Metabolismo de nitrogenio em plantas de soja [Glycine max (L.) Merr. cv IAC-17] submetidas a deficiencia de O2 no sistema radicular

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The soybean (Glycine max (L.) Merr.) is among the most frequently used models to study O IND.2 deficiency in the root system of plants. However, few studies have focussed on waterlogging of the root system and its effects on the metabolic content of the roots, especially nitrogenous compounds, and their means of transportation through the xylem and phloem. The objectives of this study were: 1) assess the effects of hypoxia of the soybean root system on the content of important metabolites of roots, xylem and phloem sap, together with the activity of the enzymes alanine aminotransferase and aspartate aminotransferase in the roots; 2) determine the time required for the re-establishment of the levels of such metabolites in the roots and in the xylem exsudate as well as alanine aminotransferase activity in the reots, after the return to normoxia; 3) partially purify and characterise the alanine aminotransferase enzyme in soybean roots under hypoxia. Non-nodulated cv IAC -17 soybean plants were cultivated in nutritive solution under normoxia (continuous aeration by compressed air) and, after reaching the V5 stage, they were used in the following basic experimental systems: a) Hypoxia: interruption of aeration together with the application of a layer of mineral oil over the solution, for up to 120 h; b) Hypoxia followed by the return to normoxia: solution aerated with N IND.2 gas for 120 h followed by the restoration of aeration by compressed air for 96 h. Under normoxia, the O IND.2 content in the nutritive solution was around 87% saturation (6,5 mg/ml) for both experimental systems. Under conditions of the first experimental system, the O IND.2 content fell gradually and after 8 h of hypoxia stabilised at 6% saturation (0,4 mg/ml). This decrease was more abrupt in the second experimental system, where the O IND.2 content dropped to around 5% (0,3 mg/ml) after 6 h and 4 % (0,2 mg/ml) after 24 h of hypoxia. During hypoxia, the starch and water soluble polissacharids contents of the roots showed an increase after 24 h, amino acids after 48 h and total soluble sugar, sucrose and protein from 48 to 96 hours. The N0 IND.3 content decreased after 96 h of hypoxia. In the xylem exsudate, amino acid levels increased during 48 h of hypoxia, while N0 IND.3 decreased abruptly within the first 24 h. Phloem exsudates presented a 50% decrease of amino acids, total soluble sugar and sucrose after 96 h of hypoxia, compared to normoxia values. After normoxia was re-established, the metabolite content of the roots and xylem exsudates were normal after 48 h, except for N0 IND.3 and protein, which reached control levels after 72 hours. The content of Ala and lactate in the soybean roots increased within 48 h of hypoxia while pyr and ethanol increased up to 120 h. It appears that under hypoxia, the principal metabolic fate of pyr was its conversion to Ala, which accumulated in the proportion of 5:1 and 6:1 in relation to lactate and ethanol, respectively. After returning to normoxia, the roots recovered the levels of these metabolites to those observed before the hypoxia within 48 hours. Under normoxia, Asn was the predominant amino acid in the roots and xylem exsudate. However, during root hypoxia, Asn decreased sharply while the content of Ala and Gaba rose dramatically.When normoxia was re-established, these amino acids reached their original levels within 48 h

ASSUNTO(S)

raizes soja plantas - efeito do nitrogenio

ACESSO AO ARTIGO

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