ALLELOCHEMICALS PRODUCED DURING SINIGRIN DECOMPOSITION IN SOIL

Although allelochemicals are produced from glucosinolates contained in Brassica spp. tissues, little is known concerning allelochemical formation and fate in soil. Enzymatic decomposition of sinigrin by myrosinase was determined in buffered and unbuffered solutions, soil extracts, and soils. Both allylnitrile and allyl isothiocyanate were identified as products in buffered solutions, with allylnitrile formation dominating at pH values below 4.0 and allyl isothiocyanate at higher pH values. The addition of Fe2+ to buffered solutions promoted the formation of allylnitrile, whereas Fe3+ inhibited the enzymatic reaction. Significant amounts of allylnitrile were formed in weakly buffered water extracts from soils but not in soils or ammonium acetate extracts obtained from those soils. The dominant product of sinigrin decomposition in soils and ammonium acetate extracts was allyl isothiocyanate regardless of soil characteristics. Because isothiocyanates have pesticidal activities and are dominant products formed from glucosinolates in soil, the use of Brassica spp. tissues to control soil-borne plant pests merits further attention.