Lecture 3. Photosynthesis 1

Transcription

1 Lecture 3 Photosynthesis 1

2 Constituent of plant component Plants component: water (70%), organic matter (27%), mineral (3%) - dry matter Water eg. Tomato contain 42-93% water young shoot 90-95% water cereal/grain 10-16% water

3 Organic matter protein, CHO, lipid and etc. Mineral 17 elements (macro mg/g dry matter, micro ug/g dry matter) water (CH2O)n Pn Carbon dioxide oxigen E (from solar radiation)

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6 Leaf absorption of radiation on leaf surface reflected (2%), absorbed (15%) and transmitted (2%) Not all light been used for Pn but been reflected or been transmitted from low wavelength to high, called fluorescence.

7 Light the provider of life Through a series of nuclear reactions occurring within the sun, mass is converted into energy E= mc 2 Agriculture is a system of exploiting solar energy through Pn Yield is dependent upon the size and efficiency of the photosynthetic system Pigment excitation is dependent upon the interaction between a photon and a pigment, a measure of light used in Pn is often based on photon flux density

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9 Light quantification Electromagnet theory light travels through space as a wave and the number of waves passing a given point in a certain time interval is a frequency Quantum theory light travels in a stream of particles called photons. The energy present in one photon is called a quantum Photon flux density number of photons striking a given surface area per unit of time

10 Light and measurement Photometric units Radiometric units Photon flux density also known as irradiance

11 Measurements of Sunlight Env. Photometric (kilolux) Radiometric J/m 2 /s Photon Flux Density ( nm) ( umol/m 2 /s) Full Sun ( ) Overcast Deeply shaded

12 Solar radiation Radiation linkage of wavelength, max intensity occurs at 500nm Plants appear to have adapted to utilize solar radiation between nm Solar radiation level decreases as it passed through the atmosphere due to absorption and scattering - electromagnet spectrum - transfer energy (E) through free media eg. Leaf will reflect green color but absorb blue color

13 Solar radiation (cont..) Solar radiation absorbed during the daytime by a crop surface % - used to evaporate water % - sensible heat storage in the soil % - sensible heat storage in the atmosphere y convection processes % - goes into Pn Wavelengths between nm are most efficiently used in Pn

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15 Light - small part of the spectrum - radiation that visible to human eyes - radiation that emitted and absorbed in discreate packets of energy called quantum - inverse rely proportional to wavelength uv - >> E than infrared

16 Photosynthetically active radiation PAR Visible radiation nm Photon flux density (PAR: μe/m2/s) (Photon per area per time)

17 Photosynthetic photon flux density (PPFD) Unit (PPF: μmol/m2/s) Full sun solar irradiance lux E must absorb by certain part from the plant. Eg. Chloroplast, photosynthetic pigments

18 Absorption and fate for light energy Pigment- biological compound that absorbs light Absorption extremely fast process (10-15 s) Energy of the absorbed photon is transformed to an electron in the molecule 1. Energy of the e- is elevated from the ground state to an elevated level known as excited of singlet state 2. A photon can only absorbed if its energy content matched the energy required to raise the electron to a higher, allowable energy state 3. An excited molecule has a very short lifespan (10-9 s) and must rid itself of any excess energy and return to ground state

19 Absorption and action spectrum Function of wavelength Action spectrum : specific for an individual molecule

20 Plants absorb light by specific pigments contained in thylakoids Organisms Cynobacteria Red algae Cryptomonad algae Dinoflagellates Brown algae, diatoms Golden algae Green algae, higher plant Pigments Chl a, phycobilins, β-carotene, myxoxanthin Chl a, phycobilins, β-carotene, lutein chl a, chl c 2, phycobilins, β-carotene, alloxanthin chl a, chl c 2, β-carotene, peridinin chl a, chl c 1, chl c 2, β-carotene, fucoxanthin Chl a, chl c 1, chl c 2, β-carotene, fucoxanthin Chl a, chl b, β-carotene, lutein

21 Photosynthesis pigments (photoreceptors) Chlorophyll Porphryin head Made of 4 nitrogen containing pyrrole rings Long hydrocarbon tail (phytol tail) Chl molecule is completed with the addition of the Mg ion chelated to the 4 nitrogen atoms Four known types of chl- a, b, c and d Absorption specrtra is very specific

22 Tetrapyrrole head Chl a Phytol tail

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24 Carotenoids Lipid soluble Includes carotenes and xanthophylls Carotenes predominately orange/red-orange Β-carotene major carotenoid in algae and higher plants May protect chl by absorbing excess blue light and combining with oxygen to form xanthophylls Absorb light of approx nm.

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27 flavonoids Include the pink, purple, scarlet and blue anthocyanins Water soluble pigments and are found predominately in vacuolar sap May protect the underlying tissue from UV radiation Attractants to insects (uv and visible spectrum)

28 Phycobilins Serve as accessory light-harvesting pigments and /or critical regulatory system in green plants Three phycobilins are involved in Pn phycoerythrin, phycocyanin, allophycocyanin and phytochromobolin) is an important photoreceptor Differ from chl in that the tetraphyrole grp is covalently linked to a protein structure

29 Phycobilins (cont..) Exist in 2 forms that are photo reversible 1. P660 (Pr) absorbs max at 660nm 2. Absorption at 660nm converts it to a second farred pigment (P735 or Pfr) a) absorption at 735nm coverts the protein back to P660 b) Pr is believed to be an active from of the pigment responsible for initiating a wide range of photomorphogenic responses