Serotonin application to Guizotia abyssinica improves growth, physiological functions, antioxidant system and alleviates the deleterious effects induced by salt stress

Serotonin is a well-known animal hormone and ubiquitous monoamine. In recent years, its presence in plants has attracted the attention of many researchers. In plants, serotonin as signaling hormone plays a pivotal role in hormonal crosstalk, regulating antioxidant metabolism and developmental processes under abiotic stresses. Among abiotic stresses, salt stress considerably influences Guizotia abyssinica growth and physio-chemical functions. The effect of exogenous serotonin was assessed to ameliorate the harmful effect of salinity stress at different levels. All the growth parameters, chlorophyll pigments, gas exchange indicators, and nitrate reductase activity were decreased under all salinity levels while 2-thiobarbituric acid reactive substances (TBARS), proline, and antioxidant activities were increased. Serotonin improved the length of roots and shoots, basal diameter, leaf number, area, width and length, root dry matter, stem dry matter, leaves dry matter, chlorophyll a, chlorophyll b, chlorophyll fluorescence, transpiration rate, stomatal conductance, photosynthetic rate, relative water content, water use efficiency, and nitrate reductase under salt stress condition. Moreover, the upregulation of antioxidant enzymes evoked by the salt stress was further enhanced. Taken together, salt stress inhibited the growth and performance of G. abyssinica, however, exogenous application of serotonin fortified its tolerance by mitigating membrane damage and improving assimilatory functions, plant water status and plant defense metabolism, thereby lowering the adverse effects of salt stress on various plant growth performance and physio-biochemical functions.