Light and scanning electron microscopy of SO₂‐induced injury to leaf surfaces of field bean (Vicia faba L.)

Exposure to low concentration of SO 2 increases stomatal conductance in field bean by c 20%. Microscopy of epidermal strips showed that this response was associated with extensive destruction of epidermal cells adjacent to the stomata. Guard cell survival was not affected signficantly. Collapsed epidermal cells were also observed in intact leaf samples using scanning electron miscroscopy, thus confirming that the damage seen in epidermal strips was not caused by the stripping procedure. These observations are discussed in relation to the hypothesis that the increased stomatal opening induced by low SO 2 concentrations results from preferential injury to the adjacent cells.