Abstract
Photoinhibition of photosystem II was studied in vivo with bean (Phaseolus vulgaris) plants grown in the presence of 0.3 (control), 4, or 15 microM Cu(2+). Although photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu(2+)-treated plants than in control leaves, thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition. Direct effects of excess Cu(2+) on chloroplast metabolism are actually unlikely, because the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves. Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection. Thus, these hypothetical effects can be eliminated as causes for Cu-enhanced photoinhibition in intact leaves. However, Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network. The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium. The addition of Fe lowered the Cu(2+) concentration of the leaves, suggesting that Cu outcompetes Fe in Fe uptake. We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu(2+)-treated plants. A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species. Plant species adapted to high-light habitats apparently benefit from thick leaves because the rate of photoinhibition is directly proportional to light intensity, but photosynthesis becomes saturated by moderate light.
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Claims 12
Claim · model-written summary
Photoinhibition was faster in Cu-treated bean leaves than controls.
Verbatim
e0“photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu(2+)-treated plants than in control leaves”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Thylakoids from Cu-treated plants did not show high photoinhibition sensitivity.
Verbatim
e0“thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Chloroplast Cu concentration was lower than leaf Cu concentration in treated plants.
Verbatim
e0“the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Excess Cu caused no severe oxidative stress, antioxidant collapse or photoprotection loss.
- Taxon
- beant0
- Treatment
- Excess Cu in the growth mediume0
- Outcome
- severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotectione0
- Direction
- did not causee0
Not reportedComparator
Verbatim
e0“Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Cu treatment lowered leaf chlorophyll concentration.
Not reportedComparator
Verbatim
e0“Cu treatment lowered the leaf chlorophyll (Chl) concentration”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Cu treatment reduced the thylakoid membrane network.
Not reportedComparator
Verbatim
e0“Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Adding excess Fe with Cu overcame chlorophyll loss and photoinhibition sensitivity.
- Taxon
- beant0
- Treatment
- adding excess Fe together with excess Cu to the growth mediume0
- Outcome
- loss of Chl and sensitivity to photoinhibitione0
- Direction
- overcomee0
Not reportedComparator
Verbatim
e0“The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Fe addition lowered leaf Cu concentration.
Not reportedComparator
Verbatim
e0“The addition of Fe lowered the Cu(2+) concentration of the leaves”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
The authors propose Cu competition with Fe uptake as a cause of iron deficiency and photosensitivity.
Verbatim
e0“Cu outcompetes Fe in Fe uptake. We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu(2+)-treated plants.”
t0“bean (Phaseolus vulgaris) plants”
Claim · model-written summary
Susceptibility to photoinhibition was causally related to leaf optical density across plant species.
Not reportedDirection
Verbatim
e0“A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species.”
Claim · model-written summary
Photoinhibition rate was directly proportional to light intensity.
Verbatim
e0“the rate of photoinhibition is directly proportional to light intensity”
t0“several plant species”
Claim · model-written summary
Photosynthesis saturated at moderate light.
Verbatim
e0“photosynthesis becomes saturated by moderate light.”
t0“several plant species”
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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.