| Abstract: | An uncommonly harsh winter occurred in Finland in 1986/1987, when the minimum monthly temperatures were lower than ‐30°C in December, January and February. This study reports the development of visible symptoms, changes in electrolyte leakage and ultrastructure in Picea abies needles from a rural and an industrial area during this period. The first frost‐induced visible symptoms, entirely or partially greyish needles, appeared in late February following a mild spell. Gradually the discoloured needles turned reddish‐brown and most of the injured needles were shed before the onset of the new season growth. Electrolyte leakage, measured as relative conductivity (RC %), showed substantially higher wintertime values (RC ca 75%) in greyish needles compared with healthy looking green needles (RC ca 30%). Light microscopy showed contracted protoplasts and collapsed cell walls in the greyish part of the needle. The main ultrastructural symptoms in all the samples were the withdrawal of plasma membrane from the cell wall, darkening of the cytoplasm, disappearance of the tonoplast (and central vacuole), contraction of the protoplast and finally collapse of the cell walls and total disintegration of the protoplast. There were no qualitative differences in the frost‐induced visible or structural symptoms between the rural and industrial area. |
