Keywords: cysteine, glutathione, hydrogen sulphide, methionine, pests, proteins, secondary sulfur compounds, stress, sulfate reduction, sulfate uptake, sulfur assimilation, sulfur dioxide.

Sulfur is an essential element for growth and physiological functioning of plants and its content varies between 0.1 and 6 % of plant dry weight. The sulfur requirement of plants varies strongly between species and can be expressed as the rate of sulfur uptake and its assimilation needed per gram plant biomass produced with time. In addition to pedospheric sulfate, plants are also able to utilise foliarly absorbed sulfur as a sulfur source and there appears to be good co-ordination between roots and shoots in the tuning of the rates of sulfur uptake and its reduction/assimilation. To some extent plants have the physiological plasticity to adapt to limited or excess sulfur supply by changing the level and expression of sulfate transporter proteins and the enzymes involved in sulfate reduction. Sulfur is utilised for the synthesis of amino acids (cysteine, methionine), proteins and various other compounds, as thiols (glutathione), sulpholipids and secondary sulfur compounds (alliins, glucosinolates, phytochelatins), which play an important role in the physiology of plants and in the protection and adaptation of plants against stress and pests. Sulfur deficiency will result in loss of plant vigour, resistance to environmental stress and pests and in decreased food quality and safety.

Luit J. De Kok, Ana Castro, Mark Durenkamp, C. Elisabeth E. Stuiver, Sue Westerman, Liping Yang and Ineke Stulen, Laboratory of Plant Physiology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands.

27 pages, 5 figures, 1 table, 86 references.