Effects of light and Dark on the Ultrastructure of Lichen Algae

Abstract

8 pages, figures, and tables statistics.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.We are pleased to acknowledge that this work was supported by an Anglo/Spanish Joint Research in Higher Education (Acciones Integradas) grant from the British Council and Ministerio de Educación y Ciencia, Spain and grant number PR 84-0169 from the Comisión Asesora de Ciencia y Technologia. We are grateful to Dr R. M. Brown for valuable discussions and Mr F. Pinto for technical assistance.Peer reviewe