Sucrose enhances phosphoenolpyruvate carboxylase activity of in vitro solanum tuberosum L. under non-limiting nitrogen conditions |
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Authors: | Boubacar Dary Sima Yves Desjardins Le Van Quy |
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Institution: | (1) Centre de Recherche en Horticulture, Département de Phytologie, Faculté des Sciences de l'Agriculture et de l'Alimentation, Université Laval, GIK 7P4 Sainte-Foy, Québec, Canada |
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Abstract: | Summary The effect of sucrose on in vitro potato (ev. Kennebec) metabolism was evaluated. Plants were grown in three different media: Murashige and Skoog basal medium
containing high nitrogen concentration with 0 or 20 g l−1 sucrose; or modified medium containing reduced nitrogen amount and 20 g l−1 sucrose. Plants fed with 20 g l−1 sucrose and high N exhibited higher phosphoenolpyruvate carboxylase (PEPC) and pyruvate kinase activities and high PEPC protein
concentration at 7, 20 and 33 d of culture compared to those grown with 20 g l−1 sucrose and low N, or with 0 g l−1 sucrose and high nitrogen (control). The highest accumulation of starch and sucrose was found in plants grown with sucrose
and low nitrogen. This accumulation occurred concomitantly with a reduced enzyme activity resulting from a low utilization
of α-ketoglutarate by nitrogen assimilation, when plants were grown with reduced nitrogen. Our investigations on tricarboxylic
acid cycle activity showed that sucrose led to the reduction of organic acid amounts in both leaves and roots when high nitrogen
was supplied to plants. This was probably due to the intense exit of α-ketoglutarate, which was confirmed by measurements
of cytosolic isocitrate dehydrogenase activity. The low leaf glutamine/glutamate ratio observed in plants grown with 20 g
l−1 sucrose and high nitrogen compared to their counterparts cultivated with low nitrogen might be due to glutamine conversion
into proteins when nitrogen assimilation was intense. These results demonstrate that sucrose enhanced PEPC activity by increasing
protein synthesis. They also suggest that sucrose metabolism is involved in the replenishment of the tricarboxylic acid cycle
by providing carbon skeletons required to sustain phosphoenolpyruvate utilization during high nitrate assimilation. |
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Keywords: | nitrogen phosphoenolpyruvate carboxylase (PEPC) Solanum sucrose |
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