Light Acts as a Signal for Regulation of Growth and Development
Plants utilise light not only for photosynthesis but also as a signal to regulate optimal growth and development throughout their life cycle. The light quality (spectral composition), amount, direction and duration change depending on the season, latitude
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Light Acts as a Signal for Regulation of Growth and Development Yohei Higuchi and Tamotsu Hisamatsu
Abstract Plants utilise light not only for photosynthesis but also as a signal to regulate optimal growth and development throughout their life cycle. The light quality (spectral composition), amount, direction and duration change depending on the season, latitude and local conditions. Therefore, to adapt to diverse light conditions, plants have evolved unique photoreceptor systems to mediate light responses to a broad range of wavelengths from ultraviolet-B to far-red light. Light signals can regulate changes in structure and form, such as seed germination, de-etiolation, leaf expansion, phototropism, neighbour avoidance, stem elongation, flower initiation and pigment synthesis. Plant hormones and transcriptional factors play an important role in the internal signalling that mediates light-regulated processes of development. Plants rely on their circadian clock to modify their growth and development in anticipation of predictable changes in environmental light and temperature conditions. The light signals perceived by photoreceptors affect the circadian clock and directly activate the induction of the light responses. Keywords Circadian rhythm • De-etiolation • Gating effect • Photoreceptor • Phototropism • Seed germination • Shade avoidance response
5.1
Photoreceptors and Their Function
As sessile and photosynthetic organisms, plants monitor ambient light conditions and regulate numerous developmental switches to adapt to continually changing environments. A recent molecular genetic approach in the model plant Arabidopsis revealed that multiple photoreceptors act as light sensors for perceiving different light wavelengths (Fig. 5.1). These include phytochromes (phy), cryptochromes
Y. Higuchi Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan T. Hisamatsu (*) Institute of Vegetable and Floriculture Science, National Agriculture and Food Research Organization (NARO), Fujimoto, Tsukuba, Ibaraki 305-0852, Japan e-mail: [email protected] © Springer Science+Business Media Singapore 2016 T. Kozai et al. (eds.), LED Lighting for Urban Agriculture, DOI 10.1007/978-981-10-1848-0_5
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Y. Higuchi and T. Hisamatsu
(A) Wavelength (nm)
300
UV-B
UVR8
400
UV-A
500
600
700
Blue
Red
800
Far-red
cryptochrome phototropin
phytochrome
ZTL/FKF1/LKP2
(B) Phytochromobilin
Phytochrome
GAF Pterin
Cryptochrome
PAS
PHY
CCE
FMN LOV
ZTL/FKF1/LKP2
LOV
HKRD
FAD PHR
Phototropin
PAS
FMN LOV
Kinase
FMN F-box
Kelch repeat
Trp Trp
UVR8
β-Propeller
C27
Fig. 5.1 Photoreceptors in higher plants. (a) Photoreceptors perceiving different parts of the light spectrum. (b) Structure of photoreceptor proteins. Domain structure and binding chromophores are shown. GAF cGMP-stimulated phosphodiesterase; Anabaena adenylate cyclases and Escherichia coli FhlA; PAS Per (period circadian protein), Arn (Ah receptor nuclear translocator protein) and Sim (si
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