title: Nutritional regulation in mixotrophic plants: new insights from Limodorum abortivum.
abstract: Partially mycoheterotrophic (mixotrophic) plants gain carbon from both photosynthesis and their mycorrhizal fungi. This is considered an ancestral state in the evolution of full mycoheterotrophy, but little is known about this nutrition, and especially about the physiological balance between photosynthesis and fungal C gain. To investigate possible compensation between photosynthesis and mycoheterotrophy in the Mediterranean mixotrophic orchid Limodorum abortivum, fungal colonization was experimentally reduced in situ by fungicide treatment. We measured photosynthetic pigments of leaves, stems, and ovaries, as well as the stable C isotope compositions (a proxy for photosynthetic C gain) of seeds and the sizes of ovaries and seeds. We demonstrate that (1) in natural conditions, photosynthetic pigments are most concentrated in ovaries; (2) pigments and photosynthetic C increase in ovaries when fungal C supply is impaired, buffering C limitations and allowing the same development of ovaries and seeds as in natural conditions; and (3) responses to light of pigment and (13)C contents in ovaries shift from null responses in natural conditions to responses typical of autotrophic plants in treated L. abortivum, demonstrating photoadaptation and enhanced use of light in the latter. L. abortivum thus preferentially feeds on fungi in natural conditions, but employs compensatory photosynthesis to buffer fungal C limitations and allow seed development.
authors.affiliation: Dipartimento di Chimica e Biologia, Università degli Studi di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano, Salerno, Italy, alessandro_bellino@gmx.com.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Bellino
authors.forename: Anna
authors.initials: A
authors.lastname: Alfani
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Selosse
authors.forename: Rossella
authors.initials: R
authors.lastname: Guerrieri
authors.forename: Marco
authors.initials: M
authors.lastname: Borghetti
authors.forename: Daniela
authors.initials: D
authors.lastname: Baldantoni
mesh_terms: D005075:Biological Evolution; D002247:Carbon Isotopes / Q000378:metabolism; D038821:Mycorrhizae / Q000502:physiology; D009747:Nutritional Physiological Phenomena; D029595:Orchidaceae / Q000378:metabolism / Q000382:microbiology / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D010860:Pigments, Biological / Q000378:metabolism; D018514:Plant Structures / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010860:Pigments, Biological