Interazioni ormonali nello sviluppo del frutto e del seme di pomodoro
Author(s)
Mariotti, Lorenzo
Date Issued
October 14, 2008
Type
Doctoral Thesis
Abstract
Fruit and seed development are well coordinated processes, subjected to hormone control. Several experimental evidences support the involvement of hormones in the control of parthenocarpic fruit development; however the molecular events that regulate fruit-set, the successive phases of fruit growth and the endogenous system of hormonal regulation are poorly known.
The endogenous levels of gibberellins (GAs), indoleacetic acid (IAA), cytokinins (CK) and ethylene were determinated; successively, the expression of some key-genes of the gibberellins biosynthesis was analysed in normal fruits and parthenocarpic fruits obtained with chlorophenoxy-acetic acid.
During the first ten days following pollination/treatment the concentration of GA1, GA3 and GA8 is higher in parthenocarpic than pollinated fruits. In the following development stages, on the contrary, the concentration GA1 and GA8, which is mainly localised in seeds and locular tissues, is constantly higher in pollinated fruits.
Analysis of genes expression (GA20 oxidases and GA3 oxidases), indicate that both GA3 oxidase genes (GA3ox-1 and 2), are expressed at a low level either in pollinated fruits or treated fruits, GA20 oxidase genes are, instead, much more expressed in both fruits. The relative expression level of the GA20 oxidase genes principally expressed in the tomato fruit (GA20ox-1 and GA20ox-3) is higher in treated than in pollinated fruits and it is localised predominantly in locular tissues, being always low in the pericarp. Before anthesis endogenous level IAA and ethylene production in the ovary are high. After pollination/treatment the level of both hormones falls drastically in both fruits, but faster in treated ones. Successively, the endogenous level of IAA in treated fruits keeps low while increasing again in pollinated fruits. Ethylene production is maintained low until green maturation, in both fruit. The analysis of IAA levels in fruit tissues shows that in pollinated fruit after 10 days of development, the hormone is principally located in seeds and locular tissues being always low in the pericarp. The endogenous levels of CK show that free bases are predominant CK forms, while ribosilated CK represent a small fraction. A clear peak of free CK was observed at stage 3 DAP. In parthenocarpic fruit the endogenous level of CK is reduced respect to pollinated fruits and the peak at 3 DAT barely detect.
Our datas show that parthenocarpic fruit development, obtained by auxin application, is the result of different hormonal interactions, rather than the results of the general increase of hormone level. While confirming the cross-talking between auxin and GAs, the hormone dynamic during tomato fruit development, suggest significant variations respect to the most described model of Pisum. In tomato, the site of GA synthesis is localized in seeds and locular tissues and not in the pericarp. Moreover auxin stimulates the increase of bioactive GAs (GA1) through the regulation of GA20 oxidases expression and not GA3 oxidases. In the parthenocarpic fruit development, stimulated by auxin treatment, GAs and IAA, perhaps produced by pseudoembryos, seem to play an important role only in the control of the first growth phase coinciding with high cellular division.
The analysis of several parameters of fruit quality at harvest and a few days after did not show significant differences between fruits obtain by auxin application and fruit deriving from pollination. The main difference was the higher weight of parthenocarpic fruits respect pollinated fruits.
Additional information
Dottorato di ricerca in Ortoflorofrutticoltura
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