Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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PLANT PHYSIOLOGY , Vol 111, Issue 1 109-113, Copyright © 1996 by American Society of Plant Biologists

WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY

Water Deficit-Induced Changes in Concentrations in Proline and Some Other Amino Acids in the Phloem Sap of Alfalfa

C. Girousse, R. Bournoville and J. L. Bonnemain
Laboratoire de Zoologie, Institut National de la Recherche Agronomique Lusignan, 86600 Lusignan France (C.G., R.B.)

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.




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Copyright © 1996 by the American Society of Plant Biologists