EFFECT OF HUMIC SUBSTANCES ON NITROGEN UPTAKE AND ASSIMILATION IN TWO SPECIES OF PINUS

The effects of a humic fraction, with a high molecular weight (Hsp) extracted from a soil with a Fagus sylvatica vegetal cover were compared on ammonium (NH+ 4) and nitrate (NO− 3) uptake in two different coniferous species (Pinus pinaster and Pinus laricio). The activity of malate dehydrogenase (MDH; EC 1.1.1.37), glutamate dehydrogenase (GDH; EC 1.4.1.3) and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) key enzymes involved in nitrogen metabolism were tested. The data obtained indicate that the humic fractions, at all concentrations, increased ammonium uptake by both species, while nitrate uptake was unaffected. In P. laricio seedlings this fraction increased only leaf malate dehydrogenase activity, while in P. pinaster seedlings an increase of glutamate dehydrogenase in leaves, and of phosphoenolpyruvate carboxylase activity in both roots and leaves was observed. These results show that humic substances stimulate only ammonium uptake and differently influence ammonium assimilation in the two species of Pinus. This diverse behavior might be related to the different environmental conditions where these two species live.

[1]  S. Nardi,et al.  EFFECTS OF HUMIC SUBSTANCES ON NITRATE UPTAKE AND ASSIMILATION IN BARLEY SEEDLINGS , 1986 .

[2]  D. Vaughan,et al.  Effects of Humic Acid on Protein Synthesis and Ion Uptake in Beet Discs , 1971 .

[3]  T. Ingestad.  Studies on the Nutrition of Forest Tree Seedlings. III Mineral Nutrition of Pine , 1957 .

[4]  M. M. Bradford.  A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. , 1976, Analytical biochemistry.

[5]  G. Gebauer,et al.  Nitrate reduction and nitrate content in ash trees (Fraxinus excelsior L.): distribution between compartments, site comparison and seasonal variation , 1992, Trees.

[6]  F. J. Stevenson.  HUmus Chemistry Genesis, Composition, Reactions , 1982 .

[7]  P. Schweizer,et al.  Effect of Nitrate and Ammonium Nutrition of Nonnodulated Phaseolus vulgaris L. on Phosphoenolpyruvate Carboxylase and Pyruvate Kinase Activity. , 1985, Plant physiology.

[8]  T. Postelnicu,et al.  Sokal, R. R., and I. J. Rohlf: Biometry. W. H. Freeman and Company, San Francisco 1969, XXI + 776 S., 89 Abb., 56 Tab., Preis 126/— , 1970 .

[9]  A. Piccolo,et al.  Structural characteristics of humic substances as related to nitrate uptake and growth regulation in plant systems , 1992 .

[10]  Donald Voet,et al.  Biochemistry, 2nd ed. , 1995 .

[11]  G. Concheri,et al.  Nitrate uptake and ATPase activity in oat seedlings in the presence of two humic fractions , 1991 .

[12]  R. H. Garrett,et al.  Biochemistry, 2nd ed. , 1999 .

[13]  B. Ord,et al.  Influence of Humic Substances on Biochemical Processes in Plants , 1985 .

[14]  O. Queiroz.  Photoperiodisme et activite enzymatique (PEP carboxylase et enzyme malique) dans les feuilles de Kalanchoe blossfeldiana , 1969 .

[15]  M. W. Weatherburn.  Phenol-hypochlorite reaction for determination of ammonia , 1967 .

[16]  H. Mohr,et al.  Assimilation of nitrate and ammonium by the Scots pine (Pinus sylvestris) seedling under conditions of high nitrogen supply , 1992 .

[17]  M. Drew,et al.  Induction of nitrate transport in maize roots, and kinetics of influx, measured with nitrogen-13. , 1990, Plant physiology.

[18]  S. Robinson,et al.  The role of glutamate dehydrogenase in plant nitrogen metabolism. , 1991, Plant physiology.

[19]  S. Nardi,et al.  Antidote action of humic substances on atrazine inhibition of sulfate uptake in barley roots , 1981 .

[20]  D. Turpin,et al.  Integration of Carbon and Nitrogen Metabolism in Plant and Algal Cells , 1994 .