• Proceedings of the Botanical Society of Korea Conference
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• 1994.09a
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• pp.41-51
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• 1994

Tomato (Lycopersicon esculentum Mill.) has been chosen as a model species for the study of hotomorphogenesis. The aurea (au) and yellow-green-2 (yg-2) mutants which are severely photochrome deficient appear to be phytochrome chromophore mutants. Mutants modified with respect to specific members of the phytochrome gene family: the far-red light-insensitive mutant (fri, for phytochrome A) and the temporarily red light-insensitive mutant (tri, for phytochrome B1) have been identified. Mutants that exhibit an exaggerated phytochrome response are putative transduction-chain mutants affecting an amplification step in phytochrome signal transduction. These mutants are being used to understand the complexities of juvenile anthocyanin in the hypocotyl during seedling de-etiolation.

• Journal of Life Science
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• v.22 no.4
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• pp.559-564
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• 2012

In order to investigate the effect of phytochromes on the regulation of ethylene biosynthesis, we measured the ethylene production and the activities of enzymes involved in ethylene biosynthesis using phytochrome mutants such as $phyA$, $phyB$, and $phyAB$ of Arabidopsis. The ethylene production was decreased in mutants grown in white light. In particular, double mutants showed a 37% decrease compared to the wild type in ethylene production. When Arabidopsis roots were grown in the dark, mutants did not show a decrease in ethylene production; however, production was significantly decreased in the double mutant grown in red light. Only $phyB$ did not show the decrease in the ethylene production in far-red light. Unlike the ACO activities, the ACS activities of mutants showed the same pattern as the ethylene production under several light conditions. The results of ACS activities confirmed the expression of the ACS gene by RT-PCR analysis. The decrease of ethylene production in mutants was due to the lower activity of ACC synthase, which converts the S-adenosyl-L-methionine (AdoMet) to 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene. These results suggested that both phytochrome A and B play an important role in the regulation of ethylene biosynthesis in Arabidopsis roots in the conversion step of AdoMet to ACC, which is regulated by ACS.

• Journal of Life Science
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• v.18 no.2
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• pp.148-153
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• 2008

Phytochrome double mutant (PhyAB) showed the delayed root gravitropic response compared to the wild type (WT) in Arabidopsis. After 8 hr of gravistimulation, the gravitropic response of mutant showed 48% of the WT. The delayed response started at 1.5 hr after gravistimulation. And we measured the ethylene production in the root segments of WT and mutant for 12 hr. Ethylene production of mutant decreased about 40% of the WT at 12 hr. This result suggested that the phytochrome might be linked with ethylene production in some way. Generally, ethylene inhibits the growth of plant organs including roots. We measured the root growth rate in the presence of ACC (1-aminocyclopropane-1-carboxylic acid), a precursor of ethylene. And WT showed the inhibition of root growth with ACC, but mutant did not show the inhibition as WT did. To confirm the relationship between the ethylene and gravitropic response, we measured the gravitropic response with ACC. In the presence of $10^{-6}$ M ACC, WT showed the 37.4% inhibition compared to the control (no ACC), whereas mutant showed the only 6.6% inhibition of control (no ACC). This research suggested the relationship between phytochrome and gravitropic response through an ethylene production.

• Journal of Life Science
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• v.22 no.5
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• pp.681-686
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• 2012

Light, one of the environmental stimuli, is fundamental to the growth and development of plants. Red and far-red light are sensed using the phytochrome family of plant photoreceptors. To investigate the effect of light on root growth and gravitropism, we used the Arabidopsis phytochrome mutants grown in several light conditions. The root growth of $phyA$ reared in all light conditions except white light and was stimulated compared to the WT. The stimulation of root growth was obvious in $phyA$ grown in red light. On the other hand, the root growth of $phyB$ grown in all light conditions decreased, and the lowest rate of decrease was observed in $phyAB$ grown in white and red light. The gravitropic response of $phyA$ was stimulated compared to the WT when it was grown in all light conditions except far-red light. $PhyAB$ grown in all light conditions showed the inhibition of gravitropic response. The transcript level of ACS, one of the enzymes regulating ethylene biosynthesis, increased in $phyA$ grown in white and red light, but not in $phyA$ grown in far-red light. In conclusion, these results suggested that the $P_{fr}$ form of $phyB$ regulates the root growth and gravitropism.

• Journal of Integrative Natural Science
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• v.1 no.1
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• pp.24-31
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• 2008

Brassinosteroids (BRs) are a special class of plant steroid hormones that are essential for normal growth and development. Part of confusion is whether BRs are unique to plants, because they have overlapping physiological roles with other better-studied hormones and with physiological responses caused by light. In systems designed to assay for cytokinins, the effects of BRs vary. We measured hypocotyl length for testing the ability of brassinolide (BL) to rescue double mutant between det2 and the photoreceptor null mutant phytochrome B (phyB). PHYB involved in controlling hypocotyl elongation in increased concentration of BL whereas phyBdet2 double mutant just partially rescue to phyB in white and red light indicated the involvement of BRs in PHYB regulated cell elongation. BRs regulated hypocotyl growth was delayed by BAP, a cytokinin treatment but inhibitory effects of BAPs on hypocotyl growth was slightly recovered by BL. The result indicated that the mode of action of BR and cytokinin is independent or sequential in the downstream light-regulated response control on hypocotyl elongation and also light modulated the action of BR and cytokinin in some extent.

