Surface infrared spectroscopy

Plant cells are immobile; thus, plant growth and development depend on cell expansion rather than cell migration. The molecular mechanism by which the plasma membrane initiates changes in the cell expansion rate remains elusive. We found that a secreted peptide, RALF (rapid alkalinization factor), suppresses cell elongation of the primary root by activating the cell surface receptor FERONIA in Arabidopsis thaliana. A direct peptide-receptor interaction is supported by specific binding of RALF to FERONIA and reduced binding and insensitivity to RALF-induced growth inhibition in feronia mutants. Phosphoproteome measurements demonstrate that the RALF-FERONIA interaction causes phosphorylation of plasma membrane H+–adenosine triphosphatase 2 at Ser899, mediating the inhibition of proton transport. The results reveal a molecular mechanism for RALF-induced extracellular alkalinization and a signaling pathway that regulates cell expansion.

/pdf/a-peptide-hormone-and-its-receptor-protein-kinase-regulate-3330ive7as.pdf

A Peptide Hormone and Its Receptor Protein Kinase Regulate Plant Cell Expansion

The influence of surface defects on the infrared spectra of adsorbed species

Infrared−visible sum frequency generation (SFG) has been used to monitor the surface vibrational spectrum in situ during ethylene hydrogenation on Pt(111). Measurements were made near 1 atm of total pressure of ethylene and hydrogen and at 295 K. Kinetic information was obtained simultaneously with the surface vibrational spectroscopy by monitoring the reaction rate with gas chromatography. The macroscopic turnover rate and surface adsorbate concentration could then be correlated. During the reaction ethylidyne, di-σ-bonded ethylene, ethyl, and π-bonded ethylene were observed on the surface in various amounts depending on conditions. Ethylidyne, a spectator species during hydrogenation, competed directly for sites with di-σ-bonded ethylene and its surface concentration could be shown to be completely uncorrelated with the rate of hydrogenation. In contrast, π-bonded ethylene did not compete for sites with the ethylidyne overlayer and was observed on the surface regardless of the surface concentration of e...

Ethylene Hydrogenation on Pt(111) Monitored in Situ at High Pressures Using Sum Frequency Generation

Effect of eluent on the ionization process in liquid chromatography-mass spectrometry.

Molecular Characterization of Mutant Arabidopsis Plants with Reduced Plasma Membrane Proton Pump Activity

The authors used transmission FTIR to study the adsorption and hydrogenation of ethylene on 3% Pt/Al/sub 2/O/sub 3/ below room temperature. They find that ethylene adsorbs at least three distinct forms: a di-sigma-bonded form, a ..pi..-bonded form, and the ethylidyne species (CCH/sub 3/). Adsorption at 150 K yields primarily the di-sigma- and ..pi..-bonded forms. Upon warming ethylene to room temperature, they find that only the di-sigma-bonded form rearranges to produce ethylidyne. They have studied the hydrogenation of these three kinds of adsorbed species by following the changes in the IR spectra during hydrogenation. They find that the di-sigma and ..pi..-bonded forms react much faster with hydrogen than does ethylidyne.

Infrared identification of the low-temperature forms of ethylene adsorbed on platinum/alumina

We have studied the infrared spectrum of ethylidyne, CCH3, chemisorbed on the Pt(111) surface over the temperature range 82 to 350 K. We observe three infrared active fundamentals: the C–C stretch at 1118 cm−1, the symmetric CH3 bend at 1339 cm−1, and the symmetric C–H stretch at 2884 cm−1. The absence of three other fundamentals in our spectra confirms that the molecule has C3v symmetry on the surface with the C–C axis oriented along the surface normal as had been determined from other studies. Our IR spectra demonstrate the strict validity of the surface dipole selection rules. We also observe a weak band at 2795 cm−1 which we attribute to the first overtone of the asymmetric CH3 bend at 1410 cm−1. The intensity of the overtone is enhanced by a Fermi resonance with the symmetric C–H stretch. At 82 K the symmetric bend has an unusually narrow intrinsic width of only 1.4 cm−1. The narrowness of this band makes it a good choice for investigating the influence of free rotation about the single C–C bond on t...

Infrared vibration–rotation selection rules for chemisorbed molecules with free internal rotation: Results for ethylidyne on Pt(111)

Kinetics of ethylidyne formation on Pt(111) From time-dependent infrared spectroscopy

The authors have used infrared spectroscopy to study ethylene adsorption of alumina-supported Rh, Ir, Pd, and Pt at and below room temperature. The adsorption of ethylene at room temperature gives a set of infrared bands indicating the presence of both {pi}-bonded ethylene and ethylidyne on the surface of each metal. At lower temperatures di-{sigma}-bonded ethylene is formed which converts to ethylidyne as the temperature is raised. The C-C stretch and the CH{sub 2} scissors mode of {pi}-bonded ethylene have been used as a measure of the bond strength between the molecule and the metal surface. The bond strength follows the sequence Rh > Pd, Ir > Pt. They have attempted to explain the difference in the bond strengths among these metals by using simple qualitative arguments.

Sheher B. Mohsin

Papers

Molecular Characterization of Mutant Arabidopsis Plants with Reduced Plasma Membrane Proton Pump Activity

Infrared identification of the low-temperature forms of ethylene adsorbed on platinum/alumina

Infrared vibration–rotation selection rules for chemisorbed molecules with free internal rotation: Results for ethylidyne on Pt(111)

Kinetics of ethylidyne formation on Pt(111) From time-dependent infrared spectroscopy

Identification of ethylene-derived species on alumina-supported rhodium, iridium, palladium and platinum catalysts by infrared spectroscopy