ACCLIMATION OF LEAF CAROTENOID COMPOSITION AND ASCORBATE LEVELS TO GRADIENTS IN THE LIGHT ENVIRONMENT WITHIN AN AUSTRALIAN RAIN-FOREST

The influence of the growth photon flux density (PFD) on the size and composition of the carotenoid pool and the size of the reduced ascorba te pool was determined across a light gradient from the forest floor t o the canopy and the forest edge of a sub-tropical rainforest in New S outh Wales, Australia, Nineteen plant species (most collected from mul tiple sites) representing a broad taxonomic range consistently possess ed larger total carotenoid pools when found growing in more exposed si tes, There was a significant positive correlation between beta-caroten e content and growth PFD and a significant negative correlation betwee n alpha-carotene content and growth PFD, Neoxanthin content exhibited no significant trend while the trend in lutein content varied with mod e of expression. The pigments of the xanthophyll cycle (violaxanthin, antheraxanthin and zeaxanthin) exhibited the most pronounced response to growth PFD; they comprised a much greater portion of the total caro tenoid pool in high light-acclimated plants, The pool of reduced ascor bate was also several-fold greater in high light-acclimated plants. Th ese acclimatory changes in carotenoid and ascorbate content are consis tent with a need for a greater capacity to dissipate excessive absorbe d light energy in high light-acclimated plants.