Proteomic and enzymatic response of poplar to cadmium stress.

This study highlights proteomic and enzymatic changes in roots and leaves of actively growing poplar plants upon a cadmium stress exposure. Proteomic changes in response to a short-term (14 days), as well as a longer term (56 days) treatment are observed between the different organs. In leaves, stress-related proteins, like heat shock proteins, proteinases and pathogenesis-related proteins increased in abundance. A response similar to a hypersensitive response upon plant-pathogen interaction seemed to be induced. Concerning roots it appeared that the metabolic impact of cadmium was more deleterious than in leaves. This is evidenced by the early increase in abundance of many typical stress-related proteins like heat shock proteins, or glutathione-S-transferases, while most proteins from the primary metabolism (glycolysis, tricarboxylic acid cycle, nitrogen metabolism, sulfur metabolism) were severely decreased in abundance. Additionally the impact of cadmium on the glutathione metabolism could be assessed by activity assays of several important enzymes. Cadmium treatment had an inhibitory effect on glutathione reductase and ascorbate peroxidase in leaves, but not in roots. Conversely, glutathione-S-transferase showed a higher activity (and abundance) in roots but not in leaves.

Combining proteomics and metabolite analyses to unravel cadmium stress-response in poplar leaves.

A proteomic analysis of poplar leaves exposed to cadmium, combined with biochemical analysis of pigments and carbohydrates revealed changes in primary carbon metabolism. Proteomic results suggested that photosynthesis was slightly affected. Together with a growth inhibition, photoassimilates were less needed for developmental processes and could be stored in the form of hexoses or complex sugars, acting also as osmoprotectants. Simultaneously, mitochondrial respiration was upregulated, providing energy needs of cadmium-exposed plants.

Quantitative changes in protein expression of cadmium-exposed poplar plants.

Cadmium (Cd) pollution is a worldwide major concern having, among others, deleterious effects on plants. In the present work, the effects of a 20 microM Cd exposure in hydroponics culture during 14 days were evaluated in young poplar leaves. Proteins were analysed by 2-D DIGE, followed by MALDI-TOF-TOF identification. Additionally, growth and other physiological parameters were monitored during the experiment. Treated plants exhibited an inhibition of growth and visual symptoms appeared after 7 days. A significant accumulation of Cd in all organs was recorded by ICP-MS analysis. A number of changes in the expression of proteins with various functions were identified; in particular a decreased abundance of oxidative stress regulating proteins, whereas pathogenesis-related proteins showed a drastic increase in abundance. Furthermore, a large number of proteins involved in carbon metabolism showed a decrease in abundance, while proteins involved in remobilizing carbon from other energy sources were upregulated. In conclusion, the negative effect of Cd could be explained by a deleterious effect on protein expression from the primary carbon metabolism and from the oxidative stress response mechanism. Accumulation of Cd in stems of poplar, coupled with a low impact of Cd on physiological parameters, promotes the use of poplar trees for phytoremediation purposes.