Accumulation of phenolic compounds in the necrotic areas of Austrian and red pine needles after spraying with sulphuric acid: a possible bioindicator of air pollution

Abstract

summary Austrian pine ( Pinus nigra Arn.) and red pine ( P. resinosa Ait.) were tested for needle damage caused by sulphuric acid spray. Morphology and histology of newly grown needles were compared in 3‐ and 6‐yr‐old plants growing in the greenhouse under controlled conditions. Potted plants covered with plastic bags were sprayed daily either with distilled H 2 O or sulphuric acid of pH 2.5, 3.5 and 4.5. Needle tips, mid‐parts and bases were fixed after 1, 3 and 24 h, and 3, 7 and 30 d in glutaraldehyde + 0.1% caffeine for intracellular precipitation of phenolics. Histochemical reactions and electron microscopic observations showed that the morphological damage is linked to increased deposition of phenolic compounds in mesophylla cells, beginning directly under the stomata. Disorganization of membranes leads to death of the mesophyll cells, even before morphological damage is recognizable as brown spots on the needle surface. Thus the histochemical reactions and observations of cell structure revealed damage earlier than macroscopic observations.