There is a great number of well known herbal plants such as horseradish, garlic and mustard with various bioactive compounds, such as glucosinolates, alliins, glutathione, but little is known about the specific effect of a compound and its interaction with other constituents. An oil extract from nasturtium (Tropaeolum majus) for example is 20 times more effective than the synthetically produced analogue (Winter 1954, Klesse and Lukoschek 1955).

Glucotropaeolin is the characteristic, aromatic glucosinolate found in T. majus which has been indicated for the treatment of scurvy, bronchitis, cystitis, pyelitis and as a general tonic and stimulant (Bardeau 1978). In the pharmaceutical industry it has long been recognised for its antimicrobial action against urethral infections (Dannenberg et al. 1956, Bergmann et al. 1966). The active component is benzylisothiocyanate, which is released after enzymatic cleavage of glucotropaeolin by myrosinase. Benzylisothiocyanate derived from T. majus may also have the ability to induce the synthesis of protective enzymes, which reduces the effects of chemical carcinogens (Fahey et al. 1997).

Variation of glucosinolate concentration within a plant is caused by genotypical differences and numerous environmental factors such as plant age, plant part, temperature, light intensity and plant pathogen interactions (Elliot and Stowe 1971, Rosenthal and Janzen 1979, Gershenzon 1984, Schnug 1987, Fieldsend and Milsford 1994, Rosa et al. 1997, Rosa and Rodrigues 1998). Besides these natural fluctuations, glucosinolates are prone to degradation after activation of the myrosinase enzyme following cellular disruption. This means that losses of the intact glucosinolate are inevitable during harvest and preservation of the crop (Bones and Rossiter 1996) and therefore a principal, major handicap for the pharmaceutical use of T. majus. The strongest exogenous factor influencing the glucosinolate content in both, vegetative and generative tissues of Brassica crops, proved to be, however, the sulphur supply (Schnug 1987, Walker and Booth 1994). N fertilisation did not significantly affect the glucotropaeolin content of T. majus (Figure 10, Bloem et al. 2001b).

S fertilisation, however, increased the glucotropaeolin content in leaves and stems by about 0.43 and 0.11 ^mol kg-1 applied S, respectively. The glucotropaeolin content of seeds of Tropaeolum majus was almost doubled by S fertilisation from 33 to 56 ^mol g-1 (Bloem et al. 2001b). The results reveal the significance of an optimum nutrient supply in order to achieve a consistently high crop quality, a criterion which is of particular relevance if the phytopharmaceuticals are directly prepared from the harvested plant material (Bloem et al. 2003).

leaves stems leaves stems

Figure 10. Influence of sulphur and nitrogen fertilisation on the glucotropaeolin content in leaves and stems of T. majus at the start of flowering (Bloem et al. 2001b).

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