WATER POTENTIAL MODULATES EXTENSIBILITY OF RYE COLEOPTILE CELL-WALLS

Extensibility of walls of frozen/thawed rye (Secale cereale) coleoptil e segments as a function of the water potential of the incubation solu tion (Psi(0)) was analyzed employing the creep test method. Negative P si(0) exerts an inhibiting effect on extension of isolated walls. The lower the Psi(0) of polyethylene glycol 6000 (PEG), the less the walls of frozen/thawed segments extended under load. This inhibiting effect of Psi(0) on wall creep was reversible and independent of the preincu bation temperature of the segments. An increase in Psi(0) resulted in increased extension rate within 2-4 min, whereas a decrease in Psi(0) resulted in gradually decreasing extension rate after 8-12 min. This f inding implies that wall extension changes during growth induced by ch anges of Psi(0) in vivo are not only due to changes of turgor pressure but also due to a direct influence by negative Psi(0) on physical wal l properties. The results are discussed with respect to the regulation of extension growth during conditions of water stress.