Partial alleviation of zinc induced oxidative stress by polyamines in Plantago ovata Forsk

Key message In this study we have demonstrated the alleviation of zinc-induced stress in Plantago ovata with the exogenous addition of polyamine and the effect of polyamine addition on the relative expression of Metallothionein type 2 in P. ovata. Zinc causes toxicity to the plants in an excess concentration and it is manifested by chlorosis, rolling of leaf margins, and disruption of membrane integrity. The heavy metal stress also triggers the stimulation of enzymatic and non-enzymatic antioxidant systems. Polyamines are naturally occurring, secondary metabolites, protecting plants from heavy metal-induced stress. Plants also up-regulate the mRNA expression of Metallothionein in response to heavy metal-induced oxidative stress. The alteration in Metallothionein type 2 (PoMT2) expression of a medicinally important herb Plantago ovata in presence of polyamines like Putrescine, Spermidine, and Spermine in addition to ZnSO4 center dot H2O by the semi-quantitative and the quantitative methods have been demonstrated in the present study. We have observed reductions in the expression of the Metallothionein type 2 gene in the presence of the aforementioned polyamines which implies their protective and antioxidant properties to fight against the zinc induced stress. 1 mM Put has been more efficient in increasing the total chlorophyll content (compared to 2 mM Put) by about 36% each in 1000 mu M ZnSO4 treated P. ovata seedlings. Spermidine also enhanced chlorophyll content. However, 2 mM Put and 0.5 mM Spm have shown better efficiency in increasing the total antioxidant and DPPH radical scavenging activities. The lipid peroxidation has been found to decrease in Put and Spm supplemented samples by up to about 47% in both cases. Significant reductions in lipid peroxidation and down-regulation of PoMT2 gene expression indicate the roles of polyamines in partially alleviating Zn-induced oxidative damage.