Effects of Na application on the capacity of N03-assimilation were studied in Na-deficient Amaranthus tricolor L. cv Tricolor plants. On day 30 after germination, Na-deficient A. tricolor plants received either 0.5 millimolar NaCI or KCI. The level of nitrate reductase activity doubled within 24 hours by the addition of Na and the enhanced level was maintained thereafter. When the plants were exposed to 2 millimolar 15N03-, total 15N taken up by the plants was greater in the Na-treated plants than in the Ktreated plants within 24 hours of the Na treatment. Incorporation of 15N into the 80% ethanol-insoluble nitrogen fraction of the Natreated plants in the light period was about 260% of those of the K-treated plants indicating greater capacity of N03-assimilation in the Na-treated plants. From these results, it was demonstrated that Na application to the Na-deficient A. tricolor plants promoted N03-reduction and its subsequent assimilation into protein, resulting in growth enhancement.As Na is required by C4 plants for their normal growth and not by C3 plants, Na is anticipated to be involved in C4 photosynthetic pathway (2). However, some C4 plants, such as corn and sugarcane have not been shown to require Na (6). Accordingly, it is probable that some metabolic reactions other than those of the C4 photosynthetic pathway occur which require Na. Recently, we reported that N03-uptake and induction ofNR2 activity in the Na-deficient Amaranthus tricolor plants were stimulated by Na (1 1, 12). In this paper, we present evidence that the enhanced level of NR activity by Na had significant effects on the growth of A. tricolor plants. MATERIALS AND METHODS Plant MaterialsSeedlings of Amaranthus tricolor L. cv Tricolor were cultured under Na-deficient conditions as described previously (8, 11). The basal culture solution (pH 6.0) prepared in distilled and deionized water contained 2 mM KNO3, 1 mM CaC2, 0.25 mm (NH4)2HP04 and 0.5 mM MgS04. 7H20. The composition of the micronutrients was that of Arnon's cited by Hewitt (5) except that all the iron was supplied as ferric citrate. The concentration of Na as an impurity in the culture 'Present Address;

Pyruvate kinase enzymes were partially purified from leaves of halophytes, Atriplex gmelini C. A. Mey., Chenopodium acuminatum Wild, and Spergularia salina J. et C. Presl., grown hydroponically in the presence of 250 mM NaCl in a greenhouse, to determine their Km values for potassium. The values were all ca 10−3M, as also reported for the glycophyte enzymes. However, the Km values were reduced by 60 to 70% by the addition of betaine to a concentration of 1 M.

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