Amount and activity changes of 20S proteasome modified by oxidation in salt-treated wheat root tips

To study the response of 20S proteasome in wheat (Triticum aestivum L.) roots to salt stress, the root tips from wheat seedlings treated with 200 mM NaCl for different times were used for studying its carbonyl level, caseinolytic activity, protein abundance and other biochemical characteristics. The contents of carbonylated and ubiquitinated proteins (Ub-P) were also investigated. During this stressed process, both the productive rate of O-2 (-) and the content of H2O2 gradually increased, with the concomitant increase in carbonyl level of total soluble proteins and 20S proteasome, together with the gradual increase in the activities of the total and 20S proteasome in salt-treated root tips. However, the amounts of 20S proteasome decreased particularly during this process. Moreover, metal-catalyzed oxidation of proteins from control plants in vitro validated that the oxidative modification also could increase the activity of 20S proteasome, but decrease its abundance. In addition, the amounts of Ub-P with molecular weights above 35 kDa remained similar to the control plants, but that below 35 kDa decreased significantly in treated root tips. The changes in the proteasome activity and amount argue in favor of the active involvement of this proteolytic system in salt-stressed plants.