The fruit development and ripening are organized and complex processes where phytohormones, like indol-3-acetic acid (IAA) and abscisic acid (ABA) and ethylene have a pivotal role. In mango fruit one of the main metabolisms that have direct impact in the fruit quality is the starch degradation. The b-amylase is an enzyme that has emerged as fundamental for the starch mobilization, mainly during the ripening period. There are little information about relationship between changes in the phytohormones content and starch metabolism enzymes activities and gene expression. The aim of this work was to assess the phytohormones levels and their possible correlation to changes in b-amylase expression and activity.
A method for ABA and IAA quantitation was developed using de isotope dilution technique, employing hormones labeled with 13C, and measurement by gas chromatography-mass spectrometry (CG-MS) after methylation with diazomethane. Ethylene was determined by CG with flame ionization detection.
The mango b-amylase levels were assessed by Northern Blotting and hybridization with radioactive probes synthesized from a b-amylase cDNA isolated from banana pulp. Total RNAs to the transcription analysis were extracted from mango pulp of fruit at three development stages and six stages after harvest.
The highest levels of IAA were detected at 90 days post anthesis, that is, at the initial development stage, decreasing throughout the ripening. ABA showed the opposite profile, that is, low levels during development increasing during ripening, reaching the highest level at the end of the period. Concomitantly, the expression and activity of b-amylase increasing soon after the onset of ABA synthesis, time correlated to the starch degradation. The results indicate a possible regulation of b-amylase mediated by ABA, given that the ethylene levels found during the ripening of the mango Keitt were low and without any significant variation.
Supported by FAPESP and CAPES