Photobiology

1. Photobiology 3rd Year Student of biophysics

2. Prepared ByProf. Dr. Mohammed Naguib Abd El-Ghany Hasaneen Professor Of Plant Metabolism And Biotechnology Academic Year 2005 - 2006

3. Contents • Introduction • Radiation • Visible light • Ultraviolet light • Ultraviolet light damage • Phytochrome concept • Distribution and translocation of phytochrome • Physiological effects of phytochrome

4. Introduction Light in Plants We see visible light (350-700 nm) Plants sense Ultra violet (280) to Infrared (800) Examples Seed germination - inhibited by light Stem elongation- inhibited by light Shade avoidance- mediated by far-red light There are probably 4 photoreceptors in plants We will deal with the best understood; PHYTOCHROMES

5. A Primer on Radiation

6. Some important plant responses to radiation • (“light” is only one form of radiation): • Photosynthesis • Photomorphogenesis; • Photropism; Photoperiodism • Energy balance/temperature • respiration • enzyme activity • transpiration • UV-responses • mutagenesis (note that there is a much more detailed table and discussion of responses of plants to light in chapter 1 of Hart: Light and Plant Growth)

7. In what form does energy from the sun travel to Earth? • Energy travels to Earth in the form of electromagnetic waves • Electromagnetic waves are classified according to wave length • Radiation is the direct transfer of energy by electromagnetic waves

8. Most of the energy from the sun reaches Earth in the form of • Visible light • Infrared radiation • A small amount of ultraviolet radiation

9. The different colors of light make up the visible spectrum. • Red has the longest wave length • Violet has the shortest wave length

10. Infrared radiation has the following properties: • Wavelengths longer than red light • It is not visible • It can be felt as heat • Used to warm food or baby chicks in an incubator

11. Ultraviolet light has the following properties: • Wave lengths shorter than violet light • Can cause skin damage • Can cause eye problems

12. Radiation and radiation laws The way we describe and quantify radiation, and the units used, vary depending on the kind of process we’re interested in Properties of radiation that are important to plants includeQuality, Quantity, Direction (including diffuse vs. direct) and Periodicity.

13. Radiation quality (or “color”, for visible light) is a function of its wavelength (or frequency) distribution Note these two charts are arrayed in opposite directions – one by increasing wavelength/decreasing energy and the other by increasing frequency/increasing energy The symbol “l” is often used for wavelength

14. Radiation measurements • Radiation quantity is measured in one of three ways, depending on the application: • Quantum measurements (numbers of photons) • Radiometric measurements (amount of energy) • Photometric measurements (light intensity, based on human perception)

15. The amount of radiation is expressed as fluence (also known as density; quantity per area), rate (also known as flux; quantity per time) or fluence rate (also known as flux density; amount per area per time)

16. For studies of photosynthesis and photomorphogenesis, the quantity of radiation is usually measured in quantum units (quantum flux density; quantum fluence rate): mmol m-2 s-1 usually, only the visible, or photosynthetically active part of the spectrum is measured, or in the case of photomorphogenesis, only specific wavelengths Note that “mol” refers to a mole of photons, and that 1 mol photons=1 Einstein. A quantum is one indivisible “package” of radiation, or one photon. PPFD = photosynthetically active photon flux density PAR = photosynthetically active radiation (400-700 nm)

17. For energy balance studies, radiation is measured in radiometric units, for example: Watts m-2 (note: 1 Watt = 1 Joule s-1)

18. The energy of a photon is proportional to its frequency and inversely proportional to wavelength: E = hn = hc/l Energy per photon (joules) wavelength (in meters) Planck’s constant: 6.63 x 10-34 joules s Frequency (s-1) Speed of light 3 X 108 m s-1 Radiometric and quantum units are interconverted based on the amount of energy in photons. See link from website to “working with light” or p. 28 of the handout by Hart or any good reference on radiation for more information on this conversion)

19. Because most light sources contain a wide range of wavelengths, it is difficult to convert precisely between quantum and radiometric units. Usually an approximation is used that assumes a “typical” distribution of wavelengths for a particular light source

20. Wien’s Law: lmax = 2897/T Temperature of radiating body, in degrees Kelvin All objects emit radiation (i.e., they “radiate”) as a function of their temperature (in addition to the emissivity of the material). Temperature affects both the amount and the quality (wavelength) of radiation emitted.

21. Notice that the range of photosynthetically active wavelengths is very small relative to the range of the solar spectrum The “bulk” of solar radiation is “shortwave” (visible plus near infrared)

22. Spectral Quality • visible =400-700 nm, about 45% of incident insolation • solar IR =700-5000 nm, about 46% of incident • UV =190-400 nm, about 9% of incident

23. Restating this as a rough “rule of thumb”: When the sky is clear, the photosynthetically active part of the solar spectrum accounts for about HALF of the total solar energy, IR accounts for the other half

24. Radiance vs. Irradiance: Radiance is the radiation that is emitted from an object Irradiance is the radiation that impinges upon an object In this case, radiation is commonly described as a flux (rate), or amount per unit time. This could be either a radiant flux or a quantum flux In this case, radiation is commonly described as a flux density, or amount per unit time per unit area. Again, the flux could be quantified either with either radiometric or photometric units.

