Study of anatomical and Acc (1-aminocyclopropane-1-carboxylate) during flower budabscission indicate an important role of alternate bearing

Abstract

This study investigates whether, and how, 1-aminocyclopropane-1-carboxylic acid (ACC) is concerned in flower bud abscission of pistachio (Pistacia vera L.). Abscission was studied about the activation of the abscission zone, located between shoot and flower bud, from Uzun pistachio cultivar where the abscission profiles and the scanning electron micrographs pictorial differences in the abscission program, under natural conditions of flower bud. ACC content was investigated in the flower bud abscission zone during growth and abscission using liquid chromatography coupled with electrospray tandem mass spectrometry (UPLC/ESI-MS/MS). Results showed that abscission layers were started at first 45 days after full blooming (DAFB) and accomplished on 55 and 65 DAFB from 'On' year sampling. The activities of ACC in the flower bud abscission zone were significantly increased and decreased by flower bud abscission. A strong rise of ACC synthase in leaf and panicle was observed at the beginning of abscission, corresponding to stage 45 DAFB. High levels of ACC activity were found in whole abscission period indicating a possible role of ACC in pistachio flower bud abscission. At the end of the period (65 DAFB), the ACC levels gradually decreased and reached to minimum. Consequently, abscission-promoting effect of ACC depends on the phenological periods. These results provide strong evidence of flower abscission zone and the role of ACC in flower bud abscission possibly for the first time.