Responses of phytochelatin and proline-related genes expression associated with heavy metal stress in Solanum lycopersicum

The expression of stress related-genes against adverse environmental conditions has essential importance for plants. This study, using RT-qPCR, determined the expression of P5CS and PCS genes to investigate their roles in the leaves of tomato plants grown under heavy metal conditions. The expression of the PCS1 gene is significantly induced under such conditions. Transcript expression of P5CS I, a gene responsible for proline synthesis, changed depending on heavy metal doses; treatments of Cu (20 and 50 ppm), Cd and Pb (10 and 20 ppm) remarkably increased P5CS1 expression. However, the P5CS1 gene expression at 10 ppm dose of Cu and 50 ppm doses of Pb and Cd was not significantly different from that in control plants. The metal-chelating potency of the extract of tomato leaves exposed to Pb and Cd was higher than that of untreated plants. The proline content as assessed in the leaves of stressed plants was significantly increased by applications of 10 and 20 ppm of Cd and Pb, and high doses of Cu. In addition, the results showed that the proline content had a positive correlation with the P5CS1 gene expression in tomato leaves under application of these tree heavy metals and that there was a positive relation between the PCS1 gene expression and metal-chelating ability of Cd-stressed plants.