Blue Light-Induced Phototropism of Inflorescence Stems
and Petioles is Mediated by Phototropin Family Members
phot1 and phot2
Regular Paper
Takatoshi Kagawa1,2,3,5,∗, Mitsuhiro Kimura1,6 and Masamitsu Wada2,4,7
1Graduate
School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8577 Japan
of Biological Regulation and Photobiology, National Institute for Basic Biology, Okazaki, 444-8585 Japan
3SORST, Japan Science and Technology Corporation, 1–8, Honcho 4-chome, Kawaguchi-city, Saitama, 332-0012 Japan
4Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, Tokyo, 192-0397 Japan
2Division
Phototropin family photoreceptors, phot1 and phot2, in
Arabidopsis thaliana control the blue light (BL)-mediated
phototropic responses of the hypocotyl, chloroplast
relocation movement and stomatal opening. Phototropic
responses in dark-grown tissues have been well studied
but those in de-etiolated green plants are not well
understood. Here, we analyzed phototropic responses of
inflorescence stems and petioles of wild-type and
phototropin mutant plants of A. thaliana. Similar to the
results obtained from dark-grown seedlings, inflorescence
stems and petioles in wild-type and phot2 mutant plants
showed phototropic bending towards low fluence BL,
while in phot1 mutant plants, a high fluence rate of BL was
required. phot1 phot2 double mutant plants did not show
any phototropic responses even under very high fluence
rates of BL. We further studied the photoreceptive sites
for phototropic responses of stems and petioles by partial
tissue irradiation. The whole part of the inflorescence
stem is sensitive to BL and shows phototropism, but in the
petiole only the irradiated abaxial side is sensitive. Similar
to dark-grown etiolated seedlings, phot1 plays a major
role in phototropic responses under weak light, but phot2
functions under high fluence rate conditions in green
plants.
Keywords: Arabidopsis thaliana • Blue light • Leaf movement
• Partial irradiation • Phototropin mutants • Photoreceptor.
Abbreviations: BL, blue light; LED, light emitting diode; WT,
wild type.
Introduction
Plants use light to produce chemical energy by photosynthesis. In order to obtain optimum conditions for photosynthetic processes, plants modulate their shape to maximize
the amount of light they receive under their living conditions. Phototropism is one of the typical examples of such
modulation and is easily observed under natural conditions.
Plant seedlings show this type of positive phototropic
response in nature; however, most of the experiments on
phototropism have been carried out using dark-grown seedlings of both monocotyledonous and dicotyledonous plants
(review by Iino 2001).
Non-phototropic hypocotyl mutants, nph1-4, defective in
the phototropic response to blue light, were isolated in
Arabidopsis thaliana (Liscum and Briggs 1995, Liscum and
Briggs 1996). Genomic analysis of the nph1 mutants revealed
that the NPH1 protein was a photoreceptor for phototropism in etiolated hypocotyls (Huala et al. 1997). However,
when nph1 mutant plants were irradiated with high fluence
rates of BL, the phototropic response still occurred. The
second photoreceptor identified for phototropism was
NPH1-like protein (NPL1), a paralogous gene of NPH1 (Sakai
et al., 2001). NPH1 and NPL1 were subsequently renamed
5Present
address: National Institute of Agrobiological Sciences, Kannondai 2-1-1, Tsukuba, 305-8602 Japan
address: Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, M5S 3B2, Canada
7Present address: Department of Biology, Faculty of Science, Kyushu University, Hakozaki 6-10-1, Fukuoka, 812-8581 Japan
∗Corresponding author: E-mail, [email protected]; Fax, +81-29-838-7463.
6Present
Plant Cell Physiol. 50(10): 1774–1785 (2009) doi:10.1093/pcp/pcp119, available online at www.pcp.oxfordjournals.org
© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.
All rights reserved. For permissions, please email: [email protected]
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Plant Cell Physiol. 50(10): 1774–1785 (2009) doi:10.1093/pcp/pcp119 © The Author 2009.
