Effect of Salinity on Arginine Biosynthesis in Leaves of Phaseolus vulgaris L. P. acutifolius A. Gray

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 ability of the two species to tolerate salinity during the vegetative growth phase. Research into the effect of salinity on P. acutifolius relative to P. vulgaris is limited. Plants were hydroponically cultured until 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) P. acutifolius shoot dry weight (35 and 43% for two lines) than P. vulgaris [<25% for Linden and Ferry Morse 53 (FM 53) cultivars]. Root growth was unaffected in both species. Salt reduced the capacity of leaves of P. acutifolius to incorporate NaH 14 CO 3 but not [ 14 C]citrulline into arginine plus urea (ΣA + U) per gram fresh weight tissue (80% for both lines, P < 0.05). Arginine de novo synthesis in P. vulgaris was unaffected. Incorporation of NaH 14 CO 3 into ΣA ÷ U was increased by added ornithine but remained lower ( P < 0.05) in salinized P. acutifolius leaves than in control leaves, suggesting that ornithine availability was not the single factor limiting arginine de novo synthesis during salination. Salination reduced activities of glutamine synthetase and carbamylphosphaste synthetase per milligram protein in P. acutifolius (both lines, 50%) and FM 53 (20–40%) but not Linden. Thus,enzyme reaction(s) leading to the formation of citrulline in arginine de novo synthesis in leaves of P. acutifolius are more affected by salt than those in P. vulgaris .