GROWTH RATE AFFECTS SALT SENSITIVITY IN TWO LENTIL POPULATIONS

Abstract

ABSTRACT In saline media, the building of high concentration of Na+ and Cl− in plant leaves may be delayed by rapid growth. This dilution effect may improve the salt tolerance of plant by increasing the time necessary for ion accumulation to reach toxic levels. This could permit new leaves to be produced faster than elimination of older leaves by excess salt accumulation. The present study is aimed at studying this hypothesis on lentil (Lens culinaris L.). Various mild environmental constraints have been used to restrict growth rate, and the effect on salt sensitivity was evaluated. Three week-old plants were cultivated for 4 or 8 weeks on medium supplemented with 10 or 36 mM NaCl and submitted to one of three environmental conditions aimed to limit growth: low illumination, high temperature, and competition (high planting density). Whole plant dry weights were used to estimate mean relative growth rates (RGR). Increasing NaCl concentration from 10 mM to 36 mM reduced RGR more severely under limited light, or at high temperature, or at high planting density. In the presence of 36 mM NaCl, this increased sensitivity of growth was concomitant with Na+ accumulation in leaves, leaf withering and leaf necrosis. In the case of the high temperature treatment, the increase in Na+ concentration in the leaves was clearly attributable to reduction of growth rate, since Na+ amounts imported into the leaves were independent of temperature. These results support the hypothesis that glycophyte plants growing slowly are more sensitive to salt than those growing rapidly. This behavior contrast with that of halophytes, for which slow growth rate can be of advantage to overcome salt stress.