Spatiotemporal variations in salicylic acid and hydrogen peroxide in sunflower seeds during transition from dormancy...

Phytohormones and reactive oxygen species mediate processes such as germination and dormancy. The elucidation of the physiological and biochemical events implicated in the transition from dormancy to germination in different plant species such as sunflower becomes a topic of interest. In this study, we investigated the spatiotemporal variation of salicylic acid (SA), hydrogen peroxide (H₂ O₂ ) and the activity of two antioxidant enzymes (catalase, CAT - EC 1.11.1.6 and ascorbate peroxidase - EC 1.11.1.11) in embryonic axis and cotyledons of dry and imbibed seeds of dormant (B123) and non-dormant (B91) sunflower lines. The results showed that embryonic axis had higher level of SA and H₂ O₂ than cotyledons in both lines. In dry seeds, B123 embryo (embryonic axis + cotyledons) showed a higher SA content than B91. After dry storage at room temperature, SA decreased in B123 embryos to a value close to that registered in B91 embryos. B123 embryonic axis of dry seeds presented higher H₂ O₂ levels than B91. Dry storage led to an increase of H₂ O₂ levels and a decrease of CAT activity in B123 embryonic axis. During imbibition, B123 seeds stored for 33 days displayed an increase in SA level in the embryonic axis (3 h of imbibition) and this lower level correlated with a decrease in H₂ O₂ (6 h of imbibition). Thus, the embryo-imposed dormancy in B123 dry seeds was associated with high levels of SA and low H₂ O₂ , whereas the dormancy release was linked with SA decrease and increase of H₂ O₂ as a consequence of lower CAT activity.