Praseodymium enhanced the tolerance of maize seedlings subjected to cadmium stress by up-regulating the enzymes in the regeneration and biosynthetic pathways of ascorbate and glutathione

Abstract

To test whether praseodymium (Pr) regulates cadmium (Cd) tolerance, we explored the effects of Pr on enzymatic activities in the regeneration and biosynthetic pathways of ascorbate and glutathione in maize seedlings under Cd stress. The findings demonstrated that Cd stress increased enzymatic activities in the regeneration pathway (ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR)) and in the biosynthetic pathway of ascorbate and glutathione (γ-ECS and GalLDH), as well as ascorbate (AsA) and glutathione (GSH) contents. However, Cd stress significantly decreased AsA/dehydroascorbic acid (DHA) ratio and GSH/oxidised glutathione (GSSG) ratio, net photosynthetic rate (P<sub>n</sub>), chlorophylls (Chl) and carotenoids (Car) contents, maximum photochemical efficiency of PSII (F<sub>v</sub>/F<sub>m</sub>), photochemical quenching (qP) and quantum efficiency of PSII photochemistry (Φ<sub>PSII</sub>), as well as plant height and biomass. Application of Pr to Cd-stressed seedlings enhanced above enzymatic activities, AsA and GSH contents, AsA/DHA and GSH/GSSG ratios, P<sub>n</sub>, Chl and Car contents, F<sub>v</sub>/F<sub>m</sub>, qP and Φ<sub>PSII</sub>, as well as plant height and biomass. Meanwhile, the application of Pr to Cd-stressed seedlings reduced malondialdehyde (MDA) content and electrolyte leakage. The above results indicated that Pr enhanced Cd tolerance of maize by up-regulating enzymatic activities in regeneration and biosynthetic pathways of ascorbate and glutathione.