Effects of exogenous application of abscisic acid and melatonin on biochemical and molecular traits of Salicornia europaea under salinity stress

Abstract

Abstract Salinity is a major factor limiting agricultural lands that causes adverse effects on plant growth and production. The use of exogenous compounds or growth regulators has often been effective in reducing the effects of environmental stresses and/or identifying stress-coping mechanisms in plants. Among 1560 halophytes, Salicornia europaea is known as a salt-tolerant species. This study aimed to understand the effects of the endogenous application of abscisic acid (ABA) and melatonin hormones and their combined effects on mechanisms involved in plant resistance to salinity stress to identify these mechanisms, genes associated with ion channels, and antioxidant enzymes involved in response to stress using real-time technology. S. europaea metabolism compounds, namely hydrogen peroxide (H2O2), malondialdehyde, proline, phenol, sodium, potassium, and calcium were studied in control plants and under 400 mM salinity stress at 0, 6, 48, and 720 h (1 month) intervals. The best effects in terms of morphological, biochemical, and molecular traits were observed in spraying with both hormones at 400 mM salinity. This treatment reduced polyphenol oxidase activity, malondialdehyde content (by 35%), and H2O2 content, while it increased shoot (2.04 times) and root (76%) wet weights, shoot dry weight (2.45 times), K (by 19%) and Ca (by 79%) contents, and the Na/K ratio (by 30%). ABA spraying elevated catalase activity at 400 mM salinity. Spraying treatments led to the overexpression of SOD (by 21 times), SOS1 (by 1218 times), NHX1 (by 16 times), APX (by 214 times), HKT1 (by 470 times), and VHA-A (by 27 times) genes in some treatments compared to NT plants. The rapid response to stress is the main difference between stress-sensitive and tolerant plants. Spraying treatments resulted in elevated overexpression of genes involved in stress-responding mechanisms at early hours of salinity stress compared to control treatments, thereby increasing the tolerance of S. europaea to salinity stress.