Impact of atmospheric sulfur deposition on sulfur metabolism in plants:H₂S as sulfur source for sulfur deprived <i>Brassica oleracea</i> L.

Brassica oleracea L. was rather insensitive to atmospheric H2S: growth was only negatively affected at greater than or equal to 0.4 mu l l(-1). Shoots formed a sink for H2S and the uptake rate showed saturation kinetics with respect to the atmospheric concentration. The H2S uptake rate was high in comparison with other species, which may reflect the high sulfur need of Brassica. The net up take of sulfate by roots of hydroponically grown plants was substantially reduced after one week of exposure to 0.25 mu l l(-1) H2S, indicating that plants switched in part from sulfate to H2S as sulfur source for plant growth. Plants were sulfur deficient after two weeks of sulfur deprivation, illustrated by reduced growth, which was more pronounced for shoots than for roots, and in enhanced shoot dry matter content. The latter could for the greater part be attributed to enhanced levels of soluble sugars and starch. Sulfur deficiency was further characterized by a low pigment content, extremely low levels of sulfate and water-soluble non-protein thiols, and by enhanced levels of nitrate and free amino acids, particularly in the shoots. Furthermore, sulfur deficient plants contained a lower total lipid content in shoots, whereas its content in roots was unaffected. The level of sulfolipids was decreased in both roots and shoots. When sulfur deprived plants were exposed to 0.25 mu l l(-1) H2S for one week, ail sulfur deficiency symptoms were abolished and growth was restored. Furthermore, plants were able to grow with 0.4 mu l l(-1) H2S as the sole sulfur source. Water-soluble non-protein thiol content was enhanced in both shoots and roots of H2S exposed plants, irrespective of the sulfate supply to the roots, whereas plants grown with H2S as sole sulfur source contained very low sulfate levels. The interaction between atmospheric and pedospheric sulfur nutrition in plants is discussed.