Ethylene Evolution and 1-Aminocyclopropane-1-carboxylate Oxidase Gene Expression during Early Development and Ripening of Peach Fruit

Abstract

The rate of ethylene biosynthesis was monitored throughout the four stages (S1, S2, S3, and S4) of peach (Prunus persica L. Batsch `Springcrest') fruit development. The highest values of ethylene production were detected during the early S1 and at ripening. During S1, the increase in the evolution of ethylene was accompanied by high activity of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO). A weak accumulation of ACO mRNA was detected in developing fruitlets, indicating that ACO may play a specific role in modulating the rate of ethylene biosynthesis during the early growth stage. When fruitlets harvested at S1 were flushed with propylene (500 mL·L-1) for 48 h, a two-fold increase of ethylene biosynthesis and a dramatic induction of ACO activity were observed. Treatment with the ethylene analogue greatly stimulated the expression of ACO gene(s). During ripening, the climacteric occurred when fruit had softened to ≈20 N. This process was preceded by an increase in ACC content and ACO activity in the mesocarp. ACO transcripts began to accumulate before the rise in whole-fruit ethylene biosynthesis with peak levels coincident with the climacteric when the highest values of ACO activity were detected. Propylene greatly enhanced ACO gene expression and stimulated the ripening-associated ethylene climacteric. ACO-related transcripts also accumulated in fruit treated with nitrogen for 72 hours.