title: Photosynthetic limitations and volatile and non-volatile isoprenoids in the poikilochlorophyllous resurrection plant Xerophyta humilis during dehydration and rehydration.
abstract: We investigated the photosynthetic limitations occurring during dehydration and rehydration of Xerophyta humilis, a poikilochlorophyllous resurrection plant, and whether volatile and non-volatile isoprenoids might be involved in desiccation tolerance. Photosynthesis declined rapidly after dehydration below 85% relative water content (RWC). Raising intercellular CO(2)  concentrations during desiccation suggest that the main photosynthetic limitation was photochemical, affecting energy-dependent RuBP regeneration. Imaging fluorescence confirmed that both the number of photosystem II (PSII) functional reaction centres and their efficiency were impaired under progressive dehydration, and revealed the occurrence of heterogeneous photosynthesis during desiccation, being the basal leaf area more resistant to the stress. Full recovery in photosynthetic parameters occurred on rehydration, confirming that photosynthetic limitations were fully reversible and that no permanent damage occurred. During desiccation, zeaxanthin and lutein increased only when photosynthesis had ceased, implying that these isoprenoids do not directly scavenge reactive oxygen species, but rather protect photosynthetic membranes from damage and consequent denaturation. X. humilis was found to emit isoprene, a volatile isoprenoid that acts as a membrane strengthener in plants. Isoprene emission was stimulated by drought and peaked at 80% RWC. We surmise that isoprene and non-volatile isoprenoids cooperate in reducing membrane damage in X. humilis, isoprene being effective when desiccation is moderate while non-volatile isoprenoids operate when water deficit is more extreme.
authors.affiliation: Department of Molecular and Cell Biology, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
authors.forename: Megan
authors.initials: M
authors.lastname: Beckett
authors.forename: Francesco
authors.initials: F
authors.lastname: Loreto
authors.forename: Violeta
authors.initials: V
authors.lastname: Velikova
authors.forename: Cecilia
authors.initials: C
authors.lastname: Brunetti
authors.forename: Martina
authors.initials: M
authors.lastname: Di Ferdinando
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Tattini
authors.forename: Carlo
authors.initials: C
authors.lastname: Calfapietra
authors.forename: Jill M
authors.initials: JM
authors.lastname: Farrant
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D005453:Fluorescence; D019684:Magnoliopsida / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis; D013729:Terpenes / Q000378:metabolism*; D055549:Volatile Organic Compounds / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D013729:Terpenes; D055549:Volatile Organic Compounds; D014867:Water; D002734:Chlorophyll