Ammonium absorption and assimilation in two rice variets: carbon-nitrogen metabolism integration / Absorção e assimilação de amônio em duas variedades de arroz: uma integração entre o metabolismo de nitrogênio e de carbono.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

About half of planet population depend on rice. In Brazil, this cereal crop is widely spread, and influenced by harsh climate conditions such as Humid Tropics one. In this region, certainly nitrogen is the most limiting nutrient. However, low insolation, acid and highly Al3+ satured soils still endangers the culture. In these soils, ammonium can be the single plants Nitrogen source for plants. Its assimilatory pathway is economic and fast, although it presents strong integration with C metabolism. This work intended to recognize ammonium assimilation integrated with carbon metabolism. Two rice varieties were used: one adapted to Humid Tropics environment - Piauí - and an improved variety represented by IAC-47, selected under high N levels. Assays were carried on with 26 days after emergency plants, cultivated in Hoagland and Arnon (1950) modified solution with N-NH4 + 0.1 mM and 1.0 mM N-NH4 +. Plasmalem (P)-H+ATPases; vacuole (V)-H+ATPases; vacuole (V)-H+PPases activity as well as glutamine sinthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) were analysed. Moreover, it was determined soluble sugars, amino-N, N-NH4 +, total-N, fresh and dry weight, and nutrition solution pH and N-NH4 + variation. Also, seminal root length was measured as well as glycolysis was analyzed through phosphofructokinase (PFK) activity at plants roots tissue. P-H+ATPases activity was higher in IAC-47 roots. On the other hand, at Piaui roots, enhances at microsomal protein were observed, and V-H+ATPases presented higher activity as well as root development was high. This allowed the adapted variety to absorb N like the improved one. However, both varieties accumulated fresh weight in shoots at treatment 1.0 mM N-NH4 + and showed roots/shoots decrease at the same treatment. Moreover, aminoN and NH4 + concentration was higher at Piauí shoots under 1.0 mM N-NH4 +. Both Piauí shoots and roots cultivated under 1.0 mM NNH4 + accumulated less soluble sugars. Also, Piaui shoots had higher a+b chorophyl concentration. PFK activity was enhanced at every plant, what accompanied ammonium levels. Piauí plants always presented low sugar oxidation levels. It also seemed to concentrate its sugars. Probably it happened to later availability for grain fullfil. To ensure this, it has high ammonium and amino-N pools. Nitrogen absorbed by 1.0 mM N-NH4 + Piauí seemed to be substrate for GDH-amination, wich activity was superior. Despite this, GDH deamination was high. In this way, Piauí could have GDH activity as an anaplerotic pathway to regulate C skeletons need. Meanwhile, GS increases were observed at IAC-47, toghether with GOGAT increases at 1.0 mM N-NH4 + shoots. IAC-47 assimilated ammonium at GS/GOGAT pathway, wich was fed by glycolysis velocity. These plants would produce constitutive protein, what doesnt mean later grain stock.

ASSUNTO(S)

oryza sativa glicolysis glicólise bioquimica n-nh4 +

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