Effect of acute exposure of sulphur dioxide on the metabolism of Holoptelea integrifolia plants

Two-month-old chilbil Holoptelea integrifolia plants were exposed to 0·06, 0·1 and 0·8 μl litre⁻¹ sulphur dioxide (SO₂) for 4 h in a continuous flow exposure chamber. Symptoms mapped 48 h after exposure indicated no visible injury. The biochemical changes included accumulation of free sugars, especially reducing sugars in tissue associated with depletion of starch, and enhanced acid phosphatase in exposed plants. Constancy in chlorophyll level and rate of CO₂ fixation, together with the absence of visual symptoms, suggest the resistant nature of the chilbil tree.