| Cucumber(Cucumis sativus L.)is one of the important vegetable crops in China,which is widely cultivated in the world because of its good economic and nutritional value.Cucumber is particularly sensitive to light environment and nitrogen supply level.Carbon and nitrogen metabolism caused by these two environmental factors,as the most basic physiological metabolic response in plants,interacts and ultimately affects plant growth and development.However,there are few studies on the effects of light and nitrogen interaction on the growth and development of cucumber seedlings,especially the effects of different wavelengths of light quality on the growth and nitrogen metabolism of cucumber seedlings under nitrogen deficiency stress.In addition,bZIP transcription factor HY5 has been proved to be the core transcription factor in the light signaling pathway.It has been found that HY5 can increase the transcription level of nitrate reductase gene and promote nitrate metabolism,but its function in cucumber has not been studied.Therefore,in this paper,cucumber was used as the research material to explore the mechanism of light quality on the efficient utilization of nitrogen in cucumber seedlings under nitrogen,and the expression pattern and function of CsHY5 were preliminarily analyzed,in order to provide a new perspective for the effective absorption and utilization of nitrogen in cucumber from the perspective of light quality regulation.The main results are as follows:1.Cucumber seedlings were treated with white light(W),red light(R)and blue light(B)and normal nitrogen concentration(10 mM NO3-)and low nitrogen concentration(2 mM NO3-)for 17 days.Under nitrogen deficiency,the whole plant dry weight and unit leaf area weight of cucumber seedlings under B treatment were significantly higher than those under W and R.Blue light improved the photosynthetic performance of cucumber leaves under nitrogen stress.At this time,the net photosynthetic rate,stomatal conductance,transpiration rate,water use efficiency and PSII effective photochemical quantum yield of cucumber leaves were significantly higher than those of white light and red light,while the intercellular CO2 concentration was significantly lower than that of white light and red light.Blue light has a more obvious promoting effect on the reduction of NO3-in cucumber,especially at low NO3-concentration.Under low NO3-supply conditions,blue light can significantly reduce the carbon-nitrogen ratio of leaves and improve the carbon-nitrogen metabolism of cucumber seedlings.In summary,under the condition of low NO3-growth,blue light improved the photosynthetic efficiency and NO3assimilation ability of cucumber seedlings,and promoted photomorphogenesis.2.Blue light can improve the NR activity of cucumber seedlings,thereby improving nitrogen metabolism,and NiR is not a limiting factor for nitrogen metabolism in cucumber seedlings under low NO3-supply.Blue light can significantly increase the activity of GS,GOGAT in leaves and GS in roots under both sufficient nitrogen and nitrogen deficiency conditions.GDH activity was significantly induced in both cucumber leaves and roots under low NO3-supply,and GDH activity under blue and red light was significantly higher than that under white light.Blue and red light could significantly increase the expression of CsNIA1 gene in roots under nitrogen deficiency,and the expression of CsNIA2 in leaves was significantly induced under blue light.Under low nitrogen conditions,the expression levels of CsGS1.1,CsGS1.2,CsGS1.3,CsGS2,CsGLU and CsGLT genes encoding GS and GOGAT in leaves increased significantly under blue light,which was consistent with the expression pattern of CsHY5.At the same time,blue light significantly increased the expression of CsNRT2.1 under low NO3-tress.It shows that under low nitrogen conditions,blue light can promote the expression level of genes related to nitrogen metabolism,thereby increasing the activity of enzymes related to nitrogen metabolism,and the expression level of CsHY5 gene is also significantly increased under blue light treatment.3.The CDS sequence length of cucumber CsHY5 gene is 474 bp,encoding 157 amino acids,and there is no significant difference in expression between tissues.Phylogenetic tree analysis showed that the amino acid sequence of cucumber CsHY5 was closely related to melon,pumpkin and zucchini.Subcellular localization showed that CsHY5 protein was localized in the nucleus.After treatment with different light qualities(W,B and R)and different nitrate concentrations(10 mM NO3-and 2 mM NO3-),the expression of CsHY5 gene in cucumber seedling leaves increased significantly with the increase of light time under both nitrogen concentrations,and the increase was the most obvious under blue light.The expression of CsHY5 gene was significantly higher than that of white light after 6 h of blue light.DAP-seq analysis showed that CsHY5 gene mainly played a role in molecular function regulation,followed by transcriptional regulation,protein ubiquitination and phosphorylation,and binding to CsNR2 promoter.Subsequently,the cucumber CsHY5 gene was silenced by VIGS technology,and the expression of CsNR2 in the silenced plants was significantly reduced.In summary,blue light increases NR activity by inducing the expression of CsHY5,thereby improving the nitrogen use efficiency of cucumber seedlings in a nitrogen-deficient environment. |
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