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THE EFFECT OF MOLYBDENUM AND NITROGEN DEFICIENCIES ON NITRATE REDUCTION IN PLANT TISSUES

E. G. MULDER, R. BOXMA and W. L. VAN VEEN
Plant and Soil
Vol. 10, No. 4 (April 1959), pp. 335-355
Published by: Springer
Stable URL: http://www.jstor.org/stable/42931786
Page Count: 21
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THE EFFECT OF MOLYBDENUM AND NITROGEN DEFICIENCIES ON NITRATE REDUCTION IN PLANT TISSUES
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Abstract

The effect of molybdenum on the nitrate-reducing capacity of plant tissue was studied by using coarsely cut tissue fragments from plants grown in Mo-deficient soil and dressed or infiltrated with a molybdate-containing solution shortly before testing. The tissue fragments were suspended under anaerobic conditions in a nitrate-containing buffer solution with malate serving as a hydrogen donor. Formation of nitrite was used as a measure for the nitrate-reducing power. Very low values for nitrate-reducing capacity were found in molybdenum-deficient tissues. As little as four hours after the application of molybdenum, however, enzyme activity had reached its maximal value. Cauliflower, spinach, and tomato plants, grown with inadequate amounts of nitrogen, showed also very low nitrate-reducing activities. Addition of nitrate to these plants, either by application to the soil or by infiltrating it into the leaves, resulted in a rapid rise in nitrate-reducing capacity. Ammonium sulphate, added to the soil, had some beneficial effect on nitrate reduction in the leaves of cauliflower plants but in the case of infiltration no effect was observed. Evidence was obtained that the nitrate-reducing activity of leaf fragments depends on the presence of undamaged cells. Grinding of the cells inactivates the enzyme system; in addition it may desorganize the electron-donor system. Furthermore a loss of nitrite may occur in leaf macerates. Addition of yeast extract, which is a source of flavin adenine dinucleotide, a co-enzyme of nitrate reductase, restored in some cases the nitrate-reductase activities of leaf macerates to a large extent. In other cases its effect was slight or negligible. Plants kept in the dark for a prolonged period of time showed lower nitrate-reducing capacities than those kept under normal light conditions. In some experiments the malic-dehydrogenase activity of molybdenum-deficient plant tissues was found to be promoted by the addition of molybdate. This effect was less consistent and far less pronounced than that on nitrate-reducing capacity. Molybdenum-deficient plant tissues usually have a lower catalase activity than plants supplied adequately with molybdenum.

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