Seed priming with blue light and ethylene modulates responses to drought and heat stress in Moringa oleifera

Blue light strongly influences plant development, but its interaction with ethylene, a seed conditioning agent for abiotic stress tolerance, is poorly understood, especially for Moringa oleifera, a crucial crop in arid regions. This study aimed to evaluate whether conditioning seeds with blue light (PB) or a combination of blue light and ethylene (PBE) could mitigate the adverse physiological and biochemical effects of water deficit and high temperature in M. oleifera seedlings. We used a 2 × 2 × 3 factorial design (water level, temperature, conditioning). Combined water and heat stress significantly impaired gas exchange, photochemical efficiency, osmotic adjustment, and biomass accumulation. However, seedlings from seeds conditioned with PB showed significant tolerance. The biological mechanism underlying this resilience was associated with the maintenance of higher antioxidant activity (CAT in leaves, TSP in roots) and greater water use efficiency (WUE) in seedlings conditioned with PBE. Under moderate drought conditions (water stress without heat), conditioning with blue light alone (PB) was more effective, increasing carboxylation efficiency. Although all abiotic stresses increased cell membrane damage (electrolyte leakage), treatment with ethylene (PBE) mitigated the most severe damage by pre-activating these protective pathways. Conditioning seeds with a combination of blue light and ethylene (PBE) is a promising strategy to enhance Moringa oleifera's resilience to moderate drought by modulating antioxidant and photosynthetic pathways. However, the effectiveness of this conditioning decreased under severe combined heat and drought conditions, indicating a critical limitation of the treatment under extreme stress. Keywords: Moringaceae; Abiotic stresses; plant hormones; light spectrum; osmotic adjustment; antioxidant mechanism