Abstract
Summary The diversity of cytokinin (CK) metabolites suggests their interconversions are the predominant regulatory mechanism of CK action. Nevertheless, little is known about their directionality and kinetics in planta . CK metabolite levels were measured in 2‐wk‐old Arabidopsis thaliana plants at several time points up to 100 min following exogenous application of selected CKs. The data were then evaluated qualitatively and by mathematical modeling. Apart from elevated levels of trans ‐zeatin (tZ) metabolites upon application of N 6 ‐(Δ 2 ‐isopentenyl)adenine (iP), we observed no conversions between the individual CK‐types – iP, tZ, dihydrozeatin (DHZ) and cis ‐zeatin (cZ). In particular, there was no sign of isomerization between tZ and cZ families. Also, no increase of DHZ‐type CKs was observed after application of tZ, suggesting low baseline activity of zeatin reductase. Among N ‐glucosides, those of iP were not converted back to iP while tZ N ‐glucosides were cleaved to tZ bases, thus affecting the whole metabolic spectrum. We present the first large‐scale study of short‐term CK metabolism kinetics and show that tZ N7‐ and N9‐glucosides are metabolized in vivo . We thus refute the generally accepted hypothesis that N ‐glucosylation irreversibly inactivates CKs. The subsequently constructed mathematical model provides estimates of the metabolic conversion rates.
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Claims 8
Claim · model-written summary
iP application elevated tZ metabolite levels.
- Taxon
- Arabidopsis
Arabidopsist0 - Treatment
- N 6 ‐(Δ 2 ‐isopentenyl)adenine (iP)e0
- Outcome
- trans ‐zeatin (tZ) metabolitese0
- Direction
- elevatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated levels of trans ‐zeatin (tZ) metabolites upon application of N 6 ‐(Δ 2 ‐isopentenyl)adenine (iP)”
t0“Arabidopsis”
Claim · model-written summary
No conversion was seen among individual cytokinin types beyond the iP-to-tZ exception.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- no conversions between the individual CK‐typese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we observed no conversions between the individual CK‐types – iP, tZ, dihydrozeatin (DHZ) and cis ‐zeatin (cZ).”
t0“Arabidopsis”
Claim · model-written summary
No tZ-to-cZ isomerization was detected.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- no sign of isomerization between tZ and cZ familiese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no sign of isomerization between tZ and cZ families.”
t0“Arabidopsis”
Claim · model-written summary
tZ application did not increase DHZ-type cytokinin levels.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- application of tZe0
- Outcome
- DHZ‐type CKse0
- Direction
- no increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no increase of DHZ‐type CKs was observed after application of tZ”
t0“Arabidopsis”
Claim · model-written summary
iP N-glucosides were not converted back to iP.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- not converted back to iPe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“those of iP were not converted back to iP”
t0“Arabidopsis”
Claim · model-written summary
tZ N-glucosides were cleaved to tZ bases.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- cleaved to tZ basese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tZ N ‐glucosides were cleaved to tZ bases”
t0“Arabidopsis”
Claim · model-written summary
tZ N7- and N9-glucosides were metabolized in vivo.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- metabolized in vivoe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tZ N7‐ and N9‐glucosides are metabolized in vivo”
t0“Arabidopsis”
Claim · model-written summary
A mathematical model estimated metabolic conversion rates.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- estimates of the metabolic conversion ratese0
- Value
- conversion ratese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The subsequently constructed mathematical model provides estimates of the metabolic conversion rates.”
t0“Arabidopsis”