Priming with L-arginine reduces oxidative damages in Carthamus tinctorius seedlings under the toxic levels of lead

Lead (Pb) stress adversely affects plant nutrient homeostasis and metabolism when present at an elevated concentrations in the surrounding media. In this research, the effects of 1mM Pb(NO3)2 on 14-day-old Carthamus tinctorius seedlings pretreated with arginine (Arg) as nitric oxide (NO) precursor, methylene blue (MB), a nitric oxide scavenger and Nω-nitro-L-Arg-methyl ester (LNAME) and a nitric oxide biosynthetic inhibitor, were investigated in the greenhouse of the Department of Biology, Shahid Bahonar University of Kerman, Iran. Pb exposure caused oxidative stress, reduced root and shoot growth and elevated malondialdehyde (MDA) content of the seedlings. Pb stress also increased the ascorbate peroxidase activity while decreasing the activity of the catalase (CAT) enzyme. Arg pretreatment decreased the harmful effects of Pb stress by increasing the root and shoot length and reducing the MDA content. Additionally, Pb-induced reduction of CAT enzyme activity in roots was reversed by the Arg pretreatment of the plants. In many characteristics which we measured, the effects of Arg pretreatment on alleviation of Pb-induced oxidative stress were reversed by LNAME and methylene blue pretreatments. Therefore, it seems that Arg induces a positive effect through NO production. Data showed that in the presence of Arg, the uptake and translocation of Pb declined and the application of Arg with LNAME or MB reversed these positive effects of Arg.  It seems that Arg can alleviate lead toxicity in plants through the prevention of Pb uptake and promoting the direct scavenging of reactive oxygen species or activating antioxidant enzymes. Also, results from the use of LNAME and MB indicated that the positive effect of Arg is probably related to its role in NO production.