Our previous work (E. Shedletzky, M. Shmuel, D.P. Delmer, D.T.A. Lamport [19901 Plant Physiol 94:980-987) showed that suspension-cultured tomato cells adapted to growth on the cellulose synthesis inhibitor 2,6-dichlorobenzonitrile (DCB) have a markedly altered cell wall composition, most notably a markedly reduced level of the cellulose-xyloglucan network. This study compares the adaptation to DCB of two cell lines from dicots (tomato [ capacity to divide and expand under conditions where cellulose synthesis is inhibited. As a result, the cell walls of tomato cells adapted to growth on 12 to 25 gM DCB contain markedly reduced levels of cellulose. In addition, they show other unique characteristics including a significant enrichment in pectic polymers and a markedly reduced level of xyloglucan. Lacking cellulose, adapted cells secrete the xyloglucan to the medium, a result that also suggests the interesting possibility that much of the xyloglucan is not further linked to other polymers within the wall.These studies, as well as other recent studies with cells adapted to growth in NaCl (16-18), point out the remarkable flexibility of plant cells to tolerate induced changes in cell wall composition, and further show that the study of such induced changes can shed light on normal wall structure. The work presented here extends our analyses of the walls of DCB-adapted cells and addresses the following issues: (a) a demonstration that adapted tomato cells growing on DCB possess a normal capacity for cellulose synthesis immediately upon removal of DCB, and that the pathway has retained its sensitivity to DCB; (b) a comparison of altered wall composition between two dicot cell lines (tomato [Lycopersicon esculentum] and tobacco [Nicotiana tabacum]) and a monocot grass (barley [Hordeum bolbosum] endosperm). These analyses were undertaken because the grasses are known to have markedly different primary walls from those of the dicots, possessing reduced levels of galacturonic acid-rich polymers, xyloglucan, and HRGPs, elevated GAX, and a mixed-linked(1--3,1--*4)-#-glucan that is lacking in dicot walls (2). Although the ratio of GAX to noncellulosic glucan, as well as the extent of substitution of GAX with glucuronic acid residues, differs between walls of endosperm and vegetative barley tissues, the endosperm line used here is considered to be, in general, representative of the grasses. Thus, it seemed possible that the compensatory changes induced to provide strength to walls with reduced cellulose might be quite different between these cell types, and that an understanding of such changes might shed light on how the polymers of these different walls interact to provide tensile strength; and (c) a comparison of the tensile strength and porosity of dicot and monocot walls from cells grown in the presence and absence of DCB. MATERIALS AND METHODS Cell CulturesCell suspensions of tomato (Lycopersicon esculentum VF 36) were cultured and adapted to DCB as described previously 120 www.plantphysiol.org on May 9, 2018 -Pu...

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