SULFATE AND MICRONUTRIENTS CAN MODULATE THE EXPRESSION LEVELS OF MYROSINASES IN SINAPIS-ALBA PLANTS

The myrosinase-glucosinolate system is considered to be a major compon ent of the preformed defence system of Brassicaceae species. This hypo thesis has influenced the belief that the components of the myrosinase -glucosinolate system are present at fixed levels which are independen t of environmental factors. In the present study we show that external availability of nutrients can modulate the expression levels of myros inase enzymes (EC 3.2.3.1). Nutrients such as sulphate, iron, copper, zinc and manganese were tested for their modulation effect on myrosina se expression levels and activity in roots, stems, cotyledons and buds of Sinapis alba seedlings at four different developmental stages. The most sensitive organ was the bud where iron deficiency approximately doubled the myrosinase activity. Removal of sulphate and all four micr onutrients reduced the myrosinase activity to approximately half of th e activity in plants supplemented with all these nutrients. The myrosi nase polypeptides can be divided into classes based on molecular mass after reduction, The nutritional status influenced mainly the 68-kDa c lass of myrosinases as revealed by western blot and laser scan densito metry of the immunolabelled blots.