Protection of Plants Against Airborne Oxidants: Cucumber Seedlings at Extreme Ozone Levels

Abstract

A variety of oxidation inhibiting or reducing substances (indole, IAA, tryptophane, mescaline, hydrazine, isonicotinyl hydrazine ascorbic acid, octadecene-1 and DPNH) protect cucumber seedlings against acute ozone exposures (2.5-5.8 mg/1 for 30 min.), the observed protective activities including both increased survival of seedling populations and reduced inhibition of hypocotyl section elongation. Compounds with little or no antioxidant activity failed to protect against ozone damage. C0Cl2 intensified ozone damage, its other protective abilities notwithstanding. A comparison of root immersion, whole seedling immersion, and aerial application showed that protection of the aerial portion of the plant can be effected by compounds supplied entirely through the roots. In general, prolonged contact between whole seedlings or hypocotyls and protectant solutions was necessary. The presence of the test compounds in the ambient medium at best prevented injury or growth inhibition only to a slight degree. The significance of these observations with respect to differences in ozone resistance among plants and a possible relation between growth promoting and ozone-protecting activities is discussed briefly.