Salt Stress Inhibits Arginine Biosynthesis in Tepary Bean (Phaseolusa Cutifolius)

Abstract

<jats:p>Two lines of tepary bean, PI 321-638 and PI 319-443, were salinized at age 7 days with Shive's nutrient solution plus 60 mM NaCl-CaCl<jats:sub>2</jats:sub> in a 2:1 molar ratio. Salt was added at the rate of 1/3 the final concentration every other day. The osmotic potential of the salinizing solution was -0.33 MPa. Fifteen days of salt treatment reduced plant growth 45% and inhibited the incorporation of NaH<jats:sup>14</jats:sup>CO<jats:sub>3</jats:sub> into the combined pool of arginine plus urea 60 and 85% for the two lines, respectively. The salt sensitive step in the arginine biosynthetic pathway was identified as carbamylphosphate synthetase in both lines, Incorporation of [<jats:sup>14</jats:sup>C]citrulline and [<jats:sup>14</jats:sup>C]carbamylphosphate plus ornithine were not inhibited by the salt treatment, but the incorporation of NaH<jats:sup>14</jats:sup>CO<jats:sub>3</jats:sub> remained inhibited even in the presence of added ornithine (10 mM). Inhibition at carbamylphosphate synthetase was confirmed by demonstration that the incorporation of NaH<jats:sup>14</jats:sup>CO<jats:sub>3</jats:sub> into UMP was also inhibited by salt stress. Evidence is provided suggesting that reduced availability of ornithine additionally compromised both arginine and pyrimidine biosynthesis during salt stress.</jats:p><jats:p>Supported by the Citrus Research Center and Agricultural Experiment Station of the University of California, Riverside.</jats:p>