Abstract
Some plants can avoid shaded conditions via rapid shoot elongation, thus growing into better lit areas in a canopy. Cell wall-modifying mechanisms promoting this elongation response, therefore, are important regulatory points during shade avoidance. Two major cell wall-modifying protein families are expansins and xyloglucan endotransglucosylase/hydrolases (XTHs). The role of these proteins during shade avoidance was studied in Arabidopsis (Arabidopsis thaliana). In response to two shade cues, low red to far-red light (implying neighbor proximity) and green shade (mimicking dense canopy conditions), Arabidopsis showed classic shade avoidance features: petiole elongation and leaf hyponasty. Measurement of the apoplastic proton flux in green shade-treated petioles revealed a rapid efflux of protons into the apoplast within minutes, unlike white light controls. This apoplastic acidification probably provides the acidic pH required for the optimal activity of cell wall-modifying proteins like expansins and XTHs. Acid-induced extension, expansin susceptibility, and extractable expansin activity were similar in petioles from white light- and shade-treated plants. XTH activity, however, was high in petioles exposed to shade treatments. Five XTH genes (XTH9, -15, -16, -17, and -19) were positively regulated by low red to far-red light conditions, while the latter four and XTH22 showed a significant up-regulation also in response to green shade. Consistently, knockout mutants for two of these XTH genes also had reduced or absent shade avoidance responses to these light signals. These results point toward the cell wall as a vital regulatory point during shade avoidance.
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Claims 9
Claim · model-written summary
Low red to far-red light induced petiole elongation and leaf hyponasty.
- Taxon
- Arabidopsis
Arabidopsise0 - Treatment
- low red to far-red lighte0
- Outcome
- petiole elongation and leaf hyponastye0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In response to two shade cues, low red to far-red light (implying neighbor proximity) and green shade (mimicking dense canopy conditions), Arabidopsis showed classic shade avoidance features: petiole elongation and leaf hyponasty.”
Claim · model-written summary
Green shade induced petiole elongation and leaf hyponasty.
- Taxon
- ArabidopsisArabidopsise0
- Treatment
- green shadee0
- Outcome
- petiole elongation and leaf hyponastye0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In response to two shade cues, low red to far-red light (implying neighbor proximity) and green shade (mimicking dense canopy conditions), Arabidopsis showed classic shade avoidance features: petiole elongation and leaf hyponasty.”
Claim · model-written summary
Green shade caused rapid proton efflux into the petiole apoplast relative to white light.
Verbatim
e0“Measurement of the apoplastic proton flux in green shade-treated petioles revealed a rapid efflux of protons into the apoplast within minutes, unlike white light controls.”
Claim · model-written summary
Apoplastic acidification may support optimal activity of cell wall modifying proteins.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- optimal activity of cell wall-modifying proteins like expansins and XTHse0
- Qualifier
- apoplastic acidificatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This apoplastic acidification probably provides the acidic pH required for the optimal activity of cell wall-modifying proteins like expansins and XTHs.”
t0“Arabidopsis”
Claim · model-written summary
Acid-induced extension, expansin susceptibility and extractable expansin activity were similar under white light and shade.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- shade-treatede0
- Outcome
- Acid-induced extension, expansin susceptibility, and extractable expansin activitye0
- Direction
- similare0
- Comparator
- white light-e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Acid-induced extension, expansin susceptibility, and extractable expansin activity were similar in petioles from white light- and shade-treated plants.”
t0“Arabidopsis”
Claim · model-written summary
Shade treatments produced high XTH activity in petioles.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- shade treatmentse0
- Gene
- XTHe0
- Outcome
- XTH activitye0
- Direction
- highe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“XTH activity, however, was high in petioles exposed to shade treatments.”
t0“Arabidopsis”
Claim · model-written summary
Low red to far-red light positively regulated five XTH genes.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- low red to far-red light conditionse0
- Gene
- XTH9, -15, -16, -17, and -19e0
- Outcome
- XTH genese0
- Direction
- positively regulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Five XTH genes (XTH9, -15, -16, -17, and -19) were positively regulated by low red to far-red light conditions”
t0“Arabidopsis”
Claim · model-written summary
Green shade significantly upregulated XTH15, XTH16, XTH17, XTH19 and XTH22.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- green shadee0
- Gene
- XTH22e0
- Outcome
- XTH22e0
- Direction
- up-regulatione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the latter four and XTH22 showed a significant up-regulation also in response to green shade.”
e1“Five XTH genes (XTH9, -15, -16, -17, and -19)”
t0“Arabidopsis”
Claim · model-written summary
Two XTH knockout mutants had reduced or absent shade avoidance responses.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- XTH genese0
- Outcome
- shade avoidance responsese0
- Direction
- reduced or absente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“knockout mutants for two of these XTH genes also had reduced or absent shade avoidance responses to these light signals.”
t0“Arabidopsis”
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