Enhancing salt tolerance in Carthamus tinctorius L. using cold plasma and melatonin: Insights from growth, biochemical, and anatomical responses

Abstract

Global climate change exposes crops to abiotic and biotic stressors, threatening growth and yield. Salinity is a significant abiotic stress, affecting crop productivity and stability. Although the individual roles of cold plasma (CP) and melatonin (MT) in enhancing stress tolerance have been studied, their synergistic effects under salinity stress remain largely unexplored, particularly in Carthamus tinctorius L. (safflower). This study addressed this gap by evaluating the combined application of CP and MT to improve plant resilience under saline conditions. Seeds were primed with CP (90 s), followed by foliar application of MT (100 µM), to assess their influence on plant resilience in conditions of salt stress (0, 60, and 120 mM NaCl). Salt stress markedly impaired water relations and compromised cell membrane integrity, evidenced by reduced relative water content (RWC) and increased electrolyte leakage (EL). Conversely, plants treated with a combination of CP and MT exhibited enhanced RWC and diminished EL, indicating improved cellular stability. Salinity stress resulted in elevated levels of unsaturated fatty acids, while levels of saturated fatty acids decreased significantly. In addition, salinity increased stomatal density while decreasing stomatal size. Co-application of CP and MT mitigated salt-induced damage at 120 mM NaCl by promoting increases in growth factors (approximately 25 %), stomatal length (19.04 %), and width (16.66 %). Additionally, this combined treatment enhanced chlorophyll a (23.97 %), chlorophyll b (24.8 %), total chlorophyll (25.28 %) content, total phenolics (10.57 %), and flavonoids (21.42 %), while reducing stomatal density (11.29 %) and limiting malondialdehyde accumulation by 22.98 %. These findings highlight, for the first time, the synergistic role of CP and MT in improving salinity tolerance in safflower, filling a critical knowledge gap and suggesting a promising strategy for enhancing crop resilience under saline environments.