Chemical analysis and immunolocalisation of lignin and suberin in endodermal and hypodermal/rhizodermal cell walls of developing maize (Zea mays L.) primary roots

The composition of suberin and lignin in endodermal cell walls (ECWs) and i n rhizodermal/hypodermal cell walls (RHCWs) of developing primary maize (Ze a mays L.) roots was analysed after depolymerisation of enzymatically isola ted cell wall material. Absolute suberin amounts related to root length sig nificantly increased from primary ECWs (Casparian strips) to secondary ECWs (suberin lamella). During further maturation of the endodermis, reaching t he final tertiary developmental state characterised by the deposition of li gnified secondary cell walls (u-shaped cell wall deposits), suberin amounts remained constant. Absolute amounts of lignin related to root length const antly increased throughout the change from primary to tertiary ECWs. The su berin of Casparian strips contained high amounts of carboxylic and 2-hydrox y acids, and differed substantially from the suberin of secondary and terti ary ECWs, which was dominated by high contents of omega-hydroxycarboxylic a nd 1,omega-dicarboxylic acids. Furthermore, the chain-length distribution o f suberin monomers in primary ECWs ranged from C-16 to C-24, whereas in sec ondary and tertiary ECWs a shift towards higher chain lengths (C-16 to C-28 ) was observed. The lignin composition of Casparian strips (primary ECWs) s howed a high syringyl content and was similar to lignin in secondary cell w alls of the tertiary ECWs, whereas lignin in secondary ECWs contained highe r amounts of p-hydroxyphenyl units. The suberin and lignin compositions of RHCWs rarely changed with increasing root age. However, compared to the sub erin in ECWs, where C-16 and C-18 were the most prominent chain lengths, th e suberin of RHCWs was dominated by the higher chain lengths (C-24 and C-26 ). The composition of RHCW lignin was similar to that of secondary-ECW lign in. Using lignin-specific antibodies, lignin epitopes were indeed found to be located in the Casparian strip. Surprisingly, the mature suberin layers of tertiary ECWs contained comparable amounts of lignin-like epitopes.