ENDO-BETA-1,4-GLUCANASES ARE INVOLVED IN PEACH FRUIT-GROWTH AND RIPENING, AND REGULATED BY ETHYLENE

During peach (Prunus persica [L.] Batsch) fruit development and ripeni ng the cell wall undergoes several structural and biochemical changes driven by several hydrolases. Among these, the endo-beta-1.4-D-glucana se (EGase, EC 3.2.1.4), or cellulase, may play a crucial role. Involve ment of EGase throughout development and ripening oi the fruit of cv. Redhaven was assessed by monitoring enzyme activity, specific polypept ide accumulation and gene transcription. During the four stages of gro wth EGase activity was high during S1 and in the early S2, declined du ring S3, and increased with the onset of ripening (S4). Two isoforms w ith isolectric points of 6.5 and 9.5 were identified. The pI 6.5 EGase was the only form present during the early stages of growth, whereas the pi 9.5 EGase was most abundant during ripening. The same isoforms were present in leaf and fruit abscission zones. The antibody raised a gainst the pi 9.5 EGase, purified from lear abscission zones, cross-re acted with a protein of 54 kDa. A cDNA clone of 753 bp encoding peach EGase was obtained by RT-PCR. EGase transcripts, detectable only after amplification of total RNA by RT-PCR, were observed during S1, and at the preclimacteric and climacteric stages. However, the strongest hyb ridisation occurred at ripening, in correspondence with the maximal en zyme activity and polypeptide accumulation, which took place before th e ethylene climacteric and in the early stage of flesh softening. Prop ylene treatments reduced EGase activity during the early stage of frui t growth but dramatically enhanced enzyme activity and the related tra nscript accumulation at ripening, and accelerated the loss of firmness . In fruit treated with 2,5-norbornadiene the softening process was st rongly inhibited and the rise in EGase transcripts and activity did no t take place, The results point to the EGases being involved in early fruit growth and the initial phases of softening. The presence of two isoforms and the dual effect of propylene on enzyme activity suggest t hat different EGase genes operate during the early and late developmen tal stages in peach fruit.