RESUMO
The effects of cadmium (Cd) on aminopeptidase (AP) activities and Leucine-AP (LAP) expression were investigated in the roots of tomato (Solanum lycopersicum L., var Ibiza) plants. Three-week-old plants were grown for 10 days in the presence of 0.3-300 µM Cd and compared to control plants grown in the absence of Cd. AP activities were measured using six different p-nitroanilide (p-NA) substrates. Leu, Met, Arg, Pro and Lys hydrolyzing activities increased in roots of Cd-treated plants, while Phe-pNA cleavage was not enhanced after Cd treatments. The use of peptidase inhibitors showed that most of the Leu-pNA hydrolyzing activity was related to one or several metallo-APs. Changes in Lap transcripts, protein and activities were measured in the roots of 0 and 30-µM Cd-treated plants. LapA transcript levels increased in Cd-treated roots, whereas LapN RNAs levels were not modified. To assess amount of Leu-pNA hydrolyzing activity associated with the hexameric LAPs, LAP activity was measured following immunoprecipitation with a LAP polyclonal antiserum. LAP activity increased in Cd-treated roots. There was a corresponding increase in LAP-A protein levels detected in 2D-immunoblots. The role of LAP-A in the proteolytic response to Cd stress is discussed.
Assuntos
Aminopeptidases/efeitos dos fármacos , Aminopeptidases/metabolismo , Cádmio/farmacologia , Raízes de Plantas/enzimologia , Inibidores de Proteases/farmacologia , Solanum lycopersicum/enzimologia , Aminopeptidases/genética , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Leucil Aminopeptidase/efeitos dos fármacos , Leucil Aminopeptidase/genética , Leucil Aminopeptidase/metabolismo , Solanum lycopersicum/efeitos dos fármacos , Solanum lycopersicum/genética , Solanum lycopersicum/metabolismo , Extratos Vegetais , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/enzimologia , Folhas de Planta/genética , Folhas de Planta/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , RNA de Plantas/genética , Plântula/efeitos dos fármacos , Plântula/enzimologia , Plântula/genética , Plântula/metabolismo , Estresse Fisiológico , Especificidade por Substrato , Fatores de Tempo , Regulação para CimaRESUMO
The effects of salinity (400 mM NaCl) on growth, biomass partitioning, photosynthesis, and leaf ultrastructure were studied in hydroponically grown plants of Aeluropus littoralis (Willd) Parl. NaCl produced a significant inhibition of the main growth parameters and a reduction in leaf gas exchange (e.g. decreased rates of photosynthesis and stomatal conductance). However, NaCl salinity affected neither the composition of photosynthesis pigments nor leaf water content. The reduction in leaf gas exchange seemed to correlate with a decrease in mesophyll thickness as well as a severe disorganisation of chloroplast structure, with misshapen chloroplasts and dilated thylakoid membranes. Conspicuously, mesophyll chloroplasts were more sensitive to salt treatment than those of bundle sheath cells. The effects of NaCl toxicity on leaf structure and ultrastructure and the associated physiological implications are discussed in relation to the degree of salt resistance of A. littoralis.