Development of carotenoid storage cells in Bixa orellana L. seed arils

Abstract

The arils of Bixa orellana L. seeds contain carotenoid storage cells (CSCs). The main compounds in these cells include bixin and norbixin, which are important pigments in the food and pharmaceutical industries. Although many studies have been conducted on these chemical constituents, the cellular events that occur during the development of the carotenoid-accumulating cells in the arils and their relationship with the final carotenoid accumulation in the vacuoles remain unknown. In this study, the development of the CSCs in B. orellana arils was analyzed by light and transmission electron microscopy. Carotenoids formed in specialized cells, whose number and size increased during aril development. At various stages of development, the cytoplasm of the CSCs contained chromoplasts that held an extensive network of tubules and plastoglobules. Next to the chromoplasts, lipid droplets may fuse one another to form osmiophilic bodies. In addition, vesicles were observed next to the tonoplast. At the final stages of development, both the osmiophilic bodies and vesicles, which became quadrangular or rectangular, were stored in the vacuoles of the CSCs. This study reported for the first time the occurrence of different storage unit types within the vacuole of carotenoid storage cells.

Isolation and functional characterization of two dioxygenasese putatively involved in bixin biosynthesis in annatto (Bixa orellana L.)

“…However, no membrane anchoring peptides were predicted in the protein sequence, suggesting that BoCCD4s could cross the chloroplastic membrane without being retained in them (Wei et al, 2016). Notably, lycopene oxidation to bixin is proposed to take place inside plastids bixin storage cells (BSC) (Louro & Santiago, 2016).…”

“…Our results also suggest this third hypothesis, where both mechanisms (A) and (B) could occur simultaneously in the plant to synthesize bixin. Once bixin synthesis has ceased in the plastids or cytoplasm, it would be transported into the vacuole in carotenoid storage cells (Krieger et al, 2009; Louro & Santiago, 2016). As has been observed for other carotenoids originating in plastids, its final storage compartments are vacuoles and intercellular spaces (Bouvier et al, 2005; Camara & Bouvier, 2004; Giuliano, Rosati & Bramley, 2003; Gómez-Gómez et al, 2017; Grilli Caiola & Canini, 2004).…”

Carotenoid Metabolism in Plants: The Role of Plastids

“…These readjustments not only affect carotenoid storage capacity but also possibly affect biosynthetic ability. Prominent carotenoid biosynthesis and accumulation occur in tobacco floral nectaries, citrus fruits, and achiote seed arils following the developmental programmed changes of amyloplasts (Horner et al, 2007;Zeng et al, 2015b;Buah et al, 2016;Louro and Santiago, 2016). These changes are achieved by activation of carotenogenic gene transcription along with other processes (Horner et al, 2007).…”

Unraveling Massive Crocins Transport and Accumulation through Proteome and Microscopy Tools during the Development of Saffron Stigma

“…They might originate from many smaller vesicle-like structures that gradually fuse together. Direct apocarotenoid transport from chromoplast to vacuole was observed in Bixa orellana [ 44 ] and fusion between carotenoid rich lipid drops and the vacuole has been described in aging spores of Puccinia distincta [ 45 ]. Our observations suggested that, in some cases, the whole chromoplast is digested by the vacuole.…”