Phototropism in the stem and petiole
phot1 and phot2, respectively, according to their roles as
photoreceptors for phototropism (Briggs et al. 2001). The
photoperceptive center of phototropins consists of two
light/oxygen/voltage (LOV)-sensitive protein domains,
LOV1 and LOV2. While biochemical signaling events downstream of photoperception by phototropins are currently
being studied (see reviews by Esmon et al. 2005, Kimura
and Kagawa 2006, Whippo and Hangarter 2006), several
questions regarding the basic physiological responses in
de-etiolated green plants remain unknown.
Leaves, as well as stems, move in response to light. Solar
tracking of leaves during the daytime is a typical example
(Ehleringer and Forseth 1980). Light-induced leaf movement
was analyzed using plants such as Lavatera cretica (Schwartz
and Koller 1978, Schwartz and Koller 1980) and Lupinus succulentus (Vogelmann and Björn 1983). The movement
occurs around the pulvinus, a special structure required for
this movement, and is not a response dependent on growth.
Inoue and co-workers suggested that leaf positioning in
A. thaliana (Inoue et al. 2008) and leaf movement of kidney
bean (Inoue et al. 2005) might be regulated by phototropin.
In order to clarify phototropin involvement in leaf movement as well as inflorescence stem phototropism, we analyzed the phototropic responses using A. thaliana phot
mutants. By means of continuous video-recording under
infra-red light, the photoreceptive sites for these responses
could be more precisely analyzed.
Results
Immunoblot analysis
In order to determine the potential role of phototropin proteins in phototropic responses in green tissues, we tested
phot1 and phot2 expression in the stems, petioles and leaves
of wild-type (WT), phot1 and phot2 single mutant and phot1
phot2 double mutant plants using anti-phot1 and antiphot2 specific antibodies (Fig. 1). The results of the immunoblot analyses show that PHOT1 and PHOT2 proteins
accumulated in all three tissues in WT plants. However,
PHOT1 and PHOT2 proteins were not detected in any
tissues of phot1 and phot2 mutant plants, respectively, nor
were they detected in phot1 phot2 double mutants. These
results indicate that stems, petioles and leaves express
PHOT1 and PHOT2 and accumulate phot1 and phot2
proteins.
Phototropic response of inflorescence stems
Plants were irradiated with unilateral BL and the phototropic response of inflorescence stems was observed (Figs. 2, 3;
Supplementary Data 2). In the dark, stems grew vertically
showing rotational movement over 24 h after transfer into
darkness (Fig. 3b, c). When plants were irradiated with continuous BL at 5 µmol m−2 s−1 after 12 h incubation in the dark,
the growing stem bent towards the light source (Fig. 3e, d).
The bending speed was rapid during the first ca. 2 h, then
slowed down (Fig. 3e). Bending ceased after removal from
the light source. This positive phototropic response was
induced by BL at a fluence rate ranging from 0.02 to
12 µmol m−2 s−1 in the stems of WT plants (Fig. 3f).
Next, we observed the phototropism of inflorescence
stems in phot1, phot2 mutant and phot1 phot2 double
mutant plants (Figs. 4, 5). In phot2 plants, phototropic
responses occurred when the stems were irradiated with BL
at 0.6 µmol m−2 s−1 (Fig. 4b). However, in phot1 (Fig. 4a) and
phot1 phot2 (data not shown) stems, little or no phototropism was observed under the same light conditions. Curvatures of phot1 and phot2 mutant plants under these
light conditions were 2.3° ± 3.5° (degree ± SD, n = 3) and
28.0° ± 1.1° (n = 3), respectively. Since the phototropic
response in phot1 hypocotyls can be induced by
Fig. 1 Immunoblot analysis of phototropins. PHOT1 and PHOT2 proteins in each tissue of WT and phototropin mutant plants were detected
using anti-phot1 and anti-phot2 polyclonal antibodies, respectively. Each lane was loaded with 5 µl of SDS–PAGE sample obtained as described
in Materials and Methods. Since chemiluminescence with the ECL detection kit was exposed to positive film in this experiment, positive signals
appear as white bands on a black background.
