Drought stress increases the production of 5-hydroxynorvaline in two C 4 grasses

Abstract

Plants produce various compounds in response to water deficit. Here, the presence and identification of a drought-inducible non-protein amino acid in the leaves of two C 4 grasses is first reported. The soluble amino acids extracted from the leaves of three different species were measured by high-performance liquid chromatography of derivatives formed with o-phthaldialdehyde and β-mercaptoethanol. One amino acid that increased in amount with drought stress had a retention time not corresponding to any common amino acid. Its identity was determined by metabolite profiling, using 1H NMR and GC–MS. This unusual amino acid was present in the dehydrated leaves of Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel, but was absent from Paspalum dilatatum Poir. Its identity as 2-amino-5-hydroxypentanoic acid (5-hydroxynorvaline, 5-HNV) was confirmed by synthesis and co-chromatography of synthetic and naturally occurring compounds. The amount of 5-HNV in leaves of the more drought tolerant C 4 grasses, C. dactylon and Z. japonica, increased with increasing water deficit; therefore, any benefits from this unusual non-protein amino acid for drought resistance should be further explored.