De rol van zwavel in planten

Samenvatting
Zwavel is een essentieel element voor de groei en de fysiologie van planten. De zwavelbehoefte van planten verschilt sterk tussen soorten en het zwavelgehalte varieert tussen de 0,1 en 6 % van het drooggewicht. Zwavel wordt als sulfaat door de wortel vanuit de bodem opgenomen; maar het moet worden gereduceerd alvorens het kan worden ingebouwd in organische zwavelverbindingen. In gebieden met een hoge luchtverontreiniging van SO₂ of H₂S zijn planten zijn ook in staat om de door het blad geabsorbeerde zwavelgassen als zwavelbron te benutten. Er bestaat een goede coördinatie tussen de wortels en de spruit (bladeren) in de afstemming van de opname en de assimilatie van sulfaat. Planten hebben de fysiologische plasticiteit zich aan te passen aan een beperkt of overmatig zwavelaanbod door het veranderen van het niveau en expressie van sulfaattransporteiwitten en sulfaat-reducerende enzymen. Zwavel wordt in de plant gebruikt voor de synthese van aminozuren (cysteïne, methionine), eiwitten en diverse andere zwavelhoudende verbindingen, zoals thiolen (glutathion), sulfolipiden en secundaire zwavelverbindingen (alliinen, glucosinolaten, fytochelatines), die een belangrijke rol spelen in de fysiologie van planten en in de bescherming tegen en aanpassing van planten aan abiotische en biotische stress. Een tekort aan zwavel resulteert in het verlies van de fitness van planten en de weerstand tegen belasting van milieufactoren, ziektes en vraat, en tevens in een verminderde voedselkwaliteit en veiligheid.

Curriculum Vitae Luit J. de Kok
Research interests
During the last decades research my 'Plant Sulfur Research Group' has generally been focused on investigating the physiological processes underlying the mechanism of adaptation of plants to the environment. The significance of membrane lipids and antioxidants (e.g. glutathione) in the adaptation of plants to various stress factors e.g. chilling, frost, salinity and air pollution is investigated. In addition the consequences of global change, in particular the effect of elevated CO₂ levels on plants are investigated. During the last decade the physiological significance of sulfur metabolism in plants has become a major research topic. The molecular/biochemical, physiological and agronomic and environmental aspects of sulfur in plants is investigated in close co-operation with various other international research groups. The regulatory aspects of the sulfur uptake and assimilation in plants in relation to the metabolic requirement for growth and the signals therein involved are investigated. The relation between expression of the various genes involved in sulfur metabolism, the level of transporters and enzymes involved in sulfur metabolism and the actual fluxes of the sulfur metabolites under various physiological conditions is studied. The modulation of sulfur nutrition by changing the levels of atmospheric and pedospheric sulfur sources, for instance by using ³⁵S-labelled sulfur compounds and molecular techniques, have shown promise to elucidate the role and significance of changes in the level and expression of sulfate transporter proteins and sulfate reducing enzymes in the regulation of the sulfur metabolism. The interactions between sulfur and nitrogen assimilation are evaluated. In addition, the pathway and regulation of the synthesis of secondary sulfur compounds are investigated. Further studies are carried out on assessing the relation between plant sulfur status and its resistance to environmental stress (e.g. toxic metals) and pests.

Expertise:
Plant physiology; Plant sulfur metabolism; Air pollution and global change; Abiotic and biotic stress.

Academic Positions:

• March 1979 - August 1979, Visiting Research Fellow, Department of Plant Biochemistry, University of California, Riverside, USA.
• September 1979 - February 1980, Research Biochemist, Statewide Air Pollution Research Center, University of California, Riverside, USA.
• September 1986 - February 1987, Visiting Research Fellow, School of Agriculture and Forestry, University of Melbourne, Australia.
• May 1988 - August 1988, Visiting Researcher, Fraunhofer Institute for Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany.
• September 2006 - onwards, Honorary Principal Fellow, Department of Forest and Ecosystem Science, Creswick, University of Melbourne, Australia.

Professional Service and Management:

• Chairman of the Management Committee and Chairman of all Meetings of COST Action 829: "Fundamental, Agronomical and Environmental Aspects of Sulfur Nutrition and Assimilation in Plants" (1997-2003).
• Member of the Scientific Board of the Julius Kühn-Institut (JKI), Germany (2009 – onwards).
• Vice President (P&D) of the International Scientific Centre of Fertilizers (CIEC) (2013 - onwards).
• Chairman/Secretary of several symposia and workshops.
• Series editor of Springer "Plant Ecophysiology" series (www.springer.com/series/6193).
• Series editor of Springer "Proceedings of the International Plant Sulfur Workshop" series (www.springer.com/life+sciences/plant+sciences/book/978-94-007-4449-3).