Isotope labelling of proteins is important for progress in the field of 
structural proteomics. It enables the utilisation of the power of nuclear 
magnetic resonance spectroscopy (NMR) for the characterisation of the 
three-dimensional structures and corresponding dynamical features of proteins. 
The usual approach to obtain isotopically labelled protein molecules is by 
expressing the corresponding gene in bacterial or yeast host organisms, which 
grow on isotope-enriched media. This method has several drawbacks. Here, we 
demonstrate that it is possible to fully label a plant with (15)N-isotopes. The 
advantage of in vivo labelling of higher organisms is that all constituting 
proteins are labelled and become available as functional, post-translationally 
modified, correctly folded proteins. A hydroponics set-up was used to create the 
first example of a uniformly (15)N-labelled (> 98%) plant species, the potato 
plant (Solanum tuberosum L., cv. Elkana). Two plants were grown at low costs 
using potassium-[(15)N]-nitrate as the sole nitrogen source. At harvest time, a 
total of 3.6 kg of potato tubers and 1.6 kg of foliage, stolons and roots were 
collected, all of which were fully (15)N-labelled. Gram quantities of soluble 
(15)N-labelled proteins (composed mainly of the glycoprotein patatin and 
Kunitz-type protease inhibitors) were isolated from the tubers. NMR results on 
the complete proteome of potato sap and on an isolated protease inhibitor 
illustrate the success of the labelling procedure. The presented method of 
isotope labelling is easily modified to label other plants. Its envisioned 
impact in the field of structural proteomics of plants is discussed.