Root GS and NADH-GDH Play Important Roles in Enhancing the Ammonium Tolerance in Three Bedding Plants.

Jinnan Song,Jingli Yang,Byoung Ryong Jeong

doi:10.3390/ijms23031061

Jinnan Song, Jingli Yang + Show 1 more

Open Access

https://doi.org/10.3390/ijms23031061

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Abstract

Ammonium is a paradoxical nutrient because it is more metabolically efficient than nitrate, but also causes plant stresses in excess, i.e., ammonium toxicity. Current knowledge indicates that ammonium tolerance is species-specific and related to the ammonium assimilation enzyme activities. However, the mechanisms underlying the ammonium tolerance in bedding plants remain to be elucidated. The study described herein explores the primary traits contributing to the ammonium tolerance in three bedding plants. Three NH4+:NO3− ratios (0:100, 50:50, 100:0) were supplied to salvia, petunia, and ageratum. We determined that they possessed distinct ammonium tolerances: salvia and petunia were, respectively, extremely sensitive and moderately sensitive to high NH4+ concentrations, whereas ageratum was tolerant to NH4+, as characterized by the responses of the shoot and root growth, photosynthetic capacity, and nitrogen (amino acid and soluble protein)-carbohydrate (starch) distributions. An analysis of the major nitrogen assimilation enzymes showed that the root GS (glutamine synthetase) and NADH-GDH (glutamate dehydrogenase) activities in ageratum exhibited a dose-response relationship (reinforced by 25.24% and 6.64%, respectively) as the NH4+ level was raised from 50% to 100%; but both enzyme activities were significantly diminished in salvia. Besides, negligible changes of GS activities monitored in leaves revealed that only the root GS and NADH-GDH underpin the ammonium tolerances of the three bedding plants.

Highlights

Nitrogen (N) is a vital factor influencing plant growth and agricultural productivity; sufficient nitrogen fertilization is necessary for a reliable yield and quality of plants [1,2]
The stomatal conductance of salvia treated with 0:100 and 50:50 NH4+:NO3− had 2.08-fold and 2.01-fold enhancement compared with those grown with 100:0 NH4+:NO3− (Figure 3C ‘Salvia part’); no significant differences in the stomatal conductance were detected in petunia plants in response to the different NH4+:NO3− ratios (Figure 3C ‘Petunia part’); we found that ageratum plants grown with the 100:0 NH4+:NO3− experienced a 7.76% increase in the stomatal conductance relative to the ageratum plants grown with 0:100 NH4+:NO3− (Figure 3C ‘Ageratum part’)
For salvia, in comparison with the plants grown with 50:50 NH4+:NO3−, the glutamine synthetase (GS) and NADH-glutamate dehydrogenase (GDH) activities in roots treated with 100:0 NH4+:NO3− decreased by 23.09% and 24.63%, respectively (Figure 6A,C ‘Salvia part’)

Summary

Introduction

Nitrogen (N) is a vital factor influencing plant growth and agricultural productivity; sufficient nitrogen fertilization is necessary for a reliable yield and quality of plants [1,2]. Foliage turning to dark green abnormally with physiological dysfunction, and lateral root growth and elongation inhibited causing lodging, are usually observed with nitrogen overdose. Ammonium (NH4+) and nitrate (NO3−) are two principal inorganic N forms for plant absorption and assimilation. Both can be taken up and utilized through the root parts, but the energetic and biochemical processes for the acquisition of the two inorganic N forms have been characterized to be dramatically different [4]. NO3− assimilation by plants requires more energy than NH4+ assimilation, which conferred NH4+ as the predominant N source for plants

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