Selaginella lepidophylla is one of only a few species of spike mosses (Selaginellaceae) that have evolved desiccation tolerance (DT) or the ability to ‘resurrect’ from an air-dried state.
Various Selaginella species including lepidophylla have been recognised for the potential therapeutic value of their anitviral, antimicrobial, or anticancer bioactivities. Widely used in traditional medicine, the authors of a recent study on the species note that little contemporary research has been undertaken.
Above, the panel of images shows a sequence of initial dry state to full rehydration and subsequent dessication. S. lepidophylla's metabolic profile was sampled over 5 stages of this cycle.
During dehydration, the microphylls curl to form a tight ball, which is an adaptive response to protect the plant against damage due to high irradiance or temperatures, or both.
Lycophytes represent a plant lineage that lies between mosses and angiosperms and thus (as the team expected) S. lepidophylla exhibited both constitutive and inducible adaptive mechanisms of DT.
S. lepidophylla exhibits an obvious predisposition for DT by expressing a majority of metabolites, such as highly abundant trehalose, sucrose, and glucose in a constitutive manner, whereas only 16.7% and 29.5% of all compounds show significant increases or decreases in abundance upon change in hydration state, respectively.
The team found many glycolysis/gluconeogenesis and TCA cycle intermediates, sugar alcohols and sugar acids were more abundant in the hydrated state. Polyols appeared to play various roles, impeding water loss as well as reabsorption during rehydration (the slower of the two processes).
Polyols might also serve as osmoprotectants in stabilizing or preventing denaturation of proteins during dehydration, in hydroxyl radical scavenging, in redox control, in reducing ROS production, and in triggering stress-adaptive gene expression.
Vanillate, a potent antioxidant, was more abundant in hydrated states. Photooxidative/oxidative damage are carefully regulated in dessication to avoid free radical damage to membranes.
Citrulline, a non-protein amino acid analog of Arg, and allantoin, a N-rich product of purine breakdown “likely serve as nitrogen reserves or attenuate ROS accumulation and cell death”, and were associated with dessication.
Several amino acid-derived secondary metabolites also appeared to play protective roles against UV-light damage including 3-(3-hydroxyphenyl) propionate and the flavonols apigenin and naringenin in all dry and partially dry states. In addition, several nitrogen-rich and γ-glutamyl amino acids that were markedly more abundant in dry or partially dry S. lepidophylla, likely play critical roles in the acquisition of DT through the scavenging of ROS via glutathione metabolism, or the remobilization of amino acids following rehydration, or both.