Abstract
Utricularia nelumbifolia is a large carnivorous plant that is endemic to Brazil. It forms an extra-ovular female gametophyte, which surpasses the entire micropylar canal and extends beyond the limit of the integument and invades the placenta tissues. Due to the atypical behavior of the female gametophyte, it is interesting to determine the interaction between the gametophyte and sporophytic tissue. Therefore, the aim of this study was to evaluate the role of the placenta, the ovular tissues, the hypertrophied central cell and the integument in guiding the pollen tube in Utricularia nelumbifolia Gardner by studying the distribution of homogalacturonans and hemicelluloses. It was also determined whether the distribution of the homogalacturonans (HG) and hemicelluloses in Utricularia are dependent on pollination. The antibodies directed against the wall components (anti-pectin: JIM5, JIM7, LM19, LM20 and the anti-hemicelluloses: LM25, LM11, LM15, LM20, LM21) were used. Because both low- and high-esterified HG and xyloglucan were observed in the placenta, ovule (integument, chalaza) and female gametophyte of both pollinated and unpollinated flowers, the occurrence of these cell-wall components was not dependent on pollination. After fertilization, low methyl-esterified HGs were still observed in the cell walls of somatic cells and female gametophyte. However, in the case of high-esterified HG, the signal was weak and occurred only in the cell walls of the somatic cells. Because xyloglucans were observed in the cell walls of the synergids and egg cells, this suggests that they play a role in sexual reproduction. Utricularia nelumbifolia with an extra ovule-female gametophyte is presented as an attractive model for studying the male-female dialogue in plants.
Highlights
IntroductionPectins are an important polysaccharide component of the cell wall and have an effect on its properties (cell wall extensibility and porosity)
Together with hemicelluloses, pectins are an important polysaccharide component of the cell wall and have an effect on its properties
We showed that the somatic cells of the placenta and mature ovule contained extremely low methyl-esterified HG
Summary
Pectins are an important polysaccharide component of the cell wall and have an effect on its properties (cell wall extensibility and porosity). Pectins play a role in many important processes, e.g., growth, morphogenesis, organogenesis, cell–cell adhesion, defense, leaf abscission and fruit and seed development, as well as ion binding. They can be divided into five main groups: homogalacturonan (HG), xylogalacturonan (XGA), apiogalacturonan (AP) and rhamnogalacturonan I and II [1,2,3]. There are pollination- and fertilization-induced changes in the occurrence of both highly and low methyl-esterified homogalacturonans in the pistil transmitting tract, the micropyle of the ovule and in the apoplast of the embryo sac cells. Koscinska-Pajak [25] did not record HG (recognized by the JIM7 and JIM5 antibodies) in the micropylar part of the embryo sac, nor in the cytoplasm of the synergids in the apomict Chondrilla juncea L
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