Sulfur deficiency in Brassica oleracea L: Development, biochemical characterization, and sulfur/nitrogen interactions

The sequence of processes characteristic for the development of sulfur deficiency and the recovery from sulfur deficiency were measured in hydroponically grown Brassica oleracea L,. (curly kale). After one week of sulfur deprivation, the plants started to show symptoms of sulfur deficiency: yellowing and a nearly halted,growth of the shoots and an increase in the shoot dry matter. Shoots were more rapidly affected by sulfur deprivation than roots. The appearance of sulfur deficiency symptoms was preceded by a dramatic decrease in sulfate and thiol content in both shoots and roots. Sulfur deprivation has a decisive impact on the uptake and assimilation of nitrate. The uptake of nitrate was strongly reduced in sulfur deficient plants, and the occurrence of sulfur deficiency symptoms was accompanied by an accumulation of nitrate and free amino acids and a loss of soluble proteins. Apparently, at this stage, the availability of sulfur-containing amino acids for protein synthesis had become the limiting factor for growth. When sulfate was added again to the nutrient solution, plants very rapidly recovered from sulfur deficiency. The levels of the different metabolites returned to that observed at sulfur-sufficient conditions. The amino acid/thiol ratio proved to be a sensitive indicator for the assessment of the sulfur status of plant tissue.