Abstract
Nitrogen (N) supply, including NO3--N and organic N in the form of amino acids can influence the morphological attributes of plants. For example, amino acids contribute to plant nutrition; however, the effects of exogenous amino acids on NO3--N uptake and root morphology have received little attention. In this study, we evaluated the effects of exogenous glycine (Gly) on root growth and NO3--N uptake in pak choi (Brassica campestris ssp. Chinensis L.). Addition of Gly to NO3--N agar medium or hydroponic solution significantly decreased pak choi seedling root length; these effects of Gly on root morphology were not attributed to the proportion of N supply derived from Gly. When pak choi seedlings were exposed to mixtures of Gly and NO3--N in hydroponic culture, Gly significantly reduced 15NO3--N uptake but significantly increased the number of root tips per unit root length, root activity and 15NO3--N uptake rate per unit root length. In addition, 15N-Gly was taken up into the plants. In contrast to absorbed NO3--N, which was mostly transported to the shoots, a larger proportion of absorbed Gly was retained in the roots. Exogenous Gly enhanced root 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and oxidase (ACO) activities and ethylene production. The ethylene antagonists aminoethoxyvinylglycine (0.5 μM AVG) and silver nitrate (10 μM AgNO3) partly reversed Gly-induced inhibition of primary root elongation on agar plates and increased the NO3--N uptake rate under hydroponic conditions, indicating exogenous Gly exerts these effects at least partly by enhancing ethylene production in roots. These findings suggest Gly substantially affects root morphology and N uptake and provide new information on the specific responses elicited by organic N sources.
Highlights
Plant growth and nitrate (NO3-) accumulation in green leafy vegetables are influenced by the sources of available nitrogen (N) [1]
Pak choi seedlings were co-treated with 0.5 or 10 mM NO3--N and varied concentrations of Gly for 5 d on agar plates. In both NO3--N treatments, exogenous Gly significantly reduced the primary root length in a concentration-dependent manner compared with NO3--N as a single N source (Fig 1A and S1 Fig)
The primary root length of pak choi seedlings exposed to 0.5 or 10 mM NO3--N supplemented with 2.5 mM Gly was 31.0% and 38.5% lower, respectively, than seedlings exposed to 0.5 and 10 mM NO3--N
Summary
Plant growth and nitrate (NO3-) accumulation in green leafy vegetables are influenced by the sources of available nitrogen (N) [1]. Consumption of vegetables containing high concentrations of NO3- has been related to risks to human health [2]. Plants accumulate NO3- when the rate of NO3--N uptake through the roots exceeds the rate of NO3- assimilation in plant tissues. Root elongation and nitrate-N uptake as affected by glycine collection and analysis, decision to publish, or preparation of the manuscript
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