Lipoic acid (LA) and melatonin (MT) are pleiotropic molecules participating in plant stress resistance by modulating cellular biochemical changes, ion homeostasis, and antioxidant enzyme activities. However, the combined role of these two molecules in counteracting the detrimental impacts of salinity stress is still unknown. In the present study, we determined the effects of exogenous LA (0.5 µM), MT (1 µM) and their combination (LA + MT) on growth performance and biomass accumulation, photosynthetic pigments, enzymatic and non-enzymatic antioxidant activities, and ions homeostatic in canola (Brassica napus L.) seedlings under salinity stress (0, 100 mM) for 40 days. The results indicate that exogenous application of LA + MT improved the phenotypic growth (by 25 to 45%), root thickness (by 68%), number of later lateral roots (by 52%), root viability (by 44%), and root length (by 50%) under salinity stress. Moreover, total soluble protein, chlorophyll pigments, the concentration of superoxide dismutase (SOD), catalase peroxidase (CAT), and ascorbic peroxidase (ASA) increased with the presence of salt concentration into the growth media and then decreased with the addition of LA + MT to saline solution. Leaf protein contents and the degradation of photosynthetic pigments were lower when LA + MT treatments were added into NaCl media. The proline and phenol contents decreased in the exogenous application of LA + MT treatments more than individual LA or MT treatments under the salinity stress. The incorporation of LA or MT or a combination of LA + MT to saline solution decreased salinity-induced malondialdehyde and electrolyte leakage. In conclusion, the alteration of metabolic pathways, redox modulation, and ions homeostasis in plant tissues by the combined LA and MT application are helpful towards the adaptation of Brassica napus L. seedlings in a saline environment. The results of this study provide, for the first time, conclusive evidence about the protective role of exogenous LA + MT in canola seedlings under salinity stress.

Crop Science Group Institute of Crop Science and Resource Conservation University Bonn 53113 Bonn Germany

Department of Agronomy Bahauddin Zakariya University Multan 60000 Pakistan

Department of Agronomy College of Agriculture University of Sargodha Sargodha 40100 Pakistan

Department of Agronomy Faculty of Agriculture University of Kafrelsheikh Kafr el Sheikh 33516 Egypt

Department of Agronomy Muhammad Nawaz Shareef University of Agriculture Multan 60000 Pakistan

Department of Biology College of Science Taif University P O Box 11099 Taif 21944 Saudi Arabia

Department of Botany and Plant Physiology Faculty of Agrobiology Food and Natural Resources Czech University of Life Sciences Prague 16500 Prague Czech Republic

Department of Environmental Sciences COMSATS University Islamabad Vehari Campus Vehari 61100 Pakistan

Department of Plant Physiology Slovak University of Agriculture 94901 Nitra Slovakia

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