title: Water Deficit-Induced Changes in Concentrations in Proline and Some Other Amino Acids in the Phloem Sap of Alfalfa.
abstract: Changes in amino acid composition of alfalfa (Medicago sativa L.) phloem sap were studies in response to a water deficit. Sap was collected by stylectomy. As the leaf water potential ([psi]) decreased from -0.4 to -2.0 MPa, there was 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 [psi] 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 [psi] threshold value of about -0.9 MPa (concentration x60 for a decrease of [psi] 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.
authors.affiliation: Laboratoire de Zoologie, Institut National de la Recherche Agronomique Lusignan, 86600 Lusignan France (C.G., R.B.).
authors.forename: C.
authors.initials: C
authors.lastname: Girousse
authors.forename: R.
authors.initials: R
authors.lastname: Bournoville
authors.forename: J. L.
authors.initials: JL
authors.lastname: Bonnemain