Ion Content, Antioxidant Enzyme Activity and Transcriptional Response Under Salt Stress and Recovery Condition in the Halophyte Grass Aeluropus Littoralis
Authors: Hashemi-Petroudi Seyyed Hamidreza , Ahmadian Gholamreza , Fatemi Farzaneh , Nematzadeh Ghorbanali , Yamchi Ahad , Kuhlmann Markus 
Published: August 2020

Abstract
Background: The production of reactive oxygen species (ROS) is a common feature of various plant cells in dealing with abiotic stresses. Plants have developed an effective enzymatic and non-enzymatic antioxidant defense systems to scavenge ROS and cope with oxidative stress. Halophyte antioxidant defense mechanisms represent one of the best examples for this trait. Several of salt-responsive promoters and genes originated here during evolution. The present work aimed to investigate a set of physiological, elemental, biochemical and molecular responses involved in tolerance to salt stress in the halophyte grass Aeluropus littoralis. Results: The content of total Chlorophyll (Chl), Chl a and Cars were increased under salinity condition, while the Chl b content was reduced. Sodium ion (Na+) in three time-points of salinity condition (S1, S2 and S3) significantly increased, and reduction was observed in three time-points of recovery condition (R1, R2 and R3). The amount of potassium ions (K+) in leaf and stem was decreased during salt stress, and increased during recovery condition. K+ accumulations in root significantly increased in S2 and S3. Calcium (Ca2+) and magnesium (Mg2+) content significantly declined in leaf, root and stem during stress treatment, whereas it increased significantly during recovery condition in the leaves. The amount of the amino acid proline, associated with drought and salt stress, as well as the activity of ROS related enzyme showed an increase during salt treatment. The APX, POD and SOD maximum activities were reported at S3 in roots while decreased at R. RT-qPCR analysis of antioxidant related genes showed up-regulation at S1 and S3 in root, but the down-regulation was observed in R. The highest transcription levels were observed in CAT and pAPX at S1 in leaf, while the maximum levels were seen in SOD and cAPX at S2.Conclusions: The halophyte mechanisms in A. littoralis, contribute to overcome ROS in oxidative stress. SOD activity was more responsive in S, indicating the importance of SOD in oxidative damage. Increasing proline content may be considered as a stress-induced marker to identify oxidative damage. During the salt stress phase an increase of mRNA abundance from genes encoding enzymes assiciated with atioxidant activities was found. The positive correlation between the transcript level of CAT and CAT activities in leaf indicated the important regulatory function during salt stress for detoxifying ROS. Based on the transcript abundance and activity CAT is proposed as the main H2O2-scavenging enzyme to keep the balance of redox reaction in A. littoralis. The salt stress tolerance is associated with high Na+ absorbtion for osmotic balance and a corresponding reduction in K+, Mg2+, and Ca2+ ions. Further it was found that plants under S3 and R2 had more chlorophyll b content as compared to chlorophyll a that demonstrated optimization of leaf function under high salt condition.