Observations have been made on the effects of different storage treatments, either 100°0 or 0°0 r.h., 12 h light:12h dark or 24 h dark for 2 days, on the ultrastructure of the phycobionts of Lobaria amplissima and Lasallia pustulata. After storage, Myrmecia, in the more desiccation-sensitive lichen L. amplissima, showed an increased number of cytoplasmic storage bodies which had more frequently dark contents and a half-moon-like appearance.Trebouxia, from the desiccation-resistant L. pustulata, showed major cellular disorganization when stored at 100°0 r.h. in the light:dark regime, whereas, in the dark, reorganization of thylakoids into a parallel arrangement occurred. Treatment at 0°0 r.h. in the light:dark regime induced an accumulation of starch around the pyrenoid of Trebouxia and, in the light:dark and dark regimes, a peripheral location of pyrenoglobuli without a decrease in the total volume of lipid material. The results are discussed in terms of the utilization and mobilization of reserve substances and the habitat preferences of the two lichens.

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SUMMARYComparisons have been made of the shape of algal cells in the lichen Parmelia sulcata which was subjected to controlled desiccation regimes inducing substantial water loss. The spherical appearance of algal cells obtained by conventional techniques for transmission electron microscopy (TEM) was shown by low temperature scanning electron microscopy (LTSEM) to be the consequence of rapid rehydration during fixation. Collapse of the walls of algal cells and fungal hyphae in the medulla and algal layer when desiccated were observed with LTSEM and shown to be reversible on rehydration. Desiccation-induced contraction of cortical fungal protoplasts was detected with LTSEM. Fixation with osmium vapour only before TEM demonstrated a similar contraction of algal protoplasts.

Quantitative ultrastructural observations have been made on the algal cells (Trebouxia) in two lichens, Parmelia sulcata and P. laevigata, stored for 48 h in the dark or under a light/dark regime. The response of the alga was found to differ in these lichens. In P. sulcata the dark treatment caused a decrease in starch grains, lipid-rich pyrenoglobuli and peripheral cytoplasmic storage bodies and an increase in pyrenoid and chloroplast protein bodies. The algae in P. laevigata contained little starch and no chloroplast protein bodies. However, after dark treatment, starch, cytoplasmic storage bodies and pyrenoid dimensions sometimes declined, while pyrenoglobuli numbers increased. Some of these apparent changes depended upon the units used for calculating the cross-sectional áreas of structures, e.g. absolute units, percentage of cell wall, protoplast or chloroplast cross-sectional área. Chloroplast área increased in the dark (as a % of cell wall área) in both species while mitochondria were larger in the dark in P. sulcata but not in P. laevigata. Ultrastructural changes were not clearly correlated with changes in photosynthetic and respiratory rates. These results directly support the suggestion that some intra-cellular structures are energy-generating reserves the dimensions of which can rapidly change.

Detached leaves of Spinacia olerácea were incubated with evernic acid, the main phenolic substance presen! in Evernia prunastri thalli. This lichen substance produced a decrease in the amount of total chlorophyll and chlorophyll a in treated spinach leaves. Chloroplast structure suffered a decrease in several parameters, i.e. chloroplast área, number of grana, granal width, number of thylakoids per granum and starch contení. The submicroscopic structure of the chloroplast membranes revealed smaller particle diameters in several of the fracture faces in the evernic acid treated samples and even a decrease in the density of partióles in the EFS fracture face. The alterations observed may be related to changes in photosynthetic activity, probably by modification of both photosystem I and photosystem II activities.