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Fig. 2 Sequential photographs of the phototropic response of an inflorescence stem in A. thaliana. (a) Time schedule for pre-culture, light
irradiation and observation. Plants that were grown under a 16L/8D light condition were set under the recording system between 18:00 and
19:00. Observation under infra-red light started before 19:00 and continued until at least 18:00 the next day for 23 h. BL was applied unilaterally
or partially from 7:00 to 13:00. (b) Sequential images of phototropism of an inflorescence stem. When a stem was irradiated from the right hand
side with BL (5 µmol m−2 s−1) continuously for 6 h, the stem bent towards the incident light source. Bar = 2 mm. uB: unilateral blue light.
10 µmol m−2 s−1 or higher fluence rates, we hypothesized that
phot2 acts as a receptor in this fluence range (Sakai et al.
2001). We tested this possibility by irradiating the stems of
phot1 and phot1 phot2 mutants with BL at 12 µmol m−2 s−1.
The stems of phot1 mutant plants bent under 12 µmol m−2 s−1
BL (Fig. 4c), but those of phot1 phot2 mutants under the
same fluence rate conditions (Fig. 4d) or higher (up to
80 µmol m−2 s−1; data not shown), did not. Maximum curvatures of the phot1 and phot2 mutants at these higher fluence
rates were 73° ± 18° (n = 3) and −0.8° ± 3.8° (n = 3), respectively. These results suggest that phot1 and phot2 work
redundantly as photoreceptors for the phototropic response
of inflorescence stems.
Phototropic responses of petioles
Since leaf orientation movement is controlled by light irradiation, we examined leaf movement of A. thaliana induced
by BL to determine phototropin involvement and possible
photoreceptive sites for this phenomenon. Leaf movement
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was analyzed using data obtained at two points, the base
and the mid-region of the petiole (Figs. 5, 6; Supplementary Data 3). In the dark, leaves moved slowly upward, specifically towards the adaxial side at the base of the petiole
without bending at the mid-region. The leaf behavior when
irradiated unilaterally with BL at 5 µmol m−2 s−1 from the
abaxial side was different from that when irradiated from
the adaxial side (Fig. 6b), although these petioles were grown
during irradiation (Supplementary Data 1). Petioles near
the light source, which were irradiated from the abaxial side,
moved downward at the basal region to become parallel to
the direction of incident light. On the other hand, petioles
irradiated from the adaxial side moved slightly upward to
become vertical to the light beam. Phototropic responses at
the mid-region of petioles also occurred depending upon
the direction of incident light. When irradiated from the
abaxial side, phototropic bending towards the light source
started at the mid-region but after some time petioles
returned to their original position, even under continuous
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Phototropism in the stem and petiole
Fig. 3 Time course of growth and phototropic response of inflorescence stems. (a) A schematic drawing illustrating the method used to measure
the length of stem and the angle (θ) of tropic response from digital images. The growth rate (b, d) and tropic curvature (c, e) of the stems of
plants kept continuously in the dark for 23 h (b, c), or kept in the dark and irradiated with BL at 5 µmol m−2 s−1 for 6 h and then transferred back
to the dark (d, e). The data from (b) and (c), and (d) and (e) were obtained using the same plants, respectively. (f) Fluence rate response curve of
phototropism in the stem. The time schedule for light irradiation was the same as Fig. 2a. Each point was obtained from at least three plants.
Bars represent the mean ± SD.
