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Investigations on the photoregulation of chloroplast movement and leaf positioning in Arabidopsis.

Han IS, Cho HY, Moni A, Lee AY, Briggs WR - Plant Cell Physiol. (2012)

Bottom Line: The effect is far-red reversible.This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant.These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Ulsan, Ulsan 680-749, Korea. hanis@ulsan.ac.kr

ABSTRACT
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

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Leaf positioning of wild-type, phot1, phot2 and phot1 phot2 mutants of Arabidopsis grown under white light. Normal leaf positioning was induced by illumination with white light (∼35 µmol m−2) for 24 h. This experiment was carried out three times with 12 plants, each time with similar results.
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pcs098-F5: Leaf positioning of wild-type, phot1, phot2 and phot1 phot2 mutants of Arabidopsis grown under white light. Normal leaf positioning was induced by illumination with white light (∼35 µmol m−2) for 24 h. This experiment was carried out three times with 12 plants, each time with similar results.

Mentions: To optimize photosynthesis, plants are capable of responding to blue light by appropriate leaf positioning (Takemiya et al. 2005). We characterized the leaf-positioning phenotypes of the selected PHOT LOV transgenic lines as previously described (Inoue et al. 2008). These plants were irradiated with white light (100 µmol m−2 s−1) from above for 24 h. Not surprisingly leaf orientation was normal in the wild type (gl1) and in both phot2-1 and phot1-5. As illustrated in Fig. 5, the first true leaves were oriented horizontally, at right angles to the incident white light in these three lines. As expected, the double mutant phot1-5 phot 2-1 lacked normal leaf positioning. Fig. 6 shows the quantitative data for the controls and the various transformant lines. Among the transformants, the PHOT1 wild-type gene (line 1-d) and PHOT1 LOV1 LOV2 transgenic line (line 2-c-1) both showed complementation, and line 3-a showed partial complementation. However, neither the PHOT1 LOV1 LOV2 gene (line 3-a) nor the PHOT1 LOV1LOV2 gene (line 4-a) provided normal leaf positioning in response to white light. Although line 7-a showed partial complementation of hypocotyl phototropism (fig. 3B in Cho et al. 2007), it failed to complement the leaf positioning response. This observation is consistent with our results (Fig. 1) indicating that LOV1 in PHOT2 does not complement the chloroplast movement response. These different apparent sensitivities suggest that different phototropin levels may be required for the different responses. Note that lines 5-a and 5-d, both expressing detectable amounts of the transformant protein (Fig. 2), complement the leaf positioning phenotype less than line 5-c. Since none of the other transgenic lines showed complementation, probably because of low protein expression levels (Supplementary Fig. S1), little can be said about the role of LOV2 in PHOT2 for this response.Fig. 5


Investigations on the photoregulation of chloroplast movement and leaf positioning in Arabidopsis.

Han IS, Cho HY, Moni A, Lee AY, Briggs WR - Plant Cell Physiol. (2012)

Leaf positioning of wild-type, phot1, phot2 and phot1 phot2 mutants of Arabidopsis grown under white light. Normal leaf positioning was induced by illumination with white light (∼35 µmol m−2) for 24 h. This experiment was carried out three times with 12 plants, each time with similar results.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539441&req=5

pcs098-F5: Leaf positioning of wild-type, phot1, phot2 and phot1 phot2 mutants of Arabidopsis grown under white light. Normal leaf positioning was induced by illumination with white light (∼35 µmol m−2) for 24 h. This experiment was carried out three times with 12 plants, each time with similar results.
Mentions: To optimize photosynthesis, plants are capable of responding to blue light by appropriate leaf positioning (Takemiya et al. 2005). We characterized the leaf-positioning phenotypes of the selected PHOT LOV transgenic lines as previously described (Inoue et al. 2008). These plants were irradiated with white light (100 µmol m−2 s−1) from above for 24 h. Not surprisingly leaf orientation was normal in the wild type (gl1) and in both phot2-1 and phot1-5. As illustrated in Fig. 5, the first true leaves were oriented horizontally, at right angles to the incident white light in these three lines. As expected, the double mutant phot1-5 phot 2-1 lacked normal leaf positioning. Fig. 6 shows the quantitative data for the controls and the various transformant lines. Among the transformants, the PHOT1 wild-type gene (line 1-d) and PHOT1 LOV1 LOV2 transgenic line (line 2-c-1) both showed complementation, and line 3-a showed partial complementation. However, neither the PHOT1 LOV1 LOV2 gene (line 3-a) nor the PHOT1 LOV1LOV2 gene (line 4-a) provided normal leaf positioning in response to white light. Although line 7-a showed partial complementation of hypocotyl phototropism (fig. 3B in Cho et al. 2007), it failed to complement the leaf positioning response. This observation is consistent with our results (Fig. 1) indicating that LOV1 in PHOT2 does not complement the chloroplast movement response. These different apparent sensitivities suggest that different phototropin levels may be required for the different responses. Note that lines 5-a and 5-d, both expressing detectable amounts of the transformant protein (Fig. 2), complement the leaf positioning phenotype less than line 5-c. Since none of the other transgenic lines showed complementation, probably because of low protein expression levels (Supplementary Fig. S1), little can be said about the role of LOV2 in PHOT2 for this response.Fig. 5

Bottom Line: The effect is far-red reversible.This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant.These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Ulsan, Ulsan 680-749, Korea. hanis@ulsan.ac.kr

ABSTRACT
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

Show MeSH