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UV resonance Raman bands of Cu-bound and protonated histidine residues have been detected in 2H2O solutions of poplar plastocyanin. For the Cu(II) protein, slow NH–2H exchange of the His37 ligand was monitored via the growth of bands at 1389 and 1344 cm−1 when Pcy was exchanged into 2H2O, or via their diminution when the protein was exchanged back into H2O; the rate constant is 7×10−4/s at pH (p2H) 7.4 at room temperature. The slow exchange is attributed to imidazole H-bonding to a backbone carbonyl. Nearby bands at 1397 and 1354 cm−1, appear and disappear within the mixing time, and are assigned to the solvent-exposed His87 ligand. The ∼10 cm−1 differences between His37 and His87 are attributed to the effect of H-bonding on the imidazole ring modes. The UVRR spectra of the Cu(I) protein in 2H2O reveal a 1408 cm−1 band, characteristic of NH–2H-exchanged histidinium, which grows in as the p2H is lowered. Its intensity follows a titration curve with pKa=4.6. This protonation is assigned to the His87 residue, whose bond to the Cu(I) is known from crystallography to be broken at low pH. As the 1408 cm−1 band grows, a band at 1345 cm−1 diminishes, while another, at 1337 cm−1 stays constant. These are assigned to modes of bound His87 and His37, respectively, shifted down 7–9 cm−1 from their Cu(II) positions. [ABSTRACT FROM AUTHOR]

Abstract Ginger (Zingiber officinale Roscoe), one of the most economically valuable plants in the Zingiberaceae family, is widely used as a spice and flavoring agent for beverages, bakery, confectionary, and pharmaceutics. Bacterial wilt disease, caused by Ralstonia solanacearum , is one of the most detrimental production constraints in ginger cultivation. Field cultivation experiments indicated that soil moisture affects the incidence of bacterial wilt disease. However, the relationship between soil moisture and bacterial wilt incidence as well as the mechanism that underlie this infection remain unclear. This study confirms that high soil moisture elevates the susceptibility to R. solanacearum infection; transcriptome sequencing was performed to elucidate the underlying mechanisms. Differential expression indicates that a small number of genes is involved in both the response to high soil moisture as well as post successful R. solanacearum infection; furthermore, a large number of genes is involved in the defense of the infection. In response to high soil moisture, higher ABA contents, and higher expression levels of ABF4 may be related to higher tiller density in ginger. More importantly, WAK16 and WAK3-2 may be determinative genes that weaken the resistance to R. solanacearum in ginger under high soil moisture. The down-regulated expression levels of PRX , CPY , and XET genes indicate that in response to successful R. solanacearum infection, the normal cell wall metabolism may be disturbed and the hypersensitive response may be inhibited. In summary, our study deepens our understanding of the molecular mechanisms of the soil moisture dependent wilt susceptibility of ginger. Graphical abstract Image 1 Highlights • High soil moisture elevates ginger susceptibility to R. solanacearum. • Comparative transcriptome analysis was performed under low and high soil moistures • High ABA and ABF4 related to high tiller density of ginger under high soil moisture. • WAK16 and WAK3-2 may weaken the resistance of ginger to R. solanacearum. • Low PRX, CPY, and XET showed cell wall metabolism was disturbed after infection. [ABSTRACT FROM AUTHOR]