Effects of Blue and Red Light On Growth And Nitrate Metabolism In Pakchoi

Xiao-Xue Fan,Hai Xu,Bo Song,Gang Xu,Long-Zheng Chen,Feng Xue

doi:10.1515/chem-2019-0038

Abstract

AbstractThis study investigated the effects of blue and red light on metabolites of nitrate, key enzymes, and the gene expression of key enzymes in pakchoi plants (Brassica campestris L. var. Suzhouqing). Plants were grown under three light quality treatments, namely, white light (W), red light (R) and blue light (B), at the same photosynthetic photon flux density (PPFD) of approximately 150 μmol m-2 s-1 for 48 hours of continuous illumination, and W was set as the control. The dynamics of net photosynthetic rate in pakchoi subjected to different light treatments were the same as the total chlorophyll contents: blue light > white light > red light. The nitrate reductase (NR) activity, nitrite reductase (NiR) activity, glutamine synthetase (GS) activity and glutamate synthase (GOGAT) activity were highest under blue light. Further, the expression levels of NR, NiR and GS genes were significantly higher under blue light. Under continuous illumination, the auxin content (IAA) in pakchoi leaves was highest under blue light, whereas the abscisic acid (ABA) content was highest under red light. In contrast, there was no significant effect for gibberellin (GA) under any type of light treatment.

Highlights

Nitrate is a main source of nitrogen, and its content reflects the nutrient status of plants
The qRT-PCR analysis in our study showed that the expression of Nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS) genes was upregulated in response to the B treatment, suggesting the induction of nitrogen metabolism enzymes possibly (Figure 3)
We found that blue light increased IAA content and NR activity in pakchoi, which was similar to the results observed in Arabidopsis [41]

Summary

Introduction

Nitrate is a main source of nitrogen, and its content reflects the nutrient status of plants. The model suggested that light could regulate NR activity through two pathways, namely, the regulation of NR gene expression by photosynthetic products and the regulation of NR state by nicotinamide adenine dinucleotide phosphate (NADP). Previous studies indicated that light quality has a significant effect on nitrate metabolism in plants. A five-minute red-blue light pulse can stimulate nitrate assimilation in red algae, this kind of effect can be neutralized by subsequent far-red light [2]. This pattern suggests that light-sensitive pigments participate in this process. The result is probably due to blue light stimulating NR absorption through photosynthesis [5], alternatively, the direct stimulation of NR because the chromophore of the blue-light receptor cryptochrome contains flavin adenine dinucleotide (FAD), and FAD is present in the prosthetic group of NR [6]

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