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.

Proteolytic activities in Phaseolus vulgaris cotyledons under copper stress

“…The obtained data confirm numerous reports that endoprotease classes are sensitive to the action of abiotic and biotic stresses, especially heavy metal exposure (Djebali et al 2007;Domash et al 2008).…”

“…The physiological significance of the increase in SP activity under copper exposure (Fig. 5) could be related to the activation of protective mechanisms under stress conditions, promoting the survival of plants (Pál et al 2006;Ahsan et al 2007;Boojar and Goodarzi 2007;Djebali et al 2007;Domash et al 2008). This is possible for multifunctional SP which has been found to be involved in several physiological processes, such as senescence, programmed cell death, infection of plant cells, pathogenesis in virus-infected plants, and germination .…”

“…Moreover, plant cells exhibit increased proteolysis during exposure to oxidative stress-inducing agents; proteins are modified, selectively recognized and degraded by proteolytic systems (Vierstra 1996). Particularly, proteolysis represents an important component together with protein oxidation in oxidative stress situations induced by heavy metals Djebali et al 2007). However, although global endoproteolytic activities can change in response to heavy metal stress Pena et al 2006;Djebali et al 2007), they are probably not representative of either the modification of proteolytic machinery, or the whole protein turnover.…”

“…Particularly, proteolysis represents an important component together with protein oxidation in oxidative stress situations induced by heavy metals Djebali et al 2007). However, although global endoproteolytic activities can change in response to heavy metal stress Pena et al 2006;Djebali et al 2007), they are probably not representative of either the modification of proteolytic machinery, or the whole protein turnover. Indeed, the present work shows that AP, CP, MP and SP activities were differently modified.…”

Evidence for the Existence in Arabidopsis thaliana of the Proteasome Proteolytic Pathway

“…Both the 20 S and 26 S proteasomes were characterized at molecular (21,22) and biochemical levels (23) in Arabidopsis thaliana. As observed in animal and yeast cells, plant proteasome has been found to be up-regulated, at transcriptional or translational levels, in oxidative conditions such as carbon starvation (24) or cadmium stress (25)(26)(27)(28), and its involvement in the response to oxidative stress has been postulated. In plants, the preferential involvement of the 20 S proteasome in the degradation of oxidized proteins was recently supported by in vivo experiments using A. thaliana mutants (29).…”