Tricin‐lignins: occurrence and quantitation of tricin in relation to phylogeny

Abstract

SUMMARYTricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as an authentic monomer in grass lignification that likely functions as a nucleation site. It is linked onto lignin as an aryl alkyl ether by radical coupling with monolignols or their acylated analogs. However, the level of tricin that incorporates into lignin remains unclear. Herein, three lignin characterization methods: acidolysis; thioacidolysis; and derivatization followed by reductive cleavage; were applied to quantitatively assess the amount of lignin-integrated tricin. Their efficiencies at cleaving the tricin-(4 0 -O-b)-ether bonds and the degradation of tricin under the corresponding reaction conditions were evaluated. A hexadeuterated tricin analog was synthesized as an internal standard for accurate quantitation purposes. Thioacidolysis proved to be the most efficient method, liberating more than 91% of the tricin with little degradation. A survey of different seed-plant species for the occurrence and content of tricin showed that it is widely distributed in the lignin from species in the family Poaceae (order Poales). Tricin occurs at low levels in some commelinid monocotyledon families outside the Poaceae, such as the Arecaceae (the palms, order Arecales) and Bromeliaceae (Poales), and the non-commelinid monocotyledon family Orchidaceae (Orchidales). One eudicotyledon was found to have tricin (Medicago sativa, Fabaceae). The content of lignin-integrated tricin is much higher than the extractable tricin level in all cases. Lignins, including waste lignin streams from biomass processing, could therefore provide a large and alternative source of this valuable flavone, reducing the costs, and encouraging studies into its application beyond its current roles.

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

“…Therefore, the increased frequencies of b-b units C and C9, along with the reduced signals from b-O-4 units A, are signs of increased monolignol dimerization in the absence of tricin. This finding is in agreement with the fact that the level of b-b units had an opposite trend to the level of tricin units in a series of wheat straw lignin fractions that differed in M r (Lan et al, 2016b). On the other hand, we cannot exclude the possibility that the shifts in coupling frequencies are a consequence of the increased flux toward monolignols or acylated monolignols in C2-Idf mutants, as determined by the increased Klason lignin content in these plants, rather than the absence of tricin per se.…”

“…*, 0.05 . P $ 0.01; and ***, P , 0.001. overestimated in HSQC spectra, so analytical thioacidolysis was used to provide accurate quantitation of the level of incorporation (Lan et al, 2016b). Also upon accurate quantitation, the tricin content was higher in leaves (about 18 mg g 21 ) than in stems (about 7 mg g 21 ).…”

“…3; Supplemental Table S3) in HSQC spectra. An accurate quantitative analytical method, thioacidolysis of cell wall material followed by liquid chromatographymass spectrometry (LC-MS) analysis (Lan et al, 2016b), was applied to determine the absolute value of tricin. For the C2 control samples, the content of tricin was 7.44 mg g 21 total lignin for the stem sample and 18.26 mg g 21 for the leaf (Table VI).…”

“…Tricin was determined by analytical thioacidolysis essentially as published (Lapierre et al, 1986) but using LC-MS detection as described (Lan et al, 2016b).…”

Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility

“…Subsequently, extensive surveys have revealed that tricin-bound lignins exist abundantly, particularly in the monocot family Poaceae, which comprises grasses including cereals. They also have been found in some commelinid monocot families outside Poaceae, such as Arecaceae (palms) and Bromeliaceae (pineapples and relatives), the noncommelinid family Orchidaceae (the orchids), particularly in the genus Vanilla, and also in certain dicots (Rencoret et al, 2013;Wen et al, 2013;Del Río et al, 2015;Lan et al, 2015Lan et al, , 2016aLan et al, , 2016bKoshiba et al, 2017).…”