HARDENING OF ROOT CELL-WALLS - A GROWTH-INHIBITORY RESPONSE TO SALINITY STRESS

Primary roots of intact maize plants (Zea mays L.) grown for several d ays in nutrient solutions containing 100 mol m(-3) NaCl and additional calcium, had relatively inhibited rates of elongation. Possible physi cal restraints underlying this salt induced inhibition were investigat ed. The inhibition did not involve reductions in osmotic potential gra dients and turgor in the tip tissues responsible for root elongation g rowth. The apparent yield threshold pressure, which is related to capa city of cell walls to undergo loosening by stress relaxation, was esti mated psychrometrically in excised root tips. Salinity increased yield threshold values. Comparative root extensibility values were obtained for intact plants by determining the initial (1 min) increase in root elongation rate induced by an 0.1 MPa osmotic jump. Comparative exten sibility was significantly reduced in the salinized root tips. Salinit y did not reduce capacities for water efflux and associated elastic co ntraction in root tip tissues of intact plants exposed to hypertonic m annitol. We conclude that cell wall hardening in the elongating root t ips is an important component of root growth inhibition induced by lon g-term salinization.