A method of water-soluble solid fraction saturation concentration evaluation in dry thalli of Antarctic lichenized fungi, in vivo

BACKGROUND: At initial steps of rehydration from cryptobiosis of anhydrobiotic organisms or at rehydration of dry tissues the liquid (1)H NMR signal increased anomaly. The surplus in liquid signal may appear if some solid constituents dissolved, or if they were decomposed by enzymatic action. METHODS: Hydration kinetics, sorption isotherm, (1)H NMR spectra and high power relaxometry were applied to monitor gaseous phase rehydration of Antarctic lichen Cetraria aculeata. Tightly and loosely bound water signal were distinguished, and the upper hydration limit for dissolution of water soluble solid fraction was not observed. A simple theoretical model was proposed. RESULTS: The hydration courses showed a very tightly bound water fraction, a tightly bound water, and a loosely bound water fraction. Sigmoidal in form sorption isotherm was fitted well by multilayer sorption model. (1)H NMR showed one Gaussian signal component from solid matrix of thallus and one or two Lorentzian line components from tightly bound, and from loosely bound water. The hydration dependency of liquid signal was fitted by rational function. CONCLUSIONS: Although in dehydrated C.aculeata the level of carbohydrates and polyols was low, the lichenase action during rehydration process increased it; the averaged saturation concentration c(s)=(57.3±12.0)%, which resembled that for sucrose. GENERAL SIGNIFICANCE: The proposed method of water soluble solid fraction saturation concentration, c(s), calculation from (1)H NMR data may be applied for other organisms experiencing extreme dehydration or for dry tissues. We recalculated the published elsewhere data for horse chestnut (Aesculus hippocastanum) bast [water-soluble solid fraction recognized as sucrose, c(s)=(74.5±5.1)%]; and for Usnea antarctica, where c(s)=0.81±0.04.