Week 6 Botany Notes
Week 6 Botany Notes PLSC101010
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This 6 page Class Notes was uploaded by Sophie Menos on Friday October 7, 2016. The Class Notes belongs to PLSC101010 at University of Delaware taught by Bais,Harsh in Fall 2016. Since its upload, it has received 9 views. For similar materials see Botany I in Plant Science at University of Delaware.
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Date Created: 10/07/16
Phloem Transport 10/4/16 phloem vascular system • translocation of photosynthate fates of G3P • conversion to starch in chloroplast • export to cytosol as trioseP • conversion to sucrose in cytosol o can accumulate in vacuole o can be transported to other tissues phloem transport • highly specialized process for transporting o photosynthates o other organic compounds § metabolites § hormones o some mineral nutrients • redistributed from o SOURCE ----- SINK o source § any exporting region that produces photosynthate above and beyond that of its own needs § ex mature leaves o sink § any non-photosynthetic organ or an organ that does not produce enough photosynthate to meet its own needs § ex immature leaves, tubers, roots, fruits the flow of water in plants is almost always from roots to leaves translocation of sucrose can be in any direction – depending on source and sink location and strength not all sources supply all sinks in a plant, certain sources preferentially supply specific sinks source-sink pathways follow patterns • proximity of source to sink is a significant factor o upper nature leaves usually provide photosynthates to growing shoot tip and immature leaves o lower leaves supply predominantly the root system o intermediate leaves export in both directions Phloem Transport 10/4/16 • development – importance of various sinks may shift during plant development o roots and shoots major sinks during vegetative growth o fruits become dominant sinks during reproductive development • vascular connections o source leaves preferentially supply sinks with direct vascular connections o a given leaf is connected via vascular system to leaves above and below in the stem • modification of translocation pathways o interference with a translocation pathway by mechanical wounding (or pruning) o vascular interconnections can provide alternate pathways for phloem transport What is transported in phloem? • sucrose o made up from glucose and fructose • water • nitrogen in o amino acids o amides • proteins • sugars NOT found in phloem o carbohydrates § non-reducing sugars because they are less reactive § ex glucose, mannose, fructose Phloem structure • main components o sieve elements § no nucleus and a sparse collection of other organelles o companion cells § provides energy Summary • Pathway o sugars and other organic materials are conducted throughout the plant in the phloem by means of sieve elements § sieve elements display a variety of structural adaptations that make them well suited for transport • Patterns Phloem Transport 10/4/16 o materials are translocation in phloem from sources (mature leaves) to sinks (roots, immature leaves) • Materials o translocated solutes are mainly carbs o sucrose is most common translocated sugar o amino acids, proteins, inorganic ions, plant hormones • Rate o movement in phloem is rapid average 1 meter/ hour Essential Elements 10/7/16 1:31 PM plants are photo-autotrophic • they use light energy to build inorganic minerals into organic compounds • they need inorganic nutrients nutrients • macro – required in large amounts o 96% - H O N C o non-mineral elements § carbon § hydrogen § oxygen o primary nutrients § nitrogen § phosphorus § potassium o secondary § calcium § magnesium § sulfur • micro – required in small amounts, minor or trace elements o iron o copper o zinc o boron o molybdenum o manganese o chlorine Deficiency • symptoms o chlorosis o necrosis o stunted growth o deformity • critical concentration o plant tissue concentration of an element just below the level that gives max growth • deficient concentration o tissue concentration below the critical concentration • adequate concentration o tissue concentration above critical concentration o growth does not increase any more even if concentration increases Mineral uptake from soil • influenced by o soil type o environmental conditions § influence mineral abundance and bioavailability • Iron Uptake o Strategy I (most plants) § phenolic compound secreted by root § binds Fe3+ , brings it to root surface § Fe-reductase in membrane reduced Fe3+ to Fe2+ § released by phenolic compound § taken up by membrane carrier o Strategy II (grasses) § phytosoiderophores (PS) secreted by root § bind Fe3+ bring it to root surface § entire complex is taken up § after uptake: Fe3+ reduced to Fe2+ § released from PS o differences between the two = the entire complex is taken up and iron is reduced after uptake then released Molecular transport across membranes • passive o requires no energy o high concentration – low concentration o diffusion § through bilayer ú not specific § through channel ú not specific § via carrier ú specific § via membrane protein: facilitated diffusion • active o requires energy (ATP) o can go against concentration gradient o always involves membrane protein o molecules pumped across membrane against concentration gradient
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