Abstract
Blue light has many direct and indirect effects on photosynthesis. The impact of blue light on mesophyll conductance (g(m)), one of the main diffusive limitation to photosynthesis, was investigated in leaves of Nicotiana tabacum and Platanus orientalis, characterized by high and low g(m), respectively. Leaves were exposed to blue light fractions between 0% and 80% of incident light intensity (300 micromol photons m(-2) s(-1)), the other fraction being supplied as red light. Leaves exposed to blue light showed reduced photosynthesis and unaltered stomatal conductance. The g(m), measured using the chlorophyll fluorescence-based method, was strongly reduced in both plant species. Such a reduction of g(m) may not be real, as several assumptions used for the calculation of g(m) by fluorescence may not hold under blue light. To assess possible artefacts, the electron transport rate measured by fluorescence (J(f)) and by gas-exchange (J(c)) were compared in leaves exposed to different fractions of blue light under non-photorespiratory conditions. The two values were only equal, a prerequisite for correct g(m) measurements, when the illumination was totally provided as red light. Under increasing blue light levels an increasing discrepancy was observed, which suggests that J(f) was not correctly calculated, and that such an error could also upset g(m) measurements. Blue light was not found to change the absorbance of light by leaves, whereas it slightly decreased the distribution of light to PSII. To equate J(f) and J(c) under blue light, a further factor must be added to the J(f) equation, which possibly accounted for the reduced efficiency of energy transfer between the pigments predominantly absorbing blue light (the carotenoids) and the chlorophylls. This correction reduced by about 50% the effect of blue light on g(m). However, the residual reduction of g(m) under blue light was real and significant, although it did not appear to limit the chloroplast CO(2) concentration and, consequently, photosynthesis. Reduction of g(m) might be caused by chloroplast movement to avoid photodamage, in turn affecting the chloroplast surface exposed to intercellular spaces. However, g(m) reduction occurred immediately after exposure to blue light and was complete after less than 3 min, whereas chloroplast relocation was expected to occur more slowly. In addition, fast g(m) reduction was also observed after inhibiting chloroplast movement by cytochalasin. It is therefore concluded that g(m) reduction under blue light is unlikely to be caused by chloroplast movement only, and must be elicited by other, as yet unknown, factors.
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Claims 13
Claim · model-written summary
Blue light reduced photosynthesis in the studied leaves.
- Taxon
- Nicotiana tabacum and Platanus orientalis
Nicotiana tabacum
Platanus orientalise1 - Treatment
- blue lighte0
- Outcome
- photosynthesise0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaves exposed to blue light showed reduced photosynthesis and unaltered stomatal conductance.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Blue light left stomatal conductance unaltered.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- blue lighte0
- Outcome
- stomatal conductancee0
- Direction
- unalterede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaves exposed to blue light showed reduced photosynthesis and unaltered stomatal conductance.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Fluorescence measured mesophyll conductance was strongly reduced in both species under blue light.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Outcome
- g(m)e0
- Direction
- reducede0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The g(m), measured using the chlorophyll fluorescence-based method, was strongly reduced in both plant species.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Fluorescence and gas exchange electron transport rates agreed only under entirely red light.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Outcome
- g(m) measurementse0
- Comparator
- red lighte0
Not reportedValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The two values were only equal, a prerequisite for correct g(m) measurements, when the illumination was totally provided as red light.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Discrepancy between electron transport estimates rose with blue light.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- blue lighte0
- Outcome
- discrepancye0
- Direction
- increasinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under increasing blue light levels an increasing discrepancy was observed”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Blue light did not change leaf light absorbance.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- Blue lighte0
- Outcome
- absorbance of light by leavese0
- Direction
- not found to changee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Blue light was not found to change the absorbance of light by leaves”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Blue light slightly decreased light distribution to PSII.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Outcome
- distribution of light to PSIIe0
- Direction
- decreasede0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“whereas it slightly decreased the distribution of light to PSII”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Correcting the fluorescence equation reduced the apparent blue light effect on mesophyll conductance by about 50%.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- correctione0
- Outcome
- effect of blue light on g(m)e0
- Direction
- reducede0
- Value
- about 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This correction reduced by about 50% the effect of blue light on g(m).”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Residual mesophyll conductance reduction under blue light was real and significant.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- blue lighte0
- Outcome
- g(m)e0
- Direction
- reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the residual reduction of g(m) under blue light was real and significant”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
The residual conductance reduction did not appear to limit chloroplast CO2 concentration.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Outcome
- chloroplast CO(2) concentratione0
- Direction
- did not appear to limite0
Not reportedTreatment
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“although it did not appear to limit the chloroplast CO(2) concentration and, consequently, photosynthesis.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
The residual conductance reduction did not appear to limit photosynthesis.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Outcome
- photosynthesise0
- Direction
- did not appear to limite0
Not reportedTreatment
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“although it did not appear to limit the chloroplast CO(2) concentration and, consequently, photosynthesis.”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Mesophyll conductance fell immediately after blue light exposure and was complete within less than 3 min.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- blue lighte0
- Outcome
- g(m)e0
- Direction
- reductione0
- Value
- less than 3 mine0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“g(m) reduction occurred immediately after exposure to blue light and was complete after less than 3 min”
e1“Nicotiana tabacum and Platanus orientalis”
Claim · model-written summary
Fast mesophyll conductance reduction also occurred after inhibition of chloroplast movement by cytochalasin.
- Taxon
- Nicotiana tabacum and Platanus orientalisNicotiana tabacumPlatanus orientalise1
- Treatment
- cytochalasine0
- Outcome
- g(m)e0
- Direction
- reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“fast g(m) reduction was also observed after inhibiting chloroplast movement by cytochalasin”
e1“Nicotiana tabacum and Platanus orientalis”
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