Influence of Mercury on the Green Alga Haematococcus lacustris. Inhibition Effects and Recovery of Impact

The influence of mercury ions on germination of the resting cells (aplanospores) and on cell division, cell structure, phototaxis, and photosynthesis during the flagellate stage of Hoemotococcus lacustris was investigated. Aplanospores possess a higher tolerance against mercury ions than flagellates. The reason could be seen in the thicker wall of the resting cells which possibly provide a detoxifying effect by immobilisation of Hg²⁺. This is confirmed by a normal phototactic orientation of flagellates formed from Hg ²⁺-influenced aplanospores. In contrast, a direct addition of Hg²⁺ (0.1 to 1 /*M) to the flagellate stage induced an immediate loss of the flagellates to react phototactically, but it was interesting that the inhibition was overcome with time. Obviously, these Hg²⁺ concentrations influence only the sensory transduction chain, whereas the energetic background is not injured because the velocity of movement and the percentage of motile cells were scarcely affected. This is supported by the high level of the photochemical efficiency of photosystem II, which remains unchanged at 1 uM Hg²⁺. Recovery of photosynthesis from inhibition by 10/iM Hg²⁺ suggests a connection between Hg²⁺ influence and metabolism of the D, protein in the reaction centre of photosystem II. The Hg²⁺ effect was reversed with time in light, but not in darkness, and streptomycin, an inhibitor of chloroplast protein synthesis, prevented recovery. In flagellates, showing no reactivation, exposure to 10uA/l Hg²⁺ caused cell swelling, a loss of the flagella, and a disorganisation in structure of the chloroplast and of nucleus.