Abstract
European Flint maize inbred lines are used as a source of adaptation to cold in most breeding programs in Northern Europe. A deep understanding of their adaptation strategy could thus provide valuable clues for further improvement, which is required in the current context of climate change. We therefore compared six inbreds and two derived Flint x Dent hybrids for their response to one-week at low temperature (10 °C day/7 or 4 °C night) during steady-state vegetative growth. Leaf growth was arrested during chilling treatment but recovered fast upon return to warm temperature, so that no negative effect on shoot biomass was measured. Gene expression analyses of the emerging leaf in the hybrids suggest that plants maintained a ‘ready-to-grow’ state during chilling since cell cycle genes were not differentially expressed in the division zone and genes coding for expansins were on the opposite up-regulated in the elongation zone. In photosynthetic tissues, a strong reduction in PSII efficiency was measured. Chilling repressed chlorophyll biosynthesis; we detected accumulation of the precursor geranylgeranyl chlorophyll a and down-regulation of GERANYLGERANYL REDUCTASE ( GGR ) in mature leaf tissues. Excess light energy was mostly dissipated through fluorescence and constitutive thermal dissipation processes, rather than by light-regulated thermal dissipation. Consistently, only weak clues of xanthophyll cycle activation were found. CO 2 assimilation was reduced by chilling, as well as the expression levels of genes encoding phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and the small subunit of Rubisco. Accumulation of sugars was correlated with a strong decrease of the specific leaf area (SLA). Altogether, our study reveals good tolerance of the photosynthetic machinery of Northern European maize to chilling and suggests that growth arrest might be their strategy for fast recovery after a mild stress.
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Claims 15
Claim · model-written summary
Maize leaf growth was arrested during chilling.
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaf growth was arrested during chilling treatment”
t0“Maize plants”
Claim · model-written summary
Maize leaf growth recovered quickly after return to warm temperature.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“recovered fast upon return to warm temperature”
e1“Leaf growth was arrested during chilling treatment”
t0“Maize plants”
Claim · model-written summary
Chilling had no measured negative effect on shoot biomass.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no negative effect on shoot biomass was measured”
e1“during chilling treatment”
t0“Maize plants”
Claim · model-written summary
Cell cycle genes were not differentially expressed in the division zone during chilling.
- Organ / stage
- division zonee0
- Treatment
- chillinge1
- Gene
- cell cycle genese0
- Outcome
- differentially expressede0
- Direction
- not differentially expressede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“cell cycle genes were not differentially expressed in the division zone”
e1“maintained a ‘ready-to-grow’ state during chilling”
t0“Maize plants”
Claim · model-written summary
Genes coding for expansins were up-regulated in the elongation zone during chilling.
- Organ / stage
- elongation zonee0
- Treatment
- chillinge1
- Gene
- genes coding for expansinse0
- Outcome
- genes coding for expansinse0
- Direction
- up-regulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“genes coding for expansins were on the opposite up-regulated in the elongation zone”
e1“maintained a ‘ready-to-grow’ state during chilling”
t0“Maize plants”
Claim · model-written summary
PSII efficiency was strongly reduced in photosynthetic tissues.
- Organ / stage
- photosynthetic tissuese0
- Treatment
- Chillinge1
- Outcome
- PSII efficiencye0
- Direction
- strong reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In photosynthetic tissues, a strong reduction in PSII efficiency was measured.”
e1“Chilling repressed chlorophyll biosynthesis”
t0“Maize plants”
Claim · model-written summary
Chilling repressed chlorophyll biosynthesis.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Chilling repressed chlorophyll biosynthesis”
t0“Maize plants”
Claim · model-written summary
Geranylgeranyl chlorophyll a accumulated in mature leaves under chilling.
- Organ / stage
- mature leaf tissuese0
- Treatment
- Chillinge1
- Outcome
- accumulation of the precursor geranylgeranyl chlorophyll ae0
- Direction
- accumulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we detected accumulation of the precursor geranylgeranyl chlorophyll a and down-regulation of GERANYLGERANYL REDUCTASE ( GGR ) in mature leaf tissues.”
e1“Chilling repressed chlorophyll biosynthesis”
t0“Maize plants”
Claim · model-written summary
GERANYLGERANYL REDUCTASE was down-regulated in mature leaves.
- Organ / stage
- mature leaf tissuese0
- Treatment
- Chillinge1
- Gene
- GERANYLGERANYL REDUCTASEe0
- Outcome
- GERANYLGERANYL REDUCTASEe0
- Direction
- down-regulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“down-regulation of GERANYLGERANYL REDUCTASE ( GGR ) in mature leaf tissues”
e1“Chilling repressed chlorophyll biosynthesis”
t0“Maize plants”
Claim · model-written summary
Excess light energy was mostly dissipated through fluorescence and constitutive thermal dissipation.
- Outcome
- Excess light energye0
- Qualifier
- fluorescence and constitutive thermal dissipation processese0
- Comparator
- light-regulated thermal dissipatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Excess light energy was mostly dissipated through fluorescence and constitutive thermal dissipation processes, rather than by light-regulated thermal dissipation.”
t0“Maize plants”
Claim · model-written summary
Only weak evidence of xanthophyll cycle activation was found.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“only weak clues of xanthophyll cycle activation were found”
t0“Maize plants”
Claim · model-written summary
Chilling reduced CO 2 assimilation.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CO 2 assimilation was reduced by chilling”
t0“Maize plants”
Claim · model-written summary
Chilling reduced expression of PEPC, PPDK and Rubisco small-subunit genes.
- Treatment
- chillinge1
- Gene
- genes encoding phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and the small subunit of Rubiscoe0
- Outcome
- expression levelse1
- Direction
- reducede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression levels of genes encoding phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and the small subunit of Rubisco”
e1“CO 2 assimilation was reduced by chilling, as well as the expression levels of genes encoding phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and the small subunit of Rubisco.”
t0“Maize plants”
Claim · model-written summary
Sugar accumulation correlated with a strong decrease in specific leaf area.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Accumulation of sugars was correlated with a strong decrease of the specific leaf area (SLA).”
t0“Maize plants”
Claim · model-written summary
The authors infer that growth arrest helps maize recover rapidly after mild chilling.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“growth arrest might be their strategy for fast recovery after a mild stress”
t0“Maize plants”
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