9cisepoxycarotenoid

9-cis-epoxycarotenoids are a subclass of carotenoids that contain an epoxide group in their structure and possess a 9-cis configuration. They are best known as precursors in the biosynthesis of abscisic acid (ABA), a plant hormone that regulates development and stress responses.

In plants, the key step is the enzymatic cleavage of 9-cis-epoxycarotenoids by 9-cis-epoxycarotenoid dioxygenase (NCED). This reaction produces xanthoxin, which is further converted to ABA. Common substrates include 9'-cis-violaxanthin and 9'-cis-neoxanthin, which are formed in plastids through the carotenoid pathway. The availability and turnover of these substrates influence the rate of ABA formation, making NCED activity a rate-limiting control point in ABA biosynthesis.

Physiologically, ABA functions as a central regulator of seed dormancy and germination, stomatal closure, and adaptive responses to drought, salinity, and cold stress. Consequently, 9-cis-epoxycarotenoids link carotenoid metabolism to broader hormonal signaling and stress physiology in plants.

Distribution and significance vary among plant species, but 9-cis-epoxycarotenoids are widely detected in vascular plants and are present in tissues such as leaves, seeds, and fruits where ABA biosynthesis is active. Research on these compounds supports agricultural applications, including breeding for improved drought tolerance and the development of strategies to modulate ABA levels under environmental stress.