Effects of molybdenum stress on antioxidant system performance of parsley seedlings (Petroselinum sativum L.) under laboratory condition

Since agricultural soils in many parts of the world are contaminated with varying amounts of heavy metals, heavy metal stress is one of the major issues in these areas that can have a negative effects on crop production. In this study, the effect of different levels of molybdenum [Control (C: 1.9 µM), C+0.5, C+2.5, C+5, C+10 µM sodium molybdate] was evaluated on the growth and function of enzymatic and non-enzymatic antioxidant system of parsley at seedling stage. The results showed that although the molybdenum stress decreased dry weight and length of both plant parts (shoot and root) as well as membrane stability index and relative water content, it had an increasing effect on proline (150% increase in proline content of shoot compared to control) and phenolic compounds (80% and 85% increase in phenolic content of shoot and root, compared to control). The activity of antioxidant enzymes catalase, benzidine peroxidase, ascorbate peroxidase and polyphenoloxidase was also increased under molybdenum stress. Therefore, it may be concluded that parsley seedlings try to "tolerate" the stress condition of molybdenum heavy metal at this physiological-growth stage by partially reducing the growth process and, in turn, enhancing its antioxidant defense systems.