Figure 9. Model showing how a cis-carotene derived apocarotenoid cleavage product controls plastid development in leaves from plants growing under a shorter photoperiod.

Shorter photoperiods that have an extended period of darkness, cause cis-carotenes to accumulate in leaf tissues from plants having impaired or lacking carotenoid isomerase activity. Plants growing under a longer photoperiod are exposed to an extended period of photoisomerisation, which stops cis-carotene from accumulating to detectable levels. A cis-carotene derived apocarotenoid signal (ACS) can perturb proplastid to chloroplast development, leading to the formation of a pseudo-chloroplast with poorly defined thylakoid and grana stacks. As a result, a yellow leaf virescence phenotype becomes visible in newly emerged leaves from carotenoid isomerase mutant plants growing under a shorter photoperiod.