Dispersed lignin in tracheary elements treated with cellulose synthesis inhibitors provides evidence that molecules of the secondary cell wall mediate wall patterning

Abstract

SummaryMesophyll cells of Zinnia elegans var. Envy that had been induced to differentiate into tracheary elements (TEs) in suspension culture were treated with the cellulose synthesis inhibitor 2,6-dichlorobenzonitrile (DCB). The deposition of cellulose into the patterned secondary cell wall thickenings typical of TEs was inhibited as demonstrated by reduced incorporation of [14C]glucose into acetichitric insoluble material and absence of cellulose detectable by fluorescence after staining with Tinopal LPW, polarization optics, or labeling with a specific cellulase. Respiration as indicated by release of I4CO2 was inhibited to a much lesser extent, supporting a selective mechanism of action of DCB on the cellulose biosynthetic pathway. Patterned secondary cell wall thickenings were deposited in DCB-treated TEs, but these were smaller and less regularly shaped than those of control TEs. These cellulose-depleted thickenings lacked another abundant component of normal thickenings, the hemicellulose xylan, as indicated by absence of labeling with a specific xylanase or an antibody to xylan. DCBtreated TEs also showed dispersed lignin after staining with phloroglucinol, whereas control TEs contained lignin specifically localized to the secondary cell wall thickenings. Isoxaben, another recently described inhibitor of synthesis of acetichitric insoluble cell wall material (putatively cellulose), caused the same absence of detectable cellulose and xylan in the thickenings and dispersed lignin. These data suggest that: (i) the localization of lignin is ultimately dependent on the localization of cellulose; (ii) normal patterned wall assembly in TEs occurs in a self-perpetuating cascade in which some molecules of the secondary cell wall mediate patterning of others.

Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements

“…Cellulose fibrils from these different layers of the wall were embedded within granules, which were omitted from Figure 6 for presentation purposes. The dimensions of the different parts of TEs, derived from our AFM analysis, were consistent with those previously observed by transmission electron microscopy (Burgess and Linstead, 1984;Taylor et al, 1992;Nakashima et al, 1997;Salnikov et al, 2001;Karlsson et al, 2005). We found that cellulose microfibrils from the primary wall were organized in a meshwork, with fibrils running in multiple directions, while they were mostly arranged in parallel in the secondary wall.…”

Collapsed xylem phenotype of Arabidopsis identifies mutants deficient in cellulose deposition in the secondary cell wall.

“…The treated cells exhibited an abnormal, dispersed pattern of lignin deposition (Taylor et al, 1992). Thus, the reduced levels of cellulose in the irx mutants may prevent normal deposition of lignin, and this lack of proper organization may have consequences for its pattern of crosslinking and/or the physical properties of the stem.…”

Control of Cellulose Synthase Complex Localization in Developing Xylem

“…The dinitroaniline herbicide oryzalin specifically binds plant tubulin, causing microtubules to depolymerize (Vaughn, 1986;Anthony et al, 1998). When microtubules are removed from developing xylem vessels using colchicine, subsequent vessel development does not exhibit the characteristic localized pattern of secondary cell wall deposition but is deposited over the entire cell (Hepler and Fosket, 1971;Brower and Hepler, 1976;Taylor et al, 1992). In plants treated with oryzalin, IRX3 localization was altered rapidly coincident with the loss of microtubule organization.…”