Abstract
Abstract Conifers contain ascorbic acid which is probably a protective against oxidative attacks. In yellow needles of damaged conifers the ascorbic acid content is increased, this suggests an induction by air pollutants and/or photooxidants of a protection mechanism in trees. To study this mechanism in more detail, a green cell suspension culture of spruce (Picea abies) has been established. These cells contain chlorophyll and have a photosynthetic capacity, but they need carbohydrates (sucrose) for growth and are thus photoheterotrophic. Their ascorbic acid content and its regulation depends on carbohydrates, the cells resemble healthy green needles in this respect; they appear to be qualified for studies on the induction of a defense mechanism. Treatment of these cells with SO2 (20 ppm, 4 days) ozone (1 ppm, 14 days) and vaporous H2O2 revealed a decrease of the ascorbic acid content and (to a lesser extent) also of chlorophyll. It is concluded that (photo-)oxidants obviously do not play such a dominant role in bleaching of needles as it is assumed. The increased ascorbic acid content found in needles of damaged conifers is probably not an induced protection mechanism against oxidants.
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