Allelopathic effects of exogenous phenylalanine: a comparison of four monocot species
Exogenous phenylalanine stunted annual ryegrass but not switchgrass or winter grain rye, with deuterium incorporation up to 3% from phenyalanine-d8. Toxicity to duckweed varied with illumination intensity and glucose uptake.
Isotopic labeling of biomolecules through biosynthesis from deuterated precursors has successfully been employed for both structural studies and metabolic analysis. Phenylalanine is the precursor of many products synthesized by plants, including the monolignols used for synthesis of lignin. Possible allelochemical effects of phenylalanine have not been reported, although its deamination product cinnamic acid is known to have deleterious effects on root elongation and growth of several plant species. The effects of phenylalanine and its deuterated analog phenylalanine-d8 added to growth media were studied for annual ryegrass (Lolium multiflorum), winter grain rye (Secale cereale), and switchgrass (Panicum virgatum) cultivated under hydroponic conditions. Growth of annual ryegrass was inhibited by phenylalanine while switchgrass and rye were not significantly affected. Growth was less affected by deuterated phenylalanine-d8 than by its protiated counterpart, which may be a typical deuterium kinetic isotope effect resulting in slower enzymatic reaction rates. Deuterium incorporation levels of 2–3% were achieved in biomass of switchgrass and annual ryegrass. Both protiated and deuterated phenylalanine were moderately toxic (IC25 values 0.6 and 0.8 mM, respectively) to duckweed (Lemna minor) grown using a 12 h diurnal cycle under photoautotrophic conditions. A significant increase in toxicity, greater for the deuterated form, was noted when duckweed was grown under higher intensity, full spectrum illumination with a metal halide lamp compared to fluorescent plant growth lamps emitting in the blue and red spectral regions. Supplementation with glucose increased toxicity of phenylalanine consistent with synergy between hexose and amino acid uptake that has been reported for duckweed.
KeywordsPhenylalanine Allelopathy Deuterium Switchgrass Ryegrass Lemna
- Cass CL, Peraldi A, Dowd PF, Mottiar Y, Santoro N, Karlen SD, Bukhman YV, Foster CE, Thrower N, Bruno LC, Moskvin OV, Johnson ET, Willhoit ME, Phutane M, Ralph J, Mansfield SD, Nicholson P, Sedbrook JC (2015) Effects of phenylalanine ammonia lyase (PAL) knockdown on cell wall composition, biomass digestibility, and biotic and abiotic stress responses in Brachypodium. J Exp Bot 66:4317–4335CrossRefPubMedPubMedCentralGoogle Scholar
- Evans BR, Shah R (2015) Development of approaches for deuterium incorporation in plants. In: Kelman Z (ed) Isotope labeling of biomolecules-labeling methods, Vol 565, Chapter 10, Methods in Enzymology. Academic Press, UK, pp 213–243Google Scholar
- King-Díaz B, Montes-Ayala J, Escartín-Guzmán C, Castillo-Blum SE, Iglesias-Prieto T, Lotina-Hennsen B, Barba-Behrens N (2005) Cobalt (II) coordination compounds of ethyl 4-methyl-5-imidazolecarboxylate: chemical and biochemical characterization on photosynthesis and seed germination. Bioinorg Chem Appl 3:93–108CrossRefPubMedCentralGoogle Scholar
- Lima RB, Salvador VH, dos Santos WD, Bubna GA, Finger-Teixeira A, Soares AR, Marchiosi R, de Ferrarese Maria LL, Ferrarese-Filho O, (2013) Enhanced lignin monomer production caused by cinnamic acid and its hydroxylated derivatives inhibits soybean root growth. PLoS ONE 8(12):e80542CrossRefPubMedPubMedCentralGoogle Scholar
- Moody M, Miller J (2005) Lemna minor Growth Inhibition Test. In: Blaise C, Férard J-F (eds) Small scale freshwater toxicity investigations. Springer Netherlands, Amsterdam, pp 271–298Google Scholar
- Parrish DJ, Casler MD, Monti A (2012) The evolution of switchgrass as an energy crop. In: Monti A (ed) Switchgrass: a valuable biomass crop for energy. Springer, London, pp 1–26Google Scholar
- Rohde A, Morreel K, Ralph J, Goeminne G, Hostyn V, De Rycke R, Kushnir S, Van Doorsselaere J, Joseleau JP, Vuylsteke M, Van Driessche G, Van Beeumen J, Messens E, Boerjan W (2004) Molecular phenotyping of the pal1 and pal2 mutants of Arabidopsis thaliana reveals far-reaching consequences on phenylpropanoid, amino acid, and carbohydrate metabolism. Plant Cell 16:2749–2771CrossRefPubMedPubMedCentralGoogle Scholar