Histological study of Austrian pine needles injured by ambient air pollutants. [Pinus nigra]

A needle blight induced by air pollutants has been common among New Jersey Austrian pines. Blighted needles are characterized by orange-brown necrosis restricted to needle tips and progressing into adjacent tissues, resembling semimature-tissue blight of white pine. Trees vary in susceptibility, but only physiologically active needles of the current year are damaged. A study of successive cross sections beginning near the tips of freshly blighted needles shows complete disorganization of both mesophyll and stele cells as the tip. Adjacent sections indicate injury to mesophyll cells with necrotic regions adjoining the substomatal chambers. Endodermis as well as transfusion cells of the stele are distorted. Sections below this point reveal less generalized damage which is restricted to the transfusion tissue. Frequently, mesophyll cells in these sections exhibit no signs of disorganization and appear healthy, contrary to results of white pine studies where comparable cross sections indicate damage confined to the mesophyll. Sections ca. 0.5 mm below the base of the blight show decreasing transfusion tissue injury and no injury to the mesophyll. Greenhouse fumigations with SO/sub 2/ and formaldehyde have produced injuries similar to those occurring in nature.