Abstract
Pollen-stigma interaction is a highly selective process, which leads to compatible or incompatible pollination, in the latter case, affecting quantitative and qualitative aspects of productivity in species of agronomic interest. While the genes and the corresponding protein partners involved in this highly specific pollen-stigma recognition have been studied, providing important insights into pollen-stigma recognition in self-incompatible (SI), many other factors involved in the SI response are not understood yet. This work concerns the study of transglutaminase (TGase), polyamines (PAs) pattern and metabolomic profiles following the pollination of Pyrus communis L. pistils with compatible and SI pollen in order to deepen their possible involvement in the reproduction of plants. Immunolocalization, abundance and activity of TGase as well as the content of free, soluble-conjugated and insoluble-bound PAs have been investigated. 1H NMR-profiling coupled with multivariate data treatment (PCA and PLS-DA) allowed to compare, for the first time, the metabolic patterns of not-pollinated and pollinated styles. Results clearly indicate that during the SI response TGase activity increases, resulting in the accumulation of PAs conjugated to hydroxycinnamic acids and other small molecules. Metabolomic analysis showed a remarkable differences between pollinated and not-pollinated styles, where, except for glucose, all the other metabolites where less concentrated. Moreover, styles pollinated with compatible pollen showed the highest amount of sucrose than SI pollinated ones, which, in turn, contained highest amount of all the other metabolites, including aromatic compounds, such as flavonoids and a cynnamoil derivative.
Highlights
In order to prevent self-fertilization, plants have evolved different strategies, from the temporally asynchronous development of male and female reproductive organs, to their specific localization within the flower, up to genetic-based strategies called “selfincompatibility” (SI) (Barrett, 2003; Ashman et al, 2004)
In the gametophytic SI (GSI) of Malinae, the stylar S locus plays an important role, since it encodes for glycoproteins with ribonuclease (S-RNase) activities that enter inside the pollen tube
A preliminary analysis was carried out to check the timing of SI response, styles of pear (NP and pollinated with compatible and incompatible pollen) were stained with aniline blue for callose reaction 48 h after pollination
Summary
In order to prevent self-fertilization, plants have evolved different strategies, from the temporally asynchronous development of male and female reproductive organs, to their specific localization within the flower, up to genetic-based strategies called “selfincompatibility” (SI) (Barrett, 2003; Ashman et al, 2004). The latter process prevents self-fertilization by the rejection of pollen of the same species. In the GSI of Malinae, the stylar S locus plays an important role, since it encodes for glycoproteins with ribonuclease (S-RNase) activities that enter inside the pollen tube. They are degraded in case of compatible pollen, allowing pollen tubes to grow, while in SI pollen the S-RNases are kept active, causing the degradation of pollen RNA and the cell death of pollen tube, which generally reaches only the upper third part of the style (De Franceschi et al, 2012)
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