Targeted induction of plant secondary metabolism in horticultural plants by controlled stress applications

Plants rely on morphological or biochemical mechanisms to protect themselves under challenging environmental conditions. This involves the accumulation of diverse bioactive secondary metabolites. Such secondary metabolites are recognized as valuable compounds for human health, as ingredients of cosmetics or for further industrial purposes, utilized after extraction of purified compounds or in plant extracts. The interdisciplinary projects InducTomE and TaReCa evaluate a novel process to make use of secondary metabolites in residual plant biomass of horticultural plants. In this process, stress treatments after the last fruit harvest are applied to increase the amount of valuable metabolites in the plant residuals. Thereby, the residual biomass can be used for the extraction of industrially relevant metabolites. In a pre-screen, young bell pepper and tomato plants were exposed to various abiotic stress treatments like water or nutrient deficiency, salt stress or cold. We identified suitable stress treatments that induced the accumulation of total phenolics, flavonoids and also valuable target metabolites, like the flavonoid rutin and the polyisoprenoid solanesol. A comparison of commercial lines and a wild relative in these experiments revealed differences in stress-induced metabolite accumulation and biosynthesis gene expression indicating genetic variability of responses of secondary metabolism to stress. According to the results of the pre-screen, stress treatment protocols for the induction of target metabolites will be developed for use in commercial greenhouses. In addition, phenotyping methods were applied to quantify plant stress responses and to monitor the intensity of the treatments. This will also help to develop easy-to-use tools to control the targeted stress application in commercial greenhouses. The proposed method for a targeted tailoring of the secondary metabolism in horticultural residuals demonstrates the valorization of underutilized by-products of horticultural food production. Thereby, it has thus the potential to generate added value and increase sustainability of the horticultural food production