In some phloem fibers, LM21 immunofluorescence labeling showed multilayered structure, suggesting the heterogeneous distribution of glucomannan.įlax (Linum usitatissinum L.) is an economically important fiber crop species as it produces long cellulosic fibers with high tensile strength. Immunogold labeling of xylan (LM11) and glucomannan (LM21) showed that xylan and glucomannan were mainly present in the S 1 layers and the G-layers, respectively. ![]() Uniform arabinogalactan protein (AGP) labeling was observed on the S 1 layers and G-layers using JIM14, but little appeared in the CML of hemp fibers, indicating that these layers of the phloem fibers contain AGP. In addition, some fiber cells showed a multilayered structure. Acriflavine staining, uniform KM1 labeling (8-5′ linked lignin substructure), and no KM2 labeling (8-8′ linked structure) were observed in the G-layer, suggesting that there is a small amount of lignin-like compound with 8-5′ linked structure in the G-layer. Ultraviolet absorption and potassium permanganate staining were observed mainly in the compound middle lamella (CML) and S 1 layers, and rarely in the G-layer of phloem fibers, suggesting that lignin concentration is high at the CML and S 1 layers, and very low at the G-layer of hemp fibers. The distribution of lignin, 8-5′ and 8-8′ linked lignin substructure, and noncellulosic polysaccharides in hemp ( Cannabis sativa L.) phloem fibers were explored based on histochemical and immunological methods. Whole-genome transcriptomics suggested that ectopic lignification of flax bast fibers could be caused by increased transcript accumulation of (1) the cinnamoyl-CoA reductase, cinnamyl alcohol dehydrogenase, and caffeic acid O-methyltransferase monolignol biosynthesis genes, (2) several lignin-associated peroxidase genes, and (3) genes coding for respiratory burst oxidase homolog NADPH-oxidases necessary to increase H2O2 supply. Immunological and chemical analyses revealed that lbf1 mutants also showed changes to other cell wall polymers. Liquid chromatography-mass spectrometry profiling showed large modifications in the oligolignol pool of lbf1 inner- and outer-stem tissues that could be related to ectopic lignification. Chemical and NMR analyses indicated that bast fiber ectopic lignin was highly condensed and rich in G-units. As a proof of concept, we characterized the lbf1 mutant and showed that the lignin content increased by 350% in outer stem tissues containing bast fibers but was unchanged in inner stem tissues containing xylem. We named this core collection the Linum usitatissimum (flax) lbf mutants for lignified bast fibers and believe that this population represents a novel biological resource for investigating how bast fiber plants regulate lignin biosynthesis. Histochemical screening of a flax ethyl methanesulfonate population led to the identification of 93 independent M2 mutant families showing ectopic lignification in the secondary cell wall of stem bast fibers.
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