Lipid Droplet Formation in Cells of the Filamentous Green Alga Klebsormidium nitens as Revealed by BODIOY-DiOC6 and BODIPY-Nile Red Double-Staining Microscopy

Abstract

Summary Lipid droplets (LDs) form at the surface of the endoplasmic reticulum (ER) in cells of fungi and animals. In algae, however, they appear to form at the surfaces of both the ER and plastids. To study the universality of this process, we observed LD formation in the filamentous green alga Klebsormidium nitens. Each cell of this alga contains one large petal-like chloroplast.Observations of cells stained with dipyrrometheneboron difluoride (BODIPY) revealed that small LD spots formed at the edge of the chloroplast in young cells, and the size of the spots increased as the chloroplast grew. The LD spots were distributed evenly on the chloroplast, and consequently, were distributed equally between the daughter chloroplasts after binary fission. In non-dividing starved cells, large LDs formed as the chloroplast degraded and the chlorophyll concentration decreased, suggesting that components of the chloroplast were converted into LDs as the chloroplast degraded. To examine the spatial relationships among LDs, the ER, and the chloroplast, we examined cells by microscopy after dihexyloxcacarbocyanideiodide (DiOC 6 ) single-staining, BODIPY-DiOC 6 double-staining, and Nile red-DiOC 6 double-staining. ERs were elongated and arranged along the edge of the chloroplast in young cells. The LDs were associated with the ER, but were absent from the area between the ER and the chloroplast. These results suggest that the ER plays an important role in LD formation in young dividing cells in the green alga. The dynamics of the ER in starved cells were obscured by the large LDs that filled the cytoplasm.

Cultivation of Acidophilic Algae Galdieria sulphuraria and Pseudochlorella sp. YKT1 in Media Derived from Acidic Hot Springs

“…Eukaryotic algae are known to accumulate triacylglycerol in lipid droplets under a nitrogen-starved condition. Consistent with previous reports in other eukaryotic algae (e.g., Wang et al, 2009; Kuroiwa et al, 2012, 2014; Simionato et al, 2013), in spring water media without any additional nitrogen source (Ta, Tsu, Ta + P, and Tsu + P), as well as in MA-N, some lipid droplets were formed in the cells along with a reduction of the chloroplasts and inhibition of growth ( Figure 2 ). In contrast with the nitrogen-depleted or otherwise limited conditions described above, we also observed lipid droplet formation in the spring water media in which additional nitrogen but not phosphate was supplemented (Ta + NH 4 + and Tsu + NH 4 + ), in which cells grow without any decrease in the chloroplasts ( Figure 2 ).…”

Existence of Lipid Bodies Surrounded by Membranes in Early Greening Cotyledonary Cells

“…One possibility for the identity of the membrane is the endoplasmic reticulum (ER). The relationship between LBs and the ER has been reported not only in plants, animals, and yeast but also in green algae (Kuroiwa et al 2014). As it is known that the ER is involved in the formation of LBs and the accumulation of lipids, the presence of a relationship between LBs and the ER in the cotyledon of developing seeds is reasonable.…”

Planimal Cells: Artificial Photosynthetic Animal Cells Inspired by Endosymbiosis and Photosynthetic Animals

“…Algae are the most important contributors to the environment because they perform 40% of photosynthesis on earth (Andersen 1992). Algae are also the most diverse organisms with over 0.2 million species (Guarnieri 2013) and varied morphologies (Camaya et al 2016, Higuchi et al 2016, Kuroiwa et al 2014, Kuroiwa et al 2015, Ota et al 2014, Sugasawa et al 2015, Suzuki et al 2014, Takahashi et al 2014, Takeshita et al 2015, Yamamoto et al 2016. About 1 to 2 billion years ago, a primitive eukaryotic cell took up a cyanobacterium in the first endosymbiosis and evolved into algae with plastids derived from the endosymbiotic cyanobacterium (McFadden 2014).…”