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Translocation - Coggle Diagram

- - - - ASK if pathway/involved chemicals should be memorized
  - - - must be loaded into sieve elements in source
      - must move out of sieve elements in sink or induce second messenger
      - must alter cellular process in sink
    - - protein relating to Flowering Locus T
      - RNAs
- - - - in apoplastic unloading, invertase cleaves sucrose in cell wall
      - in symplastic unloading, sucrose synthase cleaves sucrose in cell
- - - - mature leaves
      - storage organs during exporting phase of development, including seed germination and beginning of second growing season
  - - - non-photosynthetic tissues such as roots, tubers, bulbs, corms
      - organs that do not produce enough photosynthate to meet needs such as developing leaves and fruit
  - - - reporter genes used to show where transporters would normally be expressed
- - - - sieve tube elements in angiosperms
      - sieve tube members in gymnosperms
    - - ordinary companion cells
      - transfer cells
      - intermediate cells
  - - - synthesized in companion cell and transported into sieve elements to from filaments and bodies
      - present exclusively in some angiosperms, including all dicots and some monocots
      - during development:
        
        present as discrete P-protein bodies in immature sieve elements
        
        dispersed into fibrillar or tubular forms in mature sieve elements
    - - synthesized in PM and deposited in cell wall
      - accumulates in sieve areas to form plug pores
      - induced by damaged seive elements, mechanical stimulation, temperature, and dormancy
- - - - exogenously applied 14C sugars rapidly accumulate in minor veins
      - solutes in apoplast diffuse to vascular tissue
      - companion cells actively accumulate solutes from apoplast and transfer solutes to sieve elements
      - used by plants that export sucrose
      - bundle sheath cells and hloem parencyma cells lack plasmodesmata connections with companion cells
      - sugars must exit symplast into apoplast
      - companion cells actively take up sugars from apoplast and transfer sugars to sieve elements
      - H+ sucrose co transport occurs via ATPase creating H+ gradient; sucrose symporters localized to companion cell using flourescent Ab
      - PCMBS treatment inhibits sucrose transporter and prevents sucrose uptake from apoplast
    - - types:
        
        passive symplastic loading
        
        occurs in many tree species that only translocate sucrose
        
        abundant PD between SE/CC complex and surrounding cells
        
        lack intermediary cells; utilize ordinary companion cells
        
        no concentrating step between mesophyll cells and SE/CC complex
        
        sucrose moves by diffusion along concentration gradient
        
        polymer trapping (active)
        
        used by plants that export other non-reducing sugars in addition to sucrose
        
        sucrose moves by diffusion: mesophyll cells to budnle sheath cells to intermediary cells
        
        sucrose used to synthesize larger sugars in intermediary cells
        
        maintains sucrose gradient for diffusion
        
        larger sugars too large to diffuse back to bundle sheath cells
        
        high concnetration of sugars in intermediary cells promotes diffusion into sieve elements
      - occurs in plants that translocate other non-reducing sugars in addition to sucrose, as well as many trees that only translocate sucrose
      - sugars synthesized in mesophyll cells move to companion cells and sieve elements via plasmodesmata
      - sugars do not cross a PM as they move cell to cell
- - - - chilling to reduce metabolic rate and reduce translocation to sink
      - removal of one sink to increase translocation to alternative sinks
      - increased fruit load decreases translocation to other sinks, especially roots
      - decreased water potential in roots achieved by application of PEG or mannitol solution favors translocation to roots over shoots
      - sucrose synthase and invertase activities correlate with sink strength
      - elevated CO2 levels increases photosynthesis and increases translocation to sinks
  - - - constant shoot:root ratio not the goal
      - goal: obtaining appropriate supply of fixed C and minerals to meet plant needs
    - - turgor pressure
      - chemical messengers such as hormones, macromolecules, nutrients, transport sugars
      - sugars regulating gene expression, with carbohydrate depleting increasing photosynthetic and reserve mobilization and export processes genes, and carbohydrate abundance increasing C storage and C utilization genes
      - sucrose loading in source stimulated by auxin and inhibited by ABA
      - sucrose unloading in sink stimulated by ABA and inhibited by auxin