Milestones in plant sulfur research on sulfur-induced-resistance (SIR) in Europe

Untilthe1970’softhelastcenturysulfur(S)wasmainlyregardedasapollutantbeingthemaincontributorofacidrain,causingforestdiebackincentralEurope.WhenCleanAirActscameintoforceatthestartofthe1980’sSO2contaminationsintheairwereconsequentlyreducedwithinthenextyears.Schangedfromanunwantedpollutantintoalackingplantnutrientinagriculturesinceagriculturalfieldswerenolonger“fertilized”indirectlybyindustrialpollution.SdeficiencywasfirstnoticedinBrassicacropsthatdisplayanespeciallyhighSdemandbecauseofitscontentofS-containingsecondarymetabolites,theglucosinolates.InScotland,whereSdepositionsdecreasedevenfasterthanincontinentalEurope,anincreasingdiseaseincidencewithPyrenopezizabrassicaewasobservedinoilseedrapeinthebeginning1990’sandtheconceptofsulfur-induced-resistance(SIR)wasdevelopedafterarelationshipbetweentheSstatusandthediseaseincidencewasuncovered.SincethenalotofresearchwascarriedouttounravelthebackgroundofSIRinthemetabolismofagriculturalcropsandtoidentifymetabolites,enzymesandreactions,whicharepotentiallyactivatedbytheSmetabolismtocombatfungalpathogens.TheSstatusofthecropisaffectingmanydifferentplantfeaturessuchascolorandscentofflowers,pigmentsinleaves,metaboliteconcentrationsandthereleaseofgaseousScompoundswhicharedirectlyinfluencingthedesirabilityofacropforavarietyofdifferentorganismsfrommicroorganisms,overinsectsandslugstothepointofgrazinganimals.ThepresentpaperisanattempttosumuptheknowledgeabouttheeffectoftheSnutritionalstatusofagriculturalcropsonparametersthataredirectlyrelatedtotheirhealthstatusandbythistoSIR.MilestonesinSIRresearcharecompiled,openquestionsareaddressedandfutureprojectionsweredeveloped.