Xylogliicae‐ and cello‐oligosaccharides: Antagonists of the growth‐promoting effect of H⁺

Xyloglucan‐oligosaccharides and cello‐oligosaccharides, both of which are potential products of the action of cellulase on plant cell wail polysaccharides, inhibited acid‐induced elongation in pea (Pisum sativum L. cv. Alaska) stem segments. Xyloglucan‐derived nonasaccharide (XG9; Glc₄‐Xyl₃)Gal‐Fuc) and decasaccharide (XG10; Glc₄‐Xyl₃‐Gal₂‐Fue) inhibited acid‐induced growth at 1.0 and 0.1 nM, respectively, whereas the heptasaccharide (XG7; Glc₄‐Xyl₃) and octasaccharide (XG8; Glc₄‐Xyl₃‐Gal)₂ which lack L‐fucose, did not. XG9 at 1 nM inhibited acid‐induced growth as effectively as it inhibits auxin‐induced elongation. This suggests that XG9's effect as an inhibitor of auxin action is not mediated by a suppresion of H⁺‐efflux, but rather that XG9 blocks some step that is common to the action of both auxin and H⁺ on growth. Cello‐oligosaccharides (degree of polymerisation 4–7) also inhibited acid‐induced growth at 10 nM; these are therefore a new class of possible oligosaccha‐rin. The inhibitory effect of xyloglucan‐ and cellooligosaccharides on acid‐induced growth was rapidly reversed by washing.