Relationship between endogenous free polyamine content and ethylene evolution during fruit growth and ripening of Japanese pear (Pyrus pyrifolia Nakai)

To clarify the relationship between free endogenous polyamines (PAs) and ethylene during growth and ripening of Japanese pear fruit, the evolutions of these compounds were monitored in seven cultivars with high, moderate and low levels of maximum ethylene production at ripening. Ethylene production at 12 and/or 25 days after full bloom (DAFB) reflected their potential at ripening. Moreover, a negative correlation between PAs and ethylene was present at 12 DAFB (r = -0.81, P < 0.01) and after harvest (r= -0.94, P < 0.01). Thus, young fruitlet (12 DAFB) and ripening fruit of 'Kikusui', 'Housui', 'Nijisseiki', and 'Niitaka' with high PAs contents evolved low to moderate amounts of ethylene, whereas 'Edoya', 'Ninomiya', and 'Awayuki' produced high levels of ethylene while possessing low PAs contents at those respective stages. After harvest, negative correlation between PAs and 1-aminocyclopropane-1-carboxylic acid (ACC) might suggest competition between PAs and ethylene via S-adenosylmethionine (SAM) because SAM is an intermediate for spermidine (SPD) and spermine (SPM) synthesis while contributing to the formation of ACC. Nevertheless, the higher correlation of ethylene with putrescine (PUT) than ethylene with SPD and SPM suggests that the competitive factor might not, by itself, explain the high free PAs content, especially of PUT, that is present in low and moderate ethylene producing cultivars. However, collectively, our results indicate that the balance between ethylene and PAs may control the ripening of Japanese pear fruit.