PLANT PHYSIOLOGY

1. PLANT PHYSIOLOGY

2. Plants are dynamic! • Many physiological processes occur in each part of the plant • Materials are transported through specialized conducting systems • Energy is harnessed from the sun through photosynthesis to forms sugars and other storage products • Stored foods are broken down to yield chemical energy through respiration

3. Transport of water and minerals • Occurs in the xylem • Tracheids and vessel elements - conducting components • Source of water is the soil surrounding the roots • Water moved up through plant to the leaves often in excess of 300 ft

4. Water movement in xylem • Uptake from soil • Conduction in the xylem • Transpiration in the leaves

5. Transpiration • Transpiration is the loss of water vapor from leaves • Occurs mainly through the stomata (90%) • Driving force behind the movement of water in xylem.

6. Guard Cells and Stoma Guard Cell Stoma (opening)

7. Open stomata permit transpiration • Gas exchange can occur freely between the leaf and the atmosphere • Water vapor and oxygen diffuse out of the leaf • Carbon dioxide is able to diffuse into the leaf

8. Transpiration • Large amounts of water vapor are lost by transpiration • 2 liters of water/day for a single corn plant • 5 liters for a sunflower • 200 liters for a large maple tree • 450 liters for a date palm tree • Transpiration is a major component of the global water cycle

9. Translocation of sugars in phloem • Organic materials are translocated by the sieve tube members of the phloem • Sieve tube members are living but highly specialized cells End wall with sieve plate

10. Phloem translocation • Moves from source to sink. • In late winter, the source may be an underground storage organ translocating sugars to apical meristems (the sink) • In summer the source is usually photosynthetic leaves sending sugars for storage to sinks such as roots or developing fruits

11. Phloem translocation • Sucrose in a watery solution • In a growing pumpkin which reaches a size of 5.5 kg (11 lbs) in 33 days, approximately 8 g of solution are translocated per hour - small pumpkin • Record pumpkin over 1000 lbs

12. Metabolism • Total of all chemical reactions occurring in living organisms • Metabolic reactions that synthesize compounds require an input of energy • Reactions which break down compounds usually release energy

13. Energy • All life process are driven by energy • A cell or an organism deprived of an energy source will soon die • Among the forms of energy are radiant (light), thermal (heat), chemical, mechanical (motion), and electrical • One form of energy can be transformed into another form • ATP energy currency of the cell

14. Cellular Energy Transformations • Transfer of electrons (or H atoms) • ATP energy currency of all cells • Cells use ATP when need energy • Cells make ATP when store energy • Other energy molecules • NADP--->NADPH • NAD--->NADH

15. Photosynthesis • Transforms the energy of the sun into chemical energy • Is the basis for life on Earth • Photosynthetic organisms are at the base of all food chains • Without green plants and algae, life could not survive

16. Light absorbing pigments • When light strikes an object it can • pass through the object • be reflected from the surface • be absorbed • For light to be absorbed, pigments must be present

17. Pigments in plants • Leaf - the major organ of photosynthesis • Chloroplasts within the mesophyll cells are the actual sites of photosynthesis • The major photosynthetic pigments are the green chlorophylls • Other pigments: Carotenoids • Orange - carotenes • Yellow - xanthophylls • Normally masked by the chlorophylls

20. Thylakoid Granum

21. Two stages of photosynthesis both occur in chloroplasts:Light Reactions and Calvin Cycle Stroma (Calvin Cycle) Outer Membrane Inner membrane Thylakoids location of pigments and Light Reaction Granum

22. Light reactions • Photochemical phase of photosynthesis • Radiant energy is absorbed and then converted into chemical energy • Occur extremely rapidly powered by vast energy of the sun

23. Results of the Light Reactions • Water molecules are split releasing oxygen and electrons • Electrons used in a process that ultimately results in the formation of two energy molecules NADPH and ATP

24. Calvin Cycle (Dark reactions) • Biochemical phase of photosynthesis • The pathway is named in honor of Melvin Calvin who received a Nobel Prize in 1961 for his work determining the steps in the pathway

