RETENTION AND PASSAGE OF CALCIUM AND STRONTIUM IN STEMS OF PHASEOLUS VULGARIS AS MEDIATED BY XYLEM STREAM FLOW RATE AND DINITROPHENOL

The influence of the stem on delivery of Ca Sr to the plant top was studied by noting the extent to which the stem interfered with through passage of these elements. Tagged Ca Sr solutions were forced through bean stem sections, and solute which completed passage to the exudate was considered indicative of the nutrition normally available to the plant top. Tests were conducted over two widely different xylem stream flow rates, and with or without the addition of dinitrophenol to the source solution. Approximately identical amounts of cation were introduced into the stem for all test situations. In all cases, the stem retained the bulk of introduced cation and allowed only a fraction (ca 25 percent) to complete passage to the exudate. Within this pattern, less stem retention and greater through passage occurred at the high (versus the low) stream flow rate, and also where dinitrophenol was present in the source solution. In all cases, the stem preferentially retained Sr over Ca so that the exudate was relatively dilute in Sr. Such discrimination was less at the high (versus the low) stream flow rate. It was enhanced by the presence of dinitrophenol. Copyright © 1969, Wiley Blackwell. All rights reserved