Alanine metabolism and alanine aminotransferase activity in soybean (Glycine max) during hypoxia of the root system and subsequent return to normoxia

Alanine is one of the main products of anaerobic metabolism in plants and its formation believed to involve alanine aminotransferase (AlaAT), an enzyme induced under such conditions. Effects of hypoxia on roots of soybean (Glycine max) and the subsequent return to normoxia were studied with regard to alanine metabolism in the roots and its transport in the xylem, together with the role of AlaAT in this process. Non-nodulated plants were grown in a hydroponic system with nutrient solution containing nitrate as source of N. Subjecting the root system to hypoxia for up to 120 h led to large increases in alanine in both roots (4-44 mol%) and xylem sap (0.5-45 mol%). The increase in the roots preceded that of the xylem, consistent with alanine formation in the roots being the source of the increase in the xylem. On return to normoxia, following 120 h under hypoxia, the levels of alanine returned rapidly to pre-hypoxic levels. AlaAT activity of the roots more than doubled over the 120 h period of hypoxia. However, the bulk of this increase in activity took place after 48 h of hypoxia, long after the large increases in alanine had initiated. It is suggested that induction of AlaAT activity in soybean roots under hypoxia has only a limited role in the increase of alanine formation but may be responsible for the rapid recovery of alanine to pre-hypoxic levels on return to normoxia. (C) 2002 Elsevier Science B.V. All rights reserved.