Lectures 1 4
- 1. ACS 104: CROP PHYSIOLOGY INSTRUCTOR: Dr. C. M. Onyango
- 2. Intended learning outcomes By the end of the course it is expected that you will be able to: 1. Describe the plant cell, the parts of a plant cell, their structure and functions 2. Describe the physiology of green plants in relation to plant structure and environmental factors. 3. Explain the principles of photosynthesis and respiration including their relationship to crop yield. 4. Explain the mechanisms of water movement through plants, relate this to mineral nutrition 5. Outline the stages of plant development, the mechanisms by which these stages are regulated, plant senescence and dormancy
- 3. PLANT CELL: Different Parts (Cell membrane)
- 5. PARTS OF THE PLANT CELL 1. Cell wall 2. Cell membrane 3. Cell organelles - Nucleus - Chloroplasts - Endoplasmic reticulum - Golgi apparatus - Ribosomes - Mitochondria - Plastids
- 6. Cell organelles • Nucleus • Chloroplasts • Endoplasmic reticulum • Golgi apparatus • Ribosomes • Mitochondria • Plastids
- 7. Plastids • Proplastids - small, precursors to the other plastid types, found in young cells, actively growing tissues; • Chloroplasts - sites of photosynthesis (energy capture). • Chromoplasts - non-photosynthetic, colored plastids; give some fruits (tomatoes, carrots) and flowers their color; • Amyloplasts - colorless, starch-storing plastids; • Leucoplast - another term for amyloplast; • Etioplast - plastid whose development into a chloroplast has been arrested (stopped).
- 8. PHYSIOLOGY OF GREEN PLANTS What distinguishes green plants from animals?
- 10. What distinguishes green plants from animals? • Autotrophism! • An autotroph makes its own food (energy-rich organic compounds) from simple, inorganic materials in the environment. • Plants use light as their energy source, hence they are photosynthetic
- 11. CONSEQUENCES OF A STATIONARY LIFESTYLE A non-motile organism is unable to move to a more favorable location to carry out its vital functions. Thus, plants have at least three major problems to contend with: i) Environmental Positioning/Location - or, Getting Started in the Right Spot. i) The need to sense & respond to the environment -plants, like other organisms, must be able to respond to changes in their environment iii) Physical and biological dangers in the environment - a non-motile organism cannot flee when conditions get tough. It must "fight" it out. Both the physical environment and biological environment threaten the well being of plants.
- 12. ENVIRONMENTAL POSITIONING • Axis orientation:-Once a seed germinates in a favorable environment it must determine which way is up/down to insure that the roots grow down and shoots up. • Fine Tuning:-Even non-motile organisms need to "fine- tune" their position in the environment. Thus plants have a variety of mechanisms that enable them to optimize their position in the environment including: - Phototropism; Skototropism; Thigmomorphogenesis; Solar tracking; Leaf mosaics; Etiolation;
- 13. PHOTOTROPISM: growth toward light, maximize light reception
- 14. SKOTOTROPISM: growth of vines toward a darkened region of the environment. Mechanism by which some tropical vines find a support to grow up
- 15. THIGMOMORPHOGENESIS - response to touch in which the plant is shorter with thicker stems - prevents plants from getting too spindly and reduces risk of breaking in wind
- 16. SOLAR TRACKING: (e.g. flowers follow the movement of the sun) - keeps pollen dry, maximize photosynthesis.
- 17. Etiolation: the response of plants to growth in the dark or with reduce light
- 18. THE NEED TO SENSE & RESPOND TO THE ENVIRONMENT • Plants typically respond by various growth movements to unpredictable, usually short-term environmental fluctuations, like changes in temperature or light. E.g. flowers that are temperature sensitive open when it is warm and close when it is cooler. • Plants responds to the environment. Light is one of the most important environmental signals for plant development. This phenomenon is called photomorphogenesis and one classic example is etiolation.
