apocarotenoids

Apocarotenoids are a diverse class of organic compounds derived from carotenoids by enzymatic cleavage of the carbon backbone, resulting in shorter molecules. Most apocarotenoids contain roughly 10 to 13 carbon atoms, although a range of lengths exists. They are typically produced by carotenoid cleavage dioxygenases (CCDs) in plants, and analogous enzymes in fungi and bacteria.

Well-known examples include β-ionone and α-ionone, which are fragrance compounds formed by the cleavage of β-carotene; another example is β-cyclocitral, a volatile apocarotenoid derived from β-carotene. These volatiles contribute to aroma and flavor in various fruits and flowers.

Biosynthesis and diversity: In plants, cleavage can occur at different double bonds in carotenoids, producing volatile aroma compounds or non-volatile regulatory molecules. Some apocarotenoids serve as precursors to plant hormones, including abscisic acid (ABA) and strigolactones, which regulate stress responses, development, and rhizosphere signaling. ABA is a key stress hormone derived from apocarotenoid catabolic pathways, while strigolactones act as hormones controlling shoot branching and as signaling molecules for symbiotic relationships with fungi.

Functions and significance: In fruits and flowers, apocarotenoid volatiles contribute to characteristic scents and flavors. In leaves and other tissues, apocarotenoids can participate in signaling pathways that influence gene expression and physiology. Strigolactones and ABA exemplify the hormonal roles of certain apocarotenoids in plant growth, development, and stress adaptation.

Applications: Due to their distinctive aromas, apocarotenoids are valuable in the flavor and fragrance industries. Research into their biosynthesis informs agriculture, crop quality, and the understanding of plant developmental and defense processes.