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Fig. 4 Time course of phototropic responses in inflorescence stems of phototropin mutants. The stems of phot1 (a) and phot2 (b) were irradiated
with BL at 0.6 µmol m−2 s−1 for 6 h. The stems of phot1 (c) and phot1 phot2 (d) were irradiated with BL at 12 µmol m−2 s−1 for 6 h. Other details are
the same as in Fig. 3.
irradiation (Fig. 6d). When irradiated from the adaxial side,
bending at the mid-region was rarely observed (Fig. 6c).
When whole leaves were irradiated from the side, the petioles of these leaves grew and twisted slightly to make the leaf
surface face towards the light source (Fig. 5). Under these
conditions, a slight phototropic response also occurred.
Since the phototropism of inflorescence stems appears to
be controlled by phototropins, we further studied whether
leaf movement is also controlled by these photoreceptors
(Figs. 7, 8). When WT plants of A. thaliana were irradiated
with BL at 0.6 µmol m−2 s−1, leaf movement was observed at
the abaxial side but not at the adaxial side (Fig. 7a–c). Petioles of phot2 plants also show a response to weak BL irradiation, even at 0.6 µmol m−2 s−1 (Fig. 7g–i), while petioles of
phot1 mutants responded to BL irradiation at higher rates
of 12 µmol m−2 s−1 (Fig. 8a–c), but not at 0.6 µmol m−2 s−1
(Fig. 7d–f). A phot1 phot2 double mutant, however, showed
neither phototropic responses (Fig. 8d–f) nor twisting (data
not shown) of petioles even at higher BL fluence rates up to
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12 µmol m−2 s−1. These results indicate that phot1 and phot2
mediate phototropism of petioles.
Photoreceptive site in the inflorescence stem and
petiole
Next, we set up an instrument to determine the photoreceptive sites for phototropism in inflorescence stems and
petioles using partial BL irradiation with an optical fiber.
When inflorescence stems of WT plants were partially irradiated, at any region, they bent towards the light source at a
position slightly lower than that of the irradiated point (Fig. 9;
Supplementary Data 4). When a small portion of the stem
beneath the apical part with juvenile leaves and flowers, or
the lowest portion of stem, was irradiated, stems bent
towards the light source at a region around the irradiated
area (Fig. 9b, c; Supplementary Data 5, 6).
Finally, unilateral light application induced petiole bending at the mid-region by partial irradiation. Partial irradiation of the abaxial side of a petiole with a B-beam induced
Plant Cell Physiol. 50(10): 1774–1785 (2009) doi:10.1093/pcp/pcp119 © The Author 2009.
Phototropism in the stem and petiole
Fig. 5 Sequential photographs of phototropic responses of leaves. Plants with fully grown leaves under 16L/8D conditions were transferred to the
dark and observed continuously under infra-red light. The leaves were irradiated with unilateral BL (5 µmol m−2 s−1) for 6 h from the right hand
side. The time schedule was the same as in Fig. 2a. Bar = 2 mm.
continuous bending of this petiole during irradiation but
not in other non-irradiated petioles of the same plant
(Fig. 10a–c; Supplementary Data 7, 8). When petioles
were irradiated from the adaxial side with the same B-beam,
neither irradiated nor non-irradiated petioles showed a
bending response (Fig. 10d–f). These results indicate that
petioles can bend only towards the abaxial side but not
towards the adaxial side.
Discussion
Phototropin family photoreceptors phot1 and phot2, redundantly control several B-mediated physiological phenomena,
such as hypocotyl phototropism (Sakai et al. 2001), chloroplast relocation movement (Jarillo et al. 2001, Kagawa et al.
