Spatial and temporal localization of homogalacturonans in Hyacinthus orientalis L. ovule cells before and after fertilization

Abstract

Key message The composition of homogalacturonans (HGs) in the ovule and the female gametophyte cell walls was shown to be rearranged dynamically during sexual reproduction of H. orientalis. Abstract In angiosperms, homogalacturonans (HGs) play an important role in the interaction between the male gametophyte and the pistil transmitting tract, but little is known about the participation of these molecules at the final stage of the progamic phase and fertilization. The aim of our study was to perform immunocytochemical localization of highly (JIM7 MAb) and weakly (JIM5 MAb) methyl esterified and Ca 2? -associated HG (2F4 MAb) in the ovule and female gametophyte cells of Hyacinthus orientalis before and after fertilization. It was found that pollination induced the rearrangement of HG in (1) the micropylar canal of the ovule, (2) the filiform apparatus of the synergids, and (3) the region of fusion between sperm cells and their target cells. Fertilization led to further changes in pectin composition of these three regions of the ovule. A new cell wall was synthesized around the zygote with a characteristic pattern of localization of all examined HG fractions, which we called ''sporoderm-like''. The developing endosperm prepared for cellularization by synthesizing highly methyl-esterified HG, which was stored in the cytoplasm. Pollination-and fertilizationinduced changes in the composition of the HG in the micropyle of the ovule and the apoplast of female gametophyte cells are discussed in the context of: (1) micropylar pollen tube guidance, (2) preparation of the egg cell and the central cells for fusion with sperm cells, and (3) the polyspermy block.

Immunodetection of some pectic, arabinogalactan proteins and hemicellulose epitopes in the micropylar transmitting tissue of apomictic dandelions (Taraxacum, Asteraceae, Lactuceae)

“…In contrast to amphimictic plants (e.g. Galanthus , Śnieżko and Chudzik 2003; Olea , Suárez et al 2013; Hyacinthus , Niedojadło et al 2015), we did not observed abundant occurrence of highly methyl-esterified HG labelled by the JIM7 antibody in either the micropyle or the synergids of apomictic Taraxacum . Neither of the two HG domains (recognised by JIM7 and JIM5 antibodies) were recorded in the micropylar part of the embryo sac nor in the cytoplasm of the synergids in apomict C. juncea (Kościńska-Pająk et al 2005; Kościńska-Pająk 2006).…”

“…Wolf et al 2009). It has been well documented that homogalacturonan (HG) plays an important role in pollen-stigma and pollen tube-pistil interactions in flowering plants (see Sage et al 2009; Niedojadło et al 2015 and discussion therein). In amphimictic plants, there are pollination- and fertilisation-induced changes in the occurrence of highly (JIM7) and low (JIM5) methyl-esterified pectins in the pistil transmitting tract, the micropyle of the ovule and also in the apoplast of female gametophyte cells (Lenartowska et al 2001; Śnieżko and Chudzik 2003; Suárez et al 2013; Niedojadło et al 2015).…”

“…In fertile and mature angiosperm ovules, epitopes that were recognised by the JIM8 or JIM13 antibodies were detected on the micropylar pole in the tissues lying on the pathway of pollen tube growth (Coimbra and Salema 1997; Śnieżko and Chudzik 2003; Chudzik et al 2005b; Coimbra et al 2007); thus, the AGPs recorded in this localisation may act as lubricants and/or nutrients for the pollen tube (Suárez et al 2013). Similar to AGPs, an accumulation of homogalacturonan in both esterified and unesterified forms was found in the tissues lying on the pathway of the pollen tube growth only in fertile and mature ovules (Chudzik 2002; Śnieżko and Chudzik 2003; Niedojadło et al 2015). The question is whether the accumulation of arabinogalactan proteins and homogalacturonan occurs in the micropyle of obligatory apomicts, in which the development of both the embryo and the endosperm does not require double fertilisation.…”

Late progamic phase and fertilization affect calreticulin expression in the Hyacinthus orientalis female gametophyte

“…Commercial cultivars of Hyacinthus orientalis L. were grown at room temperature. The Hyacinthus pistil is composed of a hollow style and a dry stigma, while the female gametophyte develops according to the Polygonum type and consists of two synergids, the egg cell, the central cell containing two polar nuclei, and three antipodals (Pięciński et al 2008 ; Niedojadło et al 2012a , b , 2015 ). For fluorescence and electron microscopy studies, the ovules were mechanically dissected from unpollinated flowers before and during anthesis and from hand-cross-pollinated flowers 8 h after pollination (at the late progamic phase when the pollen tubes have reached approximately three-quarters of the style length and have not entered the ovary) and 96 h after pollination (fertilized ovules).…”

The role of the integuments in pollen tube guidance in flowering plants

“…Studies performed in several eudicots support an association of a decrease in calcium levels with a loss of receptivity, whereas an abundance of calcium in the synergids is associated with pollen tube penetration (Ge et al, 2007). Moreover, free calcium that can be released from homogalacturonans in the micropylar secretion has been related to pollen tube elongation in Hyacinthus orientalis (Niedojadło et al, 2015) and Haemanthus albiflos (Lenartowska et al, 2011). Recently, AGPs in the secretion of the obturator have also been reported to mediate pollen tube access to the micropyle in Malus 9 domestica, the apple (Losada & Herrero, 2017).…”