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Plant Functions

Plant Functions. Adapted from Slide presentation of Dr Yann Guisard Lecturer Production Horticulture School of Agriculture and Wine Sciences Orange, NSW, 2800.

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Plant Functions

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  1. Plant Functions Adapted from Slide presentation of DrYann Guisard Lecturer Production Horticulture School of Agriculture and Wine Sciences Orange, NSW, 2800

  2. The Story Of WaterTranspirationloss of water from leaf surfacesvia ‘stomata’Source: http://remf.dartmouth.edu/images/botanicalLeafSEM/source/16.html *License on site: http://remf.dartmouth.edu/imagesindex.html |Date=12-18-07)77

  3. TranspirationHelps regulate leaf temperatureSome plants have modified leaves to control rate of transpirationLeaves with waxy surface ‘cuticle’ reduce water lossPlants transpire 98% of water absorbed by roots

  4. The cross section of a root

  5. Water absorption by roots • Water moves in root via apoplast and symplast • Apoplast – water moves through the cell without crossing any membranes • Symplast – water travels from one cell to the next via the plasmodesmata

  6. Impatiens – blue dye

  7. The cross section of a leaf C4 C3 • Stomata = Small opening surrounded by guard cells • Grapevines stomatal density = 80 – 400 / mm2

  8. Stomata open carbon dioxide is absorbed and oxygen released, opening controlled by guard cells Ratio of water (g) lost per gram CO2 fixed is Water Use Efficiencylow ratio = more water efficient plant

  9. Movement of water through stomata creates transpiration pull due to water tensionUpward movement assisted by osmosis, which also draws nutrients and soluble salts

  10. Role players in Transpiration • Physics • Cohesion • Adhesion • Capilarity • Evaporative demand = transpiration pull • Plant role • Regulation: • Stomata is a valve • Plants can sense the tension (water potential)

  11. http://www.wunderground.com/data/wximagenew/m/Madrid/228.jpg The story of lightLight Dependent Reactions

  12. Photosynthesis (light-powered synthesis)carbon dioxide (CO2) and water (H2O) are converted into carbohydrates and oxygen is released

  13. Photosynthesis = two distinct processesLight dependent reactionConvert light energy into chemical energy in the form of ATP and NADPHUse water and give off oxygenLight independent reaction (dark reaction)Take carbon atoms from atmosphericcarbon dioxide and form organic compounds this process, carbon fixation, powered by ATP and NADPH

  14. Photosynthesis = two distinct processesLight dependent reactionConvert light energy into chemical energy in the form of ATP and NADPHUse water and give off oxygenLight independent reaction (dark reaction)Take carbon atoms from atmosphericcarbon dioxide and form organic compounds this process, carbon fixation, powered by ATP and NADPH

  15. Capture of the energy of light(aka Light Dependent Reactions) • It all happens in the chloroplasts

  16. Chloroplasts contained within plant cells, responsible for capturing light energy Sun/light energy absorbed by thylakoid membranes0.5-3.5% of total light energy used in photosynthesisRemainder lost in heat and evaporation of water Stroma Grana Thylakoid stacks

  17. On the grana of the chloroplast Split water Create E Hydrolysis

  18. Review – Light Dependent Reactions H2O2H++2e-+O PS2ATP PS1NADPH

  19. The story of carbon capture and fixation: Light independent reactions

  20. Most abundant enzyme in the world. In the stroma of the chloroplast The C3 (Calvin) cycle 3 turns  1 PGAL (3C) 6 turns  2 PGAL (6C)  1 glucose (6C)

  21. Photosynthesis in C3 plants is inefficient:Photorespiration • C3 plants = 85% of all plants • Competition with photosynthesis for RuBP • Inefficiency of C3 plants • Uses up oxygen

  22. C4 plants (Corn, Sugarcane, Sorghum) • First detectable molecule formed by CO2 fixation is a 4 C molecule (C4)

  23. C4 • Oxaloacetate is found in very high concentration in the mesophyll cells • Environment is saturated with CO2 • Very rare to observe photorespiration

  24. CAM (Pineapple, Cacti) • Crassulacean Acid Metabolism • Stomata open during night times and fix CO2 in the vacuoles (4 C compound, Malic Acid) • Stomata closed during daytime (to save water) and C3 pathway is used

  25. C3 – named due to first stable compound formed in dark reactions is a 3-carbon compound (stomata opened during day)C4 – carbon is incorporated into 4-carbon compound, before dark reactions (stomata open or closed during day)CAM – similar to C4 (stomata opened during night)

  26. C3 – carbon dioxide absorbed during day with stomata open with glucose formed in the dark reactionsStomata open all day can increase respiration during times of heat stress and droughtLimited by excess light exposure and high temperatures

  27. C4 – carbon dioxide absorbed before it enters dark reactionsStomata can be closed during day while carbon dioxide is captured by internal respiration, rather than carbon dioxide from outsidePhotosynthesis can occur under conditions of moisture stress, when C3 plants would be limited Despite C3 limitations, majority of world food production comes from such C3 plants as rice and wheat

  28. CAM (crassulacean acid metabolism) photosynthesisSimilar to C4 photosynthesisStomata closed during day and opened at nightLoss of moisture reduced Carbon dioxide stored and processed during day in dark reactionCAM plants sacrifice growth and photosynthetic rates in exchange for tolerance of extreme conditions

  29. C3 plants – cotton, grapevines, serrated tussockrepresent approx. 90% earths plant biomassgrow better in cooler weather, good soil moisture

  30. C4 plants – maize, sugar cane, mostly in grasses, i.e., PoaceaeKangaroo grassrepresent approx. 3% earths plant biomassare more tolerant of drought, heat and nitrogen deficiency

  31. CAM plants – cactus, agave, hopbush (native to Australia)Open stomata at night to avoid increased transpiration during heat of dayCarbon dioxide stored at night converted to carbohydrates with radiant energy during day

  32. Comparison of C3, C4 and CAM photosynthesis pathways

  33. Translocationtransfer of food materials or products of metabolism throughout plantssugar produced in photosynthesis is the primary metabolite that is translocated from leaf to fruit, roots and grainsmost translocation occurs in the phloem, up and down movement

  34. XylemThick secondary cell walls, often deposited unevenly in a coil-like pattern so that they may stretch Dead at functional maturity (wood)Involved in conduct of water and ions in the plant PhloemInvolved in transport of sucrose, other organic compounds, and some ions Living at functional maturity

  35. Carbon Movement : Translocation Pressure flow theory

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