title: Modifications in endopeptidase and 20S proteasome expression and activities in cadmium treated tomato (Solanum lycopersicum L.) plants.
abstract: The effects of cadmium (Cd) on cellular proteolytic responses were investigated in the roots and leaves of tomato (Solanum lycopersicum L., var Ibiza) plants. Three-week-old plants were grown for 3 and 10 days in the presence of 0.3-300 microM Cd and compared to control plants grown in the absence of Cd. Roots of Cd treated plants accumulated four to fivefold Cd as much as mature leaves. Although 10 days of culture at high Cd concentrations inhibited plant growth, tomato plants recovered and were still able to grow again after Cd removal. Tomato roots and leaves are not modified in their proteolytic response with low Cd concentrations (< or =3 microM) in the incubation medium. At higher Cd concentration, protein oxidation state and protease activities are modified in roots and leaves although in different ways. The soluble protein content of leaves decreased and protein carbonylation level increased indicative of an oxidative stress. Conversely, protein content of roots increased from 30 to 50%, but the amount of oxidized proteins decreased by two to threefold. Proteolysis responded earlier in leaves than in root to Cd stress. Additionally, whereas cysteine- and metallo-endopeptidase activities, as well as proteasome chymotrypsin activity and subunit expression level, increased in roots and leaves, serine-endopeptidase activities increased only in leaves. This contrasted response between roots and leaves may reflect differences in Cd compartmentation and/or complexation, antioxidant responses and metabolic sensitivity to Cd between plant tissues. The up-regulation of the 20S proteasome gene expression and proteolytic activity argues in favor of the involvement of the 20S proteasome in the degradation of oxidized proteins in plants.
authors.affiliation: Département de Biologie, Faculté des Sciences de Tunis El Manar, Unité de Recherche de Biologie et Physiologie Cellulaires Végétales, 1060 Tunis, Tunisia.
authors.forename: Wahbi
authors.initials: W
authors.lastname: Djebali
authors.forename: Philippe
authors.initials: P
authors.lastname: Gallusci
authors.forename: Cécile
authors.initials: C
authors.lastname: Polge
authors.forename: Latifa
authors.initials: L
authors.lastname: Boulila
authors.forename: Nathalie
authors.initials: N
authors.lastname: Galtier
authors.forename: Philippe
authors.initials: P
authors.lastname: Raymond
authors.forename: Wided
authors.initials: W
authors.lastname: Chaibi
authors.forename: Renaud
authors.initials: R
authors.lastname: Brouquisse
mesh_terms: D002104:Cadmium / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D015227:Lipid Peroxidation / Q000502:physiology; D018551:Solanum lycopersicum / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D010084:Oxidation-Reduction; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D050050:Protein Carbonylation / Q000502:physiology
chemical_list: D002104:Cadmium; D010450:Endopeptidases; D046988:Proteasome Endopeptidase Complex