Abstract
Nitrate content is an essential indicator of the quality of vegetables but can cause stress at high levels. This study aimed to elucidate the regulatory mechanisms of nitrate stress tolerance in spinach (Spinacia oleracea L.). We studied the effects of exogenous application of 15 (control), 50, 100, 150, 200, and 250 mM NO3- on spinach growth, physiology, and photosynthesis. The results showed that all the nitrate treatments inhibited the growth of the aerial parts of spinach compared to the control. In contrast, low nitrate levels (50 and 100 mM) promoted spinach root formation, but this effect was inhibited at high levels (150, 200, and 250 mM). Treatment with 150 mM NO3- significantly decreased the root growth vigor. Low nitrate levels increased the chlorophyll content in spinach leaves, whereas high levels had the opposite effect. High nitrate levels also weakened the net photosynthetic rate (Pn), the actual photochemical efficiency of PSII Y(II), and increased non-photochemical quenching (NPQ), reducing photosynthetic performance. Nitrate stress increased the activity of nitrate reductase (NR) and promoted the accumulation of nitrate in spinach leaves, exceeding the health-tolerance limit for nitrate in vegetables, highlighting the necessity of mitigating nitrate stress to ensure food safety. Starting with the 150 mM NO3- treatment, the proline and malondialdehyde content in spinach leaves and roots increased significantly as the nitrate levels increased. Treatment with 150 mM NO3- significantly increased soluble protein and flavonoid contents, while the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were significantly reduced in leaves. However, spinach could resist nitrate stress by regulating the synthesis of osmoregulatory substances such as proline, thus showing some nitrate tolerance. These results provide insights into the physiological regulatory mechanisms of nitrate stress tolerance and its mitigation in spinach, an essential vegetable crop.
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Claims 14
Claim · model-written summary
Nitrate treatments inhibited spinach aerial growth versus the control.
- Taxon
- spinach
Spinacia oleraceae0 - Treatment
- nitrate treatmentse0
- Outcome
- growth of the aerial partse0
- Direction
- inhibitede0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all the nitrate treatments inhibited the growth of the aerial parts of spinach compared to the control”
Claim · model-written summary
Low nitrate levels promoted spinach root formation.
- Taxon
- spinachSpinacia oleraceae0
- Treatment
- low nitrate levels (50 and 100 mM)e0
- Outcome
- root formatione0
- Direction
- promotede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“low nitrate levels (50 and 100 mM) promoted spinach root formation”
Claim · model-written summary
High nitrate levels inhibited spinach root formation.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- high levels (150, 200, and 250 mM)e0
- Outcome
- this effecte0
- Direction
- inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this effect was inhibited at high levels (150, 200, and 250 mM)”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
The 150 mM nitrate treatment significantly decreased spinach root growth vigor.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- 150 mM NO3-e0
- Outcome
- root growth vigore0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Treatment with 150 mM NO3- significantly decreased the root growth vigor”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
Low nitrate increased spinach leaf chlorophyll content.
- Taxon
- spinachSpinacia oleraceae0
- Treatment
- Low nitrate levelse0
- Outcome
- chlorophyll contente0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Low nitrate levels increased the chlorophyll content in spinach leaves”
Claim · model-written summary
High nitrate decreased spinach leaf chlorophyll content.
- Taxon
- spinachSpinacia oleraceae1
- Treatment
- high levelse0
- Outcome
- chlorophyll contente1
- Direction
- opposite effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“high levels had the opposite effect”
e1“chlorophyll content in spinach leaves”
Claim · model-written summary
High nitrate weakened spinach net photosynthetic rate and PSII efficiency.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- High nitrate levelse0
- Outcome
- net photosynthetic rate (Pn), the actual photochemical efficiency of PSII Y(II)e0
- Direction
- weakenede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High nitrate levels also weakened the net photosynthetic rate (Pn), the actual photochemical efficiency of PSII Y(II)”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
High nitrate increased spinach non-photochemical quenching.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- High nitrate levelse0
- Outcome
- non-photochemical quenching (NPQ)e0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High nitrate levels also weakened the net photosynthetic rate (Pn), the actual photochemical efficiency of PSII Y(II), and increased non-photochemical quenching (NPQ)”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
Nitrate stress increased nitrate reductase activity in spinach.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- Nitrate stresse0
- Gene
- nitrate reductase (NR)e0
- Outcome
- activity of nitrate reductase (NR)e0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Nitrate stress increased the activity of nitrate reductase (NR)”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
Nitrate stress promoted nitrate accumulation in spinach leaves beyond the vegetable health tolerance limit.
- Taxon
- spinachSpinacia oleraceae0
- Treatment
- nitratee0
- Outcome
- accumulation of nitrate in spinach leavese0
- Direction
- promotede0
- Qualifier
- exceeding the health-tolerance limit for nitrate in vegetablese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“promoted the accumulation of nitrate in spinach leaves, exceeding the health-tolerance limit for nitrate in vegetables”
Claim · model-written summary
From 150 mM nitrate, proline and malondialdehyde content in spinach leaves and roots increased significantly as nitrate rose.
- Taxon
- spinachSpinacia oleraceae0
- Organ / stage
- leaves and rootse0
- Treatment
- 150 mM NO3- treatmente0
- Outcome
- proline and malondialdehyde contente0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Starting with the 150 mM NO3- treatment, the proline and malondialdehyde content in spinach leaves and roots increased significantly as the nitrate levels increased”
Claim · model-written summary
The 150 mM nitrate treatment significantly increased spinach soluble protein and flavonoid contents.
- Taxon
- spinachSpinacia oleraceat0
- Treatment
- 150 mM NO3-e0
- Outcome
- soluble protein and flavonoid contentse0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Treatment with 150 mM NO3- significantly increased soluble protein and flavonoid contents”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
The 150 mM nitrate treatment significantly reduced four antioxidant enzyme activities in spinach leaves.
- Taxon
- spinachSpinacia oleraceat0
- Organ / stage
- leavese0
- Treatment
- 150 mM NO3-e1
- Outcome
- activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)e0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were significantly reduced in leaves”
e1“Treatment with 150 mM NO3- significantly increased soluble protein and flavonoid contents”
t0“spinach (Spinacia oleracea L.)”
Claim · model-written summary
The authors interpret proline regulation as contributing to spinach nitrate tolerance.
- Taxon
- spinachSpinacia oleraceae0
- Outcome
- nitrate tolerancee0
- Qualifier
- regulating the synthesis of osmoregulatory substances such as prolinee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spinach could resist nitrate stress by regulating the synthesis of osmoregulatory substances such as proline, thus showing some nitrate tolerance”
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