Beneficial Effects of Exogenous Melatonin on Overcoming Salt Stress in Sugar Beets (Beta vulgaris L.)

Abstract

Melatonin has been regarded as a promising substance that enhances the abiotic stress tolerance of plants. However, few studies have devoted attention to the role of melatonin in improving salt tolerance in sugar beets. Here, the effects of different application methods (foliar application (100 μM), root application (100 μM), and combined foliar and root application) of melatonin on the morphological and physiological traits of sugar beets exposed to salt stress were investigated. The results showed that melatonin improved the growth of sugar beet seedlings, root yield and sugar content, synthesis of chlorophyll, photosystem II (PS II) activity, and gas exchange parameters under salt stress conditions. Moreover, melatonin enhanced the capacity of osmotic adjustment by increasing the accumulation of osmolytes (betaine, proline, and soluble sugar). At the same time, melatonin increased the H+-pump activities in the roots, thus promoting Na+ efflux and K+ influx, which maintained K+/Na+ homeostasis and mitigated Na+ toxicity. In addition, melatonin strengthened the antioxidant defense system by enhancing the activities of antioxidant enzymes, modulating the ASA-GSH cycle, and mediating the phenylalanine pathway, which removed superoxide anions (O2•−) and hydrogen peroxide (H2O2) and maintained cell membrane integrity. These positive effects were more pronounced when melatonin was applied by combined foliar and root application. To summarize, this study clarifies the potential roles of melatonin in mitigating salt stress in sugar beets by improving photosynthesis, water status, ion homeostasis, and the antioxidant defense system.

Synergistic Effects of Salicylic Acid and Melatonin on Modulating Ion Homeostasis in Salt-Stressed Wheat (Triticum aestivum L.) Plants by Enhancing Root H+-Pump Activity

“…An increase in root H + -pump activity could increase Na + exclusion and increase K + uptake [ 12 ]. Strong evidence has demonstrated that MT increases the root H + -pump activity, thereby promoting Na + efflux and K + influx as well as maintaining the K + /Na + ratio [ 34 ]. The observed increases in H + -ATPase activity caused by SA and MT could be attributed to the fact that SA and MT may operate directly as an antioxidant to scavenge ROS or indirectly by triggering antioxidant responses [ 9 , 19 , 21 ] ( Table 2 and Figure 6 a–c).…”

Regulation of Reactive Oxygen Species and Antioxidant Defense in Plants under Salinity

“…Chen et al [136] also reported that seed priming with MT reduces the accumulation of H2O2 and MDA and the percentage of EL and enhances the germination rate under salt stress conditions. Furthermore, Zhang et al [137] observed that both foliar and root application of MT (100 µM) increased SOD, POD, CAT and APX activities under salt stress and decreased H2O2, O2•− and MDA accumulation in Beta vulgaris. AsA content reduced by 70%, whereas an increase in GSH (305%) and GSSG (353%) contents was noticed.…”

Sustainable Biochar and/or Melatonin Improve Salinity Tolerance in Borage Plants by Modulating Osmotic Adjustment, Antioxidants, and Ion Homeostasis

“…Melatonin represents the earliest phylogenetic indole substance found in entire biota [ 9 , 13 , 28 ], at 0.1 pg g −1 (FW) to 20~30 µg g −1 (FW) [ 29 ]. Since 1995, it was initially detected in vascular plants, and the assimilation processes and metabolic occupations have been largely recognized [ 28 , 30 ]. This examination twisted the awareness for Mt as a potential efficient feature to motivate stress tolerance.…”

“…This examination twisted the awareness for Mt as a potential efficient feature to motivate stress tolerance. The Mt function in plants within a stressful environment is not completely implicit, and it introduces an enthusiastic calculation, whether it performs as an antioxidant and/or plant promoter [ 12 , 28 , 31 , 32 ]. The advantageous function of Mt in stress lessening is generally attributable to elevated photosynthesis, enhancement of redox homeostasis, mitigation of oxidative burst, and regulation of the stress-responsive gene expression implicated in signal transduction [ 9 , 11 , 30 ].…”