Abstract
We studied the effect of drought on photosynthesis, growth, and sugar accumulation in field-grown sweet sorghum (Sorghum bicolor (L.) Moench). Stomata closed when drought stress developed during the day. As a consequence, photosynthesis was reduced. The water use efficiency of drought-stressed leaves was slightly lower than that of controls and this reduction was more pronounced early in the morning and in the evening. This suggested that not only stomata limit photosynthesis under drought: photosynthesis at high CO2 was lower in drought-stressed than in control leaves, suggesting that carbon metabolism was inhibited. Electron transport was also reduced, but an increased number of electrons appeared necessary to fix CO2 under drought. Before anthesis, growth was not affected by drought but, after anthesis, elongation of the last internodes was greater in controls than in drought- stressed plants. Both controls and drought-stressed plants accumulated sucrose and starch in the stem after anthesis. The accumulation was low and ceased early in the stem apex. It is likely that seeds in the panicle compete with the apex for carbon. During panicle maturation sucrose and starch content was higher in drought-stressed than in control stems. At the end of our experiments, however, the sucrose content per plant was similar in all samples. We conclude that sugar accumulation is less sensitive to drought than photosynthesis. Irrespective of drought conditions, (i) before anthesis growth is the predominant sink for photosynthates; (ii) after anthesis sugar accumulation in the stem becomes the preferential sink at the expense of growth of apical internodes.
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Claims 15
Claim · model-written summary
Stomata closed as daytime drought developed.
Verbatim
e0“Stomata closed when drought stress developed during the day”
t0“Sweet Sorghum”
Claim · model-written summary
Drought reduced photosynthesis.
Not reportedComparator
Verbatim
e0“As a consequence, photosynthesis was reduced”
e1“drought stress developed during the day”
t0“Sweet Sorghum”
Claim · model-written summary
Drought-stressed leaves had slightly lower water-use efficiency, especially morning and evening.
Verbatim
e0“The water use efficiency of drought-stressed leaves was slightly lower than that of controls and this reduction was more pronounced early in the morning and in the evening”
t0“Sweet Sorghum”
Claim · model-written summary
Photosynthesis at high CO2 was lower in drought-stressed leaves than controls.
Verbatim
e0“photosynthesis at high CO2 was lower in drought-stressed than in control leaves”
t0“Sweet Sorghum”
Claim · model-written summary
Electron transport was reduced under drought.
Not reportedComparator
Verbatim
e0“Electron transport was also reduced”
e1“suggesting that carbon metabolism was inhibited. Electron transport was also reduced, but an increased number of electrons appeared necessary to fix CO2 under drought”
t0“Sweet Sorghum”
Claim · model-written summary
More electrons appeared needed to fix CO2 under drought.
Verbatim
e0“an increased number of electrons appeared necessary to fix CO2 under drought”
t0“Sweet Sorghum”
Claim · model-written summary
Before anthesis, drought did not affect growth.
- Taxon
- Sweet Sorghumt0
- Organ / stage
- Before anthesise0
- Treatment
- droughte0
- Outcome
- growthe0
- Direction
- not affectede0
Not reportedComparator
Verbatim
e0“Before anthesis, growth was not affected by drought”
t0“Sweet Sorghum”
Claim · model-written summary
After anthesis, final internodes elongated more in controls.
Verbatim
e0“after anthesis, elongation of the last internodes was greater in controls than in drought- stressed plants”
t0“Sweet Sorghum”
Claim · model-written summary
Both groups accumulated sucrose and starch in stems after anthesis.
Verbatim
e0“Both controls and drought-stressed plants accumulated sucrose and starch in the stem after anthesis”
t0“Sweet Sorghum”
Claim · model-written summary
Stem-apex sugar accumulation was low and ceased early.
Verbatim
e0“The accumulation was low and ceased early in the stem apex”
t0“Sweet Sorghum”
Claim · model-written summary
During panicle maturation, drought-stressed stems contained more sucrose and starch.
Verbatim
e0“During panicle maturation sucrose and starch content was higher in drought-stressed than in control stems”
t0“Sweet Sorghum”
Claim · model-written summary
At experiment end, sucrose content per plant was similar across samples.
Verbatim
e0“At the end of our experiments, however, the sucrose content per plant was similar in all samples”
e1“drought-stressed than in control stems”
t0“Sweet Sorghum”
Claim · model-written summary
Sugar accumulation was less drought-sensitive than photosynthesis.
Verbatim
e0“sugar accumulation is less sensitive to drought than photosynthesis”
t0“Sweet Sorghum”
Claim · model-written summary
Before anthesis, growth was the predominant photosynthate sink.
Verbatim
e0“before anthesis growth is the predominant sink for photosynthates”
t0“Sweet Sorghum”
Claim · model-written summary
After anthesis, stem sugar accumulation became the preferred sink at the expense of apical internode growth.
Verbatim
e0“after anthesis sugar accumulation in the stem becomes the preferential sink at the expense of growth of apical internodes”
t0“Sweet Sorghum”
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