Plant Biology MSc course Plants and their Environment 2007 I: Abiotic interactions Thijs Pons and Marcel Proveniers Role of Phytochromes in Shade Avoidance Ecophysiological and Molecular aspects

Energy - for photo-autotrophic growth Light as source of: Energy - for photo-autotrophic growth Information – maximize/optimize resource acquisition Shade Avoidance in (shade avoiding) plants: Avoidance of shade by neighbors in time and space by adjustment of growth and development that optimizes light capture for photosynthetic utilization (and may suppress light capture by neighbors)

Perception of the light climate Aspects of light climate Perception by pigments (photoreceptors) Presence of light Spectral Photon Distribution Photon Flux Density (PFD) Directional component Photoperiod phytochromes phototropins cryptochromes chlorophylls Other physiological processes indirectly associated with light availability

Photoreceptors in the life cycle

Phytochromes, involvement in shade avoidance during the life cycle process Seed Dormancy enforced in: Darkness Continuous light, low R:FR High PFD Seedling De-etiolation when emerging: High R:FR Low R:FR Vegetative plant Response to low R:FR in (or under) a leaf canopy Petiole hyponasty Elongation of internodes, petioles and leaves Phototropy Leaf Senescence; Reallocation of Photosynthetic capacity, Increased apical dominance Allocation to stems, away from storage, roots, leaves Mature plant Early flower induction at low R:FR Reduced seed set at low R:FR Photoperiod sensitivity

In this part of the course we will investigate the role of Phytochromes in different aspects of shade avoidance Significance in a Plant’s life cycle Physiological characterization of the process Which phytochromes are involved in perception and signal transduction Interaction with other photoreceptors, other signaling mechanisms and phytohormones Transcription under phytochrome control Downstream molecular processes Life cycle process Seed Dormancy and germination in soil and on the soil surface under a leaf canopy or in the open exposure to light of short duration or very low intensity exposure to continuous canopy shade light of variable R:FR Vegetative plant Response to low R:FR in leaf canopies petiole hyponasty elongation of internodes and petioles

Organization the course MSc course Plants and their Environment Part I: Abiotic interactions Monday 23 April Short introduction by lecturers Distribution of topics for preparation of presentations Private Study: Preparation of presentations Study of the subject of other presentations Write Essay Tuesday 1 & Thursday 3 May Presentations of selected topics Discussions chaired by other students from the group Tuesday 8 May Hand in Essay that describes in your own words the main topics that were discussed.

Phytochrome spectra R:FR Pfr/P: PFD 655-665 nm PFD 725-735 nm synthesis Physiological action R:FR PFD 655-665 nm PFD 725-735 nm open: 1.2 canopy: 0.2 Pfr/P: open: 0.6 canopy: 0.1 R: 0.8 FR: 0.02 Labile phytochrome phyA type II (seedling phytochrome) Stable phytochrome phyB (+C, D, E) type I (seed phytochrome) Smith 2000

Red – Farred reversibility an indication that phytochroom is involved

Light responses in seeds Relative importance of the 3 response types is very different between species and history of the seed Lactuca sativa (lettuce seeds) The three response types are also observed in seedlings Pons, 2000 VLFR = Very Low Fluence Response (phyA). a low concentration of Pfr breaks dormancy LFR = Low Fluence Response (phyB) a higher threshold value of Pfr is required for dormancy breaking HIR = High Irradiance Response irradiation of long duration inhibits germination; effect increases with increasing irradiance FR-HIR most effective at 710 – 720 nm and low R:FR (phyA) R-HIR most effective in red and white light (phyB in seedlings)

Germination in the soil and on the surface VLFR Exposure of the weed seed population to light during soil cultivation Scopel et al. 94

Canopy shade Germination of Plantago major Pons 2000

Shade avoidance in seeds Avoidance of germination at a time when the resulting seedling would be subject to competition from established plants Dormancy enforced by darkness in soil. Breaking of dormancy by short exposure to light during disturbance. Functional significance: Germination is delayed until after a disturbance event. - Dormancy enforced by canopy shade light (low R:FR) - Germination is delayed until an opening in the leaf canopy is created typically by a disturbance event. - Dormancy is enforced until the seed is buried in the soil and darkness maintains dormancy further.

Shade avoidance in vegetative plants Light environment in leaf canopies Lysimachia vulgaris different canopy densities

Vegetative development shade avoidance in leaf canopies Nicotiana Vegetative development shade avoidance in leaf canopies Arabidopsis High Light Spectral Shade Low High canopy density Petiole hyponasty Petiole elongation Internode elongation Leaf Senescence Boonman 06 Pierik et al. 2005

Spectral and neutral shade effects Arabidopsis High Light Spectrally Neutral Shade erect creeping stem stoloniferous Low R:FR Huber et al. 1996 Pierik et al. 2005

R:FR effects independent of PAR Chenopodium a shade avoiding species Adapted from H. Smith

Reflected light FR absorbed by stems increases with increasing LAI before PAR (R & B) incident on the leaves decreases. This triggers internode elongation and a phototropic response under control of phytochrome. FR R & B Ballare 99

Use of phy mutants Wt phyB Mutants lacking phyB have a constitutive shade avoidance phenotype. Long petioles, long internodes, low chlorophyll, early flowering; phyA resembles very much the wild type. This means that the spectrally sensitive component of shade avoidance is largely under control of phyB. There are also other phytochromes involved. Wt phyB

Photomorphogenesis under control of phytochrome in vegetative plants Shade avoidance - largely under control of phyB Functional significance: Maximize capture of light and its photosynthetic utilization when similar-sized plants compete for light. (shade tolerant species do not show a pronounced shade avoidance response)

Vegetative Plants (thursday 3 may) Topics for literature discussions on Involvement of Phytochrome in shade avoidance in seeds and vegetative plants Seeds (tuesday 1 May) 1. Role of different phytochromes in Arabidopsis Shinomura et al. (1994), Botto et al. (1996), Hennig et al. (2002) 2. Role of different phytochromes in Tomato Sinchijo et al. (2001), Appenroth et al. (2006) 3. Interaction between light and temperature effects Donohue et al. (2007), Penfield et al. (2005) 4. Downstream regulation Oh et al. (2004), Oh et al. (2006) Vegetative Plants (thursday 3 may) 5. Role of different phytochromes 1 Devlin et al. (1996), Devlin et al. (1998) 6. Role of different phytochromes 2 Devlin et al. (1999), Franklin et al. (2003) 7. Regulation of gene expression Salter et al. (2003), Sessa et al. (2005) 8. Primary target genes Devlin et al. (2003), Roig-Villanova et al. (2006)