Abstract
Transgenic tobacco (Nicotiana tabacum L. cv. W38) plants with an antisense gene directed against the mRNA of the small subunit of Rubisco were used to investigate the role of O2 as an electron acceptor during photosynthesis. The reduction in Rubisco has reduced the capacity for CO2-fixation in these plants without a similar reduction in electron transport capacity. Concurrent measurements of chlorophyll fluorescence and CO2 assimilation at different CO2 and O2 partial pressures showed close linear relationships between chloroplast electron transport rates calculated from chlorophyll fluorescence and those calculated from CO2-fixation. These relationships were similar for wild-type and transgenic plants, indicating that the reduced capacity for CO2 fixation in the transgenic plants did not result in extra electron transport not associated with the photosynthetic carbon reduction (PCR) or photorespiratory carbon oxidation (PCO) cycle. This was further investigated with mass spectrometric measurements of 16O2 and 18O2 exchange made concurrently with measurements of chlorophyll fluorescence. In all tobacco lines the rates of 18O2 uptake in the dark were similar to the 18O2 uptake rates at very high CO2 partial pressures in the light. Rates of oxygenase activity calculated from 18O2 uptake at the compensation point were linearly related to the Rubisco content of leaves. The ratios of oxygenase to carboxylase rates were calculated from measurements of 16O2 evolution and 18O2 uptake at the compensation point. These ratios were lower in the transgenic plants, consistent with their higher CO2 compensation points. It is concluded that although there may be some electron transport to O2 to balance conflicting demands of NADPH to ATP requirements, this flux must decrease in proportion with the reduced demand for ATP and NADPH consumption in the transgenic lines. The altered balance between electron transport and Rubisco capacity, however, does not result in rampant electron transport to O2 or other electron transport acceptors in the absence of PCR and PCO cycle activity.
Abstract from the paper’s OpenAlex record, shown for indexing and research. Copyright remains with the authors or the publisher. Read at the source ↗
The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.
Claims 8
Claim · model-written summary
Reduced Rubisco reduced CO2 fixation capacity without a similar electron transport loss.
- Taxon
- tobacco
Nicotiana tabacumt0 - Treatment
- reduction in Rubiscoe0
- Outcome
- capacity for CO2-fixatione0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The reduction in Rubisco has reduced the capacity for CO2-fixation in these plants without a similar reduction in electron transport capacity”
t0“transgenic tobacco”
Claim · model-written summary
Fluorescence and CO2 fixation estimates of electron transport were linearly related.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- chloroplast electron transport ratese0
- Comparator
- CO2-fixatione0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“close linear relationships between chloroplast electron transport rates calculated from chlorophyll fluorescence and those calculated from CO2-fixation”
t0“transgenic tobacco”
Claim · model-written summary
The relationships were similar in wild type and transgenic plants.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- relationships were similare0
- Comparator
- wild-type and transgenic plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These relationships were similar for wild-type and transgenic plants”
t0“transgenic tobacco”
Claim · model-written summary
Reduced CO2 fixation capacity did not produce extra electron transport outside PCR or PCO cycles.
- Taxon
- tobaccoNicotiana tabacumt0
- Treatment
- reduced capacity for CO2 fixatione0
- Outcome
- extra electron transporte0
- Direction
- did not resulte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the reduced capacity for CO2 fixation in the transgenic plants did not result in extra electron transport not associated with the photosynthetic carbon reduction (PCR) or photorespiratory carbon oxidation (PCO) cycle”
t0“transgenic tobacco”
Claim · model-written summary
Dark oxygen uptake resembled light uptake at high CO2 across tobacco lines.
- Taxon
- tobaccoNicotiana tabacume0
- Outcome
- rates of 18O2 uptake in the darke0
- Comparator
- 18O2 uptake rates at very high CO2 partial pressures in the lighte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In all tobacco lines the rates of 18O2 uptake in the dark were similar to the 18O2 uptake rates at very high CO2 partial pressures in the light”
Claim · model-written summary
Calculated oxygenase activity was linearly related to leaf Rubisco content.
- Taxon
- tobaccoNicotiana tabacumt0
- Gene
- Rubiscoe0
- Outcome
- Rates of oxygenase activitye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rates of oxygenase activity calculated from 18O2 uptake at the compensation point were linearly related to the Rubisco content of leaves”
t0“transgenic tobacco”
Claim · model-written summary
Oxygenase to carboxylase ratios were lower in transgenic plants.
- Taxon
- tobaccoNicotiana tabacumt0
- Treatment
- transgenic plantse0
- Outcome
- ratiose0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These ratios were lower in the transgenic plants”
t0“transgenic tobacco”
Claim · model-written summary
Electron flow to oxygen was inferred to decline with reduced ATP and NADPH demand.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- fluxe0
- Direction
- decreasee0
- Qualifier
- reduced demand for ATP and NADPH consumptione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this flux must decrease in proportion with the reduced demand for ATP and NADPH consumption in the transgenic lines”
t0“transgenic tobacco”
The same questions in other papers
co2 · physiology: photosynthesis · Nicotiana tabacum (tobacco)Positive and negative results
5 papers in the same direction as this paper · 10 in the opposite direction
- positive
- positive
- positive
12 papers more in this group
See all 16 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.