2001, Sakai et al. 2001) and stomatal opening (Kinoshita
et al. 2001). This work suggests that the phototropism of
inflorescence stems and leaf petioles is also controlled by
phototropins. phot1 works as a major photoreceptor under
low and high light conditions, while phot2 works predominantly under high light conditions. This redundancy is similar to the case of hypocotyl phototropism. As gene expression
of PHOT1 and PHOT2 differ under different light conditions
(Kanegae et al. 2000, Jarillo et al. 2001, Kagawa et al. 2001),
the PHOT1/PHOT2 ratio may be different between darkand light-grown plants. Nevertheless, in phototropism of
dark-grown hypocotyls, light-grown stems and petioles,
phot1 plays a major role as photoreceptor, while phot2
appears to contribute redundantly under higher fluence rate
conditions. Both phot1 and phot2 contribute almost equivalently to chloroplast accumulation movement and stomatal opening; however, chloroplast avoidance movement
is mediated specifically by phot2 (Kagawa et al. 2001).
Although phot1 and phot2 are highly homologous in amino
acid sequence and their photochemical characteristics are
similar (Kasahara et al. 2002), the different roles of phot1
and phot2 in physiological responses have not been completely elucidated.
For plant survival, leaf orientation towards light is very
important, particularly under weak light conditions. Efficiency of photosynthesis in leaves of Syringa vulgaris differs
depending on the direction of incident light, that is, the efficiency of light perception is higher in a leaf irradiated from
the adaxial side than from the abaxial side (Terashima and
Hikosaka 1995). Thus, when an adaxial leaf surface is irradiated with unilateral light, light absorption by chlorophyll is
more efficient because of leaf structure and stoichiometry.
In this work, it was found that leaves of A. thaliana responded
to unilateral BL dependent upon the direction of illumination. In summary, leaves irradiated from the adaxial side
raised themselves vertically to face the incident light while
leaves irradiated from the abaxial side bent downward at the
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Fig. 6 Time course of the phototropic response in leaves. (a) Schematic drawing for leaf movement measurements. Angles of petioles that were
irradiated from the adaxial or abaxial side, were measured at the basal region (ϕb, ϕd) and the mid-region (θb, θd) of the petioles, respectively.
Plants were irradiated with BL at 5 µmol m−2 s−1 for 6 h and the angles of the basal region (b) and the mid-region (c, d) of petioles were measured.
The plants were the same as those used in Fig. 5.
petiole to face the adaxial side of the blade to the incident
light. It remains unclear whether leaf bending at the base
region also occurs with hypocotyl tropism. This behavior of
leaf movement is very reasonable from the viewpoint of the
leaf structure where palisade cells are gathered at the adaxial
side. Furthermore, chloroplasts in leaf cells relocate their
position depending upon light conditions to mediate photosynthetic processes. Chloroplasts move towards a more
illuminated area under weak light, but avoid strong light for
protection against chloroplast photodamage (Kasahara
et al. 2002). Chloroplast movement is also mediated by phototropins (Kagawa et al. 2001, Sakai et al. 2001). It is interesting, and perhaps indicative of the importance of integration
of both responses, that chloroplast relocation movement
and phototropism share the same photoreceptors.
The photoreceptive site for phototropism in monocotyledonous plants was shown to be at the tip of the coleoptile
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more than 100 years ago in Phalaris canariensis (Darwin and
Darwin 1890). In the case of light-grown hypocotyls with
green cotyledons, of L. cretica, solar-tracking leaf was induced
by light absorbed at the lamina (Schwartz and Koller 1980,
Koller et al. 1990). Photoperception for floral heliotropism in
Ranunculus adoneus occurred primarily in the portion of the
peduncle just beneath the floral receptacle (Sherry and
Galen 1998). The photoreceptive site of the pulvinar phototropic response in Phaseolus vulgaris was found in all sectors (Koller and Ritter 1994). Here, we demonstrate that the
photoreceptive sites for phototropism in stems and petioles
are localized throughout their tissues but are not restricted
to portions of the tissues.
