3.3.2. Land Plants

In land plants, most of the carotenogenesis pathways and the functionally confirmed enzymes are known (Figure 2). Hydroxyl groups are introduced into Ά-carotene to produce zeaxanthin by 

Ά-carotene hydroxylase (CrtR, CrtR-b, BCH). Epoxy groups are introduced into zeaxanthin by zeaxanthin epoxidase (Zep, NPQ) to produce violaxanthin through antheraxanthin. Under high light conditions, violaxanthin is changed into zeaxanthin by violaxanthin de-epoxidase (Vde) for dispersion of excess energy from excited chlorophylls. One end group of violaxanthin is changed to an allene group of neoxanthin by neoxanthin synthase (Nsy). Because all neoxanthin in chloroplasts has the 

9<sup>ȝ</sup>-*cis* form, unknown 9ȝ-isomerase for all *trans* neoxanthin to 9<sup>ȝ</sup>-*cis* neoxanthin should be present [11]. 
