Salinity Stress Alters the Secondary Metabolic Profile of M. sativa, M. arborea and Their Hybrid (Alborea)

Abstract

Increased soil salinity, and therefore accumulation of ions, is one of the major abiotic stresses of cultivated plants that negatively affect their growth and yield. Among Medicago species, only Medicago truncatula, which is a model plant, has been extensively studied, while research regarding salinity responses of two important forage legumes of Medicago sativa (M. sativa) and Medicago arborea (M. arborea) has been limited. In the present work, differences between M. arborea, M. sativa and their hybrid Alborea were studied regarding growth parameters and metabolomic responses. The entries were subjected to three different treatments: (1) no NaCl application (control plants), (2) continuous application of 100 mM NaCl (acute stress) and (3) gradual application of NaCl at concentrations of 50-75-150 mM by increasing NaCl concentration every 10 days. According to the results, M. arborea maintained steady growth in all three treatments and appeared to be more resistant to salinity. Furthermore, results clearly demonstrated that M. arborea presented a different metabolic profile from that of M. sativa and their hybrid. In general, it was found that under acute and gradual stress, M. sativa overexpressed saponins in the shoots while M. arborea overexpressed saponins in the roots, which is the part of the plant where most of the saponins are produced and overexpressed. Alborea did not perform well, as more metabolites were downregulated than upregulated when subjected to salinity stress. Finally, saponins and hydroxycinnamic acids were key players of increased salinity tolerance.

Quercus suber Roots Activate Antioxidant and Membrane Protective Processes in Response to High Salinity

“…In addition, the increase in the activities and gene expression of SOD, CAT, APX, POX, and glutathione reductase (GR) in Hordeum vulgare roots five days after a treatment with 200 mM NaCl was correlated with H 2 O 2 detoxification [38]. The accumulation of secondary metabolites, such as saponins and lignans that have antioxidant capacity, in Medicago sativa and Medicago arborea roots exposed to 100 mM NaCl for 10 days increased salt stress tolerance [39]. In Olea europaea, long exposure of roots to 75 and 100 mM NaCl induced the accumulation of polyphenols and the increase of TAA, which was related to protection against salinity stress [40].…”

Metabolomics and Chemoinformatics in Agricultural Biotechnology Research: Complementary Probes in Unravelling New Metabolites for Crop Improvement

“…In contrast, the secondary metabolism provides specialized metabolites that facilitate the salinity stress response through such mechanisms as antioxidant synthesis pathways for ROS scavenging and the reduction of oxidative damage [ 57 , 86 ]. A recent Fourier transform mass spectrometry LTQ orbitrap (FTMS)-based metabolomics study by Sarri and colleagues [ 89 ] found that secondary metabolites from saponins and hydroxycinnamic acids play a significant role in increased salinity-stress tolerance in Medicago sativa and Medicago arborea species. Similar findings were reported by Cai and co-workers [ 90 ], who found differential accumulation of secondary metabolites in salt-stressed plants compared to controls as determined through an HPLC-triple TOF-MS/MS.…”

Saponin Biosynthesis in Pulses

“…Increased accumulation of saponin was observed in the leaves of Quillaja brasiliensis when exposed to abiotic elicitors such as salicylic acid, jasmonic acid, UV light and mechanical damage [73]. Furthermore, saponins might play a key role in plant salinity tolerance [74]. With inevitable climate changes in the frequency and severity of drought, further research is necessary to unravel the molecular mechanism of saponin fluctuation in response to environment changes, leading to tolerance toward stressors.…”