- 19. PHYSICALAND BIOLOGICAL DANGERS IN THE ENVIRONMENT • A non-motile organism cannot flee when conditions get tough. It must "fight" it out. Both the physical environment and biological environment threaten the well being of plants Physical dangers - wind, water (flood), drought, cold (winter) are among the physical dangers that a plant faces Biological dangers - predators (=herbivores) and competitors (=other plants)
- 20. PHYSICAL DANGERS - how do plants cope? • In general, plants cope with these by dormancy, senescence, and even death • The evergreen and deciduous lifestyle are in part a response to adverse conditions • Evergreens are much better able to tolerate cold, dry conditions. They also do better in poor soil because they don't loose as many leaves • Plants also respond to environmental challenges morphologically - for example, reduce their Surface area/Volume ratio to minimize water loss
- 21. Biological dangers - predators (=herbivores) and competitors (=other plants)
- 22. Mimicry- "tricking"predators. E.g. lithops in S. African deserts look likepebbles - are stonemimics. mistletoeleaves look just likethehost tree leaves to avoid being eaten. Someplants, likewild tobacco, when attackedby herbivores releasevolatile chemicalsthat summon predatory insects to the damaged plants. Theseinsectsin turn, kill theherbivores.
- 23. • Produce toxic chemicals. Allelopathy is chemical warfare between plants. • Phytoalexins are chemicals produced by plants to resist microbial infection.
- 25. Properties and functions of water Properties •a liquid at physiological temperatures (i.e., between 0-100 C) - water has a high boiling point and a high melting point •has a high heat of vaporization - it takes a lot of energy to convert water from a liquid to a gas; Water resists evaporation. •has a high specific heat (heat capacity)- It takes a lot of energy to raise the temperature of water. Thus, water is slow to heat up and cool down, i.e. water resists temperature changes. •has a high heat of fusion- It takes a lot of energy to convert water from a solid to a liquid, or put another way, water resists freezing
- 26. • has a high surface tension - It takes a lot of energy to break through the surface of water Thus, water acts as though it has a skin. • The density of water decreases on crystallization • a universal solvent • has high tensile strength and incompressibility • transparent to light • chemically inert • dissociates into protons and hydroxide ions - basis for the pH system • Water affects the shape, stability & properties of biological molecules
- 27. FUNCTIONS OF WATER • is a major component of cells • is a solvent for the uptake and transport of materials • is a good medium for biochemical reactions • is a reactant in many biochemical reactions (e.g., photosynthesis) • provides structural support via turgor pressure (i.e., leaves) • is the medium for the transfer of plant gametes (sperms swim to eggs in water, some aquatic plants shed pollen underwater) • offspring (propagule) dispersal (think "coconut") • plant movements are the result of water moving into and out of those parts (i.e., diurnal movements, stomatal opening, flower opening) • cell elongation and growth • thermal buffer
- 28. WATER TRANSPORT IN PLANTS
- 30. • There are two major ways to move molecules in plants. These are: i) Bulk or mass flow: is the mass movement of molecules in response to a pressure gradient. The molecules move from hi → low pressure, following a pressure gradient i) Diffusion: This is the net, random movement of individual molecules from one area to another. The molecules move from high → low, following a concentration gradient.
- 32. Specialized forms of diffusion Osmosis: it represents the diffusion of a solvent (typically water) across a membrane.
- 33. Dialysis: another specialized case of diffusion; however is different from osmosis because it involves the movement of a solute and not a solvent as is the case with osmosis. It is the diffusion of solute across a semi-permeable membrane e.g. - consider a cell containing a sugar dissolved in water. If water (the solvent) moves out of the cell into the surroundings it moves osmotically; if the sugar (solute) moves into the surroundings, it is an example of dialysis
- 34. Factors influencing the rate of diffusion • A. Concentration Gradient. - from an area of high concentration to one of lower concentration. Fick’s Law - is an equation that relates the rate of diffusion to the concentration gradient (C1 – C2) and resistance (r). Diffusion rate, also called flux density (Js, in units of mol m-2 s-1) can be expressed in the simplified version of Fick's equation as: Js = (C1 - C2) / r • Molecular Speed • Temperature - increases the rate of molecular movement, therefore, increases the rate of diffusion • Pressure - increases speed of molecules, therefore, increase the rate of diffusion • Solute effect on the chemical potential of the solvent- Solute particles decrease the free energy of a solvent.
