Water deficit-induced changes in concentrations in proline and some other amino acids in the phloem sap of alfalfa
1996
Girousse, C. | Bournoville, R. | Bonnemain, J.L.
Changes in amino acid composition of alfalfa (Medicago sativa L.) phloem sap were studied in response to a water deficit. Sap was collected by stylectomy. As the leaf water potential decreased from -0.4 to -2.0 MPa, there was a significant increase of the total amino acid concentration, due to that of some amino acids: proline, valine, isoleucine, leucine, glutamic acid, aspartic acid, and threonine. Asparagine concentration, which is the main amino acid assayed in the phloem sap of alfalfa (it accounts for 70% of the total content), did not vary with the plant water status. The other amino acid concentrations remained stable as leaf water potential varied; in particular, gamma-amino butyric acid concentration remained unchanged, whereas it varied in response to wounding. The more striking change in the sieve tubes was the accumulation of proline which was observed below a leaf water potential threshold value of about -0.9 MPa (concentration x60 for a decrease of leaf water potential from -0.9 to -2.0 MPa). The role of such changes in phloem sap amino acid concentration in osmotic adjustment of growing tissues is discussed.
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