© 2007 The Author(s).
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RESEARCH PAPER |
Amino acid pattern and glutamate metabolism during dehydration stress in the ‘resurrection’ plant Sporobolus stapfianus: a comparison between desiccation-sensitive and desiccation-tolerant leaves
1Dipartimento di Scienze Agronomiche e Gestione del Territorio Agroforestale, Facoltà di Agraria, Università degli Studi di Firenze, I-50144 Firenze, Italia
2Unité de Nutrition Azotée des Plantes, INRA, Route de Saint Cyr, F-78000 Versailles, France
* To whom correspondence should be addressed. E-mail: tommaso.martinelli{at}unifi.it
The present study analyses changes in nitrogen compounds, amino acid composition, and glutamate metabolism in the resurrection plant Sporobolus stapfianus during dehydration stress. Results showed that older leaves (OL) were desiccation-sensitive whereas younger leaves (YL) were desiccation-tolerant. OL lost their soluble protein more rapidly, and to a larger extent than YL. Enzymes of primary nitrogen assimilation were affected by desiccation and the decrease in the glutamine synthetase (GS, EC 6.3.1.2) and ferredoxin-dependent GOGAT (Fd-GOGAT, EC 1.4.7.1) activities was higher in OL than in YL, thus suggesting higher sensibility to dehydration. Moreover, YL showed higher total GS enzyme activity at the end of the dehydration stress and was shown to maintain high chloroplastic GS protein content during the entire stress period. Free amino acid content increased in both YL and OL between 88% and 6% relative water content. Interestingly, OL and YL did not accumulate the same amino acids. OL accumulated large amounts of proline and 
-aminobutyrate whereas YL preferentially accumulated asparagine and arginine. It is concluded (i) that modifications in the nitrogen and amino acid metabolism during dehydration stress were different depending on leaf development and (ii) that proline and -aminobutyrate accumulation in S. stapfianus leaves were not essential for the acquisition of desiccation tolerance. On the contrary, the accumulation of large amounts of asparagine and arginine in the YL during dehydration could be important and serve as essential nitrogen and carbon reservoirs useful during rehydration. In this context, the role of GS for asparagine accumulation in YL is discussed.
Key words: Arginine, asparagine, GABA, glutamine synthetase, GOGAT, proline
Received 26 February 2007; Revised 4 June 2007 Accepted 12 June 2007
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