Effect of GA3 on the Molecular Mass of Polyuronides in the Cell Walls of Alaska Pea Roots

The role of cell wall matrix polysaccharides in gibberellin-regulated root growth is unknown. We examined pectic polysaccharides from pea roots treated with or without gibberellin A3 (GA3) in the presence of ancymidol, an inhibitor of gibberellin biosynthesis. Pectic polymers solubilized by CDTA (trans-l,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid) at 23°C and subjected to gel permeation analysis exhibited high polydispersity with a molecular mass in excess of 500 kDa. Subsequent extraction of cell walls with CDTA at 100°C solubilized polymers with an average mol mass of 10 to 40 kDa. Subjecting the high molecular mass pectic polymers extracted at 23°C to 70–100°C for 2h generated 10 to 40 kDa fragments, similar in size distribution to those solubilized directly from cell walls by CDTA solutions at 100°C. Pectic polymers from (GA3+Anc)-treated roots were of higher average mol mass than those from Anc-treated roots in both the elongation zone and in the basal maturation zone. Since (GA3+Anc)-treated roots elongate more quickly than Anc-treated roots [Tanimoto (1994) Plant Cell Physiol. 35:1019], the slender, GA3-treated roots may produce and deposit highly integrated pectins more rapidly than the thicker, Anc-treated roots in the elongating or elongated cell walls.