Quantitative contributions of blue light and PAR to the photocontrol of plant morphogenesis in Trifolium repens (L.).

Shade-avoidance is a major adaptive response of plants, and is usually considered to be controlled by phytochromes through the perception of changes in the red:far red light ratio. However, few studies on the effects of blue light (BL) and of light intensity [photosynthetically active radiation (PAR)] on light-grown plants have been conducted, especially concerning changes in PAR at constant BL. The objective here was to quantify the photocontrol of aerial morphogenesis by BL and PAR. Experiments were conducted varying BL and PAR independently, with three BL levels (4, 38, and 83 micromol m(-2) s(-1)) at constant PAR (300 micromol m(-2) s(-1)) and three PAR levels (338, 705, and 163 micromol m(-2) s(-1)) at constant BL (36 micromol m(-2) s(-1)). Effects on morphogenetic processes were analysed as quantitative modulations of ontogenic trends and response curves were produced. White clover (Trifolium repens L.) was used, as it is a typical shade-avoider displaying the whole syndrome of shade-avoidance in a purely vegetative stage. Morphological responses were strongly controlled by both BL and PAR changes, through antagonist effects on leaf appearance rate and additive effects on petiole elongation. All the other responses appeared to be the indirect consequences of changes in the leaf appearance rates. BL acted as a light signal for plant morphogenesis. However, the PAR control probably implicates two distinct mechanisms, such as a trophic effect and a signal. Both PAR and BL actions involved organ-specific differences, which are central in the control of the shade-avoidance responses.

[1]  T. Dougher,et al.  Evidence for Yellow Light Suppression of Lettuce Growth ¶ , 2001, Photochemistry and photobiology.

[2]  Chentao Lin,et al.  Cryptochrome structure and signal transduction. , 2003, Annual review of plant biology.

[3]  J. Botto,et al.  Modes of action of phytochromes , 1998 .

[4]  A. Davies.  Leaf tissue remaining after cutting and regrowth in perennial ryegrass , 1974, The Journal of Agricultural Science.

[5]  J. Simon,et al.  Compétition pour la lumière et morphologie du trèfle blanc (Trifolium repens L.) : émission des feuilles et des ramifications , 1989 .

[6]  T. Dougher,et al.  Differences in the Response of Wheat, Soybean and Lettuce to Reduced Blue Radiation¶ , 2001, Photochemistry and photobiology.

[7]  H. Gautier,et al.  Effects of Blue Light on the Vertical Colonization of Space by White Clover and their Consequences for Dry Matter Distribution , 1997 .

[8]  Keara A Franklin,et al.  Phytochromes and shade-avoidance responses in plants. , 2005, Annals of botany.

[9]  J. C. Sager,et al.  Photosynthetic Efficiency and Phytochrome Photoequilibria Determination Using Spectral Data , 1988 .

[10]  J. P. Grime.  Plant strategies in shade , 1981 .

[11]  H. Huber,et al.  Differential effects of light quantity and spectral light quality on growth, morphology and development of two stoloniferous Potentilla species , 1998, Oecologia.

[12]  G. E. Carlson.  Growth of Clover Leaves — Developmental Morphology and Parameters at Ten Stages1 , 1966 .

[13]  C. Ballaré,et al.  Foraging for light: photosensory ecology and agricultural implications , 1997 .

[14]  C. Ballaré,et al.  Photocontrol of stem elongation in plant neighbourhoods: effects of photon fluence rate under natural conditions of radiation , 1991 .

[15]  Garry C. Whitelam,et al.  The shade avoidance syndrome: multiple responses mediated by multiple phytochromes , 1997 .

[16]  J. Nösberger,et al.  Branch and root formation in Trifolium repens is influenced by the light environment of unfolded leaves , 1997, Oecologia.

[17]  H. Tsukaya,et al.  Genetic control of petiole length in Arabidopsis thaliana. , 2002, Plant & cell physiology.

[18]  K. McConnaughay,et al.  Interpreting phenotypic plasticity : the importance of ontogeny , 2002 .

[19]  François Tardieu,et al.  Modelling leaf expansion in a fluctuating environment: are changes in specific leaf area a consequence of changes in expansion rate? , 1999 .

[20]  Bradley C. Bennett,et al.  Perspectives on Plant Population Ecology , 1984 .

[21]  R. Littell.  SAS System for Mixed Models , 1996 .

[22]  R M Wheeler,et al.  Soybean stem growth under high-pressure sodium with supplemental blue lighting. , 1991, Agronomy journal.

[23]  H. Gautier,et al.  Comparison of Horizontal Spread of White Clover (Trifolium repensL.) Grown Under Two Artificial Light Sources Differing in their Content of Blue Light , 1998 .

[24]  C. E. Powell,et al.  Growth of White Clover, Dependent on N2 Fixation, in Elevated CO2 and Temperature , 1992 .

[25]  H. Huber,et al.  Shade-induced changes in the branching pattern of a stoloniferous herb: functional response or allometric effect? , 1997, Oecologia.

[26]  L. Fukshansky,et al.  Action Spectroscopy of Photoreversible Pigment Systems , 1983 .

[27]  Paul Galland,et al.  Action Spectrum for Cryptochrome-Dependent Hypocotyl Growth Inhibition in Arabidopsis1 , 2002, Plant Physiology.

[28]  B. Saugier,et al.  Alimentation azotée et croissance de la fétuque élevée. I: Assimilation du carbone et répartition entre organes , 1986 .

[29]  T. Dougher,et al.  Evidence for Yellow Light Suppression of Lettuce Growth¶ , 2001 .

[30]  Hirokazu Tsukaya,et al.  The different growth responses of the Arabidopsis thaliana leaf blade and the petiole during shade avoidance are regulated by photoreceptors and sugar. , 2005, Plant & cell physiology.

[31]  Harry Smith,et al.  Phytochromes and light signal perception by plants—an emerging synthesis , 2000, Nature.

[32]  C. Messier,et al.  Light quantity and quality on the forest floor of pioneer and climax stages in a birch–beech–sugar maple stand , 1988 .

[33]  Eberhard Schäfer,et al.  Phytochromes control photomorphogenesis by differentially regulated, interacting signaling pathways in higher plants. , 2002, Annual review of plant biology.

[34]  H. Kroon,et al.  Morphological plasticity in clonal plants: the foraging concept reconsidered. , 1995 .

[35]  Bruno Moulia,et al.  A Quantitative Analysis of the Three‐Dimensional Spatial Colonization by a Plant as Illustrated by White Clover (Trifolium repens L.) , 2003, International Journal of Plant Sciences.