Exposure to water stress causes changes in the biosynthesis of cell wall polysaccharides in roots of wheat cultivar varying in drought tolerance

The in vivo changes in the growth and in the biosynthesis of cell wall polysaccharides (pectins, hemicelluloses and a-cellulose) were studied in apical and Subapical root segments isolated from water stressed and unstressed wheat seedlings (Triticum durum Desf.) cv. Capeiti 'drought tolerant' and cv. Creso 'drought sensitive'. In both cultivars, water stress imposed by a 20% solution of polyethylene glycol 4000, corresponding to a water potential (psi(w)) of -0.5 NIPa, inhibited differentially root and coleoptile growth. Although root growth was inhibited to the same extent in both cultivars, the overall decrease in the newly synthesised cell wall polysaccharides such as pectins. hemicelluloses and a-cellulose during water stress was quantitatively and qualitatively different not only between the cv. Capeiti 'drought tolerant' and cv. Creso 'drought sensitive' but also between the apical and subapical segments of the same cultivar. This decrease was generally lower in the cv. Capeiti than the cv. Creso. Significant changes were observed in the quantitative glycosyl residue composition of pectins and hemicelluloses solubilised from the apical segments of water stressed roots of both cultivars. In particular, the almost unaltered incorporation of radioactive galactosyl, arabinosyl, xylosyl, rhamnosyl and uronic acid residues into matrix polysaccharides during water stress may play a key role in given water stress tolerance in cv. Capeiti.