Crop physiology

• Photosynthetic rates are highest at temperatures between 15-30°C, with an optimum around 25°C.
• High temperatures can cause enzyme denaturation or damage to chlorophyll pigments, leading to decreased photosynthetic efficiency.
• The rate of photosynthesis is influenced by the amount of light, temperature, CO2 concentration, water availability, nutrient supply, and plant age.
• Temperatures above the optimum can cause damage to enzymes involved in photosynthesis.
• High light intensity is beneficial up to a certain point but beyond that it becomes detrimental due to photodamage.
• Low temperatures also affect photosynthesis by reducing the rate of electron transport and ATP synthesis.
• Increasing temperature above TNZ leads to increased respiration and reduced net carbon gain due to higher energy requirements.
• Light intensity affects the rate of photosynthesis through photochemical reactions that convert absorbed energy into chemical energy.
• The rate of photosynthesis increases as CO2 concentration increases until saturation occurs.
• Temperature influences the rate of photosynthesis as it determines the speed of biochemical reactions involved in the process.
• The optimal temperature range for photosynthesis is typically within the thermo neutral zone (TNZ) where metabolic heat production equals heat loss.
• CO2 concentration directly impacts the rate of photosynthesis due to its role in the Calvin cycle.
• Water stress reduces stomatal conductance, which limits gas exchange and affects photosynthesis.
• Light intensity affects the rate of photosynthesis through photon flux density (PFD) and quantum yield.
• Photosynthetic rates increase with increasing light intensity until saturation occurs at high intensities.
• Light intensity affects photosynthesis through its effect on the rate of electron transfer reactions and the activity of Calvin cycle enzymes.
• CO2 levels affect photosynthesis as plants require carbon dioxide to produce glucose through the Calvin cycle.
• First half of discussion

  1. Role of light in photosynthesis

  2. History of photosynthesis and how the photosynthetic apparatus were discovered

  3. How the process of photosynthesis starts

  4. What are the steps

  5. What are the end products of light reaction

  
• Light


  Particle nature
• Light


  • Has frequency-like properties when used a prism to split sunlight into its component colors
  • Has both particle nature and wave nature

  
• Huygens' principle


  Established by Dutch physicist Christian Huygens in 1678, the wave theory of light

  
• Leaf structure


  • Cuticle
  • Epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Guard cells
  • Stoma/stomata
  • Vascular bundle
• Pigment


  Groups of light absorbing molecules
• Chlorophyll


  Pigment in green plants
• Stages of photosynthesis


  • Photo stage: light dependent reactions, energy fixing reactions, convert light energy to make ATP & NADPH
  • Synthesis stage: "dark" / light-independent reactions, Calvin cycle, carbon fixing reactions, uses ATP to convert inorganic molecules to organic fuel containing stored potential energy in the bonds

  
• Cyclic electron flow


  Non-cyclic electron flow: Z-scheme
• Dark reaction


  Second step in the mechanism of photosynthesis, chemical processes occurring independent of light, takes place in the stroma of chloroplast, slower than light reaction, occurs also in the presence of light, CO2 is fixed to energy rich carbohydrates using ATP and NADPH2 from light reaction

  
• Calvin cycle


  Cyclic reaction occurring in the dark phase of photosynthesis, CO2 is converted into sugars, first stable compound is a 3 carbon compound (3 phosphoglyceric acid), also called C3 cycle, occurs in 4 phases: carboxylative, reductive, carbohydrate formation, regenerative
• Blackman demonstrated the existence of dark reaction, also called Blackman's reaction
• Applied areas of plant physiology

  • Production physiology
  • Stress physiology
  • Growth regulators physiology
  • Nutrio-physiology
• Production physiology


  Deals with the relationship between crop productivity and photosynthesis, factors governing photosynthetic efficiency: net photosynthetic rate, total photosynthetic surface (LAI), leaf area duration (LAD)

  
• Stress physiology


  Deals with biotic stress (insects, pathogens, nematodes, weeds) and abiotic stress (drought, heat, cold, high light, pollution, salinity), study of resistance mechanisms enables selection of resistant crop varieties
• Growth regulator physiology


  Growth regulators used in agriculture for improving yield, quantity of produce, suppressing excessive vegetative growth, rooting of cuttings, killing weeds
• Nutrio-physiology


  Deals with the supply of different nutrients in correct proportions for increased productivity, foliar fertilization for problem soils
• Source


  Leaves and other green tissues that produce photosynthesis (carbohydrates)

  
• Sink


  Organs which utilize the photosynthates for their growth and then store the photosynthates

  
• Assimilate partitioning


  Transport of assimilates (carbohydrates) from source to sink through phloem in the form of sucrose
• Harvest index


  Ratio of economic yield to the biological yield
• Global warming


  Warming of earth surface due to accumulation of gases like CO2, water vapour, methane, oxides of nitrogen, chlorofluorocarbons, leads to rise in temperature and average rise in sea level
• CO2 enrichment


  Increases photosynthesis and productivity, decreases transpiration, increases yield and yield components