Feruloylation and structure of arabinoxylan in wheat endosperm cell walls from RNA i lines with suppression of genes responsible for backbone synthesis and decoration

Summary Arabinoxylan ( AX ) is the major component of the cell walls of wheat grain (70% in starchy endosperm), is an important determinant of end‐use qualities affecting food processing, use for animal feed and distilling and is a major source of dietary fibre in the human diet. AX is a heterogeneous polysaccharide composed of fractions which can be sequentially extracted by water ( WE ‐ AX ), then xylanase action ( XE ‐ AX ) leaving an unextractable ( XU ‐ AX ) fraction. We determined arabinosylation and feruloylation of AX in these fractions in both wild‐type wheat and RNA i lines with decreased AX content (Ta GT 43_2 RNA i, Ta GT 47_2 RNA i) or decreased arabinose 3‐linked to mono‐substituted xylose (Ta XAT 1 RNA i). We show that these fractions are characterized by the degree of feruloylation of AX , <5, 5–7 and 13–19 mg bound ferulate (g −1 AX ), and their content of diferulates (di FA ), <0.3, 1–1.7 and 4–5 mg (g −1 AX ), for the WE , XE and XU fractions, respectively, in all RNA i lines and their control lines. The amount of AX and its degree of arabinosylation and feruloylation were less affected by RNA i transgenes in the XE ‐ AX fraction than in the WE ‐ AX fraction and largely unaffected in the XU ‐ AX fraction. As the majority of di FA is associated with the XU ‐ AX fraction, there was only a small effect (Ta GT 43_2 RNA i, Ta GT 47_2 RNA i) or no effect (Ta XAT 1 RNA i) on total di FA content. Our results are compatible with a model where, to maintain cell wall function, di FA is maintained at stable levels when other AX properties are altered.