Interaction of genes and hormones associated with germination in onion seeds under accelerated aging conditions

Due to their limited storage longevity, onion seeds are more prone to deterioration compared to many other vegetable seeds. Understanding the mechanisms that enhance seed viability and delay deterioration is essential. This study investigated the effects of aging on germination, along with biochemical, physiological, and molecular attributes, in three Iranian onion seed populations: Horand, Kazerun, and Zargan. The seeds were exposed to different aging conditions, including a control (non-aged seeds), three and six days of accelerated aging, and one year of natural aging. A factorial experiment (3 × 4) was conducted in a completely randomized design with four replications to evaluate the effects of seed aging (control, 3-day and 6-day accelerated aging, and 1-year natural aging) on one onion cultivar (Zargan) and two landraces (Horand and Kazerun) collected from different climatic regions of Iran. Accelerated aging was performed at 40 °C and ~ 100% humidity. Germination traits, electrical conductivity, malondialdehyde (MDA), DPPH radical scavenging activity, total phenolic and flavonoid content, and endogenous levels of ABA and GA1 were measured. Gene expression (WRKY20, LIG4, GAI1, LOX2, NCED1, NCED5) was quantified using qRT-PCR. Data were analyzed by ANOVA and Duncan’s test using SAS and R software. The findings revealed that membrane damage, malondialdehyde (MDA), phenol, and abscisic acid (ABA) levels increased in all three populations (Horand, Kazerun, and Zargan) with the highest increases observed in the Kazerun lot. In Kazerun, MDA increased by up to 225% and ABA by up to 192% under 6-day aging compared to the control. Electrolyte leakage also rose sharply in Kazerun, reaching a 99% increase. In terms of seed viability, the germination percentage in Kazerun decreased significantly—by 28%, 54%, and 41% under 3-day, 6-day, and 1-year aging, respectively—while the reduction in Horand was more moderate, with only 12% under 1-year aging. DPPH radical scavenging activity decreased by 36% and flavonoid content by 49% in Kazerun after 6-day aging, which were more pronounced reductions than in Horand and Zargan. Aging significantly reduced GA1 levels in all seed populations, with the sharpest decrease observed in Kazerun (up to 55% after 6 days). Gene expression analysis showed that the expression of WRKY20, LOX2, NCED1, and NCED5 in Kazerun increased by up to 2.34-, 7.33-, 4.85-fold, and 164%, respectively, compared to the control. These increases were higher than those in Horand and Zargan. This study highlights the adverse effects of seed aging on onion seed quality, emphasizing the importance of both physiological traits and gene expression patterns in determining seed viability. The findings suggest that specific molecular markers and stress-responsive genes may serve as key indicators of seed deterioration. A better understanding of these mechanisms could contribute to the development of strategies for improving seed storage and extending seed longevity in onion and other crops. Further integrative research combining physiological, biochemical, and molecular approaches is recommended to elucidate the complex regulatory networks involved in seed aging.