Use of plant roots for phytoremediation and molecular farming.

Alternative agriculture, which expands the uses of plants well beyond food and fiber, is beginning to change plant biology. Two plant-based biotechnologies were recently developed that take advantage of the ability of plant roots to absorb or secrete various substances. They are (i) phytoextraction, the use of plants to remove pollutants from the environment and (ii) rhizosecretion, a subset of molecular farming, designed to produce and secrete valuable natural products and recombinant proteins from roots. Here we discuss recent advances in these technologies and assess their potential in soil remediation, drug discovery, and molecular farming.

Hyperaccumulation, complexation and distribution of nickel in Sebertia acuminata.

The nickel content in different parts of the hyperaccumulating tree Sebertia acuminata was analysed by atomic absorption spectroscopy. Nickel was found to be mainly located in laticifers. The total nickel content of a single mature tree was estimated to be 37 kg. By gel filtration and NMR spectroscopy, citric acid was unequivocally identified as counter ion for about 40% of this metal present. Nitrate was assumed to be a further partner for a complete ionic balance. Phytochelatins were not found to be involved in nickel detoxification in Sebertia. The localization of nickel complexes inside the laticifers was demonstrated by light microscopy as well as by scanning electron microscopy in combination with an EDX system for the analysis of elements. A repellent effect of the plant sap was observed on the fruit fly Drosophila melanogaster indicating that in hyperaccumulating plants nickel functions as an agent to prevent predation.

Saccharomyces cerevisiae and Neurospora crassa contain heavy metal sequestering phytochelatin.

In fungi, cellular resistance to heavy metal cytotoxicity is mediated either by binding of metal ions to proteins of the metallothionein type or by chelation to phytochelatin-peptides of the general formula (gamma-Glu-Cys)n-Gly. Hitherto, only one fungus, Candida glabrata has been shown to contain both metal inactivating systems. Here we show by unambiguous FAB-MS analysis that both a metallothionein-free mutant of Saccharomyces cerevisiae as well as a wildtype strain synthesize phytochelatin (PC2) upon exposure to 250 microM Cd2+ ions. The presence of Zn and/or Cu ions in the nutrient broth also induces PC2 synthesis in this organism. By 109Cd exchange and subsequent monobromobimane fluorescence HPLC, it could be shown that the presence of Cd2+ in the growth medium also induces phytochelatin synthesis in Neurospora crassa, which contains metallothioneins.