Response of corn and tomato plants to fluoride concentration in solution culture

To understand and control the delicate balance between beneficial and detrimental contents of F in plants, the functional relationships between F concentration in ambient solutions and F uptake rate by plants must be known. The objectives of the present work were: (i) to study the effect of F solution concentration (C_F) on F content in plants and on the rate of dry matter production and root elongation in young corn (Zea mays L.) and tomato (Lycopersicon esculentum L.) plants, and (ii) to define fluxes of F uptake versus C_F in the two crops. The growth rate (GR) of corn and tomato plants decreased significantly as C_F increased from 0.26 to 0.53 and from 0.05 to 0.26 mmol/L, respectively. The root elongation rate (RER) of corn 2 to 7 d old was maximum at C_F = 0.26 mmol/L, and decreased when C_F was raised to 2.63 mmol F/L. Tomato RER decreased when C_F was increased from 0 to 0.53 mmol/L, and was unaffected when C_F was raised further to 2.63 mmol/L. The threshold F shoot content at which the GR started to decline was about 12 mg F/kg in both crops. At any C_F, F content in the roots exceeded that in the shoots by a factor that varied between 1.2 and 10. The maximal F content in shoots and roots of corn and tomato plants was 54 and 680, and 126 and 1310 mg F/kg, respectively, obtained at a C_F of 2.63 mmol/L. The C_F had no effect on N, P, and K contents in tomato, but had a suppressive effect on K content in the shoots of corn plants. At a C_F between 0.05 and about 3 mmol F/L in the solution, the rate of F uptake per unit root weight (F_F) increased exponentially with C_F in both test crops, indicating a diffusive F permeation into the roots. At a C_F of about 3 mmol F/L, F_F of tomato was nearly twice that of corn.