EFFECT OF SALINITY ON ARGININE-BIOSYNTHESIS IN LEAVES OF PHASEOLUS-VULGARIS L AND PHASEOLUS-ACUTIFOLIUS GRAY,A.

The objective of this study was to quantify the effect of salinity on the capacity of leaves of Phaseolus vulgaris L. and P. acutifolius A. Gray to synthesize arginine de novo and to determine the relative abil ity of the two species to tolerate salinity during the vegetative grow th phase. Research into the effect of salinity on P. acutifolius relat ive to P. vulgaris is limited. Plants were hydroponically cultured unt il age 5 d and then salinized for 16 d with 40 mM NaCl plus 20 mM CaCl 2. Salination caused greater reduction (P < 0.05) in P. acutifolius sh oot dry weight (35 and 43% for two lines) than P. vulgaris [<25% for L inden and Ferry Morse 53 (FM 53) cultivars]. Root growth was unaffecte d in both species. Salt reduced the capacity of leaves of P. acutifoli us to incorporate (NaHCO3)-C-14 but not [C-14]citrulline into arginine plus urea (Sigma A + U) per gram fresh weight tissue (80% for both li nes, P < 0.05). Arginine de novo synthesis in P. vulgaris was unaffect ed. Incorporation of (NaHCO3)-C-14 into Sigma A + U was increased by a dded ornithine but remained lower (P < 0.05) in salinized P. acutifoli us leaves than in control leaves, suggesting that ornithine availabili ty was not the single factor limiting arginine de novo synthesis durin g salination. Salination reduced activities of glutamine synthetase an d carbamylphosphate synthetase per milligram protein in P. acutifolius (both lines, 50%) and FM 53 (20-40%) but not Linden. Thus, enzyme rea ction(s) leading to the formation of citrulline in arginine de novo sy nthesis in leaves of P. acutifolius are more affected by salt than tho se in P. vulgaris.