Stress-induced changes of bioactive compounds in Tropaeolum majus L.
The glucosinolate (GSL) content is an important quality parameter of crops, such as mustard, horseradish or nasturtium, which are grown for their taste as condiments or for medical purposes. Accordingly, an enhancement of the GSL content should promote the large-scale cultivation of these plants. It is well known that GSLs reveal a high significance in plant defense, and that several stress factors cause an increase in the GSL concentration. The goal of the present study was to evaluate the means to stimulate the GSL biosynthesis during plant growth by applying moderate stress. The impact of different treatments on the GSL content and on growth of Tropaeolum majus L. was investigated in a greenhouse trial. Moderate stress was induced by drought, by the addition of salt, or the application of growth regulators (methyl jasmonate, salicylic acid). Moreover, cell wall lysate was applied to the plants to mimic biotic stress, such as pathogen attack. Evapotranspiration (ETP), biomass development, specific leaf weight (SLW), plant pigments, and thiol contents had been recorded to evaluate physiological changes in response to the treatments. The glucotropaeolin (GT) content, representing the sole GSL of T. majus was measured as target compound. Drought and MeJA application increased the GT concentration on dry weight basis and impacted on ETP, dry matter content, SLW and plant pigments, too. Application of salt, SA and cell wall lysate did not affect the GT concentration in a consistent way. Moderate drought and the application of MeJA are suitable tools to increase the GT concentration in T. majus. However, in case of drought the higher GT concentration was only reached at the expense of biomass production. High GT concentrations together with reasonable yields were only achieved by MeJA application.