25. Direct irradiance Diffuse irradiance Irradiance usually has both direct and diffuse components:

26. Lambert’s Cosine Law: The amount of energy in direct-beam irradiance is strongly affected by the angle between the surface and the beam

27. Solar angle and leaf angle can have a very big influence on irradiation, dramatically affecting photosynthesis, transpiration and leaf temperature • definitions: • Heliotropic:“sun tracking” • Paraheliotropic: leaf stays parallel to direct beam of sun • Diaheliotropic:leaf stays perpendicular to direct beam

28. Connections between matter and energy A short, painless review of simple organic chemistry …… to develop the connection between cycles of organic biomass and cycles of energy

29. CO2 methane increasing potential energy (energy stored in chemical bonds) (organic hydrocarbons. The molecules are becoming increasingly reduced) ethane ethene ethyne (Inorganic; not a hydrocarbon. This is a highly oxidized form of carbon)

30. general deterioration of #4 green

31. shade from trees and tower general deterioration of #4 green

32. shade from trees and tower poor air circulation from trees and shrubs general deterioration of #4 green concentrated traffic between trap and green

33. shade from trees and tower poor air circulation from trees and shrubs general deterioration of #4 green concentrated traffic between trap and green poor internal and surface drainage

34. shade from trees and tower poor air circulation from trees and shrubs general deterioration of #4 green concentrated traffic between trap and green poor internal and surface drainage

35. shade from trees and tower poor air circulation from trees and shrubs delicate turfgrass hot, humid microenvironment general deterioration of #4 green O2-deficient rootzone concentrated traffic between trap and green poor internal and surface drainage

36. Wavelength - ENERGY • Photons in short wavelengths pack a lot of energy • Visible light (400-750nm): • 1 mole of photons = 250kJ energy • Ultraviolet light (< 400 nm): • 1 mole of photons = 500 kJ energy • Photons in longer wavelengths do not • Infrared radiation (>750 nm) • 1 mole of photons = 85 kJ energy

37. What happens when sunlight hits the wall of a building? • Some reflected back to space (no effect) (this depends upon the COLOR of the wall!) • Most is absorbed. Then what? • Absorption of radiation makes the temperature of the object rise • How hot? • The hotter  the more radiation emitted (as infrared) • Heats until energy in = energy out • Or energy absorbed = energy re-radiated

39. The Thermal Environment • Energy is gained and lost through various pathways: • radiation - all objects emit electromagnetic radiation and receive this from sunlight and from other objects in the environment • conduction - direct transfer of kinetic energy of heat to/from objects in direct contact with one another • convection - direct transfer of kinetic energy of heat to/from moving air and water • evaporation - heat loss as water is evaporated from organism’s surface (2.43 kJ/g at 30oC) change in heat content = metabolism - evaporation + radiation + conduction + convection

40. Organisms must cope with temperature extremes. • Unlike birds and mammals, most organisms do not regulate their body temperatures. • All organisms, regardless of ability to thermoregulate, are subject to thermal constraints: • most life processes occur within the temperature range of liquid water, 0o-100oC • few living things survive temperatures in excess of 45oC • freezing is generally harmful to cells and tissues

41. So how do organisms regulate temperature? • Manipulating the energy balance equation! • Net radiation • Color, Orientation to sun, Minimizing/maximize IR losses (insulation) • Conduction • Use warm or cool surfaces • Convection: • Minimize or maximize exposure to wind or water (boundary layers, exposure, immersion) • Evaporation: • Minimize or maximize evaporation to control heat loss • Metabolism: Generate or limit generation of heat! • These can be morphological, physiological, or behavioral adaptations

42. Conserving Water in Hot Environments • Animals of deserts may experience environmental temperatures in excess of body temperature: • evaporative cooling is an option, but water is scarce • animals may also avoid high temperatures by: • reducing activity • seeking cool microclimates • migrating seasonally to cooler climates

43. Conserving Water in Hot Environments • Desert plants reduce heat loading in several ways already discussed. Plants may, in addition: • orient leaves to minimize solar gain • shed leaves and become inactive during stressful periods

44. The Kangaroo Rat - a Desert Specialist • These small desert rodents perform well in a nearly waterless and extremely hot setting. • kangaroo rats conserve water by: • producing concentrated urine • producing nearly dry feces • minimizing evaporative losses from lungs • kangaroo rats avoid desert heat by: • venturing above ground only at night • remaining in cool, humid burrow by day

45. Tolerance of Freezing • Freezing disrupts life processes and ice crystals can damage delicate cell structures. • Adaptations among organisms vary: • maintain internal temperature well above freezing • activate mechanisms that resist freezing • glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution) • glycoproteins can also impede the development of ice crystals, permitting “supercooling” • activate mechanisms that tolerate freezing

46. Organisms maintain a constant internal environment. • An organism’s ability to maintain constant internal conditions in the face of a varying environment is called homeostasis: • homeostatic systems consist of sensors, effectors, and a condition maintained constant • all homeostatic systems employ negative feedback -- when the system deviates from set point, various responses are activated to return system to set point

47. Temperature Regulation: an Example of Homeostasis • Principal classes of regulation: • homeotherms (warm-blooded animals) - maintain relatively constant internal temperatures • poikilotherms (cold-blooded animals) - tend to conform to external temperatures • some poikilotherms can regulate internal temperatures behaviorally, and are thus considered ectotherms, while homeotherms are endotherms

48. Homeostasis is costly. • As the difference between internal and external conditions increases, the cost of maintaining constant internal conditions increases dramatically: • in homeotherms, the metabolic rate required to maintain temperature is directly proportional to the difference between ambient and internal temperatures

49. Limits to Homeothermy • Homeotherms are limited in the extent to which they can maintain conditions different from those in their surroundings: • beyond some level of difference between ambient and internal, organism’s capacity to return internal conditions to norm is exceeded • available energy may also be limiting, because regulation requires substantial energy output

50. Partial Homeostasis • Some animals (and plants!) may only be homeothermic at certain times or in certain tissues… • pythons maintain high temperatures when incubating eggs • large fish may warm muscles or brain • hummingbirds may reduce body temperature at night (torpor)