Brachialactone isomers and derivatives of Brachiaria humidicola reveal contrasting nitrification inhibiting activity

Konrad Egenolf; Jürgen Conrad; Jochen Schöne; Christina Braunberger; Uwe Beifuß; Frank Walker; Jonathan Nuñez; Jacobo Arango; Hannes Karwat; Georg Cadisch; Günter Neumann; Frank Rasche

doi:10.1016/j.plaphy.2020.06.004

Brachialactone isomers and derivatives of Brachiaria humidicola reveal contrasting nitrification inhibiting activity

Plant Physiol Biochem. 2020 Sep:154:491-497. doi: 10.1016/j.plaphy.2020.06.004. Epub 2020 Jul 9.

Authors

Affiliations

¹ Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany; The Alliance of Bioversity International and the International Center for Tropical Agriculture (CIAT), Km 17 Recta Cali-Palmira, A.A, 6713, Cali, Colombia.
² Institute of Chemistry, University of Hohenheim, 70593, Stuttgart, Germany.
³ Institute of Phytomedicine, University of Hohenheim, 70593, Stuttgart, Germany.
⁴ The Alliance of Bioversity International and the International Center for Tropical Agriculture (CIAT), Km 17 Recta Cali-Palmira, A.A, 6713, Cali, Colombia.
⁵ Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany.
⁶ Institute of Crop Sciences, University of Hohenheim, 70593, Stuttgart, Germany.
⁷ Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, 70593, Stuttgart, Germany. Electronic address: frank.rasche@uni-hohenheim.de.

PMID: 32663650
DOI: 10.1016/j.plaphy.2020.06.004

Abstract

Biological Nitrification Inhibition (BNI) of Brachiaria humidicola has been mainly attributed to the root-exuded fusicoccane-type diterpene brachialactone. We hypothesized, however, that according to the high diversity of fusicoccanes described for plants and microorganisms, BNI of B. humidicola is caused by an assemblage of bioactive fusicoccanes. B. humidicola root exudates were collected hydroponically and compounds isolated by semi-preparative HPLC. Chemical structures were revealed by spectroscopic techniques, including HRMS as well as 1D and 2D NMR. Nitrification inhibiting (NI) potential of isolated compounds was evaluated by a Nitrosomonas europaea based bioassay. Besides the previously described brachialactone (1), root exudates contained 3-epi-brachialactone (2), the C3-epimer of 1 (m/z 334), as well as 16-hydroxy-3-epi-brachialactone (3) with an additional hydroxyl group at C16 (m/z 350) and 3,18-epoxy-9-hydroxy-4,7-seco-brachialactone (4), which is a ring opened brachialactone derivative with a 3,18 epoxide ring and a hydroxyl group at C9 (m/z 332). The 3-epi-brachialactone (2) showed highest NI activity (ED₅₀ ~ 20 μg mL^-1, ED₈₀ ~ 40 μg mL^-1), followed by compound 4 with intermediate (ED₅₀ ~ 40 μg mL^-1), brachialactone (1) with low and compound 3 without activity. In coherence with previous reports on fusicoccanes, stereochemistry at C3 was of high relevance for the biological activity (NI potential) of brachialactones.

Keywords: BNI (Biological nitrification inhibition); Brachiaria humidicola; Forages; Fusicoccanes; Nitrosomonas europaea; Poaceae; Tropical savannas.

MeSH terms

Brachiaria / chemistry*
Lactones / chemistry*
Nitrification*
Nitrosomonas europaea
Plant Exudates / chemistry*
Plant Roots

Substances

Lactones
Plant Exudates