the translocation of minerals in trees - Canadian Forest Service

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FIGURE 1. Monitoring movement of rubidium86 in yellow birch with portable scintillation counter. The operator is holding the probe in his left hand, with the counter strapped to his waist. potassium chloride was placed in a water-tight trough constructed around part of the tree trunk. A i-inch chisel with its face parallel to the vertical axis was used to make an under-water incision to a depth of one inch. U e of the potassium chloride facilitated the entrance and movement of the isotope in the translocation stream. The maximum rate of upward movement of the rubidium86 in the xylem of yellow birch approximated one foot per minute along a narrow channel spiralling upward (usually dextrally) from the point where the isotope was first introduced. Movement in decadent yellow birch was very slow with an: apparent increa e of permeability of the bark tissue as indicated by lateral diffusion of the isotope. In October no upward movement was discerned in healthy trees but rather a downward translocation in the phloem which may have been associated with the removal of certain minerals from the senescent leaves. Samples of phloem and xylem ,vere removed with an increment borer for radioactive assay, to facilitate the interpretation of the external monitoring observations. 10
Calcium45 injected into the white pine trunk had a localized distribution similar to that of the rubidium86 in yellow birch. In the white pine trunk the isotope moved upwards from the point of infection, along a relatively narrow channel. Only two branches, both within six feet of the ground, were found to contain appreciable activity. Monitoring records on August 22, six weeks after injection, indicated an accumulation of calcium in the main trunk at a point where the upper active branch had its origin. From this position in the trunk, most of the calcium was carried out into the branch. The isotope was not evenly distributed throughout the branch, as in any given whorl of twigs some were much more active than others. The internal distribution of the calcium was investigated by autoradiographs. In this technique (Belanger and Leblond, 1946) sections of tissue are coated with a photographic emulsion and left for different periods of exposure ranging from a few hours to several weeks depending on the degree of localization of the radioisotope and consequent inten ity of radiation to which the photographic emulsion in contact with the section is exposed. The autoradiographs of ections of the stem (Figure 2) showed activity in the sieve cells of the phloem in the white pine. During September some of the calcium45 concentrations had materialized into visible crystals. Figure 3 shows a cross section of crystals in the phloem cells. By focusing up on the photographic emulsion covering the section of these cells, the dark dots (Figure 4) represent exposure of the photographic emulsion indicating that these cells contain calcium45• Presence of calcium45 was also noted in the buds of yellow birch. Figure 5a presents photographs of the buds, whereas Figure 5b show autoradiographs of the same buds indicating the presence of calcium45 in the peripheral parts of these buds. Moreland (1950) introduced roots of loblolly pine into jars containing phosphorus32 solution and noted a maximum translocation rate of more than four feet per hour. Yli-Vaakuri (1954) in Finland showed that movement of phosphorus32 would take place from tree to tree and also between trees and stumps through natural root grafts. Kuntz and Riker (1955) in Wisconsin studied more extensively the use of radioisotopes for ascertaining the role of root grafts in the translocation of minerals between trees. Their experiments with iodine131 and rubidium86 included the insertion of cut branches or roots into a bottle containing a radioactive solution, or injection of a solution from a cone or trough similar to the technique used by Fraser and Mawson (1953). The usual rate of upward movement of the isotope in the translocation stream of oaks in full sunlight and with low relative humidity was between It and 3 feet per minute. A limited downward movement into the roots was noticed. Greater movement occurred in roots naturally grafted onto those of other trees. Radioactivity was detected within 20 minutes in most branches, twigs, and leaves of pin oak (Quercus ellipsoidalis E. J. Hill) 35 feet high. Radioactivity appeared only in narrow vertical streaks which originated at the chisel cuts, and in certain branches of the bur oak (Quercus macro carp a Michx.). The diffuse movement of the isotopes throughout trunks and the crown of the northern pin oak was quite different from the limited linear flow in the trunk and certain branches of the bur oak. In this respect the bur oak behaved like the yellow birch and white pine in the experiments by Fraser and Mawson (1953). Movement of the isotopes was reduced by very low light intensities, free moisture on the leaves, and absence of functional leaves. Little movement occurred during the dormant period. When dominant and suppressed trees were connected by root grafts, isotopes moved both ways but most commonly from the 11
Page 1 and 2: CANADA Department of Northern Affai
Page 3: CONTENTS PAGE INTRODUCTION. . . . .
Page 6 and 7: on the fact that the living cell is
Page 8 and 9: solutions and determining the miner
Page 12 and 13: FIGURE 2. Autoradiograph of longitu
Page 14 and 15: SUMMARY AND CONCLUSIONS It appears
Page 16: STEDIBACH, H. B. 1951. Permeability

the translocation of minerals in trees - Canadian Forest Service

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