Autolysis Promotes the Extension Capacity of Zea mays Coleoptile Cell Walls in Response to Acid pH Solutions

Abstract

The relationship between autolytic degradation of β(1–3),(1–4)-D-glucan and acid pH-induced extension of isolated Zea mays cell walls has been investigated using a constant-load extension technique. Acidic buffer (4.5) was able to induce an additional extension (Ea) on cell walls already extended at pH 6.8 buffer under a 20 g-mass load, indicating that the additional extension (Ea) was the parameter that better represented the effect of the different treatments on the mechanical properties of maize coleoptile cell walls. The additional extension in response to acidic pH was higher when cell walls had been previously autolysed for 24 h at pH 5.5. Furthermore, the acid-pH effect was dependent on the presence during the constant load extension of some thermo-labile factors, suggesting the participation of expansins. Acid pH increased Ea of native cell walls through an increase in the plastic extension (Ep) in agreement with a one step mechanism leading directly to irreversible (plastic) wall extension as suggested by Cosgrove (1977). The autolytic degradation of β(1–3), (1–4)-D-glucan was also able to modify the mechanical properties of maize coleoptile cell walls increasing its elastic extension (Ee) in response to pH 4.5 buffer but that modification only leads to an increase in wall extension when expansins are active, suggesting a cooperation between β-glucan turnover and expansin action.