Physiological responses of Vicia faba plants to sulfur dioxide.

Exposure of broad bean (Victa faba L.) plants to 270 +/- 32 and 670 +/- 45 micrograms m 3SO2 for 1.5 hr daily between 40 and 85 days of their ages resulted in an increase in their transpiration rate, water saturation deficit, phenol content, and peroxidase activity and a decrease in protein content. With the increase in number of exposures of plants to SO2, chlorotic and brown, necrotic visible injury signs were also developed in leaves. It was further noted that the magnitude of undesirable biochemical changes, which possibly helped in the formation of new pigment characteristic of necrotic tissue of SO2-exposed plants, was not totally dependent on the pollutant concentration.