Effect of ancymidol on cell wall metabolism in growing maize cells.

Abstract

Ancymidol inhibits the incorporation of cellulose into cell walls of maize cell cultures in a gibberellin-independent manner, impairing cell growth; the reduction in the cellulose content is compensated with xylans. Ancymidol is a plant growth retardant which impairs gibberellin biosynthesis. It has been reported to inhibit cellulose synthesis by tobacco cells, based on its cell-malforming effects. To ascertain the putative role of ancymidol as a cellulose biosynthesis inhibitor, we conducted a biochemical study of its effect on cell growth and cell wall metabolism in maize cultured cells. Ancymidol concentrations ≤500µM progressively reduced cell growth and induced globular cell shape without affecting cell viability. However, cell growth and viability were strongly reduced by ancymidol concentrations≥1.5mM. The I50 value for the effect of ancymidol on FW gain was 658µM. A reversal of the inhibitory effects on cell growth was observed when 500µM ancymidol-treated cultures were supplemented with 100µM GA3. Ancymidol impaired the accumulation of cellulose in cell walls, as monitored by FTIR spectroscopy. Cells treated with 500µM ancymidol showed a ~60% reduction in cellulose content, with no further change as the ancymidol concentration increased. Cellulose content was partially restored by 100µM GA3. Radiolabeling experiments confirmed that ancymidol reduced the incorporation of [14C]glucose into α-cellulose and this reduction was not reverted by the simultaneous application of GA3. RT-PCR analysis indicated that the cellulose biosynthesis inhibition caused by ancymidol is not related to a downregulation of ZmCesA gene expression. Additionally, ancymidol treatment increased the incorporation of [3H]arabinose into a hemicellulose-enriched fraction, and up-regulated ZmIRX9 and ZmIRX10L gene expression, indicating an enhancement in the biosynthesis of arabinoxylans as a compensatory response to cellulose reduction.