Change in root apical protein and peroxidase activity in response to aluminum in tolerant and sensitive maize inbred lines

Abstract

The effects of a short-term (80 min) exposure to 222 μM aluminum (A1) on the protein content and expression and on peroxidase activity and isoenzymes in the primary root of maize were evaluated. Two inbred lines differing in their level of tolerance to A1 were used: Cateto 237 (tolerant) and L36 (sensitive). The apical 20 mm of the primary root was divided into 2-mm-long segments that were analyzed for total protein content and peroxidase activity. These results demonstrate that the total protein content along the root apex was not affected by A1 in the tolerant inbred line, but decreased in the sensitive line. In the apical 2 mm of the root of the sensitive line, the expression of low molecular weight proteins (43 kDa or smaller) was decreased. Expression of low molecular proteins increased in the tolerant inbred line, even though total protein content did not increase. This suggests that some of these proteins could play a role in metal tolerance, perhaps as binding peptides. While the peroxidase activity of the tolerant inbred line did not change with exposure to A1, peroxidase activity in the apical 6 mm of the root of the sensitive line decreased. The tolerant inbred line constitutively expressed more anionic peroxidase isoforms. These results demonstrate that maintenance of protein expression may be an important component of the plant's resistance to A1 stress, and that resistance to A1 stress is associated with the higher expression of anionic peroxidase isoforms.