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P. Tonutti, P. Casson, and A. Ramina

Ethylene evolution and ACC levels were determined throughout the growth and development of peach fruit (Prunus persica L. Batsch cv. Redhaven). In the four stages of growth (I, II, III, IV), as indicated by weekly monitoring of fresh (FW) and dry (DW) weight accumulation, ethylene biosynthesis in whole fruit decreased during FWI and remained almost undetectable during FWII and FWIII. In pericarp disks, ethylene evolution followed the same trend, although a peak at 78 days after full bloom and a slight increase before the onset of the climacteric were observed. The high rates of ethylene evolution were associated with a concurrent increase in ACC content. Enhancement of ACC synthase and ethylene-forming enzyme (EFE) activities was responsible for the peak of ethylene evolution detected before the beginning of FWIII and DWIII. At the climacteric, which occurred at the FWIII-FWIV transition, sequential events were observed in different fruit tissues. An increase of ethylene production in the mesocarp preceded the onset of the climacteric rise in whole fruit. The high amount of ethylene detected during the climacteric appeared to be related to increased EFE activity in the epicarp. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).

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A. Masia, A. Zanchin, N. Rascio, and A. Ramina

`Redhaven' peach [Prunus persica (L.) Batsch.] fruit growth, expressed as cheek diameter, displayed a double-sigmoid pattern in which four stages were defined (SI, SII, SIII, SIV). Free IAA concentration, as determined by polyclonal antibodies (PcAb) enzyme-linked immunosorbent assay (ELISA), paralleled fruit growth rate, peaking at 30 and 85 days after full bloom (AFB), concurrently with the exponential phases of growth. The highest peroxidase (EC 1.11.1.7) (POD) and IAA oxidase (IAAox) activities occurred during endocarp lignification. The main structural events described were mesocarp cell division within the first 2 weeks AFB and, later, cell enlargement, modifications of the epicarp cells, lignification of the endocarp, differentiation of the chloroplasts, and changes in their starch content. Chemical name used: indole-3-acetic acid (IAA).