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02 Crop Adaptations

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02 Crop Adaptations

  1. 1. Crop adaptations• Adaptations of the leaves in C4 plants (e.g. sugarcane and maize): – In photorespiration, enzyme Rubisco acts as catalyst for combination of O2 with RuBP instead of CO2 – Results in overall intake of O2 and output of CO2 and means that less RuBP is available for CO2 fixation – Tropical grasses have a leaf structure which allows them to avoid photorespiration ALBIO9700/2006JK
  2. 2. ALBIO9700/2006JK
  3. 3. • Structural features of the leaves which distinguish C4 plants: – Groups of cells around vascular bundle (bundle sheath cells) – contain RuBP and Rubisco but no contact with air (low concentrations of O2) – Mesophyll cells around bundle sheath cells – no air spaces between them, ensuring no O2 reaches the bundle sheath cells – Mesophyll cells contain an enzyme (PEP carboxylase) – catalyses combination of CO2 with a compound called phosphoenolpyruvate (PEP) – formation of oxaloacetate – Oxaloacetate converted to malate – passed on to the bundle sheath cells – CO2 removed and combined with RuBP – Calvin cycle ALBIO9700/2006JK
  4. 4. Corn leaf t.s. showing bundle sheaths ALBIO9700/2006JK
  5. 5. How sorghum is adapted to survive in arid environments• Fifth most important cereal crop that’s able to grow in areas of low water supply and shows xerophyte characteristics: – Dense root system – widespread and deep – efficient uptake of water – Leaves covered with thick, waxy cuticle – reduces evaporation – Specialised motor cells (bulliform cells) on upper-side of leaves and strengthening tissue (sclerenchyma) below vascular bundles – cause leaf to roll inward when water is in short supply (hiding stomata). Build up of water vapour – reducing diffusion of water vapour from leaves – Number of stomata is low and air spaces inside leaf are small – found away from vascular tissue – C4 plant – can continue photosynthesis even when very hot and sunny as long as there is sufficient water ALBIO9700/2006JK
  6. 6. Sorghum ALBIO9700/2006JK
  7. 7. How rice is adapted to grow with its roots submerged in water• ‘Swamp plants’• Partly submerged in paddy fields – fields flooded, ploughed and young rice plants planted in mud• O2 levels in mud fall rapidly (used by bacteria in mud) and remain very low in flooded paddy fields since O2 can only diffuse slowly through water ALBIO9700/2006JK
  8. 8. ALBIO9700/2006JK
  9. 9. • Rice plants adaptations which allow then to grow in conditions of low O2 availability: – Stems and leaves possess very large air spaces – allow O2 to get through to the roots from the air – Roots are very shallow – allows them some access to the higher levels of O2 in the surface water – Roots able to respire anaerobically – production of alcohol (usually toxic). Rice root cells show an unusually high tolerance to alcohol – able to produce high levels of the enzyme alcohol dehydrogenase ALBIO9700/2006JK
  10. 10. Rice leaf t.s. ALBIO9700/2006JK

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