DOI: 10.5061/dryad.sqv9s4n1t
title: Terrestrial green algae show higher tolerance to dehydration than do their aquatic sister-species: Raw data and analysis files

description: Diverse algae possess the ability to recover from extreme desiccation
 without forming specialized resting structures. Green algal genera such
 as Tetradesmus (Sphaeropleales, Chlorophyceae) contain
 temperate terrestrial, desert, and aquatic species, providing an
 opportunity to compare physiological traits associated with the transition
 to land in closely related taxa. We subjected six species from distinct
 habitats to three dehydration treatments varying in relative humidity (RH
 5%, 65%, 80%) followed by short- and long-term rehydration. We tested the
 capacity of the algae to recover from dehydration using the effective
 quantum yield of photosystem II as a proxy for physiological activity. The
 degree of recovery was dependent both on the habitat of origin and the
 dehydration scenario, with terrestrial, but not aquatic species,
 recovering from dehydration. Distinct strains of each species responded
 similarly to dehydration and rehydration, with the exception of one
 aquatic strain that recovered from the mildest dehydration treatment. Cell
 ultrastructure was uniformly maintained in both aquatic and desert species
 during dehydration and rehydration, but staining with an amphiphilic
 styryl dye indicated damage to the plasma membrane from
 osmotically-induced water loss in the aquatic species. These analyses
 demonstrate that terrestrial Tetradesmus possess a
 vegetative desiccation tolerance phenotype, making these species ideal for
 comparative omics studies.
description: YII data June 2018, YII data June 2020
 Desiccation experiments were carried out using desiccation
 chambers previously described by Karsten et al. (2014). Different levels
 of relative humidity (RH) in the chamber were achieved by adding one of
 three different desiccants to the chambers: 100 g of CaSO4 (W. A. Hammond
 DRIERITE Co. LTD, Xenia, OH, USA) achieving ~5 % RH, a solution of 33g
 LiCl in 100 ml of dH2O for RH 65%, and a saturated solution of KCl in dH2O
 (100 ml) for RH 80%. Algal cell suspensions (50 μl,
 approximately 150,000 cells corresponding to chlorophyll concentration
 30–40 mg ml-1) were placed onto glass fiber filters (Whatman, Maidstone,
 United Kingdom) in replicates of four. Three filters at a time were then
 positioned on a perforated metal grid inside a desiccation chamber
 containing the appropriate desiccant. RH levels in the chambers were
 monitored using PCEMSR145S-TH mini data logger (PCE Instruments, Meschede,
 Germany). The chambers were kept under dim light of ~10 μmol photons
 m-2s-1 at 22˚C. Measurements of ΔF/Fm’ of PSII (FPSII) were taken using a
 PAM 2500 chlorophyll fluorometer (Heinz Walz GmbH, Effeltrich, Germany)
 for T. obliquus, T. deserticola, T. adustus, and T. bajacalifornicus (the
 light probe was adjusted outside of desiccation chamber in 12 mm distance
 from the algae samples). Strains of T. dissociatus and T. sp.
 “raciborskii" (CCAP 276/35) were acquired later. Experiments
 involving these species, along with a previously measured aquatic and
 terrestrial strain, followed the same protocol except that their
 chlorophyll fluorescence was recorded using a Junior PAM (Heinz Walz GmbH,
 Effeltrich, Germany). Measurements were taken every 10
 min during the desiccation period (PAM settings: measuring light 3,
 saturation pulse 6, actinic light 3). The desiccation was assumed complete
 when the mean of measured ΔF/Fm’ for the algae on all filters reached
 zero. The samples were then rehydrated by adding 50 μL of the KSM growth
 medium to each replicate on the filter and the desiccant in a chamber was
 replaced with 100 ml of tap water to achieve higher RH (96%) after which
 the measurements were resumed at the same intervals.
description: YII data June 2018 (described in the article as original data):
 was collected using a PAM 2500 chlorophyll fluorometer (Heinz Walz GmbH,
 Effeltrich, Germany) YII data June 2020: was collected
 using a Junior PAM (Heinz Walz GmbH, Effeltrich, Germany)
 2020FluorescenceR.Rproj: R script used for data visualization and
 cluster analysis Tetradesmus_concat_alignment.nex:
 alignment of 3 genes used in phylogenetic analysis (rbcl, tufA,
 ITS2)