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Dudley Notes and Figures - Dudley's Material How do plants...

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Dudley’s Material How do plants sense their neighbours aboveground? Same material as in lecture, but presented is a different order. Plants photosynthesize, so light is the resource Light – both a wave and a particle Wave – wavelength X frequency = speed of light λν= C Particle – energy of a photon is proportional to frequency (lots of photons with long wavelengths can’t do the work of one photon of shorter wavelength) Visible light is only a small part of overall electromagnetic spectrum Note (get familiar) with the colours and corresponding wavelengths (energy in Kilojoules/mole photons) Ultraviolet <400 471 Violet 400-425 292 Blue – 425-490 260 Green – 490-560 230 Yellow – 560-585 210 Orange – 585-640 193 Red – 640-740 176 Infrared -- >740 85 Nature of wavelengths, coming from sun is seen in the solar signature Note that the visible wavelengths are most abundant in solar influx, not so energetic as to be damaging (UV and below = ionizing radiation) or so weak as to be biologically unusable (infrared and above, mostly absorbed by water, increases heat of biological molecules) see that not all wavelengths are transmitted equally ozone absorbs in UV CO2 and H20 have characteristic absorbance peaks, especially in infrared Pigments (substance that absorbs light) harvest different wavelengths of light Absorbance spectrum – see overhead for how this is measured Reflectance, transmittance – light that is not absorbed – why chlorophyll is green Action spectrum – measure a biological activity at each wavelength – e.g. photosynthesis Light as information – photoreceptors and pigments Pigment – any molecule that absorbs certain wavelengths of visible light and reflects or absorbs other wavelengths Photoreceptor – a molecule, a cell, or an organ specialized to detect light –has a pigment (chromophore) part, and a signal transduction part. Sources of shade (not human-caused) Clouds Hills Rocks Water Night sunset Other plants trees
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Intraspecific and interspecific competition for light In competition, taller plants get more light, and shade their neighbours – being tall means being more competitive Without competition (or under trees), being tall wastes biomass on stems, plants may be more fragile How plants respond to neighbours Common to see density dependent stem elongation – Phenotypic plasticity Same genotype produces different phenotypes in different environments Different genotypes may do this differently Doesn’t imply adaptation, but can be, if doing ‘right’ thing in each environment How plants sense neighbours Plants have phytochrome as a mechanism of sensing other plants (here we ignore that it is a gene family) Phytochrome is a photoreceptor – switches state from Pr (red absorbing form) to Pfr (far-red absorbing form) depending on whether it receives a photon of red or far-red light
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