4+NutrientCycles_EcolOfPhotosynt

C4 spatial separation of light dependent reactions

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Unformatted text preview: ve affinity for CO2? C4 - spatial separation of light-dependent reactions from C-fixation - initial fixation with PEP-carboxylase to 4-C compound (malate) (high affinity for CO2; no photorespiration) - then CO2 released to C3 pathway (still have C3 biochemistry) - initial 4-C fixation in mesophyll cell - 4-C compound diffuses to bundle sheath cells - CO2 released within bundle sheath cell mesophyll cells bundle-sheath cells - mostly monocots (grasses, sedges) 50% all grasses; few dicots (< 1%) - mostly subtropical & tropical - several important crops (corn, sugar cane, sorghum, millets) raise [CO2] in bundle-sheath ➡ lower [CO2] in leaf spaces ➡ RuBisCO works better more diffusion of CO2 into leaf - derived pathway - many independent origins CAM - temporal separation of light-dependent reactions & C-fixation - initial fixation with PEP-carboxylase to malate, storage - CO2 released to C3 pathway during day - stomata open at night - better H2O preservation - lower rates of photosynthesis - daytime photosynthesis constrained by storage capacity of vacuole - usually have fleshy water-storing leaves/stems - derived pathway many independent origins desert succulents many tropical epiphytes (orchids, bromelidas), - some aquatic plan...
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