Turgor-dependent Changes in Avena Coleoptile Cell Wall Composition

The effects of reduced turgor pressure on growth, as measured by cell elongation, and on auxin-mediated changes in cell walls, as measured by analyses of wall composition, were examined using Avena coleoptile segments. Although moderate (1-4 bar) decreases in turgor resulted in a progressive decline in growth proportional to the decrease in turgor, the major auxin-induced change in wall composition, a decrease in noncellulosic wall glucose, was unaffected. Severe (5-8 bar) decreases, however, did inhibit this auxin effect on the wall, and with turgor decreases of 9 bars or more this auxin effect was no longer apparent. The results show that turgor pressure is required for this auxin-mediated wall modification and also that this modification of wall glucose occurs at turgor pressures less than those required for wall extension. Changes in other wall components were generally unaffected by altering turgor pressure.