Responses of Sphagnum species to atmospheric nitrogen and sulphur deposition

The responses of Sphagnum species to atmospheric pollution by sulphur and nitrogen oxides are reviewed. An explanation of the tolerance of sulphur dioxide in Sphagnum cuspidatum is provided. This involves an exclusion mechanism by the oxidation of bisulphite ions to less toxic sulphate ions catalysed by the presence of iron and possibly other metals on the cell wall cation-exchange sites. Tolerance is influenced by changing the iron content of the plants. A similar mechanism may account for sulphur dioxide tolerance in Sphagnum recurvum.
Evidence for a close coupling of nitrate assimilation with the atmospheric nitrogen supply in ombrotrophic Sphagnum species in unpolluted regions is reviewed, and this coupling is shown to be lost in polluted environments with high atmospheric nitrogen supply. The potential effects of a supra-optimal atmospheric nitrogen supply to Sphagnum species on the ecology of mires is discussed.
The effects of nitrogen and sulphur pollutants on Sphagnum species are used to make broad generalizations as to how other bryophyte species might respond to these pollutants and to explain known effects of atmospheric pollution on bryophyte communities.     

Studies on the efficiency of mRNA translation during cold shifts in Tetrahymena

The effects of temperature shifts on the synthesis of proteinhave been studied in Tetrahymena pyriformis treated with ActD. Temperatures significandy below the growth optimum reducenet protein syndiesis, apparendy by decreasing the yield ofprotein produced on each template molecule. High temperaturesynchronizing shifts produce similar effects on amino acid incorporationbut have considerably less effect on another ribosome-associatedbiosynthetic pathway,complex lipid synthesis. The results indicatethat division-synchronizing heat and cold have similar effectson the messenger translational efficiency in Tetrahymena pyriformis (Received November 21, 1970; )