Abstract

<jats:p>Photosynthetic capacities, xanthophyll cycle components, and the capacity for photoprotective dissipation of excess excitation in the chlorophyll pigment bed were compared in two groups of species acclimated to different growth irradiance. These were sun leaves of three species with moderately high maximal photosynthetic capacities, tulip, rose, and periwinkle (Vinca minor), and leaves which had developed under very low irradiance from three shade-tolerant species, Monstera deliciosa, Philodendron caudatum and Schefflera arboricola. All sun leaves possessed larger xanthophyll cycle pools and greater maximal zeaxanthin (and antheraxanthin) contents and also displayed a greater maximal capacity for photo-protective energy dissipation in the pigment bed than the leaves acclimated to very low irradiance. The sun leaves also maintained a considerably lower reduction state of photosystem II at full sunlight than the leaves acclimated to very low irradiance. Thus, during exposure to full sunlight, these sun leaves were able to dissipate a major portion of the absorbed light through the combination of photosynthesis and energy dissipation in the pigment bed. Under the same conditions, these two processes combined were able to dissipate only a small fraction of the absorbed light in the leaves acclimated to very low irradiance. Most of the above differences between sun-acclimated leaves and leaves acclimated to very low irradiance existed not only between species but also within a species. Acclimation of Monstera deliciosa to a high growth irradiance resulted in leaves with a larger xanthophyll cycle pool, a greater maximal zeaxanthin (and antheraxanthin) content, and a greater capacity for energy dissipation in the pigment bed.</jats:p>