Magnesium deficiency-induced changes in organic acid metabolism of Citrus sinensis roots and leaves
2013
Yang, L.T., Fujian Agriculture and Forestry Univ., Fuzhou (China). Coll. of Resources and Environmental Sciences | Yang, G.H., Fujian Agriculture and Forestry Univ., Fuzhou (China). Inst. of Horticultural Plant Physiology, Biochemistry and Molecular Biology | You, X., Fujian Agriculture and Forestry Univ., Fuzhou (China). Inst. of Horticultural Plant Physiology, Biochemistry and Molecular Biology | Zhou, C.P., Fujian Agriculture and Forestry Univ., Fuzhou (China). Inst. of Horticultural Plant Physiology, Biochemistry and Molecular Biology | Lu, Y.B., Fujian Agriculture and Forestry Univ., Fuzhou (China). Coll. of Resources and Environmental Sciences | Chen, L.S., Fujian Agriculture and Forestry Univ., Fuzhou (China). Coll. of Resources and Environmental Sciences
Organic acid (OA) metabolisms are of fundamental importance but very limited data are available on the responses of plant OA metabolisms to Mg-deficiency. Seedlings of Citrus sinensis were irrigated with Mg-deficient (0, 50, or 500 microM MgSO4) or Mg-sufficient (2000 microM MgSO4) nutrient solution every other day for 12 weeks. Thereafter, we investigated the content of Mg, malate, and citrate as well as the activities of acid metabolizing enzymes in roots and leaves. Root malate content remained stable except for an increase in the highest Mg content and root citrate content increased with increasing root Mg content. As leaf Mg content increased, leaf malate and malate + citrate content decreased whereas leaf citrate content increased. Mg-deficiency decreased or did not affect activities of citrate synthase (CS), aconitase (ACO), phosphoenolpyruvate carboxylase (PEPC), NADP-isocitrate dehydrogenase (NADP-IDH), NAD-malate dehydrogenase (NAD-MDH), NADP-malic enzyme (NADP-ME), and pyruvate kinase (PK) in roots, whereas phosphoenolpyruvate phosphatase (PEPP) activity slightly increased. In contrast, Mg-deficient leaves had higher or similar activities of enzymes above mentioned except PEPP, NAD-MDH, and NADP-ME. In conclusion, both glycolysis and tricarboxylic acid (TCA) cycle may be up-regulated in Mg-deficient leaves but down-regulated in Mg-deficient roots.
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