Dynamics of the truncated lutein epoxide cycle in avocado (Persea Americana L.): implications for efficiency of light harvesting

Leaves of avocado (Persea americana) accumulate the α-xanthophyll lutein-epoxide (Lx) in excess of violaxanthin (V) in shaded habitats. On transfer to strong light both Lx and V are deepoxidised by violaxanthin de-epoxidase (VDE) to lutein (L) and to antheraxanthin (A) and zeaxanthin (Z) respectively, with about the same kinetics. However, whereas Z and A are rapidly epoxidised to form V by zeaxanthin epoxidase (ZE) when in shade or darkness, lutein is converted to Lx about 250 × more slowly, and hence Lx remains low in sun leaves. We investigated relationships between xanthophyll pool sizes and PSII efficiency (dark adapted Fv/Fm) in avocado leaves and discuss implications for the regulation of light harvesting efficiency arising from the differing epoxidation kinetics of these two co-located xanthophyll cycles