Genotypic differences in nitrate uptake, translocation and assimilation of two Chinese cabbage cultivars [Brassica campestris L. ssp. Chinensis (L.)]

Abstract

A hydroponic trial was conducted to investigate genotypic differences in nitrate uptake, translocation and assimilation between low nitrate accumulator L18 and high accumulator H96 of Chinese cabbage [Brassica campestris L. ssp. Chinensis (L.)]. The results suggested that H96 could uptake more nitrate than L18 in the root but lower transport inside leaf cells and assimilation in the leaf. It was showed that root morphology parameters - length, surface area and volume of H96 were 18.0%, 31.6% and 46.5% higher than L18. Nitrate transporters NRT1.1 and NRT2.1 transcription levels were 41.6% and 269.6% higher than those of L18 respectively. NRT1.1 and NRT2.1 expression amount in leaf blade of two cultivars were opposite to in the root, L18 NRT1.1 and NRT2.1 expressions were 279.2% and 80.0% higher than H96. In addition, nitrate assimilation capacity of L18 was significantly higher than H96 in leaf. It was showed that Nitrate Reductase (NR; EC 1.7.1.1) activity and NIA expression level of L18 leaf were 234 0.4% and 105.4% higher than those of H96, Glutamine Synthetase (GS; EC 6.3.1.2) activity, Gln1 and Gln2 expression levels in the leaf blade of L18 were 43.9%, 331.5% and 124.8% higher than those of H96 respectively. Nitrate assimilation products-Glu, total amino acid, soluble protein content in the leaf of L18 were all significantly higher than those of H96. The results above suggested that nitrate accumulation differences were due to differential capacities to uptake, mechanisms for nitrate transport in leaves and assimilate nitrate. Comparing contribution of three aspects in nitrate accumulation, translocation and assimilation were contributed more in low nitrate concentration in the leaf blade.

Keywords: Assimilation; Chinese cabbage; GOGAT; GS; GSA; Glu; HATS; LATS; N; NR; NRA; NiR; Nitrate; RT-PCR; Translocation; Uptake; glutamate synthase; glutamic acid; glutamine synthetase; glutamine synthetase activity; high-affinity transport system; low-affinity transport system; nitrate reductase; nitrate reductase activity; nitrite reductase; nitrogen; real-time polymerase chain reaction.