title: Evidence for the absence of enzymatic reactions in the glassy state. A case study of xanthophyll cycle pigments in the desiccation-tolerant moss Syntrichia ruralis.
abstract: Desiccation-tolerant plants are able to withstand dehydration and resume normal metabolic functions upon rehydration. These plants can be dehydrated until their cytoplasm enters a 'glassy state' in which molecular mobility is severely reduced. In desiccation-tolerant seeds, longevity can be enhanced by drying and lowering storage temperature. In these conditions, they still deteriorate slowly, but it is not known if deteriorative processes include enzyme activity. The storage stability of photosynthetic organisms is less studied, and no reports are available on the glassy state in photosynthetic tissues. Here, the desiccation-tolerant moss Syntrichia ruralis was dehydrated at either 75% or <5% relative humidity, resulting in slow (SD) or rapid desiccation (RD), respectively, and different residual water content of the desiccated tissues. The molecular mobility within dry mosses was assessed through dynamic mechanical thermal analysis, showing that at room temperature only rapidly desiccated samples entered the glassy state, whereas slowly desiccated samples were in a 'rubbery' state. Violaxanthin cycle activity, accumulation of plastoglobules, and reorganization of thylakoids were observed upon SD, but not upon RD. Violaxanthin cycle activity critically depends on the activity of violaxanthin de-epoxidase (VDE). Hence, it is proposed that enzymatic activity occurred in the rubbery state (after SD), and that in the glassy state (after RD) no VDE activity was possible. Furthermore, evidence is provided that zeaxanthin has some role in recovery apparently independent of its role in non-photochemical quenching of chlorophyll fluorescence.
authors.affiliation: Department of Plant Biology and Ecology, University of the Basque Country (UPV/EHU), Aptdo. 644, 48080 Bilbao, Spain. beatriz.fernandezm@ehu.es
authors.forename: Beatriz
authors.initials: B
authors.lastname: Fernández-Marín
authors.forename: Ilse
authors.initials: I
authors.lastname: Kranner
authors.forename: María
authors.initials: M
authors.lastname: San Sebastián
authors.forename: Unai
authors.initials: U
authors.lastname: Artetxe
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Laza
authors.forename: José Luis
authors.initials: JL
authors.lastname: Vilas
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Pritchard
authors.forename: Jayanthi
authors.initials: J
authors.lastname: Nadajaran
authors.forename: Fátima
authors.initials: F
authors.lastname: Míguez
authors.forename: José María
authors.initials: JM
authors.lastname: Becerril
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: García-Plazaola
mesh_terms: D044002:Bryophyta / Q000737:chemistry* / Q000201:enzymology* / Q000378:metabolism; D003890:Desiccation; D010088:Oxidoreductases / Q000378:metabolism*; D010788:Photosynthesis; D010940:Plant Proteins / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism; D014867:Water / Q000032:analysis / Q000378:metabolism; D024341:Xanthophylls / Q000096:biosynthesis
chemical_list: D010940:Plant Proteins; D024341:Xanthophylls; D014867:Water; C005613:violaxanthin; D010088:Oxidoreductases; C023290:violaxanthin de-epoxidase
keywords: Darkness; Tortula; desiccation tolerance; glassy state; long-term desiccation; molecular mobility; rapid desiccation; slow desiccation; xanthophyll cycle.