The Effect of Exogenous Nitrate on LCO Signalling, Cytokinin Accumulation, and Nodule Initiation in Medicago truncatula

Abstract

Nitrogen fixation by rhizobia is a highly energy-demanding process. Therefore, nodule initiation in legumes is tightly regulated. Environmental nitrate is a potent inhibitor of nodulation. However, the precise mechanism by which this agent (co)regulates the inhibition of nodulation is not fully understood. Here, we demonstrate that in Medicago truncatula the lipo-chitooligosaccharide-induced accumulation of cytokinins is reduced in response to the application of exogenous nitrate. Under permissive nitrate conditions, perception of rhizobia-secreted signalling molecules leads to an increase in the level of four cytokinins (i.e., iP, iPR, tZ, and tZR). However, under high-nitrate conditions, this increase in cytokinins is reduced. The ethylene-insensitive mutant Mtein2/sickle, as well as wild-type plants grown in the presence of the ethylene biosynthesis inhibitor 2-aminoethoxyvinyl glycine (AVG), is resistant to the inhibition of nodulation by nitrate. This demonstrates that ethylene biosynthesis and perception are required to inhibit nodule organogenesis under high-nitrate conditions.

Low Salicylic Acid Level Improves Pollen Development Under Long-Term Mild Heat Conditions in Tomato

“…IS were used at an end concentration of 100 nM per compound per sample. Samples were extracted as previously described ( Schiessl et al, 2019 ; Gühl et al, 2021 ) with the addition that, prior to the elution of CKs, acid phytohormones were eluted with 1 ml of 100% MeOH. All solvents were evaporated in a speed vacuum system (SPD121P, ThermoSavant, Hastings, United Kingdom) at room temperature and the residue stored at –20°C until further analysis.…”

“…Argon was used for fragmentation by collision-induced dissociation. Multiple reaction monitoring (MRM) was used for quantification ( Gühl et al, 2021 ). Parent–daughter transitions for the different (stable isotope-labeled) compounds were set using the IntelliStart MS Console.…”

Local light signalling at the leaf tip drives remote differential petiole growth through auxin-gibberellin dynamics

“…Samples were filtered through a 0.45 μm Minisart SRP4 filter (Sartorius, Goettingen, Germany) and measured on the same day. IAA was analyzed on a Waters Xevo TQs tandem quadruple mass spectrometer as previously described 49,50 .…”

Light regulation of quality and growth of basil

“…Hormone content (jasmonic acid and abscisic acid) was measured according to Gühl et al (2021). Briefly, 10 mg of ground frozen basil leaves were extracted with 1 mL of 100 % methanol (MeOH) with internal standards 1 mL of 100 % methanol (MeOH) containing stable isotope-labeled internal standards (IS, Table S1).…”

“…Samples were resuspended in 100 µL of acetonitrile/water (0.1% formic acid) (20:80, v/v), and filtered through a 0.45 mm Minisart SRP4 filter (Sartorius, Goettingen, Germany). Analyses of plant hormones was performed by comparing retention times and mass transitions with those of unlabeled standards (Table S1) using a Waters XevoTQs mass spectrometer equipped with an electrospray ionization source coupled to an Acquity UPLC system (Waters, Milford, USA) as previously described (Schiessl et al, 2019;Gühl et al, 2021).Chromatographic separations were conducted on an Acquity UPLC BEH C18 column (100 mm, 2.1 mm, 1.7 mm; Waters, USA) by applying an acetonitrile/water (0.1 % formic acid) gradient. The column was operated at 40 °C with a flow rate of 0.25 mL min -1 .…”