Light intensity affects the uptake and metabolism of glycine by pakchoi (Brassica chinensis L.)

Abstract

The uptake of glycine by pakchoi (Brassica chinensis L.), when supplied as single N-source or in a mixture of glycine and inorganic N, was studied at different light intensities under sterile conditions. At the optimal intensity (414 μmol m−2 s−1) for plant growth, glycine, nitrate, and ammonium contributed 29.4%, 39.5%, and 31.1% shoot N, respectively, and light intensity altered the preferential absorption of N sources. The lower 15N-nitrate in root but higher in shoot and the higher 15N-glycine in root but lower in shoot suggested that most 15N-nitrate uptake by root transported to shoot rapidly, with the shoot being important for nitrate assimilation, and the N contribution of glycine was limited by post-uptake metabolism. The amount of glycine that was taken up by the plant was likely limited by root uptake at low light intensities and by the metabolism of ammonium produced by glycine at high light intensities. These results indicate that pakchoi has the ability to uptake a large quantity of glycine, but that uptake is strongly regulated by light intensity, with metabolism in the root inhibiting its N contribution.

Elevated CO2 levels enhance the uptake and metabolism of organic nitrogen

“…The roots of seedlings were placed in the tube through a small hole in the lid, and the hole was sealed with Nanda 704 silicone rubber (Kangda, Nanjing, China) after 1 day of growth. The seedlings attached to the tube lids were then transferred to new 50 ml centrifuge tubes (covered with tin foil) containing the full nutrient solution (Ma et al ), and was defined as day 1. The nutrient solution without N contained 4 m M CaCl 2 , 2 m M KH 2 PO 4 , 2 m M K 2 SO 4 , 1 μ M ZnSO 4 ·7H 2 O, 0.4 μ M CuSO 4 ·5H 2 O, 0.1 μ M NaMoO 4 ·2H 2 O, 1.4 m M MgSO 4 ·7H 2 O, 8 μ M H 3 BO 3 , 18.3 μ M FeSO 4 ·7H 2 O, 5 μ M Na 2 EDTA and 10 μ M MnCl 2 , and the pH was 6.2.…”

“…The effects of eCO 2 on passive and active uptake were tested with carbonyl cyanide 3‐chlorophenylhydrazone (CCCP) (Ma et al ). CCCP inhibits active uptake of N by the roots, and the 15 N in CCCP‐treated plants is therefore transported via passive absorption; the 15 N in CCCP‐untreated plants minus the 15 N in CCCP‐treated plants provides a measure of the active uptake.…”

“…The uptake of different N sources was calculated by the 15 N‐atom percentage in treated seedlings minus the natural 15 N‐atom percentage in controlseedlings. The amount of NH 4 + , glycine and NO 3 − taken up from the mixed N source was calculated by Eqn (Ma et al ): where N uptake is the amount of NH 4 + , glycine, or NO 3 − absorbed into pakchoi shoots or roots; N Total − N is the total N content in roots or shoots; A s is the 15 N‐atom percentage in roots or shoots; A c is the 15 N‐atom percentage in the ‘blank’ seedlings; A f is the 15 N‐atom percentage of the 15 N‐labelled source (glycine 5.0%, NO 3 − 5.0%, or NH 4 + 5.0% for experiment 1; glycine 98.1% for experiment 2).…”

“…Studies have shown that fast‐growing plant species tend to absorb nitrates, while plants with low growth rates and biomass tend to absorb more organic N (Weigelt et al , Harrison et al ). Environmental factors such as light intensity, temperature, soil pH and soil moisture affect the uptake and metabolism of amino acids (Ma et al ). So, it is useful to explore and predict the effects of changing environment on plant N uptake.…”

“…Amino acids are mostly absorbed by plant roots via H + ‐ATPase driven proton co‐transporters in the form of active uptake. However, the uptake pattern can vary among different environments; for example, the passive uptake of glycine increases under lower pH and higher light intensity conditions (Ma et al , Ma et al ). After root uptake, glycine is transformed to serine via aminotransferase, which is possibly catalysed by serine glyoxylate aminotransferase (SGAT) (Schmidt and Stewart , Näsholm et al ).…”