Figure 1.
Schematic illustration of the experimental design.
Four combinations of pre-cultivation conditions, four desiccation regimes (a–d; d applied only on samples pre-cultivated on agar) and final recovery after rewetting. For details see methodology section of the text.
Figure 2.
Phylogenetic tree of Zygnematophyceae showing the positions of the strains investigated in this study.
A midpoint-rooted Bayesian tree of rbcL sequences is shown. Values at the branches indicate Bayesian posterior probabilities (BI PP), maximum likelihood (ML), and maximum parsimony (MP) bootstrap values (BS). Asterisks indicate BI PP = 1.00, and ML and MP BS = 100; dashes indicate BI PP<0.8, and ML and MP BS<50. Strains used in this study are in bold.
Figure 3.
Light micrographs of the strains pre-cultivated on agar medium for 9 weeks.
A–D: cultures grown on regular BBM medium (A BBM); E–H: cultures grown on BBM without nitrate (A BBM-N). The images were taken prior to the desiccation experiments; a Zygnema akinete with a distinct brown mesospore is marked with an asterisk. Scale bars: 10 µm.
Figure 4.
Effective quantum yield (ΦPSII) under different desiccation scenarios.
A–D: rapid desiccation, approximately 10% relative humidity (rh); E–H: slow desiccation, 86% rh; I–L: very slow desiccation, 86% rh plus additional moistening of samples with 10 µl BBM. All strains shown were pre-cultivated on regular agar medium (A BBM) or on medium without nitrate (A BBM-N). Results are means ± standard deviations of four independent experimental replicates.
Figure 5.
Recovery of effective quantum yield (ΦPSII) during rehydration after 24 hours desiccation.
Each panel compares the performance of the same culture desiccated under different conditions; no plots were constructed for those regimes that were lethal for all of the cells. Samples were collected from cultures pre-cultivated on agar media: A–D: cultures grown on regular agar medium (A BBM); E–H: cultures grown on BBM without nitrate (A BBM-N). Results are means ± standard deviations of four independent experimental replicates.
Table 1.
Relative values of the effective quantum yield during recovery of algal samples pre-cultivated on agar (A BBM and A BBM-N cultures).
Table 2.
Viability of cultures pre-cultivated on agar following 48 hours of rehydration in water (A BBM and A BBM-N cultures).
Figure 6.
Transmission electron micrographs of pre-akinetes prior to desiccation.
A: Zygnema sp. B. Large lipid bodies and chloroplast with starch grains are indicated. B: Zygnema sp. C. Lipid bodies and electron-dense particles (arrow) are indicated. C: Zygnema sp. E. Lipid bodies in the cell periphery, electron-dense particles (arrows) and cell walls with a fibrillose mucilage layer are marked. D: Zygnemopsis sp. L. Chloroplast lobes with starch grains, electron-dense particles (arrows), and lipid bodies are marked. All cultures were cultivated on agar medium without nitrate (A BBM-N) for 9 weeks. Abbreviations: Chl: chloroplast; L: lipid body; M: mitochondrion; ML: mucilage layer; PG: plastoglobules; S: starch. Scale bars: 1 µm.
Figure 7.
Transmission electron micrographs of pre-akinetes following desiccation for 2.5 hours at 86% rh.
A–C: Zygnema sp. B; D: Zygnema sp. C; E–F: Zygnema sp. E; and G: Zygnemopsis sp. L. Note the following features: A: dense structure of the chloroplast and fusions of lipid bodies; B: dense structure of Golgi body and chloroplast; C: nucleus with less electron-dense areas of heterochromatin (arrow); D: accumulation of lipid bodies in the cell periphery; E: starch grains, lipid bodies in the cell periphery and the cell wall covered by a fibrillose mucilage layer; F: accumulations of ribosomes (arrows) next to the nucleus; and G: accumulation of vesicles and small electron translucent compartments next to the lipid bodies. Abbreviations: Chl: chloroplast; G: Golgi body; L: lipid body; M: mitochondrion; ML: mucilage layer; N: nucleus; S: starch. Scale bars: A–D and G: 1 µm; E: 2 µm; F: 0.5 µm.