In plant organs and tissues, the neutral storage lipids are confined to discrete spherical organelles called oil bodies. Oil bodies from plant seeds contain 0.6–3% proteins, including oleosins, steroleosins, and caleosins. In this study, a caleosin isoform of ∼30 kDa was identified in the olive pollen grain. The protein was mainly located at the boundaries of the oil bodies in the cytoplasm of the pollen grain and the pollen tube. In addition, caleosins were also visualized in the cytoplasm at the subapical zone, as well as in the tonoplast of vacuoles present in the pollen tube cytoplasm. The cellular behaviour of lipid bodies in the olive pollen was also monitored during in vitro germination. The number of oil bodies decreased 20-fold in the pollen grain during germination, whereas the opposite tendency occurred in the pollen tube, suggesting that oil bodies moved from one to the other. The data suggest that this pollen caleosin might have a role in the mobilization of oil bodies as well as in the reorganization of membrane compartments during pollen in vitro germination.

Pistil structure and composition are critical in recognizing and permitting the germination of suitable pollen grains. We have studied the structure of the different component tissues of the pistil, their organization and cytochemical features of olive flowers, Olea europaea L., at anthesis, an essential first step for understanding the processes of pollen-pistil interaction and fertilization. The pistil from olive cv. Picual trees is characterized by a wet bilobed stigma, a solid style and a bilocular ovary containing four ovules. The stigma is composed of external multicellular papillae and a non-papillate inner region of secretory cells. An exudate is observed on the surface of the papillae at anthesis, the moment when the flowers (first) open, but the anthers are not yet dehiscent. The inner secretory cells of the stigma and those of the stylar transmitting tissue are continuous, constituting a funnel-shaped zone which extends from within the stigma to the style base. The outer surface of the ovary and style epidermis is surrounded by a cuticle layer, while internally, the locule wall, formed by the innermost cells of the endocarp, consists of two layers of periclinally oriented cells with thicker cell walls. Starch granules are distributed differentially, concentrated most densely in the style (adjacent to the vascular bundles), in the distil region of the ovary, and in the micropylar ends of the ovules. Well-developed vascular bundles are present in the lower part of the stigma, the style and in the pericarp of the ovary. The histochemical identification of sugars and lipid substances within and around the vascular bundles suggests that they are involved in the transport of these materials. Ultrastructural observations confirm the presence of exudates on the papillar surface and confirm the secretory characteristics of the inner stigmatic cells. They also demonstrate marked differences in size, form, and vacuolar and cytoplasmic contents among the cells of the various style and upper ovary tissues. We provide the first detailed cytological description at anthesis of all the olive pistil tissues, indicating the structural and cytochemical basis for the pistil behavior which will transpire during the progamic phase.

Cell wall components in the pistil are involved in cell-cell recognition, nutrition and regulation of pollen tube growth. The aim of this work was to study the level, whole-organ distribution, and subcellular localization of pectins and arabinogalactan proteins (AGPs) in the olive developing pistil. Western blot analyses and immunolocalization with fluorescence and electron microscopy were carried out using a battery of antibodies recognizing different types of pectin epitopes (JIM7, JIM5, LM5, and LM6) and one anti-AGPs antibody (JIM13). In the olive pistil, highest levels of acid esterified and de-esterified pectins were observed at pollination. Moreover, pollination was accompanied by a slight decrease of the galactose-rich pectins pool, whereas arabinose-rich pectins were more abundant at that time. An increased expression of AGPs was also observed during pollination, in comparison to the pistil at the pre-anthesis stage. After pollination, the levels of pectins and AGPs declined significantly. Inmunofluorescence localization of pectins showed their different localization in the olive pistil. Pectins with galactose residues were located mainly in the cortical zones of the pistil, similar to the neutral pectins, which were found in the parenchyma and epidermis. In turn, the neutral pectins, which contain arabinose residues and AGPs, were localized predominantly in the stigmatic exudate, in the cell wall of secretory cells of the stigma, as well as in the transmitting tissue of the pistil during the pollination period. The differences in localization of pectins and AGPs are discussed in relation to their roles during olive pistil developmental course.

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Pectins and AGPs are newly synthesized in the pollen tube during pollen germination. The synthesis and secretion of these compounds are temporally and spatially regulated. Galactans might provide mechanical stability to the pollen tube, reinforcing those regions that are particularly sensitive to tension stress (the pollen tube-pollen grain joint site) and mechanical damage (the tip). Arabinans and AGPs might be important in recognition and adhesion phenomena of the pollen tube and the stylar transmitting cells, as well as the egg and sperm cells.