ETHYLENE BIOSYNTHESIS IN PEACH FRUITLET ABSCISSION

Ethylene biosynthesis was studied in the peach (Prunus persica L. Bats ch) fruitlet abscission zone (AZ), located between pedicel and pericar p and responsible for the shedding of the fruit, Explants, made up of the abscission layer and small parts of pedicel and pericarp, were flu shed with air or air + propylene (500 cm(3) m(-3)) for up to 72 h, Par ameters of ethylene biosynthesis were monitored in excised zone and no n-zone tissues. Both treatments induced an increase of ethylene biosyn thesis in all tissues examined and a climacteric-like behaviour was ob served: ethylene evolution peaked at 12 and 48 h in air + propylene an d 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 pr oduction, ACO activity and mRNA accumulation was in general observed m oving from the distal (pericarp side) to the proximal (pedicel side) n on-zone, through the abscission zone. The content of 1-aminocyclopropa ne-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 mal l hydrolase involved in cell separation, appeared to be up-regulated b y propylene and its activity was almost exclusively confined to the ab scission layer, Similarly, EG transcript accumulation occurred in zone but not in non-zone tissues. In air-treated and air + propylene-treat ed explants the ethylene climacteric preceded the increase of EG activ ity and the cell separation at the level of the abscission zone.