SALT SENSITIVITY AND LOW DISCRIMINATION BETWEEN POTASSIUM AND SODIUM IN BEAN-PLANTS

Bean plants (Plaseolus vulgaris) were very sensitive to moderate conce ntrations of NaCl, showing a dramatic decrease in their K+ content in the presence of this salt. Increasing the KCl content of the nutrient medium released the inhibitory effect of NaCl by increasing the Kf con tent of the plants. Likewise moderate concentrations of KCI were toxic for bean plants because they produced a large K+ loading. NaCl partia lly released this toxicity by inhibiting the K+ loading. When compared to the moderately salt tolerant sunflower plants (Helianthus annuus), bean plants showed a lower capacity to discriminate between K+ and Na +, at high Na+ levels, and an uncontrolled K+ uptake at moderate conce ntrations of K+. It is concluded that this low capacity of discriminat ion of the KS uptake system of bean plants in presence of Na+ can acco unt for by the NaCl sensitivity of bean plants.