title: Xanthophyll cycle pool size and composition in relation to the nitrogen content of apple leaves.
abstract: The objective of this study was to determine xanthophyll cycle pool size and composition in response to N status and their relationships to non-photochemical quenching in apple leaves. Bench-grafted Fuji/M.26 trees were fertilized with different N concentrations (0-20 mM) in a modified Hoagland's solution for 6 weeks to create a wide range of leaf N status (1-4.4 g m(-2)). Chlorophyll content, xanthophyll cycle pool size, lutein, total carotene, and neoxanthin on a leaf area basis all increased linearly with increasing leaf N. However, only the ratios of the xanthophyll cycle pool and of lutein to chlorophyll were higher in low N leaves than in high N leaves. Under high light at midday, both zeaxanthin (Z), expressed on a chlorophyll basis, and the percentage of the xanthophyll cycle pool present as Z, increased as leaf N decreased. Thermal dissipation of excitation energy, measured as non-photochemical quenching of chlorophyll fluorescence, was positively related to, whereas efficiency of excitation transfer and photosystem II quantum efficiency were negatively related to, Z, expressed on a chlorophyll basis or on a xanthophyll cycle pool basis. It is concluded that both xanthophyll cycle pool size (on a chlorophyll basis) and conversion of violaxanthin to zeaxanthin are enhanced in response to N limitation to dissipate excessive absorbed light under high irradiance.
authors.affiliation: Department of Horticulture, 134A Plant Science Bldg, Cornell University, Ithaca, NY 14853-4203, USA. LC89@Cornell.edu
authors.forename: Lailiang
authors.initials: L
authors.lastname: Cheng
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D027845:Malus / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010507:Periodicity; D018515:Plant Leaves / Q000378:metabolism*; D024341:Xanthophylls / Q000378:metabolism*
chemical_list: D024341:Xanthophylls; D002734:Chlorophyll; D009584:Nitrogen