Studies of the Molybdenum Nutrition of Plants With Radioactive Molybdenum

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Abstract
Two radioactive isotopes of molybdenum of high specific activity were prepared by alpha bombardment of ZrO2 in a cyclotron. They were isolated in "carrier-free" amts. by ether extraction. Identity of the isotopes with Mo was made by adding stable Mo salts to the radioactive material extracted by ether and then showing a constant ratio of Mo to radioactivity in products of subsequent chem. separation. Absorption expts. were made with tagged Mo using young tomato plants. Three-wks.-old plants were placed in jars and oxygen was supplied during the absorption period by passing air through sintered aerators into the culture soln. Some expts. were done with Mo93 being the dominant radioisotope, and others using Mo99 In each case l microgram of Mo was tagged with the radioisotope and added to the culture soln. as a salt for adsorption studies with plants. A complete accounting of the absorption and distribution of a single micro-gram of Mo in growing plants was obtained. Radio-autographs showed a diff. type of distribution of Mo in the plant tissues than for other mineral nutrients. Roots accumulated Mo rapidly from culture solns., even though the concn. was initially 1 part per billion. Translocation of these tiny amts. from roots to upper parts of the plant also occurred rapidly, but the amts. translocated were influenced by the concn. of P ion in the culture soln. Mo was accumulated in interveinal areas in direct contrast with the K pattern. It was not accumulated by stem tissue to any great degree. In the absence of Mo, loss of chlorophyll occurred in the same interveinal regions. Areas within the leaf where Mo accumulated were also areas having the greatest number of stomatal openings.