Abstract
Both light and NO3- are necessary for the appearance of nitrate reductase (NR) activity (NRA) in photosynthetic tissues. To define the light effect more precisely, we examined the response to light/dark transitions on NRA, NR protein (NRP), and NR mRNA in 6-d-old maize (Zea mays cv W64A x W182E) seedlings that had been grown in a light/dark regime for 5 d and then induced with 5 mM KNO3 for 24 h. The decay of NRA and NR mRNA in the shoot was immediate, but there were only minor changes in NRP during the initial 4 h in the dark. In root tissues, in contrast, there was a 4-h delay in the loss of NRA, NRP, and NR mRNA after transfer to the dark. When the seedlings were returned to light after a 2-h interval in the dark, shoot NRA reached 92% of the initial levels within 30 min of illumination. These results indicate that in the shoots (a) NR message production requires light and (b) the NRP that appears with light treatment and that is active is inactivated in the dark. The NRP can be reactivated when the light is turned on after short periods of darkness (2 h). Root tissues, on the other hand, probably respond to the supply of photosynthetically produced metabolites rather than to immediate products of the light reactions of photosynthesis.
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Claims 7
Claim · model-written summary
In maize shoots, NRA and NR mRNA declined immediately after transfer to darkness.
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The decay of NRA and NR mRNA in the shoot was immediate, but there were only minor changes in NRP during the initial 4 h in the dark.”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
Shoot NR protein changed only slightly during the first four hours of darkness.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“there were only minor changes in NRP during the initial 4 h in the dark.”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
Root NRA, NRP and NR mRNA loss was delayed four hours after dark transfer.
- Organ / stage
- root tissuese1
- Treatment
- darke1
- Gene
- NRe1
- Outcome
- NRA, NRP, and NR mRNAe1
- Direction
- losse1
- Value
- 4-he1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In root tissues, in contrast, there was a 4-h delay in the loss of NRA, NRP, and NR mRNA after transfer to the dark.”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
After two hours of darkness, renewed illumination restored shoot NRA to 92% of initial levels in 30 minutes.
- Treatment
- returned to lighte1
- Outcome
- shoot NRAe1
- Direction
- reachede1
- Value
- 92%e1
- Comparator
- initial levelse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“When the seedlings were returned to light after a 2-h interval in the dark, shoot NRA reached 92% of the initial levels within 30 min of illumination.”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
The authors infer that shoot NR message production requires light.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“in the shoots (a) NR message production requires light”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
The authors infer that active shoot NR protein becomes inactive in darkness and can reactivate with light.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“the NRP that appears with light treatment and that is active is inactivated in the dark. The NRP can be reactivated when the light is turned on after short periods of darkness (2 h).”
e2“maize (Zea mays cv W64A x W182E) seedlings”
Claim · model-written summary
The authors propose that root responses depend on photosynthetically produced metabolites.
- Organ / stage
- Root tissuese1
- Outcome
- responde1
- Qualifier
- supply of photosynthetically produced metabolitese1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Root tissues, on the other hand, probably respond to the supply of photosynthetically produced metabolites rather than to immediate products of the light reactions of photosynthesis.”
e2“maize (Zea mays cv W64A x W182E) seedlings”
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