Abstract
Nodulation in pea ( Pisum sativum L.) grown in hydroponic and sand culture systems is stimulated by low concentrations (<1.0 m M ) of ammonium, but the physiological mechanisms underlying this stimulation are unknown. The current study involves a series of experiments, which investigate if the ammonium‐induced stimulation of nodulation involves changes in endogenous hormone (auxin and cytokinin) levels. P. sativum L. cv. Express was grown in growth pouches for 1 week with mineral N (0.5 and 2.0 m M NH 4 + or NO 3 – ) or for 3 weeks exposed to exogenous indole‐3‐acetic acid (IAA) or 6‐benzylaminopurine (BAP) at a range of concentrations (10 ‐9 −10 ‐5 M ). Ammonium enhanced nodulation on the basis of both early whole plant (nodules plant −1 ) and specific nodulation (nodules g −1 root DW), especially in 0.5 m M treatment in which nodulation was approximately 4‐fold of the mineral‐N‐free control 1 week after inoculation. Correspondingly, the roots treated with ammonium contained much higher levels of t ‐zeatin (Z) and lower t ‐zeatin riboside (ZR) than that the control or nitrate‐treated plants. There was no significant difference in IAA levels between the control and ammonium treatments. Exogenous application of BAP for 3 weeks at concentrations of 10 ‐7 −10 ‐5 M strongly inhibited nodulation. However, 10 −9 M BAP, but not IAA, significantly enhanced nodulation. These data support the theory that a relatively high ratio of cytokinin:auxin in roots is favourable for nodule initiation, but that an excessively high level of cytokinin inhibits nodulation. Based on these results we propose that stimulation of nodulation by low concentrations of ammonium may be mediated through increasing Z level in roots, which alters the balance of cytokinin and auxin, which in turn induces cortical cell divisions leading to nodule initiation.
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Claims 8
Claim · model-written summary
Ammonium enhanced whole plant and specific nodulation.
- Taxon
- Pisum sativum
Lathyrus oleraceust0 - Treatment
- Ammoniume0
- Outcome
- early whole plant (nodules plant −1 ) and specific nodulation (nodules g −1 root DW)e0
- Direction
- enhancede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“Ammonium enhanced nodulation on the basis of both early whole plant (nodules plant −1 ) and specific nodulation (nodules g −1 root DW)”
Claim · model-written summary
The 0.5 mM ammonium treatment yielded approximately fourfold nodulation relative to the nitrogen-free control.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Treatment
- 0.5 m M treatmente0
- Outcome
- nodulatione0
- Value
- approximately 4‐folde0
- Comparator
- mineral‐N‐free controle0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“especially in 0.5 m M treatment in which nodulation was approximately 4‐fold of the mineral‐N‐free control 1 week after inoculation”
Claim · model-written summary
Ammonium raised root t-zeatin levels.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Organ / stage
- rootse0
- Treatment
- ammoniume0
- Outcome
- levels of t ‐zeatin (Z)e0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“roots treated with ammonium contained much higher levels of t ‐zeatin (Z)”
Claim · model-written summary
Ammonium lowered root t-zeatin riboside.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Organ / stage
- rootse0
- Treatment
- ammoniume0
- Outcome
- t ‐zeatin riboside (ZR)e0
- Direction
- lowere0
- Comparator
- control or nitrate‐treated plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“roots treated with ammonium contained much higher levels of t ‐zeatin (Z) and lower t ‐zeatin riboside (ZR) than that the control or nitrate‐treated plants”
Claim · model-written summary
IAA levels did not differ significantly between control and ammonium treatments.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Treatment
- ammonium treatmentse0
- Outcome
- IAA levelse0
- Direction
- no significant differencee0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“There was no significant difference in IAA levels between the control and ammonium treatments”
Claim · model-written summary
BAP at 10−7 to 10−5 M inhibited nodulation.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Treatment
- BAP for 3 weeks at concentrations of 10 ‐7 −10 ‐5 Me0
- Outcome
- nodulatione0
- Direction
- inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“Exogenous application of BAP for 3 weeks at concentrations of 10 ‐7 −10 ‐5 M strongly inhibited nodulation”
Claim · model-written summary
Low BAP concentration significantly enhanced nodulation.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Treatment
- 10 −9 M BAPe0
- Outcome
- nodulatione0
- Direction
- enhancede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“10 −9 M BAP, but not IAA, significantly enhanced nodulation”
Claim · model-written summary
IAA at the tested low concentration did not enhance nodulation.
- Taxon
- Pisum sativumLathyrus oleraceust0
- Treatment
- IAAe0
- Outcome
- nodulatione0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pisum sativum”
e0“10 −9 M BAP, but not IAA, significantly enhanced nodulation”
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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.