New Strategies to Produce High-Value Secondary Plant Metabolites from Shoot Cultures Involving a Sustainable Photobioreactor System

Abstract

At present, the bulk of the market products such as secondary metabolites from higher plants are collected in the wild, providing an opportunity for developing production strategies that are environmentally sustainable and economically viable. On the other hand, total synthesis of some important phytopharmaceuticals is possible, but not economic. To increase yields, plant cell biotechnology seems to be a promising approach; however, drawbacks here include-a very labor-intensive process and notoriously low yields of desired products. Our approach to develop an effective supply strategy is to focus on ways to increase the levels of the metabolites synthesized in plant cells, and to optimize production strategies for the important plant constituents through genetic and culture manipulation. As an alternative way for growing the plant cell cultures, we are developing a new way to grow shoot cultures as morphologically differentiated structures containing high-value metabolites continuously in a two-stage photobioreactor system. The first stage fosters rapid shoots biomass accumulation in liquid media. The second stage is the hydrophonic cultivation of shoots on floatable platforms for high-density plant cultivation in a proposed photobioreactor system. We are planning to use several pharmaceutically important plants shoot cultures growing in the photobioreactor system for obtaining secondary metabolites year-round at relatively low cost. We have found that secondary metabolites are an important source of pharmaceuticals. These occur primarily in aerial parts of the plants that are described below. Hypericum perforatum - well known for antidepressive, anticancer, antiviral activities due to hyperforin and hypericin; Crataegus monogyna and C. laevigata, hawthorn-the source of the anti-heart disease drugs; Camptotheca accuminata- anti-prostate cancer drug, camptothecin, located primarily in young vegetative shoots; Azadiracta indica, azadirachtin from the neem tree, an anti-cancer drug, natural insecticide, and anti-inflammatory; Artemisia annua, artemisinin source of an important anti-malarial drug; Pueraria lobata, kudzu vine, source of the anti-colon cancer and antiosteoporosis isoflavonoid drugs, genistein and daidzein.