• 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.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 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.