Breaking the apple embryo dormancy by nitric oxide involves the stimulation of ethylene production

Mature seeds of apple (Mallus domestica Borb. cv. Antonowka) are dormant and do not germinate unless their dormancy is removed by several weeks of moist-cold treatment. We investigated the effect of short-term (3 h) nitric oxide (NO) pretreatment on breaking of apple embryonic dormancy expressed as inhibition of germination and morphological abnormalities of young seedlings. Imbibition of embryos isolated from dormant apple seeds with sodium nitroprusside (SNP) or S-nitroso, N-acetyl penicillamine ( SNAP) as NO donors resulted in enhanced germination. Moreover, NO treatment removed morphological abnormalities of seedlings developing from dormant embryo. The NO scavenger 2-(4-carboxyphenyl)4,4,5,5- teramethylimidazoline-1-oxyl-3 oxide (cPTIO) removed the above effects. NO-mediated breaking of embryonic dormancy correlated well with enhanced ethylene production. Inhibitor of ethylene synthesis (AOA) reversed the stimulatory effect of NO donors on embryo germination. Additionally SNP reduced embryo sensitivity to exogenously applied ABA ensuing dormancy breakage. We can conclude that NO acts as a regulatory factor included in the control of apple embryonic dormancy breakage by stimulation of ethylene biosynthesis.