Regulation of Nitrogen Assimilation by Sulfur in Bean

Abstract

The objective of the present work was to determine the impact of sulfur(s) deficiency or toxicity on NO₃ ⁻ metabolism in bean plants (Phaseolus vulgaris cv. ‘Strike’). Sulfur was applied to the nutrient solution for 30 d at three dosages: 0 mM (S0), considered deficient; 1.875 mM (S1), considered optimal; and 18.75 mM (S2), considered toxic. The results indicated that the bean plants were comparatively much more sensitive to the deficient than to the toxic S application. The S deficiency translated as decreased assimilation of NO₃ ⁻, with the lowest activities in S0 of the enzymes involved in this process (nitrate reductase, nitrite reductase, glutamine synthase, and glutamate synthase) and a notable decline in biomass production. Finally, the application of high rates of S in our experiment also reduced NO₃ ⁻ assimilation, possibly due to an antagonism between SO₄ ⁼ and NO₃ ⁻.

Keywords:

• bean
• S deficiency
• nitrogen assimilation
• Phaseolus vulgaris
• S toxicity