9cisneoxanthin

9-cis-neoxanthin is a cis isomer of neoxanthin, a 40-carbon xanthophyll carotenoid commonly found in photosynthetic organisms such as higher plants and some algae. The term “9-cis” denotes the geometry of one double bond in the polyene chain, giving the molecule a distinct shape and light-absorption profile compared with the all-trans form of neoxanthin.

In plant metabolism, neoxanthin and its cis isomers play a role as precursors in the biosynthesis of abscisic acid (ABA), a plant hormone involved in stress responses. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) cleaves 9-cis-epoxycarotenoids, including 9-cis-neoxanthin, to produce xanthoxin, which is subsequently converted to ABA. Thus, 9-cis-neoxanthin contributes to ABA production, particularly under abiotic stress conditions such as drought or salinity.

Biosynthesis and occurrence: 9-cis-neoxanthin is formed in plastids during pigment biosynthesis and can arise from the isomerization of other carotenoids or neoxanthin itself. Its relative abundance in leaves varies with light conditions, developmental stage, and environmental stress. It is typically present in smaller amounts than some other carotenoids but remains a detectable component of the plant pigment pool.

Analytical notes: Identification and study of 9-cis-neoxanthin rely on chromatographic separation coupled with spectroscopic methods to distinguish its cis geometry from the all-trans isomer. Its presence is often considered in studies of ABA biosynthesis and carotenoid metabolism.