Ethylene biosynthesis in peach seed and fruit tissues

Mesocarp and epicarp ethylene evolution was high during early development then it dropped to a basal level, maintained until the onset of the climacteric occurred. Epicarp showed constantly higher ethylene levels than mesocarp at all sampling dates. A similar pattern was observed only in seed of Redhaven. In Springcrest seed a gradual rise of ethylene evolution started immediately after the drop that occurred 50 days after full bloom (AFB), whereas in Fayette the hormone level dropped after the first sampling date (42 days AFB) and remained at basal level throughout seed development. Seed ethylene evolution was constantly higher than that registered in fruit tissues. Ethylene evolution of fruit tissues and seed was related to the 1-aminocyclopropane-1-carboxilic acid (ACC) content and/or ACC oxidase (ACO) activity. Mesocarp and epicarp ACO activity kinetics were paralleled by changes of specific mRNA accumulation. Mesocarp, epicarp and seed differently responded in terms of ethylene production to propylene treatments. At 42 and 63 days AFB the gas stimulated ethylene biosynthesis dramatically in seed and slightly in fruit tissues: at ripening, ethylene evolution was greatly enhanced in epicarp, but strongly inhibited in seed.