The support of plant growth by small peptides in two functionally different plant species

Background/Question/Methods

Organic nitrogen (ON) is the most abundant nitrogen (N) form in most soils and includes compounds ranging from single amino acids to high molecular weight proteins. Despite increasing recognition that many species access amino acids as a N source, more complex forms of ON have not previously been considered accessible to plants. Furthering the recent suggestion that some plants can use di-peptides and proteins as an N source under sterile conditions, we assessed the capacity of two functionally different species to access a range of small peptide sources. We compared the innate ability of non-mycorrhizal model plant Arabidopsis thaliana (the species most commonly used in laboratory amino acid uptake studies) and uncultivated species Lobelia anceps (naturally endomycorrhizal but grown without symbionts) to grow using peptides as a sole N source. Plants were grown axenically on gel media containing di-, tri- or tetra-peptides, their constituent amino acids or inorganic N. At harvest we determined plant root/shoot biomass, total %N and concentrations of amino acids, inorganic N and source peptides in tissue.

 Results/Conclusions       

Arabidopsis could use all small peptides sources supplied for growth, with some di-peptides enabling up to 74% of the maximum biomass production supported by inorganic N. While Lobelia could also use all supplied peptide sources, overall growth rates were lower than for Arabidopsis with peptides supporting <37% of maximal biomass. Metabolite analysis demonstrated intact uptake of some peptides and traceable metabolite signatures of specific peptide sources in plant tissues. Glycine-based peptides had marked species- and peptide-specific effects on root growth and biomass allocation, ranging from complete repression to three-fold greater root proliferation of Lobelia plants grown with Gly-Gly-Gly-Gly. Our results demonstrate species- and source-specific responses to peptide-N and thus caution the use of Arabidopsis as the sole plant model. Additional evidence that plants can access an N pool previously considered unavailable has far-ranging implications for N nutrition in both natural and agricultural systems, particularly for sustainable bioproduction. Future goals lie in determining the abundance of small peptides in soils, how much the capacity to access peptide-N varies across plant families and the effect of specific mycorrhizal associations on facilitating access to small peptides.