Phellem Cell-Wall Components Are Discriminants of Cork Quality in Quercus suber

Abstract

Cork is a renewable, non-wood high valued forest product, with relevant ecological and economic impact in the Mediterranean-type ecosystems. Currently, cork is ranked according to its commercial quality. The most valuable planks are chosen for cork stoppers production. Cork planks with adequate thickness and porosity are classified as stoppable quality cork (SQC). The chemical composition of cork is known, but the regulation of metabolic pathways responsible of cork production and composition, hence of cork quality, is largely unknown. Here, we tested the hypothesis that post-genomic events may be responsible for the development of SQC and N-SQC (non-stoppable quality cork). Here, we show that combined proteomics and targeted metabolomics (namely soluble and cell wall bound phenolics) analyzed on recently formed phellem allows discriminate cork planks of different quality. Phellem cells of SQC and N-SQC displayed different reducing capacity, with consequential impact on both enzymatic pathways (e.g., glycolysis) and other cellular functions, including cell wall assembly and suberization. Glycolysis and respiration related proteins were abundant in both cork quality groups, whereas the level of several proteins associated to mitochondrial metabolism was higher in N-SQC. The soluble and cell wall-bound phenolics in recently formed phellem clearly discriminated SQC from N-SCQ. In our study, SQC was characterized by a high incorporation of aromatic components of the phenylpropanoid pathway in the cell wall, together with a lower content of hydrolysable tannins. Here, we propose that the level of hydrolysable tannins may represent a valuable diagnostic tool for screening recently formed phellem, and used as a proxy for the quality grade of cork plank produced by each tree.

High-Throughput Quantification of 32 Bioactive Antioxidant Phenolic Compounds in Grapes, Wines and Vinification Byproducts by LC–MS/MS

“…The method utilizes a LC–MS/MS triple quadrupole instrument and is suitable for the analysis of samples from grapes, wines and vinification byproducts. To date, the available analytical methods for the determination of these compounds mainly concern the simultaneous detection of only a limited number of compounds [ 45 , 46 ]. Thus, the efficient determination of their holistic phenolic profile still constitutes the subject of several research efforts.…”

Multiomics Molecular Research into the Recalcitrant and Orphan Quercus ilex Tree Species: Why, What for, and How

“…The first report on the proteome in Quercus analyzed the protein profiles of Q. suber somatic and gametic in vitro culture-derived embryos using differential gel electrophoresis coupled with MALDI-TOF/TOF [ 115 ]. Subsequent papers dealt with somatic embryogenesis [ 116 ], responses to the oomycete P. cinnamomi [ 117 ], and cork-forming tissues, framed in a project aimed at studying cork quality [ 118 , 119 ].…”

“…Buche et al [ 141 ], using untargeted LC-MS, described relevant compounds of Q. robur and Q. petraea wood samples, proposing the use of metabolite signatures as markers of wood quality. In the same direction, the phenolic composition of phellem and its relationship with wood quality has been evaluated in Q. suber [ 119 ]. In Q. robur , differences in primary and secondary metabolites between insect-resistant and -susceptible individuals were found.…”

Cork Development: What Lies Within

“…Polyphenolics are another group of extractives found in cork cells that are much less studied, with more heterogenous composition among phellems, which include simple phenols and/or polymeric phenols such as tannins. Out of the few studies on polyphenols in cork, Pinheiro et al (2019) [ 44 ] were able to establish a comparison of phenolic compositions between cork samples of higher and lower quality findings that in cork of higher quality, aromatic phenylpropanoid components were incorporated into the cell wall in larger amounts than hydrolysable tannins. This work was carried out in parallel with a transcriptomic analysis using the same cork samples.…”