In-vivo measurement of cell-wall extensibility in maize coleoptiles: Effects of auxin and abscisic acid.

Plastic and elastic in-vivo extensibilities (Epl and Eel, respectively) of cell walls of growing maize (Zea mays L.) coleoptile segments were measured by stretching living tissue at constant force (creep test) in an extensiometer. The linear displacement transducer used as a measuring device permits the determination of load-induced extensions in the range of 0-1% of the segment's length, leading to a minimal disturbance of the hydraulic parameters of the tissue and allowing the measurement of unidirectional cell-wall creep at virtually unchanged turgor and metabolic activity. A rein-vestigation of the time-course of indole-3-acetic acid-promoted and abscisic acid-inhibited wall loo-sening revealed that the in-vivo creep test yields results very similar to those obtained previously with the in-vitro creep test [Kutschera and Schopfer, 1986, Planta 167, 527-535]. The hormones affect elongation rate and Epl in a closely correlated manner both in step-up as well as step-down growth changes whereas Eel remains unaltered. It is argued that both hormones influence growth by modifying Epl of the outer epidermis and that this effect can be quantitatively measured, in relative units, by either the in-vivo or the in-vitro creep test.