Lipoic acid can provide homeostasis of reactive oxygen species and induce ascorbate and glutathione biosynthesis in osmotic stressed maize

Abstract

Abstract Lipoic acid (LA), an incomparable antioxidant compound, can stimulate antioxidant defense system in plants subjected to abiotic stresses. Here, we aimed to determine the relation between LA, reactive oxygen species (ROS) and biosynthesis of ASC and GSH in osmotic stressed maize seedlings. ROS, ASC and GSH levels were diminished by using N, N’-dimethylthiourea (DMTU), a ROS scavenger, acriflavine (AF), an inhibitor of ASC biosynthesis and L-buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis, respectively. The seedlings were grown in pots containing Hoagland Nutrient solution for 21 days. The pots were divided into nine groups consisting of a non-stressed group (NS), Mock (PEG alone), LA free DMTU, BSO and AF treatments and LA combined Mock, DMTU, BSO and AF treatments under PEG-induced osmotic stress. ROS content of the LA combined DMTU treatment did not return to the content of NS treatment and there were moderate reductions in ROS contents of the LA combined treatments. LA, GSH and ASC contents and the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR)) reduced when ROS, GSH and ASC levels were decreased by the scavenger and inhibitors. However, LA combined scavenger and inhibitor treatments alleviated all these reductions. Additionally, the relative expression levels of SOD, CAT1 and APX1 genes were consistent with the findings of the antioxidant enzyme activities. These results revealed that lowering ROS, GSH and ASC levels causes the decrease in LA content deteriorating the ROS homeostasis in osmotic stressed maize. Exogenous LA can provide ROS homeostasis and thus induce ASC and GSH biosynthesis to strengthen the antioxidant defense system.