RAPID AND REVERSIBLE MODIFICATIONS OF EXTENSION CAPACITY OF CELL-WALLS IN ELONGATING MAIZE LEAF TISSUES RESPONDING TO ROOT ADDITION AND REMOVAL OF NACL

A creep extensiometer technique was used to provide direct evidence th at short (20 min) and long-term (3 d) exposures of roots to growth inh ibitory levels of salinity (100 mol m(-3) NaCl) induce reductions in t he irreversible extension capacity of cell walls in the leaf elongatio n zone of intact maize seedlings (Zea mays L.). The long-term inhibiti on of cell wall extension capacity was reversed within 20 min of salt withdrawal from the root medium. Inhibited elongation of leaf epiderma l tissues was also reversed after salt removal. The salt-induced chang es in wall extension capacity were detected using in vivo and in vitro assays (shortly after localized freeze/thaw treatment of the basal el ongation zone). The rapid reversal of the inhibition of wall extensibi lity and leaf growth after salt removal from root medium of long-term salinized plants, suggested that neither deficiencies in growth essent ial mineral nutrients nor toxic effects of NaCl on plasmamembrane viab ility were directly involved in the inhibition of leaf growth. There w as consistent agreement between the scale, direction and timing of sal inity-induced changes in leaf elongation growth and wall extension cap acity. Rapid metabolically regulated changes in the physical propertie s of growing cell walls, caused by osmotic (or other) effects, appear to be a factor regulating maize leaf growth responses to root saliniza tion.