- 35. WATER POTENTIAL Definition: Water potential is a measure of the energy state of water. This is a particularly important concept in plant physiology because it determines the direction and movement of water. • Equation for water potential (must account for the factors that influence the diffusion of water) Ψw= Ψp + Ψs + Ψg • Where: Ψw = water potential; Ψp = pressure potential; Ψs = solute or osmotic potential; Ψg = gravity potential
- 36. Important terms • Solute (or osmotic) potential (Ψs): This is the contribution due to dissolved solutes. Solutes always decrease the free energy of water, thus their contribution is always negative • Pressure Potential; (Ψp): Due to the pressure build up in cells. It is usually positive, although may be negative (tension) as in the xylem. • Matric potential: This is the contribution to water potential due to the force of attraction of water for colloidal, charged surfaces. It is negative because it reduces the ability of water to move. However, it can be very important in the soil, especially when referring to the root/soil interface. • Gravity (Ψg): Contributions due to gravity which is usually ignored unless referring to the tops of tall trees.
- 37. Terms used for Solutions • Hypertonic Solution: a higher solute concentration outside the cell than the cytoplasm. Water diffuses out of the cell. Protoplast and vacuoles will shrink causing the plasma membrane to pull away from the cell wall - called plasmolysis
- 38. Isotonic solution: has the same concentration inside and outside the cell. No net movement of water.
- 39. Hypotonic solution: refers to a solution that contains less Solute (more water) outside compared to the inside of the of the cell
- 40. HOW DOES WATER MOVE TO THE TOP OF TREES?
- 43. •We defined Autotrophs as organisms that are able to synthesize organic molecules (A molecule that contains both carbon and hydrogen) from inorganic materials •Photoautotrophs - are organisms that use light as an energy source and carbon dioxide as its carbon source; absorb and convert light energy into the stored energy of chemical bonds in organic molecules through a process called photosynthesis.
- 45. • Plants, algae, and bacteria known as cyanobacteria are known as oxygenic photoautotrophs - they synthesize organic molecules from inorganic materials, use water as an electron source, and generate oxygen as an end product • Some bacteria, such as the green and purple bacteria, are known as anoxygenic phototrophs - do not use water as an electron source during photosynthesis and, as a result, do not evolve oxygen • The electrons come from compounds such as hydrogen gas, hydrogen sulfide, and reduced organic molecules
- 46. In this section on photosynthesis, we will be concerned with the oxygenic phototrophs • Photosynthesis is composed of two stages: i) the light-dependent reactions ii) the light-independent reactions.
- 47. • The light-dependent reactions convert light energy into chemical energy, producing ATP and NADPH- occur in the thylakoids • The light-independent reactions use the ATP and NADPH from the light-dependent reactions to reduce carbon dioxide and convert the energy to the chemical bond energy in carbohydrates such as glucose - Occur in the stroma ATP- Adenosinetriphosphate NADPH is the reduced form ofNADP (Nicotinamideadeninedinucleotide phosphate)
- 48. The overall reaction for photosynthesis Note that carbon dioxide is reduced to produce glucose while water is oxidized to produce oxygen
- 49. Before the photosynthetic reactions- need to understand the electromagnetic spectrum and chloroplasts • Visible light constitutes a very small portion of a spectrum of radiation known as the electromagnetic spectrum. • All radiations in the electromagnetic spectrum travel in waves and different portions of the spectrum are categorized by their wavelength. • At one end of the spectrum are television and radio waves with longer wavelengths and low energy. • At the other end of the spectrum are gamma rays with a very short wavelength and a great deal of energy. • Visible light is the range of wavelengths of the electromagnetic spectrum that humans can see, a mixture of wavelengths ranging from 380nm to 760nm. It is this light that is used in photosynthesis.
