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Ammonium and nitrate nutrition and cyanide-resistant respiration in soybean seedling

Shi Zhengqiang

College of Biology,Beijing Agricultural University. Beijing 100094

Abstract

Soybean seedlings were grown with N-free (-N), NH~(+)_(4) and NO~(-)_(3) nutrient solutions for 20 days, NH~(+)_(4) ions were less accumulated in leaf and root tissues and a higher organic N content was found in NH~(+)_(4) grown seedlings (Table　1). NO~(-)_(3) ions were largely accumulated in soybean tissues grown with NO~(-)_(3) nutrient solution, accompagnied by a higher dry weight (Table 1, Fig.1). The oxidative and phosphorylative properties of the mitochondria isolated from roots and leaves were measured with malate as substrate. NH~(+)_(4) and NO~(-)_(3) supplies stimulated oxidative activities of both cytochrome pathway and cyanide-resistant pathway (Fig.2). Compared with NO~(-)_(3)　nutrition, NH~(+)_(4) nutrition resulted in a higher cytochrome pathway activity in root mitochondria and a higher cyanide-resistant pathway activity in leaf mitochondria (Fig.2). The assimilation of NH~(+)_(4) into amino acids was carried　out exclusively in roots and the higher rate of organic N synthesis might need a higher cytochrome pathway activity to produce more ATP to supply the energy needed. The involvement of photosynthetic energy in nitrogen metabolism in leaves reduced the utilization of respiratory energy. That resulted in an increased activity of cyanide-resistant pathway in leaf mitochondria.In this case, leaf mitochondria appeared to produce more carbon skeletons than ATP for amono-acid synthesis. NO~(-)_(3) reduction was occurred mainly in aves that needed a large amount of mitochondrial NADH as reducing power and less NADH was oxidized by cyanide-resistant pathway. The higher growth of soybean seedlings with NO~(-)_(3) nutrition was probably linked to a lower cyanide-resistant respiration in leaves to avoid consuming more carbon sources.

Key words: Nitrogen nutrition;Mitochondrial oxidation;Cyanide-resistant pathway;Soybean

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Citing This Article：

Shi Zhengqiang. Ammonium and nitrate nutrition and cyanide-resistant respiration in soybean seedling. Acta Physiol Sin 1997; 49 (2): (in Chinese with English abstract).