Abstract
Several experiments were conducted in order to investigate mechanisms involved in repression of Mn absorption by effect of high salt solutions, with the aid of radioactive tracer techniques.
Rates of Mn absorption by intact plants and excised roots of tomato were determined by incubating them in the experimental solutions for 24 and 3 hours respectively for intact plants and excised roots. Higher salt concentrations raised by multiplying a Hoagland solution repressed the incorporation of Mn into leaf, stem and root of intact plants, especially into physiologically active upper leaves, and also into excised roots. On the contrary, addition of polyethylene glycol to a Hoagland solution to give isosmotic potentials with multiples of it had only a slight effect upon Mn incorporation into intact plant leaves, and into excised roots as well.
Kinetic studies revealed that high salt solutions repressed Mn absorption by competing with Mn for the binding sites, and that the main competing ions might be K and Ca. In addition, the possibility that higher salt solutions disturb normal metabolism of roots to decrease mineral absorption in general including Mn in a long-term experiment was also suggested.