The relationship between the photoreceptive site and
bending region appears to be dependent upon the types and
mechanisms of phototropism. In our experiments, stems
and petioles accumulate phototropin in WT (Fig. 1) and it
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Phototropism in the stem and petiole
Fig. 7 Time course of the phototropic response in petioles of WT (a–c), phot1 (d–f) and phot2 (g–i). The plants of WT, phot1 and phot2 were
irradiated with BL at 0.6 µmol m−2 s−1 for 6 h, and phototropic bending was measured as the angle between the petiole (a, d, g) and mid-region of
the petiole (θd: b, e, h; θb: c, f, i). Other details were the same as for Fig. 6a.
has been demonstrated that fluorescence of a PHOT1–GFP
translational fusion driven by the native promoter was
detected in the region of the xylem parenchyma, rudimentary
cambium and several parenchyma cell groups (Sakamoto and
Briggs 2002). Some or all cells among the GFP-fluorescing
tissues are proposed to function as ‘photoreceptive cells’. In
these ambiguous situations, further analyses on the mechanisms of phototropism (such as the contribution of specific
photoreceptors, determination of photoreceptive sites at
specific cell levels, lateral auxin transport and changes in
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Fig. 8 Time course of the phototropic response in petioles of phot1 (a–c) and phot1 phot2 (d–e). The plants of phot1 and phot1 phot2 were
irradiated with BL at 12 µmol m−2 s−1 for 6 h, and phototropic bending was measured as the angle of the petiole (a, d) and mid-region of the
petiole (θd: b, e; θb: c, e). Other details were the same as for Fig. 6.
turgor pressure and cell growth) would be needed for a general explanation of the relationship between the site of light
perception and the site of phototropic bending.
Materials and Methods
Plant materials
The background of all WT, phot1-5, phot2-1 and phot1-5
phot2-1 double mutant seedlings of A. thaliana (L.) Heynh.
was the Columbia ecotype with gl-1. Seeds sterilized with
0.5% NaClO and 0.05% Triton X-100 were sown on rock
wool (M30S30; Nitto Boseki Co. Ltd, Tokyo, Japan) with
commercial mineral solution (HYPONeX; HYPONeX Japan
Corp. Ltd, Osaka, Japan) diluted 500 times, and grown under
a 16 h light/8 h dark cycle (7:00–23:00 light/23:00–7:00 dark)
at 22°C for 3–5 weeks (see Fig. 2a). These plants were
then used for phototropism experiments and immunoblot
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analyses. For the phototropic responses of the petioles,
plants with four to six leaves were used.
Light source
BL at less than either 12 or 80 µmol m−2 s−1 was obtained by a
light emitting diode (LED; E1L51-3B; Toyoda Gosei Co. Ltd,
Aichi, Japan), or in combination with four LEDs (E1L51-3B)
and three LEDs (E1L53-3B), respectively. A set of LEDs was
placed ca. 10 cm from plants. The peak wavelength of B-LEDs
is 475 nm and the half-intensity wavelength is 25 nm. Infrared light was obtained using 16 LEDs (GL538; Sharp Co.,
Osaka, Japan), whose peak emission wavelength and halfintensity wavelength are 950 nm and 45 nm, respectively.
Neutral density filters of ND13 and ND3 (Hoya Corp., Tokyo,
Japan) were used when necessary. Partial tissue irradiation
was performed using an optical fiber (Eska diameter 0.5 mm;
Mitsubishi Rayon Co. Ltd, Tokyo, Japan) combined with an
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Phototropism in the stem and petiole
LED (E1L51-3B), and the fluence rate was 6 µmol m−2 s−1 at
1 mm from the tip of the optical fiber. A silicon photodiode
(S1227-66BR; Hamamatsu Photonics KK, Shizuoka, Japan)
was used to measure the fluence rate.
