Flesh softening and phosphorylation of soluble polypeptides in relation to ethylene production in Prunus persica fruits with different ripening patterns

In peach fruit, it is desirable to individuate simple biochemical/physiological parameters, genetically determined and useful for marker-assisted selection to obtain improved genotypes for flesh firmness. The accumulation of proteins involved in cell wall re-organisation, such as endo-polygalacturonases (endo-PGs) and expansins, has been studied in fruits of two genotypes with either Non-Melting(NMF) or Melting Flesh (MF) texture, and in fruits of three 'Slow-Ripening' ('SR': altered ripening pattern) genotypes. In the flesh cell walls of MF fruits, the amounts of an endo-PG-like polypeptide were relevant and increased with ripening, while it was produced in extremely low amounts in NMF fruits. A similar pattern was observed for expansins. NMF fruits produced more ethylene than the MF ones. The Ca2+-dependent phosphorylation of a soluble polypeptide (Mw approximate to 52 kDa) decreased with ripening in NMF fruits and remained constant in the MF ones. In 'SR' genotypes, phosphorylation of this polypeptide was detectable only in ethylene-producing fruits, which softened their flesh and expressed the endo-PG-like polypeptide. The data suggest that phosphorylation of the 52-kDa polypeptide may be involved in the modulation of ethylene signalling and flesh softening.