Effects of SO 2 on ascorbic acid in crop plants

Abstract

The effects of low levels of SO 2 (78·6, 131 and 262 μg m −3) on ascorbic acid were evaluated in three crop plant species, namely Brassica nigra L., Phaseolus radiatus L. and Zea mays L. Z. mays, which is relatively SO 2-resistant, possesses a comparatively high amount of ascorbic acid. The ascorbic acid contents of B. nigra and P. radiatus, which are relatively SO 2-sensitive species, decreased markedly within one week following SO 2 fumigation. However, fumigation of Z. mays with SO 2 was accompanied by a significant reduction in ascorbic acid only after 6 weeks of fumigation with 131 and 262 μg m −3 of SO 2. The results of this investigation indicate a positive correlation between ascorbic acid content and SO 2 sensitivity of plants. The ascorbic acid acts as a powerful reductant and seems to mediate the reduction of sulphite to hydrogen sulphide, thereby reducing the toxicity of SO 2. It appears that Z. mays is relatively resistant to SO 2 because initially it has a high ascorbic acid content. It is unlikely that the ascorbic acid in plants plays an important role in determining their relative resistance to sulphur dioxide pollution.