Unraveling ZnO-NPs priming–driven salt tolerance in germinating castor seeds via integrated lipidomic and transcriptomic analyses

Castor (Ricinus communis) is a globally important oilseed crop whose germination is highly sensitive to soil salinity. We assessed whether 24 h priming with 1000 mg L⁻¹ ZnO-NPs (Z2) enhances salt tolerance compared to unprimed controls (Z1) under 0–150 mM NaCl (S1–S4). Under 100 mM NaCl (S3), Z2 seeds displayed a cumulative germination percentage nearly 1.5-fold higher than the control and a 26.1 % reduction in malondialdehyde (MDA) content. Lipidomic profiling revealed ZnO-NPs priming stabilized membrane fluidity by elevating phosphatidylcholine (PC), phosphatidic acid (PA), phosphatidyl ethanolamine (PE), phosphatidylglycerol (PG), and lysophosphatidylcholine (LPC) levels and increasing overall lipid unsaturation. Transcriptomic analysis identified 349 differentially expressed genes between (Z2, S3) and (Z1, S3), and integrated pathway analysis demonstrated upregulation of “glyoxylate and dicarboxylate” and “starch and sucrose” metabolism to drive lipid-to-carbohydrate conversion. Key lipase, nonspecific lipid transfer proteins (nsLTPs), and oleosin genes were also induced, and MAPK signaling was enhanced, to sustain germination vigor under salt stress. These dual mechanisms—antioxidant-mediated membrane protection and transcriptome-guided regulation of metabolic pathways—underscore the potential of ZnO-NPs priming to enhance castor seed resilience under salt stress.