FURTHER OBSERVATIONS ON THE ABSORPTION AND TRANSLOCATION OF INORGANIC SOLUTES USING RADIOACTIVE ISOTOPES WITH PLANTS

Abstract

With the use of abscised barley roots immersed in radioactive bromide solns., it has been possible to delimit more closely the modes of migration of electrolyte into tissues at low and high temps. as well as into systems of previously high- or low-salt content. This study suggests that there is a rapid exchange of isotopes between the external medium and roots; that under favorable temp. conditions isotopic or ion exchange is less important than migration by metabolic accumulation; that with high-salt roots at low temp., migration may be restricted almost exclusively to adsorption exchange; and that metabolic accumulation may be pronounced even with roots at low temp., provided they are currently in a relatively low-salt condition. With the use of decapitated barley plants and isotopes of bromide it has been shown that 2 pathways are afforded for the migration of inorganic solutes into roots: with low-salt plants, salt may migrate across the cytoplasm of cells into vacuoles as well as to more remote lumina, e.g., the xylem; where the roots are initially in a relatively high-salt condition, subsequent migration takes place differentially along continuous protoplasmic paths (the symplast) to the xylem, circumventing, in a measure, movement into or through intervening vacuoles. Where depletion of vacuolar solute occurs through translocation, the probable pathway is likewise along the protoplasmic continuum.