Effect of methylglyoxal bis-(guanylhydrazone) on polyamine and ethylene biosynthesis of apple fruit after harvest

Polyamine and ethylene both play important roles in fruit ripening, whose biosynthetic pathways share a common substrate, S-adenosylmethionine (SAM). To unravel the interrelationship between polyamine and ethylene, their metabolism and expression of relevant genes were investigated in apple fruit (Malus domestica Borkh.) treated with methylglyoxal bis-(guanylhydrazone) (MGBG). The MGBG-treated fruit had higher ethylene production until 16 days after treatment (DAT) with preceding accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC) than control fruit and then decreased to nearly the same level as control. Ethylene promotion at the early stage by MGBG was accompanied by increased expression of apple ACCsynthase (Md-ACS1) and ACC oxidase (MdACO). The expression of apple SAM synthase (MdSAMS) in MGBG-treated fruit was slightly higher than that in control. On the other hand, significant changes in free polyamine titers were observed at some stages, but the changes did not show consistent trends. Based on these observations, possible relationship between polyamine and ethylene pathways was discussed.