Lipotubuloids in ovary epidermis of Ornithogalum umbellatum act as metabolons: suggestion of the name ‘lipotubuloid metabolon’

Abstract

A metabolon is a temporary, structural-functional complex formed between sequential metabolic enzymes and cellular elements. Cytoplasmic domains called lipotubuloids are present in Ornithogalum umbellatum ovary epidermis. They consist of numerous lipid bodies entwined with microtubules, polysomes, rough endoplasmic reticulum (RER), and actin filaments connected to microtubules through myosin and kinesin. A few mitochondria, Golgi structures, and microbodies are also observed and also, at later development stages, autolytic vacuoles. Each lipotubuloid is surrounded by a tonoplast as it invaginates into a vacuole. These structures appear in young cells, which grow intensively reaching 30-fold enlargement but do not divide. They also become larger due to an increasing number of lipid bodies formed in the RER by the accumulation of lipids between leaflets of the phospholipid bilayer. When a cell ceases to grow, the lipotubuloids disintegrate into individual structures. Light and electron microscope studies using filming techniques, autoradiography with [(3)H]palmitic acid, immunogold labelling with antibodies against DGAT2, phospholipase D1 and lipase, and double immunogold labelling with antibodies against myosin and kinesin, as well as experiments with propyzamide, a microtubule activity inhibitor, have shown that lipotubuloids are functionally and structurally integrated metabolons [here termed lipotubuloid metabolons (LMs)] occurring temporarily in growing cells. They synthesize lipids in lipid bodies in cooperation with microtubules. Some of these lipids are metabolized and used by the cell as nutrients, and others are transformed into cuticle whose formation is mediated by cutinsomes. The latter were discovered in planta using specific anti-cutinsome antibodies visualized by gold labelling. Moreover, LMs are able to rotate autonomously due to the interaction of microtubules, actin filaments, and motor proteins, which influence microtubules by changing their diameter.

Subcellular Lipid Droplets in Vanilla Leaf Epidermis and Avocado Mesocarp Are Coated with Oleosins of Distinct Phylogenic Lineages

“…Individual LDs within a tapetosome are coated with T oleosin of an independent oleosin lineage. The second type is the much lessstudied solitary and clustered LDs in epidermis of green organs of most Asparagales species, whose biochemical structure, biogenesis, and function are mostly unknown (this report; Kwiatkowska et al, 2010Kwiatkowska et al, , 2015. Pursuit of this knowledge will require different technical approaches in addition to electron microscopy and guidance from the Brassicaceae tapetosome studies.…”

“…The heterogeneity of the proteins in the isolated LD fraction should reflect that in vivo, the LD clusters are associated with cytoskeleton and other subcellular constituents ( Fig. 1B; Kwiatkowska et al, 2015).…”

“…Earlier, TEM studies showed clustered LDs associated with cytoskeleton and other subcellular structures in the epidermis of the ovary of Ornithogalum and, with lesser detail, leaves of Haemanthus; both species belong to the Order Asparagales (Kwiatkowska et al, 2010(Kwiatkowska et al, , 2015. We used confocal laser scanning microscopy (CLSM) to examine comprehensively LDs in epidermis of leaves and other green organs of species of the Asparagales families obtained locally.…”

“…Other than those in seeds, LDs in high or low abundance are present in diverse cell types of all or restricted phylogenic plant groups (Lersten et al, 2006;Kim et al, 2002;Hsieh and Huang, 2004;Chapman et al, 2012;Kwiatkowska et al, 2015). They are present in moderate amounts, along with coating oleosin, in pollen of all examined species.…”

“…Two types of much-less studied LDs are present in special cells or tissues of restricted plant groups. The first type is the LD clusters in the epidermis of ovaries of Ornithogalum and leaves of Haemanthus (Kwiatkowska et al, 2010(Kwiatkowska et al, , 2015 in the Order Asparagales. These LD clusters could include cytoskeleton and other organelles such as mitochondria, Golgi, and small vesicles and vacuoles.…”