Effect of Boron in the Substrate on the Rate of Nitrate Absorption and on Nitrogen Distribution in Nasturtium

Abstract

Boron was not conisidered indispensable for the normal growth and development of higher plants prior to 1923. In this year WARINGTON (32) proved conclusively that boron was essential for the growth and normal development of Vicia faba and several other members of the Leguminoseae. Subsequent investifgators, JOHNSTON and DORE (8, 9), MCHARGUE and CALFEE (11, 12), MCMURTREY (13), SHIVE (24) and others have shown that a small continuous supply of boron is essential for the vegetative growth and reproduction of higher green plants, that the effective range of concentration varies with the species and environmental conditions, and that a deficiency of boroni produces characteristic abnormal anatomical and cytological changes within the plant.The purpose of the experiments here reported was to determine the effect of boron in the substrate on the rate of nitrate absorption and on the distribution of nitrogen in plant tissues.Golden gleamii niasturtium (Tropaeolumnt majjus, var. florepleno) was selected for these investigations because it was found in preliminary experiments that this planit responded very rapidly to a deficiency of boron in the substrate ( fig. 1). Methods Seed of uniiform size was selected, disinfected with 1: 1000 mercuric chloride for five minutes, thoroughly rinsed in distilled water, and placed between cleani moist blotters. When the primary root was 3 cm. long the germinating seeds were placed on paraffined nets stretched over a complete nutrient solution after the method of SHIVE and ROBBINS (25). When the seedling had three leaves, uniform plants were tranisferred to paraffined cork stoppers (25) which were placed in holes in paraffined tin tops of one-gallon glass candy jars. These culture vessels contained a complete nutrient solution. The planits were continuously aerated and continuously supplied with nutrient solution by the method of SHIVE and STAHL (26). A three-salt stock solutioil of the following composition was used: KH2PO4, 0.0021 M; Ca(NO,)2, 0.0042 M; and MgSO4, 0.0021 M.In the complete solution boron, manganese, and zince were also supplied as boric acid, manganese sulphate, and zinc sulphate, respectively, at the rate of 0.25 p.p.m. of solution. Iron was added as ferric tartrate at the rate of 1 p.p.m. Enough sulphuric acid was added to make the initial pH of the nutrient solution 4.0 to 4.2. PLANT PHYSIOLOGYThe method of determining absorption rates was essentially that outlined by CLARK and SHIVE (4). At the end of the absorption interval of nine hours the plants were separated into leaf-blades, petioles, stems, and roots and the weight recorded. Representative aliquots of the tissue fractions, placed in trays, were carefully cut into small pieces and dried at 700 C. in an oven through which air was rapidly circulating. Dry weights of the fractions were then determined and the tissue stored .in air tight bottles. The solution in which these plants had been growing and the rinsings of the necessary supplementary vessels were collected quantitatively and made to volume. Nitrogen...

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