Phloem plant physiology by sohail

phloem
translocation
pattern of translocation
Sieve tubes
Sieve tube members
companion cells
Phloem sap
source
sink
source sink relationship
Source-sink pathways follow patterns
Materials transported
Composition of phloem sap in castor bean(Ricinus communis)
The mechanism of phloem transport
The Pressure -Flow Model
THE PRESSURE-FLOW HYPOTHESIS
PROCESS OF TRANSLOCATION OF FOOD
MECHANISM OF TRANSLOCATION OF FOOD THROUGH THE PHLOEM effect by
summary

1. TRANSPORT IN PHLOEM

2. PRESNETED BY: M.SOHAIL RIAZ PRESENTED TO: MISS IQRA MUNIR

3. phloem The phloem is the tissue that translocates the products of photosynthesis from mature leaves to areas of growth and storage, including the roots TRANSLOCATION: Is the transport of organic nutrients in the plant

4. Cont ……… Translocation stops if the phloem tissue is killed Translocation proceeds in both directions simultaneously (but not within the same tube) Translocation is inhibited by compounds that stop production of ATP in the sugar source

5. cont ……. Things Phloem Made of Living cells Cell wall thin Cell wall material Cellulose Permeability of cell wall permeable Cross walls Perforated cross walls called sieve plates

6. PATHWAYS OF TRANSLOCATION The two long-distance transport pathways—the phloem and the xylem—extend throughout the plant body The phloem is generally found on the outer side of both primary and secondary vascular tissues In plants with secondary growth the phloem constitutes the inner bark

7. Cont ……… The cells of the phloem that conduct sugars and other organic materials throughout the plant are called sieve elements . Sieve element is a comprehensive term that includes both the highly differentiated sieve tube elements typical of the angiosperms and the sieve cells of gymnos perm s . In addition to sieve elements, the phloem tissue contains companion cells and parenchyma cells

8. Cont ……… In some cases the phloem tissue also includes fibers and sclereids (for protection and strengthening of the tissue) and laticifers (latex-containing cells) However, only the sieve elements are directly involved in translocation.

9. phloem Food and minerals move through tubes formed by chains of cells, sieve-tube members: Sieve plates Companion cell

10. Sieve plates An area of relatively large pores present in the common end walls of sieve tube elements Sieve plates  are mostly  located  on the overlapping adjacent end walls They are slender,  tube -like structures composed of elongated thin-walled cells, placed end to end The main  function of sieve tubes  is to transport sugars and nutrients up and down the plant

11. Sieve-tube members Characteristics: Living cells arranged end-to-end to form food conducting cells of the phloem Lack lignin in their cell walls Mature cells lack nuclei and other cellular organelles Alive at functional maturity Its function is to transport products of photosynthesis

12. Companion cells Characteristics: Connected to sieve-tube members via plasmodesmata Transport of sugar from source to sink occur through companion cells FUNCTIONS: Support sieve-tube members May assist in sugar loading into sieve-tube members

13. Phloem sap Is an aqueous solution that is mostly sucrose Travels from a sugar source to a sugar sink

14. Citrus sinensis  L. Osbeck (Sweet Orange)

15. Source: Any exporting organ Storage organ during export phase mature leaves SINK: Any non-photosynthetic organ that does not produce enough photosynthetic products to support their own growth and development

16. Source-sink relationships Source-sink relationships can explain the direction of phloem translocation within the plant Source - produces more carbohydrates than required for its own needs Sink - produces less carbohydrates than it requires

17. Source-sink pathways follow patterns Although the overall pattern of transport can be stated as source to sink Not all sources supply all sinks in a plant Certain sources supply specific sink Proximity of source to sink is a significant factor. Importance of various sinks may shift during plant development Roots and shoots major sinks during vegetative growth

18. CONT……… Fruits become dominant sinks during reproductive development Young leaf is completely dependent on carbohydrates from other sources. So it is a strong sink As the leaf grows it increasingly provides for its own carbohydrate needs Mature leaf is largely a carbohydrate exporter (source)

19. Materials transported The phloem is the vascular system for moving (translocating) sugars produced in photosynthesis and other substances throughout the plant.

20. Composition of phloem sap in castor bean( Ricinus communis ) components concentration Sugar 80.0-106.0 Amino acids 5.2 Organic acids 2.0-3.2 Protein 1.45-2.20 Potassium 2.3-4.4 Chloride 0.355-0.675 Phosphate 0.350-0.550 Magnesium 0.109-0.122

21. The mechanism of phloem transport Phloem transports sugars from a “source” to a “sink” In source tissue: Sugars are moved from photosynthetic cells and actively loaded (uses ATP energy) into companion cells and sieve tube elements.

22. The Pressure -Flow Model Phloem loading leads to a buildup of sugars (the phloem cells become hypertonic) Due to which: 1. Solute potential decreases 2. Water potential decreases In response, water enters sieve elements from xylem via osmosis Thus phloem turgor pressure increase

23. In sink tissue: Phloem unloading leads to lower sugar concentration (the phloem cells become hypotonic) Due to which: 1. Solute potential increases 2. Water potential increases So, Water leaves the phloem and enters sink sieve elements and xylem (via osmosis) Thus phloem turgor pressure decreases

24. THE PRESSURE-FLOW HYPOTHESIS The best-supported theory to explain the movement of food through the phloem is called the pressure-flow hypothesis The pressure-flow theory explains how sap moves in a plant from source to sink

25. PROCESS OF TRANSLOCATION OF FOOD Sugars begin at a source and are pumped into phloem tube cells Osmosis moves water into the cells and raises pressure Pressure moves the sap The leaf is a source of sugar, since it makes sugar by photosynthesis Glucose and fructose made by photosynthesis are linked to make sucrose

26. Cont …… Active transport is used to load sucrose into phloem tubes against a diffusion gradient The high concentration of sucrose in the sieve tube cells of the phloem causes water to move in by osmosis, which raises pressure and causes the sap to move A developing fruit is one example of a sink Sucrose may be actively transported out of phloem into the fruit cells

27. Cont …….. In a root, sucrose is converted into starch, which keeps sugar moving in by diffusion As the sugar concentration drops in the sieve tube cells, osmosis moves water out of the tube As water moves out by osmosis, the pressure in the sieve tube cells drops The pressure difference along the column of sieve tube cells keeps the sap flowing

28. MECHANISM OF TRANSLOCATION OF FOOD THROUGH THE PHLOEM effect by: Translocation through the phloem is dependent on metabolic activity of the phloem cells Chilling its petiole slows the rate at which food is translocated out of the leaf Oxygen lack also depresses it Killing the phloem cells puts end to it

29. summary Locations that produce or release sugars for the growing plant are referred to as  sources . Sugars produced in sources, such as leaves, need to be delivered to growing parts of the plant via the phloem in a process called  translocation , or movement of sugar The points of sugar delivery, such as roots, young shoots, and developing seeds, are called  sinks .

30. Thank you