• Journal of Photoscience
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• v.9 no.2
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• pp.90-93
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• 2002

Phytochrome A (phyA) and phytochrome B (phyB) perceive light and adapt to fluctuating circumstances by different manners in terms of effective wavelengths, required fluence and photoreversibility. Action spectra for induction of seed germination and inhibition of hypocotyl elongation using phytochrome mutants of Arabidopsis showed major difference. PhyA is the principal photoreceptor for the very low fluence responses and the far-red light-induced high irradiance responses, while phyB controls low fluence response in a red/far-red reversible mode. The structural requirement of their bilin chromophores for photosensory specificity of phyA and phyB was investigated by reconstituting holophytochromes through feeding various synthetic bilins to the following chromophore-deficient mutants: hy1, hyl/phyA and hyl/phyB mutants of Arabidopsis. We found that the vinyl side-chain of the D-ring in phytochromobilin interacts with phyA apoprotein. This interaction plays a direct role in mediating the specific photosensory function of phyA. The ethyl side-chain of the D-ring in phycocyanobilin fails to interact with phyA apoprotein, therefore, phyA specific photosensory function is not observed. In contrast, both phytochromobilin and phycocyanobilin interact with phyB apoprotein and induce phyB specific photosensory functions. Structural requirements of the apoproteins and the chromophores for the specific photoperception of phyA and phyB are discussed.

• Proceedings of the Korean Society of Plant Biotechnology Conference
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• 2005.11a
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• pp.198-198
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• 2005

• Proceedings of the Korean Society of Potoscience Conference
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• spring
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• pp.97-103
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• 2003

Phytochrome controls diverse aspects of plant development in response to the ambient light conditions. HFRl, a basic helix-loop-helix protein, is required for a subset of phytochrome A (phy A)-mediated photo-responses in Arabidopsis. Here, we show that overexpression of HFR1-N105, but not the one of the full-length HFR1, confers exaggerated photo-responses. The transgenic plants overexpressing HFR1- N105 exhibited light-independence in a subset of photo-responses, including germination, de-etiolation, gravitropic hypocotyl growth, and blocking of greening. Overexpression of HFR1-N105 also caused constitutive light-responses in the expression of some light-regulated genes. In addition, the HFR1-N105 overexpressor showed hypersensitive responses under R and FR light, dependently on phyB and phyA, respectively. End-of-day far-red light response and petiole elongation were suppressed in the HFR1-N105 overexpressor plants. Together these results imply that overexpression of HFR1-N105 activated a branch of light signaling, supporting the hypothesis that transcriptional regulation in the nucleus would be the primary mechanism of light signaling in Arabidopsis. We discuss the biotechnological potential of the mutant bHLH protein, HFR1-N105 in regard to suppressed shade avoidance syndrome.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.5
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• pp.556-563
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• 1997

The endogenous gibberellin(GA) levels of sorghum grown under different photoperiodic conditions were measured by GC-MS-SIM. The effect of photoperiods on the diurnal GA levels of the 13-hydroxylation pathway was investigated by sampling every 6 h for 1 day. Levels of $GA_12$, $GA_53$, $GA_19$, $GA_20$, $GA_1$ and $GA_8$ were not constant throughout sampling times but rather rhythmic in productions. Wild-type seedlings grown under short photoperiod contained more $GA_20$ and $GA_1$ than those of long photoperiod. Although plant height of phyB-l(phytochrome B mutant) was taller than wild-type under all photoperiods tested, $GA_1$ concentration of wild-type grown under 10 h photoperiod was higher than that of phyB-l grown under the same photoperiod. These results are compatible with the idea that phytochrome B changed seedling responsiveness to GAs.

• Journal of Life Science
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• v.28 no.1
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• pp.9-16
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• 2018

Light is essential to the growth and development of plants, and it is perceived by phytochromes, which are one of the photoreceptors that regulate physiological responses in plants. Ethylene regulates the dormancy, senescence, growth, and development of organs in plants. This research focused on the interaction of phytochromes and ethylene to control hypocotyl growth and gravitropism using phytochrome mutants of Arabidopsis, phyA, phyB, and phyAB, under three light conditions: red (R) light, farred (FR) light, and white light. The mutant phyAB exhibited the most stimulation of gravitropic response of all three phytochrome mutants and wild type (WT) in all three light conditions. Moreover, phyB in the R light condition showed more negative gravitropism than phyA. However, phyB in the FR light condition showed less curvature than phyA. The hypocotyl growth pattern was similar to the gravitropic response in several light conditions. To explain the mechanism of the regulation of gravitropic response and growth, we measured the ethylene production and activities of in vitro ACS and ACO. Ethylene production was reduced in all the mutants grown in white light in comparison to the WT. Ethylene production increased in the phyA grown in R light and phyB grown in FR light in comparison to the other mutants. The ACS activity coincided with the ethylene production in the phyA and the phyB grown in R light and FR light, respectively. These results suggest that the Pfr form of phyB in R light and the Pr form of phyA in FR light increased ethylene production via increasing ACS activity.