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 gamma-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 gamma-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.