-amylase (EC 3.2.1.2) and phosphorylase (EC 2.4.1.1) were present throughout development. Most of the activity of these three enzymes was extraplastidial and therefore unlikely to be involved in starch degradation, but there were distinct plastidial and extraplastidial isoforms of all three enzymes. Activity gels indicated that distinct plastidial isoforms increase during the change from net synthesis to net degradation of starch. Plastids isolated from embryos at stages both before and after the maximum starch content could convert Glc6P to starch although the rate was lower at the later stage. The results are consistent with the idea that starch synthesis and degradation occur simultaneously during embryo development. The possible roles of transient starch accumulation during embryo development are discussed.

Coordinate Changes in Carbon Partitioning and Plastidial Metabolism during the Development of Oilseed Rape Embryos

“…The temporal separation of storage product accumulation (starch, oil, and protein) has been reported previously for developing embryos of oilseed rape (Brassica napus L.) (Murphy and Cummins, 1989;da Silva et al, 1997). In particular, there is a shift from starch to oil accumulation during the early stages of cotyledon filling (da Silva et al, 1997).…”

“…In particular, there is a shift from starch to oil accumulation during the early stages of cotyledon filling (da Silva et al, 1997). The factors that contribute to such changes in metabolism and the consequent partitioning of imported carbon in the developing embryo are not understood.…”

Quantitative metabolic profiles of tomato flesh and seeds during fruit development: complementary analysis with ANN and PCA

“…In fruit, the high starch concentrations from 8 DPA to 20 DPA corresponded to transitory storage of imported carbon reutilized during the expansion phase for soluble sugar synthesis (Schaffer and Petreikov, 1997;Obiadalla-Ali et al, 2004). In seeds, the high starch concentrations at 8 and 12 DPA corresponded to transitory storage of imported carbon reutilized later during a high rate of lipid synthesis or for the synthesis of sugar contributing to the acquisition of desiccation tolerance as described for Brassicaceae (da Silva et al, 1997;Baud et al, 2002). This early development of a capacity for starch synthesis and storage may be related to the establishment of a high sink strength in both tissues.…”

Enhanced Seed Oil Production in Canola by Conditional Expression of Brassica napus LEAFY COTYLEDON1 and LEC1-LIKE in Developing Seeds

“…5). AGP catalyzes the conversion of Glc1P to ADPGlc that is then incorporated into starch granule in developing seeds (Kang and Rawsthorne, 1994;da Silva et al, 1997). A reduced AGP activity caused a decreased accumulation of starch as well as lipids in seeds of rapeseed, indicating a positive correlation between starch synthesis and the accumulation of lipids (Periappuram et al, 2000;Vigeolas et al, 2004).…”