Ethylene biosynthesis in peach fruitlet abscission

Ethylene biosynthesis was studied in the peach (Prunus persica L. Batsch) fruitlet abscission zone (AZ), located between pedicel and pericarp and responsible for the shedding of the fruit, Explants, made up of the abscission layer and small parts of pedicel and pericarp, were flushed with air or air + propylene (500 cm(3) m(-3)) for up to 72 h, Parameters of ethylene biosynthesis were monitored in excised zone and non-zone tissues. Both treatments induced an increase of ethylene biosynthesis in all tissues examined and a climacteric-like behaviour was observed: ethylene evolution peaked at 12 and 48 h in air + propylene and air, respectively. The activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO) and related transcript accumulation paralleled ethylene evolution. Furthermore a decreasing gradient, in terms of ethylene production, ACO activity and mRNA accumulation was in general observed moving from the distal (pericarp side) to the proximal (pedicel side) non-zone, through the abscission zone. The content of 1-aminocyclopropane-1-carboxylate (ACC) showed significant difference among treatments only at 12 h of air + propylene flushing in AZ3 and non-zones, but no difference in terms of ACC synthase transcript and related polypeptide accumulation was observed. Endo-beta-1,4-glucanase (EG), the cell mall hydrolase involved in cell separation, appeared to be up-regulated by propylene and its activity was almost exclusively confined to the abscission layer, Similarly, EG transcript accumulation occurred in zone but not in non-zone tissues. In air-treated and air + propylene-treated explants the ethylene climacteric preceded the increase of EG activity and the cell separation at the level of the abscission zone.