25. Events of the Calvin Cycle • Transforms CO2 to form sugars • Uses ATP and NADPH produced in the light reactions but doesn’t use light energy directly • The end product of this pathway is the formation of a six-carbon sugar which requires the input of 6 molecules of carbon dioxide

26. Carbon dioxide for Calvin Cycle • From the atmosphere • Very small fraction (0.035%) of the Earth's atmosphere • Enters the leaf by diffusing through the stomata

27. Overall Equation for Photosynthesis CHLOROPHYLL 6CO2 + 12H2O + energy --------> C6H12O6 + 6O2 + 6H2O

28. Oxygen release from light reaction • Oxygen released when water is split • Diffuses out of the leaves into atmosphere • Earth's only constant supply of oxygen • No oxygen in early Earth atmosphere • Current 20% oxygen atmosphere is the result of three billion yrs of photosynthesis • Living organisms depend on oxygen for cellular respiration

29. Products of photosynthesis • Transported to growing fruits, storage organs, other sinks • Sucrose is translocated in the phloem • After being unloaded, sugars are usually converted to starch • Very few species store sucrose • Only sugarcane and sugar beet are important sources of sucrose

30. Sugarcane • Saccharum officinarum is a perenniel member of the grass family • Native to the islands of the South Pacific • Grown in India since antiquity • Ancient civilizations in the Near East and Mediterranean countries were acquainted with sugar through Arab trading routes • 7th century - grown in Mediterranean

31. Europe • Honey remained the principal sweetener until the 15th century • Sugar was an expensive luxury mainly use in medicines to disguise the bitter taste of herbal remedies • Early in the 15th century sugar plantations were established on islands in the eastern Atlantic

32. Caribbean Islands • Columbus introduced sugarcane on his second voyage in 1493 • By 1509 sugarcane was harvested in Santo Domingo and Hispaniola and soon spread to other islands • Many Caribbean Islands were eventually denuded of native forests and planted with sugar cane

33. Other New World Locations • Portuguese started sugar plantations in South America in 1521 • Spanish and Portuguese enslaved the native populations to work in the fields • The first sugarcane grown in the continental United States was in the French colony of Louisiana in 1753

34. Sugar and Slavery • Sugarcane was responsible for the establishment of slavery in the Americas • Decimation of the native Indian populations led to the need for workers on the sugar plantations • By the early 16th century, sugar and the slave trade became interdependent initially established in Spanish and Portuguese colonies

35. Sugar demand increasing • Supplies of honey in Europe were decreasing • Growing popularity of coffee, tea, and cocoa in Europe accelerated the demand for sugar • Sugar became the most important commodity traded in the world

36. Triangle Trade • First leg - England to West Africa with trinkets, cloths, firearms, salt • Second leg - Africa to Caribbean Islands with slaves • Third leg - Caribbean to England with rum, molasses and sugar • 10-20 million African slaves had been brought to the New World

37. Sugarcane • Provides over 50% of the world's sugar supply • Canes are 15 to 20 ft tall with individual stalks up to 6” in diameter • Moist lowland tropics and subtropics • Canes generally contain 12 to 15% sucrose.

38. Sugarcane Field in Egypt

39. Processing • Canes crushed to extract the sugary juice • Juice is concentrated and evaporated to form a syrup • Sugar is crystalized and separated from thick brown liquid (molasses) • Molasses is used in foods, or is fermented to make rum, ethyl alcohol, or vinegar • The crystallized sugar (about 96-97% pure sucrose) is refined

40. Sugar beet • Beta vulgaris, a member of the Chenopodiaceae is unrelated to sugarcane • Same species as red beets which are native to the Mediterranean region • Provide close to 40% of the world's supply of table sugar

41. Other Storage Compounds in Plants • Products of photosynthesis are stored as various organic compounds • Starch - most common storage compound • Energy reserve for plants • Energy source for the animals that feed on the plants • Other plants store oils (triglycerides) and proteins

42. Summary • Plants are dynamic metabolic systems with hundreds of biochemical reactions • Life on Earth is dependent on the flow of energy from the sun • Photosynthesis converts carbon dioxide and water into sugar using solar energy • Various compounds are stored by plants including sucrose, starch, oils, and proteins