‘Elaioplasts’ identified as lipotubuloids in Althaea rosea, Funkia sieboldiana and Vanilla planifolia contain lipid bodies connected with microtubules

In many publications the term “elaioplasts” denotes, in accordance with the meaning, plastids containing lipids [1,2]. However, in the past this name was used according to Wakker [3] who was the first to apply it with reference to lipidic structures, often as big as a cell nucleus, which he identified in five Vanilla species. Similar structures were later described in more than 120 species belonging to Monocotyledoneae and Dicotyledoneae (literature data – Tab. 1). The observations in the light microscope showed that some of these plants contain lipidic structures which were definitely not plastids but aggregates of lipid bodies (lipid droplets, oleosomes), e.g. “elaioplasts” in Malva neglecta and Althaea rosea [4], 12 species of Gentiana [5], Dahlia variabilis [6], Ornithogalum umbellatum [7], Haemanthus albiflos [8]([9] – EM observations). However, it should be noted that some “elaioplasts” in plants listed in Tab. 1 are plastids (e.g. in Iris, [10]). The above literature clearly indicates that the issue is very old, but taking into consideration the papers from the last decade it has become very “hot” once again. Lipid bodies used to be treated as passive structures being only reservoirs of storage substances. However, nowadays they are seen as active organelles playing an important role in lipid homeostasis, intracellular signal transduction and in temporary protein retention. Disturbances in their functioning cause health problems in animals and humans [11-14]. On the other hand, in plants lipids are an important industrial and food product [15,16]. All this led to the revival of interest in these structures. It has been shown that in COS7 fibroblast [17] the surface of lipid bodies is the site of lipid synthesis because it contains an enzyme, diacylglyceroacyltransferase (DGAT) involved in the conversion of diacylglycerols (DAG) into triacylglycerols (TAG). These data were obtained through EM/immunocytochemical studies with the use of coloidal gold. “Elaioplasts” being great aggregates of many lipid bodies seem ideal for this type of research. Up till now a precise description of light microscopic observations of “elaioplast” development in O. umbellatum has been given by Raciborski [18] and Kwiatkowska [7]. They are present in ovary and stipule epidermis. Ultrastructural studies have shown that they are big cytoplasm domains surrounded not by their own membranes but by a tonoplast because they invaginate into vacuoles. They consist of numerous lipid bodies, covered with a phospholipid monolayer, which contain mainly triacylglycerols and free fatty acids. EM observations at huge magnifications demonstrated that lipid bodies were entwined with microtubules running in different directions and joining them together thus the whole domain moved in a cell as one body with a progressive-rotary movement. These structures were called lipotubuloids as they contain lipid bodies and microtubules [19-27]. In the lipotubuloids in addition to lipid bodies there are numerous ribosomes, ER cisternae and vesicles and few mitochondria, microbodies, Golgi structures and at the late developmental stages autolytic vacuoles containing acid phosphatase and lipase [20]. Moreover, electron microscopic observations Abstract