Abstract
Plants synchronize metabolism with the day-night cycle, yet the interplay between circadian rhythms and nitrogen metabolism in leafy vegetables remains unexplored. We profiled spinach ( Spinacia oleracea L.) grown under high-nitrogen and low-nitrogen during four diel phases (end of dark, middle of light, end of light, middle of dark), integrating data from RNA-sequencing with measurements of gas exchange, chlorophyll fluorescence, nitrogen forms, amino acids, and enzyme activities. Nitrogen sufficiency enhanced biomass, CO 2 assimilation, chlorophyll content, and photosynthetic efficiency, with maxima in the middle of light phase. Transcriptom e ice analyses revealed that the greatest gene reprogramming occurred at the dark-to-light transition, where the expression of the morning oscillator component LHY expression peaked and coincid ed ing accumulation of dawn-biased nitrate-assimilation transcripts ( NIA and NiR ) and transporters. Peaks enzyme activities lagged transcript peaks by nearly one phase, suggesting transcriptional priming followed by daytime nitrogen assimilation, aligned with photosynthetic energy and carbon skeleton synthesis. Amino acid profiles reflected this coordination, with glutamine elevated during the day and glutamate enriched at night. Nitrogen deficiency suppressed growth, caused accumulation of reactive oxygen species, and activated circadian-regulated DNA repair genes (e.g., MSH2 and RPA2A , indicating genotoxic stress. Together, these findings support a model in which a diel/clock program, amplified by nitrogen sufficiency, gates nitrogen transport and reduction at dawn to couple daytime assimilation with photosynthesis while adjusting oxidative and DNA repair responses. This mechanistic framework clarifies how temporal regulation and nutrient status interact to shape nitrogen use efficiency and stress resilience in leafy vegetables. • Diel RNA-seq reveals circadian regulation of nitrogen assimilation in spinach. • High nitrogen enhances LHY-driven transcription of NIA, NiR, and nitrate transporters. • Nitrogen modulates diel activities of NR–NiR–GS–GOGAT and amino acid rhythms. • Low nitrogen triggers ROS buildup, triggering circadian-controlled DNA repair. • Circadian–nutrient integration model explains synchronized N and C metabolic fluxes.
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Claims 11
Claim · model-written summary
Nitrogen sufficiency enhanced biomass, carbon assimilation, chlorophyll and photosynthetic efficiency.
- Taxon
- spinach
Spinacia oleraceat0 - Treatment
- Nitrogen sufficiencye0
- Outcome
- biomass, CO 2 assimilation, chlorophyll content, and photosynthetic efficiencye0
- Direction
- enhancede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nitrogen sufficiency enhanced biomass, CO 2 assimilation, chlorophyll content, and photosynthetic efficiency, with maxima in the middle of light phase.”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
The greatest transcriptional changes occurred at the dark-to-light transition.
- Taxon
- spinachSpinacia oleraceat0
- Outcome
- gene reprogramminge0
- Direction
- greateste0
- Qualifier
- dark-to-light transitione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the greatest gene reprogramming occurred at the dark-to-light transition”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
LHY expression peaked at the dark-to-light transition.
- Taxon
- spinachSpinacia oleraceat0
- Gene
- LHYe0
- Outcome
- expressione0
- Direction
- peakede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression of the morning oscillator component LHY expression peaked”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Nitrate assimilation transcripts and transporters accumulated at dawn.
- Taxon
- spinachSpinacia oleraceat0
- Gene
- NIA and NiRe0
- Outcome
- nitrate-assimilation transcriptse0
- Direction
- accumulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“accumulation of dawn-biased nitrate-assimilation transcripts ( NIA and NiR ) and transporters”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Enzyme activity peaks lagged transcript peaks by nearly one phase.
- Taxon
- spinachSpinacia oleraceat0
- Outcome
- enzyme activitiese0
- Direction
- laggede0
- Value
- nearly one phasee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Peaks enzyme activities lagged transcript peaks by nearly one phase”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Glutamine rose during the day.
- Taxon
- spinachSpinacia oleraceat0
- Outcome
- glutaminee0
- Direction
- elevatede0
- Qualifier
- during the daye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“glutamine elevated during the day and glutamate enriched at night”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Glutamate was enriched at night.
- Taxon
- spinachSpinacia oleraceat0
- Outcome
- glutamatee0
- Direction
- enrichede0
- Qualifier
- at nighte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“glutamate enriched at night”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Nitrogen deficiency suppressed growth.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- Nitrogen deficiencye0
- Outcome
- growthe0
- Direction
- suppressede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nitrogen deficiency suppressed growth, caused accumulation of reactive oxygen species, and activated circadian-regulated DNA repair genes”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Nitrogen deficiency increased reactive oxygen species.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- Nitrogen deficiencye0
- Outcome
- reactive oxygen speciese0
- Direction
- accumulatione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nitrogen deficiency suppressed growth, caused accumulation of reactive oxygen species, and activated circadian-regulated DNA repair genes”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
Nitrogen deficiency activated circadian DNA repair genes.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- Nitrogen deficiencye0
- Gene
- MSH2 and RPA2Ae0
- Outcome
- circadian-regulated DNA repair genese0
- Direction
- activatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nitrogen deficiency suppressed growth, caused accumulation of reactive oxygen species, and activated circadian-regulated DNA repair genes (e.g., MSH2 and RPA2A”
t0“spinach synchronizes nitrogen assimilation”
Claim · model-written summary
The authors propose that diel regulation gates nitrogen transport and reduction at dawn.
- Taxon
- spinachSpinacia oleraceat0
- Outcome
- nitrogen transport and reductione0
- Qualifier
- diel/clock programe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a diel/clock program, amplified by nitrogen sufficiency, gates nitrogen transport and reduction at dawn to couple daytime assimilation with photosynthesis”
t0“spinach synchronizes nitrogen assimilation”
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See all 40 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.