- 50. • Light and other types of radiation are composed of individual packets of energy called photons (A particle of electromagnetic radiation; a single unit of radiant energy) • The shorter the wavelength of the radiation, the greater the energy per photon • When photons of visible light energy strike certain atoms of pigments during photosynthesis, that energy may push an electron from that atom to a higher energy level where it can be picked up by an electron acceptor in an electron transport chain
- 51. Interaction between a Photon and an Atom ATP can then be generated by chemiosmosis which is the production of ATPutilizing the energy released when hydrogen ions flow through an ATP synthase complex
- 52. CHLOROPLASTS • In eukaryotic cells, photosynthesis takes place in organelles called chloroplasts
- 53. • Chloroplasts are surrounded by an inner and an outer membrane. • The inner membrane encloses a fluid-filled region called the stroma that contains enzymes for the light- independent reactions of photosynthesis. • Infolding of this inner membrane forms interconnected stacks of disk-like sacs called thylakoids, often arranged in stacks called grana. • The light-dependent reactions of photosynthesis occur in the thylakoids
- 54. Pathways used in the synthesis of carbohydrates • Different plants follow different pathways in the synthesis of carbohydrates. • These pathways are: - C3 (Calvin cycle), - C4 and - the CAM pathways
- 55. The Calvin cycle (C3 pathway) • Most plants use the Calvin (C3) cycle to fix carbon dioxide • C3 refers to the importance of 3-carbon molecules in the cycle • There are three stages to the Calvin cycle: - CO2 fixation - Production of G3P - Regeneration of RuBP
- 56. Stage 1: CO2 fixation • To begin the Calvin cycle, a molecule of CO2 reacts with a five-carbon compound called ribulose bisphosphate (RuBP) producing an unstable six- carbon intermediate which immediately breaks down into two molecules of a three-carbon compound- phosphoglycerate (PGA • The carbon that was a part of inorganic CO2 is now part of the carbon skeleton of an organic molecule. • The enzyme for this reaction is ribulose bisphosphate carboxylase (Rubisco)
- 57. Stage 2: Production of G3P from PGA • The energy from ATP and the reducing power of NADPH (both produced during the light-dependent reactions) is now used to convert the molecules of PGA to glyceraldehyde-3-phosphate (G3P), another three-carbon compound • For every six molecules of CO2 that enter the Calvin cycle, two molecules of G3P are produced
- 58. Stage 3: Regeneration of RuBP from G3P • 10 of every 12 G3P produced - are used to regenerate the RuBP so that the cycle may continue • Ten molecules of the three-carbon compound G3P eventually form six molecules of the four-carbon compound ribulose phosphate (RP) • Each molecule of RP then becomes phosphorylated by the hydrolysis of ATP to produce ribulose bisphosphate (RuBP)
- 59. THE C4 PATHWAY • The C4 pathway is designed to efficiently fix CO2 at low concentrations and plants that use this pathway are known as C4 plants • This occurs in cells called mesophyll cells. First, CO2 is fixed to a three-carbon compound called phosphoenolpyruvate to produce the four-carbon compound oxaloacetate • The enzyme catalyzing this reaction, PEP carboxylase
- 60. • The oxaloacetate is then converted to another four- carbon compound called malate in a step requiring the reducing power of NADPH • The malate then exits the mesophyll cells and enters the chloroplasts of specialized cells called bundle sheath cells. Here the four-carbon malate is decarboxylated to produce CO2, a three-carbon compound called pyruvate, and NADPH • The CO2 combines with ribulose bisphosphate and goes through the Calvin cycle while the pyruvate re-enters the mesophyll cells, reacts with ATP, and is converted back to phosphoenolpyruvate, the starting compound of the C4 cycle.
- 61. THE CAM PATHWAY • CAM plants live in very dry condition and, unlike other plants, open their stomata to fix CO2 only at night • Like C4 plants, they use PEP carboxylase to fix CO2, forming oxaloacetate. • The oxaloacetate is converted to malate which is stored in cell vacuoles. During the day when the stomata are closed, CO2 is removed from the stored malate and enters the Calvin cycle
- 62. PHOTOSYNTHESIS Photosynthesis Light reaction, Calvin cycle, Electron Transport 3D Animation.mp4 PhotosynthesisPart 5- C4 and CAM.mp4