Lipid body biogenesis and the role of microtubules in lipid synthesis in Ornithogalum umbellatum lipotubuloids

Movement of Lipid Droplets in the Arabidopsis Pollen Tube Is Dependent on the Actomyosin System

The growth of pollen tubes, which depends on actin filaments, is pivotal for plant reproduction. Pharmacological experiments showed that while oryzalin and brefeldin A treatments had no significant effect on the lipid droplets (LDs) trafficking, while 2,3-butanedione monoxime (BDM), latrunculin B, SMIFH2, and cytochalasin D treatments slowed down LDs trafficking, in such a manner that only residual wobbling was observed, suggesting that trafficking of LDs in pollen tube is related to F-actin. While the trafficking of LDs in the wild-type pollen tubes and in myo11-2, myo11b1-1, myo11c1-1, and myo11c2-1 single mutants and myo11a1-1/myo11a2-1 double mutant were normal, their trafficking slowed down in a myosin-XI double knockout (myo11c1-1/myo11c2-1) mutant. These observations suggest that Myo11C1 and Myo11C2 motors are involved in LDs movement in pollen tubes, and they share functional redundancy. Hence, LDs movement in Arabidopsis pollen tubes relies on the actomyosin system.

Differentiation Disorders of Chara vulgaris Spermatids following Treatment with Propyzamide

Microtubules are cytoskeletal cell elements that also build flagella and cilia. Moreover, these structures participate in spermatogenesis and form a microtubular manchette during spermiogenesis. The present study aims to assess the influence of propyzamide, a microtubule-disrupting agent, on alga Chara vulgaris spermatids during their differentiation by means of immunofluorescent and electron microscopy methods. Propyzamide blocks the functioning of the β-tubulin microtubule subunit, which results in the creation of a distorted shape of a sperm nucleus at some stages. Present ultrastructural studies confirm these changes. In nuclei, an altered chromatin arrangement and nuclear envelope fragmentation were observed in the research as a result of incorrect nucleus-cytoplasm transport behavior that disturbed the action of proteolytic enzymes and the chromatin remodeling process. In the cytoplasm, large autolytic vacuoles and the dilated endoplasmic reticulum (ER) system, as well as mitochondria, were revealed in the studies. In some spermatids, the arrangement of microtubules present in the manchette was disturbed and the structure was also fragmented. The observations made in the research at present show that, despite some differences in the manchette between Chara and mammals, and probably also in the alga under study, microtubules participate in the intramanchette transport (IMT) process, which is essential during spermatid differentiation. In the present study, the effect of propyzamide on Chara spermiogenesis is also presented for the first time; however, the role of microtubule-associated proteins in this process still needs to be elucidated in the literature.

Histochemical observations in Piper malgassicum (Piperaceae) with a special focus on the epidermis

This is the first contribution about the histochemistry of vegetative and reproductive aerial organs in the genus Piper L. Piper malgassicum accumulates alkaloids and terpenes in the epidermis and the underlying layers of parenchyma, both in the leaves, in the stems and in anthers. Some idioblasts appear to contain a large amount of secondary metabolites. The micro-anatomical analysis showed peculiar secretory structures both in the leaves, in the anthers and in the ovary. Several lipid aggregates, alkaloid droplets and calcium oxalate crystals were observed in leaves and stems, indicating their role in defence strategies, mechanical support, and pollinators attraction. In the anthers, we observed elaioplasts whose content suggest an alternative and indirect function in pollination and defence against micro-organisms. Besides, some lipid aggregates surrounded by microtubules, detected in the anthers, were recognized as lipotubuloids. The tapetum was of secretory type.

Alkaloids and terpenes were widely distributed in the plant confirming the important biological role of this type of biomolecules and its functional range. In the anthers, terpene and polyphenol inclusions appeared particularly abundant in the epidermal layer, whereas calcium oxalate crystals were observed close to the ovule in the ovary at maturity.

The Role of Cutinsomes in Plant Cuticle Formation

The cuticle commonly appears as a continuous lipophilic layer located at the outer epidermal cell walls of land plants. Cutin and waxes are its main components. Two methods for cutin synthesis are considered in plants. One that is based on enzymatic biosynthesis, in which cutin synthase (CUS) is involved, is well-known and commonly accepted. The other assumes the participation of specific nanostructures, cutinsomes, which are formed in physicochemical self-assembly processes from cutin precursors without enzyme involvement. Cutinsomes are formed in ground cytoplasm or, in some species, in specific cytoplasmic domains, lipotubuloid metabolons (LMs), and are most probably translocated via microtubules toward the cuticle-covered cell wall. Cutinsomes may additionally serve as platforms transporting cuticular enzymes. Presumably, cutinsomes enrich the cuticle in branched and cross-linked esterified polyhydroxy fatty acid oligomers, while CUS1 can provide both linear chains and branching cutin oligomers. These two systems of cuticle formation seem to co-operate on the surface of aboveground organs, as well as in the embryo and seed coat epidermis. This review focuses on the role that cutinsomes play in cuticle biosynthesis in S. lycopersicum, O. umbellatum and A. thaliana, which have been studied so far; however, these nanoparticles may be commonly involved in this process in different plants.

Cutinsomes as building-blocks of Arabidopsis thaliana embryo cuticle

Cutinsomes, spherical nanoparticles containing cutin mono- and oligomers, are engaged in cuticle formation. Earlier they were revealed to participate in cuticle biosynthesis in Solanum lycopersicum fruit and Ornithogalum umbellatum ovary epidermis. Here, transmission electron microscopy (TEM) and immunogold labeling with antibody against the cutinsomes were applied to aerial cotyledon epidermal cells of Arabidopsis thaliana mature embryos. TEM as well as gold particles conjugated with the cutinsome antibody revealed these structures in the cytoplasm, near the plasmalemma, in the cell wall and incorporated into the cuticle. Thus, the cutinsomes most probably are involved in the formation of A. thaliana embryo cuticle and this model plant is another species in which these specific structures participate in the building of cuticle in spite of the lack of the lipotubuloid metabolon. In addition, a mechanism of plant cuticle lipid biosynthesis based on current knowledge is proposed.

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

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.