Priming-induced metabolic changes in sunflower (Helianthus annuus) achenes improve germination and seedling growth

Seed priming improves vigor, but priming agents may differ greatly in their effectiveness. The present study was performed to unravel the physiological basis of vigor improvement by priming sunflower achenes with pre-optimized levels of hydrogen peroxide (H₂O₂), salicylic acid (SA), thiourea (TU), gibberellic acid (GA₃), ascorbic acid (AA), sodium chloride (NaCl), freezing and heating. Most of the treatments induced de novo synthesis of peptides with low (37 kDa for H₂O₂, SA and NaCl treatments, and 57 kDa for SA and TU treatments) and high (157 kDa for H₂O₂, SA, TU, GA₃ and AA treatments and 167 kDa for SA treatment) molecular mass, reduced solute leakage, and an enhanced soluble sugar pool in the achenes. Priming reduced days to 50% germination (T₅₀) and mean germination time (MGT) and improved germination energy (GE) and final germination percentage (FGP). Shoot length was improved by priming with H₂O₂, GA₃, and NaCl; root length with NaCl and H₂O₂; shoot and root dry weight with H ₂O₂, SA and AA. Positive correlations between GE and FGP and expressed peptides, soluble sugars, shoot and root length, and dry weight and negative ones with EC of leachate suggested that pre-germination changes in primed achenes, in addition to improve germination, show lasting effects in promoting seedling growth. Of the treatments, H₂O₂, SA, TU and GA₃ were the most effective. Overall, the effects of priming treatments are related to de novo protein synthesis, an improved repair mechanism, and germination substrates for vigorous and earlier production of seedlings.