Tolerance or sensitivity responses of Mentha pulegium to osmotic and waterlogging stress in terms of antioxidant defense systems and membrane lipid peroxidation

This study investigated the changes in the antioxidants (Car, AsA), enzymatic antioxidant system (SOD, CAT, PODs), and lipid peroxidation levels of Mentha pulegium leaves with respect to incubation period under gradual osmotic and waterlogging stress conditions. Compared to the control levels, it was seen that, under both stress conditions, the relative leaf water, chlorophyll, and ascorbate contents were lower whereas carotenoid contents were higher. Osmotic stress generally activated all of the investigated antioxidant enzymes depending on the severity of stress. As implied by the strong positive correlation between the SOD and CAT under the high osmotic stress conditions, both activities increased by approximately a 2-fold on the 6th day. The activities of the SOD, CAT, and PODs enzymes were lower in comparison to the control levels under the waterlogged stress conditions. LPO levels increased a 2-fold for osmotic stress and a 4-fold for waterlogging stress on the 8th day. As extracted from data, it seems likely that both CAT and SOD work in a concerted way under osmotic stress as well as both studied peroxidases, which might probably act as first line against abiotic stress-induced ROS production. In addition, the profile described for CAT and SOD enzyme activities could be associated to a higher stress pressure. Consequently, the positive antioxidant response in M. pulegium might be responsible for higher tolerance to osmotic stress, whereas under waterlogging stress, the early accumulation of MDA seems to be associated to an impaired ability for radical scavenging.

► Mentha plants respond to osmotic stress increasing their antioxidant activity.
► The strong positive correlation was observed between SOD and CAT under the high osmotic stres.
► The LPO levels increased by about a 4-fold under waterlogging stress.