Plant responses to H2S and SO2 fumigation. I. Effects on growth, transpiration and sulfur content of spinach

Abstract

Exposure of spinach (Spinacia oleracea L. cv. Monosa) to 0.25 μl l−1 H2S reduced the relative growth rate by 26, 47 and 60% at 15, 18 and 25°C, respectively. Shoot to root ratio decreased in plants fumigated at 18 and 25°C. Growth of spinach was not affected by a 2‐week exposure to 0.10 or 0.25 μl l−1 SO2.Both H2S and SO2 fumigation increased the content of sulfhydryl compounds and sulfate. A 2‐week exposure to 0.25 μl l−1 H2S resulted in an increase in sulfhydryl and sulfate content of 250 to 450% and 63 to 248% in the shoots, respectively, depending on growth temperature. Exposure to 0.15 and 0.30 μl l−1 H2S at 20°C for 2 weeks resulted in a 46% increase in sulfate content of the shoots at 0.30 μl l−1 and no detectable increase at 0.15 μl l−1 H2S; the sulfate content of the roots increased by 195 and 145% at 0.15 and 0.30 μl l−1 H2S, respectively. Fumigation with 0.25 μl l−1 SO2 at 20°C for 2 weeks resulted in an increase in sulfhydryl content and sulfate content in the shoots of 285% and 300 to 1100%.H2S fumigation during the 12 h light period or only during the dark period resulted in identical growth reduction and accumulation of sulfhydryl compounds; they were about 50 and 67% of those observed in continuously exposed plants.H2S‐ and SO2‐exposed plants showed an increased transpiration rate, which was mainly caused by an increased dark‐period transpiration. No effect of H2S and SO2 on the water uptake of the plants and the osmotic potential of the leaves was detected. Plants fumigated with 0.25 μl l−1 H2S for 2 weeks were smaller and differed morphologically from the control plants by slightly more abaxially curved leaf margins. Cross sections of the leaves showed smaller cells at the margins and smaller and fewer air spaces. The increased transpiration in the H2S‐exposed plants is discussed in relation to the observed morphological changes.