A System for Measuring Penetration of Radioactive Ions Across Roots of Intact Plants

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Abstract
A technique was developed for estimating penetration of p32 across roots of intact plants (Phaseolus vulgaris) by measuring the level of isotope in the xylem stream. Penetration was defined as movement from the root surface to the xylem sap. The xylem sap measurement for P32 was made in the stem as the material ascended the plant in the transpiration stream. Stems were held near O[degree] to arrest metabolic concentration of isotope adjacent to the xylem column. A 3-layer environment control system was constructed to allow stem chilling in a manner that would not interfere with the environments of the roots or foliage. Despite these precautions some extra-xylary buildup of P32 occurred in the chilled stem. The mathematical function of the extra-xylary fraction was derived, and the difference between this value and total P32 in the stem represented xylem sap isotope.