9cisepoxycarotenoids

9-cis-epoxycarotenoids are a subset of xanthophylls, carotenoids that carry an epoxide functional group and a 9-cis double bond configuration. The best-characterized members in plants are 9-cis-violaxanthin and 9-cis-neoxanthin. These pigments reside in plastids and are related to the larger xanthophyll cycle, which involves interconversion among various oxygenated carotenoids that help regulate light harvesting and protection against photooxidative stress.

A central role for 9-cis-epoxycarotenoids is as precursors in abscisic acid (ABA) biosynthesis. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) cleaves 9-cis-epoxycarotenoids to produce xanthoxin, a direct ABA precursor that is converted through a short sequence of steps into abscisic acid. This cleavage step is rate-limiting and is strongly induced by drought, salinity, cold, and ABA signaling, linking environmental stress to hormonal responses.

Biological significance extends beyond ABA production. ABA regulates stomatal closure, seed dormancy, and various stress-adaptive processes, influencing water use efficiency and survival under adverse conditions. Because 9-cis-epoxycarotenoids sit at the intersection of carotenoid metabolism and hormone signaling, they are of interest for studies of plant stress physiology and for biotechnological approaches aiming to modify ABA levels and plant drought tolerance.

Analytical detection of 9-cis-epoxycarotenoids typically involves chromatographic separation coupled with spectrometric identification to distinguish isomeric forms and quantify their abundance in tissues such as leaves and seeds.