Cutinsomes and lipotubuloids appear to participate in cuticle formation in Ornithogalum umbellatum ovary epidermis: EM–immunogold research

Maria Kwiatkowska,Eva Domίnguez,Antonio Heredia,Justyna Teresa Polit,Katarzyna Popłońska,Dariusz Stępiński,Agnieszka Wojtczak

doi:10.1007/s00709-014-0623-2

Abstract

The outer wall of Ornithogalum umbellatum ovary and the fruit epidermis are covered with a thick cuticle and contain lipotubuloids incorporating 3H-palmitic acid. This was earlier evidenced by selective autoradiographic labelling of lipotubuloids. After post-incubation in a non-radioactive medium, some marked particles insoluble in organic solvents (similar to cutin matrix) moved to the cuticular layer. Hence, it was hypothesised that lipotubuloids participated in cuticle synthesis. It was previously suggested that cutinsomes, nanoparticles containing polyhydroxy fatty acids, formed the cuticle. Thus, identification of the cutinsomes in O. umbellatum ovary epidermal cells, including lipotubuloids, was undertaken in order to verify the idea of lipotubuloid participation in cuticle synthesis in this species. Electron microscopy and immunogold method with the antibodies recognizing cutinsomes were used to identify these structures. They were mostly found in the outer cell wall, the cuticular layer and the cuticle proper. A lower but still significant degree of labelling was also observed in lipotubuloids, cytoplasm and near plasmalemma of epidermal cells. It seems that cutinsomes are formed in lipotubuloids and then they leave them and move towards the cuticle in epidermal cells of O. umbellatum ovary. Thus, we suggest that (1) cutinsomes could take part in the synthesis of cuticle components also in plant species other than tomato, (2) the lipotubuloids are the cytoplasmic domains connected with cuticle formation and (3) this process proceeds via cutinsomes.

Highlights

A cuticle, a structure that covers aerial surfaces of terrestrial plants, has various functions: prevention of non-stomatal water loss, inhibition of organ fusion during development (Sieber et al 2000; Heredia 2003), protection from UV radiation damage (Barnes et al 1996) and imposition of a physical barrier against infection by bacterial and fungal pathogens (Jenks et al 1994)
The aim of the current paper was to verify the following hypotheses: (1) cutinsomes are involved in cuticle formation and (2) cutin synthesis mediated by cutinsomes takes place in lipotubuloids
A lipotubuloid dynamically moving and rotating around its changing axis in a cell was caught during fixation and is visible on the ultrathin cross-section near the outer epidermal wall to which it was connected via the cytoplasm

Summary

Introduction

A cuticle, a structure that covers aerial surfaces of terrestrial plants, has various functions: prevention of non-stomatal water loss, inhibition of organ fusion during development (Sieber et al 2000; Heredia 2003), protection from UV radiation damage (Barnes et al 1996) and imposition of a physical barrier against infection by bacterial and fungal pathogens (Jenks et al 1994). Biopolyester cutin, an insoluble hydrophobic matrix of polyhydroxylated C16 and/or C18 fatty acids cross-linked by ester bonds, is the main component of a cuticle (Pollard et al 2008). A fraction of waxes is deposited on the surface (epicuticular waxes) and embedded in the cutin matrix (intracuticular waxes). Cutan is another lipid polymer sometimes present in plant cuticles, either as an alternative to or in combination with cutin (Villena et al 1999; Kolattukudy 2001). Cuticle components are synthesised in epidermal cells This process can be divided into two stages: (1) chemical transformation of fatty acids synthesised in plastids into cutin and wax building blocks and (2) polymerisation and transport of the aforementioned oligomers to the epidermal surface. The first stage is mediated by numerous genetically controlled enzymes (Pollard et al 2008)

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