Protein synthesis in green‐beans under salt stress with two nitrogen sources

Abstract

Nitrogen metabolism and protein synthesis in plants are severely affected by salt stress, resulting in abnormal plant growth and lower crop yield. The purpose of this investigation was to compare protein synthesis in three green bean (Phaseolus vulgaris L.) cultivars ('Tender Improved’, ‘Slim Green’, and ‘Kentucky Wonder') under normal (non‐saline) and salt stress with two sources of nitrogen (ammonium‐¹⁵N and nitrate‐¹⁵N separately). This comparison was achieved by using ¹⁵N under normal (control = 0.3 bars osmotic pressure) and NaCl stress (3.0 bars osmotic pressure), in Hoagland nutrient solution, in a growth chamber. The 5‐day‐old green bean seedlings were grown for 5 additional days in one‐half strength Hoagland solution before and 5 days after the completion of salinization with NaCl. This was followed by a 15‐day ¹⁵N uptake period after either (¹⁵NH₄)₂SO₄ or K¹⁵N0₃ addition to the culture solutions for the ammonium‐¹⁵N or nitrate‐¹⁵N treatments, respectively. Plant tissues were analyzed for the crude protein and protein‐N (total and ¹⁵N) contents. The crude protein and protein‐N (total and ¹⁵N) content of all cultivars significantly decreased under stress conditions for both sources of nitrogen. However, the Tender Improved appeared the least and the Slim Green the most severely affected by salinity among the three cultivars. For all cultivars at each harvest, shoots were more adversely influenced than roots by salt stress when comparing the salinized plants with the controls for each plant part for either source of ¹⁵N. The control (non‐salinized) plants contained substantially higher crude protein and protein‐N (total and ¹⁵N) when treated with NO₃‐N as compared with NH₄‐N source of ¹⁵N.