title: Effects of spermidine synthase overexpression on polyamine biosynthetic pathway in tobacco plants.
abstract: Transgenic tobacco plants overexpressing the Datura stramonium spermidine synthase (EC 2.5.1.16) cDNA were produced in order to understand the role of this gene in the polyamine metabolism and in particular in affecting spermidine endogenous levels. All the analysed transgenic clones displayed a high Level of overexpression of the exogenous cDNA with respect to the endogenous spermidine synthase. No relationship was detected between the mRNA expression level of S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50), which did not change between the negative segregant control and the transgenic plants, and spermidine synthase, suggesting the existence of an independent regulatory mechanism for transcription of the two genes. The determination of enzyme activities indicated an increased spermidine synthase and S-adenosylmethionine decarboxylase activity, with the last being mainly recovered in the particulate fraction. ODC (ODC, EC 4.1.1.17) was the most active enzyme and its activity was equally distributed between the soluble and the particulate fraction, while ADC (ADC, EC 4.1.1.19) activity in the transgenic plants did not particularly change with respect to the controls. In comparison to the controls, the transformed plants displayed an increased spermidine to putrescine ratio in the majority of the clones assayed, white the total polyamine content remained almost unchanged. These findings suggest a high capacity of the transformed plants to tightly regulate polyamine endogenous levels and provide evidence that spermidine synthase is not a limiting step in the biosynthesis of polyamines.
authors.affiliation: Department of Biology e.s. and Interdepartmental Centre of Biotechnology, University of Bologna, Via Irnerio 42, Bologna 40126, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Franceschetti
authors.forename: Silvia
authors.initials: S
authors.lastname: Fornalé
authors.forename: Annalisa
authors.initials: A
authors.lastname: Tassonia
authors.forename: Katiuscia
authors.initials: K
authors.lastname: Zuccherelli
authors.forename: Melinda J
authors.initials: MJ
authors.lastname: Mayer
authors.forename: Nello
authors.initials: N
authors.lastname: Bagni
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000235:genetics / Q000378:metabolism; D002262:Carboxy-Lyases / Q000378:metabolism; D018076:DNA, Complementary / Q000096:biosynthesis; D013286:Datura stramonium / Q000201:enzymology / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D009955:Ornithine Decarboxylase / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism*; D018749:RNA, Plant / Q000096:biosynthesis / Q000235:genetics*; D011436:Spermidine Synthase / Q000096:biosynthesis* / Q000235:genetics; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic
chemical_list: D018076:DNA, Complementary; D011073:Polyamines; D018749:RNA, Plant; D011436:Spermidine Synthase; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase; C019722:arginine decarboxylase; D012437:Adenosylmethionine Decarboxylase