02 Crop Adaptations

Crop adaptationsCrop adaptations

• Adaptations of the leaves in CAdaptations of the leaves in C44 plants (e.g. plants (e.g. sugarcane and maize):sugarcane and maize):– In photorespiration, enzyme Rubisco acts as In photorespiration, enzyme Rubisco acts as

catalyst for combination of Ocatalyst for combination of O22 with RuBP with RuBP instead of COinstead of CO22

– Results in overall intake of OResults in overall intake of O22 and output of and output of COCO22 and means that less RuBP is available for and means that less RuBP is available for COCO22 fixation fixation

– Tropical grasses have a leaf structure which Tropical grasses have a leaf structure which allows them to avoid photorespirationallows them to avoid photorespiration

– Such plants are referred to as CSuch plants are referred to as C44 plants plants ALBIO9700/2006JK

ALBIO9700/2006JK

• Structural features of the leaves which Structural features of the leaves which distinguish Cdistinguish C44 plants: plants:– Groups of cells around vascular bundle (Groups of cells around vascular bundle (bundle bundle

sheath cellssheath cells) – contain RuBP and Rubisco but no ) – contain RuBP and Rubisco but no contact with air (low concentrations of Ocontact with air (low concentrations of O22))

– Mesophyll cellsMesophyll cells around bundle sheath cells – no air around bundle sheath cells – no air spaces between them, ensuring no Ospaces between them, ensuring no O22 reaches the reaches the bundle sheath cellsbundle sheath cells

– Mesophyll cells contain an enzyme (Mesophyll cells contain an enzyme (PEP PEP carboxylasecarboxylase) – catalyses combination of CO) – catalyses combination of CO22 with a with a compound called phosphoenolpyruvate (PEP) – compound called phosphoenolpyruvate (PEP) – formation of oxaloacetateformation of oxaloacetate

– Oxaloacetate converted to malate – passed on to the Oxaloacetate converted to malate – passed on to the bundle sheath cells – CObundle sheath cells – CO22 removed and combined removed and combined with RuBP – Calvin cyclewith RuBP – Calvin cycle ALBIO9700/2006JK

Corn leaf t.s. showing bundle Corn leaf t.s. showing bundle sheaths sheaths

ALBIO9700/2006JK

How sorghum is adapted to survive in How sorghum is adapted to survive in arid environmentsarid environments

• Fifth most important cereal crop that’s able to grow in Fifth most important cereal crop that’s able to grow in areas of low water supply and shows areas of low water supply and shows xerophytexerophyte characteristics:characteristics:– Dense root system – widespread and deep – efficient uptake of Dense root system – widespread and deep – efficient uptake of

waterwater– Leaves covered with thick, waxy cuticle – reduces evaporationLeaves covered with thick, waxy cuticle – reduces evaporation– Specialised Specialised motor cellsmotor cells (bulliform cells) on upper-side of leaves (bulliform cells) on upper-side of leaves

and strengthening tissue (sclerenchyma) below vascular bundles and strengthening tissue (sclerenchyma) below vascular bundles – cause leaf to roll inward when water is in short supply (hiding – cause leaf to roll inward when water is in short supply (hiding stomata). Build up of water vapour – reducing diffusion of water stomata). Build up of water vapour – reducing diffusion of water vapour from leavesvapour from leaves

– Number of stomata is low and air spaces inside leaf are small – Number of stomata is low and air spaces inside leaf are small – found away from vascular tissuefound away from vascular tissue

– CC44 plant – can continue photosynthesis even when very hot and plant – can continue photosynthesis even when very hot and sunny as long as there is sufficient watersunny as long as there is sufficient water

ALBIO9700/2006JK

ALBIO9700/2006JK

Sorghum Sorghum

ALBIO9700/2006JK

• ‘‘Swamp plants’Swamp plants’• Partly submerged in paddy fields – fields Partly submerged in paddy fields – fields

flooded, ploughed and young rice plants flooded, ploughed and young rice plants planted in mudplanted in mud

• OO22 levels in mud fall rapidly (used by levels in mud fall rapidly (used by bacteria in mud) and remain very low in bacteria in mud) and remain very low in flooded paddy fields since Oflooded paddy fields since O22 can only can only diffuse slowly through waterdiffuse slowly through water

How rice is adapted to grow with How rice is adapted to grow with its roots submerged in waterits roots submerged in water

ALBIO9700/2006JK

ALBIO9700/2006JK

• Rice plants adaptations which allow then Rice plants adaptations which allow then to grow in conditions of low Oto grow in conditions of low O22 availability: availability:– Stems and leaves possess very large air Stems and leaves possess very large air

spaces – allow Ospaces – allow O22 to get through to the roots to get through to the roots from the airfrom the air

– Roots are very shallow – allows them some Roots are very shallow – allows them some access to the higher levels of Oaccess to the higher levels of O22 in the surface in the surface waterwater

– Roots able to respire anaerobically – Roots able to respire anaerobically – production of alcohol (usually toxic). Rice root production of alcohol (usually toxic). Rice root cells show an unusually high tolerance to cells show an unusually high tolerance to alcohol – able to produce high levels of the alcohol – able to produce high levels of the enzyme enzyme alcohol dehydrogenasealcohol dehydrogenase

ALBIO9700/2006JK

Rice leaf t.s.Rice leaf t.s.