Observation and movement analysis
A single plant grown on a piece of rock wool was observed
continuously using an infra-red light-sensitive CCD camera
(C2400-77; Hamamatsu Photonics KK) for 23 h from 19:00 to
18:00 the next day. Unilateral BL irradiation was performed
for 6 h from 7:00 to 13:00 (see Fig. 2a). Plant images were
recorded at 5 min intervals during the period by a Macintosh
computer (Power Macintosh 7600; Apple Japan Inc., Tokyo,
Japan) using the public domain NIH Image program (developed at the US National Institutes of Health and available on
the Internet at http://rsb.info.nih.gov/nih-image/), and the
digital images were used for phototropism analysis. These
experiments were performed at least three times with different plants.
Immunoblot analysis
Rabbit polyclonal antibodies against keyhole limpet hemocyanin-conjugated synthetic peptides corresponding to 12
amino acid residues near the N-terminus of phot1 and phot2
were generated and affinity purified commercially (Trans
Genic Inc., Kumamoto, Japan). Anti-rabbit Ig–horseradish
peroxidase-linked donkey whole antibodies diluted 300 000
times (GE Healthcare, NJ, USA) were used as secondary
antibodies.
Extracts from stems, petioles and leave were separately
prepared by adding 4 × TE buffer (10 mM Tris–HCl pH 8.0,
1 mM EDTA), then treated with 5 × SDS–PAGE sample buffer
[100 mM Tris–HCl pH 6.8, 4% (w/v) SDS, 10% (w/v) 2-mercaptoethanol, 0.2% bromophenol blue, 20% (w/v) glycerol]
of the same tissue weight and ground for 5 min on ice. The
SDS–PAGE samples were separated by electrophoresis on
7.5% SDS–polyacrylamide gel with SDS–PAGE running
buffer [24.8 mM Tris, 1% (w/v) SDS, 192 mM glycine]. The
proteins were transferred to PVDF membranes (Bio-Rad,
Inc., Hercules, CA, USA) using a semi-dry electrophoresis
apparatus (AE-6677; ATTO, Tokyo, Japan) in transfer buffer
[48 mM Tris, 39 mM glycine, 20% (v/v) methanol, 0.02%
(w/v) SDS]. Following the protocol of ECL advance Western
Blotting Detection Kit (GE Healthcare), phototropin
proteins were detected by exposure to instant film (667;
Polaroid Corp.) using an ECL mini-camera (GE Healthcare).
Fig. 9 Sequential photographs of phototropic responses in
inflorescence stems induced by partial tissue irradiation. A part of the
stem was irradiated with BL at 6 µmol m−2 s−1 from 0 to 6 h by an
optical fiber. The distance between the stem surface and optical fiber
tip was approximately 1 mm. The time schedule of light irradiation
was the same as in Fig. 2a. Even when the stems were irradiated around
the center (a), top (b) and bottom (c) positions of the stem, tropic
responses were observed. Bar = 2 mm.
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Supplementary data
Supplementary data are available at PCP Online.
Funding
This work was supported in part by the SORST, Japan Science and Technology Corporation to T.K. and by a grant
from the PROBRAIN (Program for Promotion of Basic
Research Activities for Innovative Biosciences) and Grantin-Aid for Scientific Research (A, no. 13304061) and for
Scientific Research on Priority Areas (B, no. 13139203) from
the Ministry of Education, Sports, Science and Technology
(MEXT) of Japan to M.W.
Acknowledgments
The authors wish to thank Dr M. Watanabe, National Institute for Basic Biology, for his technical advice regarding
partial tissue irradiation. We also thank Dr Danielle Vidaurre
and Dr George Stamatiou (University of Toronto, Canada)
for valuable comments and English corrections. Anti-PHOT1
and Anti-PHOT2 antibodies were supplied by Trans Genic
Inc.
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Fig. 10 Partial irradiation at the mid-region of petioles for induction of
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Fig. 9. Sequential photographs (a, d) and time-dependent curvature of
the mid-region of petioles with (c, e) or without (b, f) irradiation.
Measured angles represented θd (b, e) and θb (c, e) as described for
Fig. 6a. Bar = 2 mm.
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(Received June 30, 2009; Accepted August 6, 2009)
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