Introduction to Phloem Translocation
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Questions and Answers

Which cells in the phloem tissue are primarily responsible for the translocation of substances?

  • Fibers
  • Parenchyma cells
  • Companion cells
  • Sieve elements (correct)

What experimental technique did M. Malpighi use to study phloem transport?

  • Incubation
  • Grafting
  • Girdling (correct)
  • Dissection

What is the primary component that Sieve tube elements are rich in?

  • Glucose
  • Water
  • P-protein (correct)
  • Chlorophyll

Which of these options describes a consequence of girdling on a plant?

<p>Formation of swellings above the girdle (C)</p> Signup and view all the answers

Which type of organisms lack P-protein in their sieve tube elements?

<p>Gymnosperms (C)</p> Signup and view all the answers

In what forms can P-protein appear in sieve tube elements?

<p>Tubular, fibrillar, granular, and crystalline (D)</p> Signup and view all the answers

What role does P-protein serve in sieve elements?

<p>It seals off damaged sieve elements (A)</p> Signup and view all the answers

What type of cells primarily store and release food molecules in phloem tissue?

<p>Companion cells (B)</p> Signup and view all the answers

What role do xylem parenchyma cells serve when modified as transfer cells?

<p>They retrieve and reroute solutes. (D)</p> Signup and view all the answers

What is a distinctive feature of intermediary cells?

<p>They possess a high number of plasmodesmata. (A)</p> Signup and view all the answers

What defines the direction of sap translocation in phloem?

<p>It is from sources to sinks, irrespective of gravity. (B)</p> Signup and view all the answers

What types of organs typically serve as sources in plants?

<p>Mature leaves capable of photosynthesis. (A)</p> Signup and view all the answers

What type of cells are primarily responsible for accumulating sugars during the first year of the wild beet's lifecycle?

<p>Storage roots. (A)</p> Signup and view all the answers

What is the primary function of plasmodesmata in xylem parenchyma and intermediary cells?

<p>They allow for cell communication, though their precise function is unclear. (A)</p> Signup and view all the answers

Which statement is true regarding sinks in plants?

<p>They do not produce enough photosynthetic products for growth. (C)</p> Signup and view all the answers

What can be inferred about the cost of maintaining plasmodesmata in cells?

<p>Their presence signifies a need for significant cellular communication. (B)</p> Signup and view all the answers

What is the primary function of phloem translocation in plants?

<p>To transport assimilates from source leaves to sink tissues (A)</p> Signup and view all the answers

Which term describes the conversion of photoassimilates to storage forms like starch or sucrose?

<p>Carbon allocation (D)</p> Signup and view all the answers

Which of the following tissues surrounds the small veins in the vascular tissue of leaves?

<p>Bundle sheath (C)</p> Signup and view all the answers

What are the cells called that conduct sugars and other organic materials in the phloem?

<p>Sieve elements (B)</p> Signup and view all the answers

Which type of plants primarily exhibit highly differentiated sieve tube elements?

<p>Angiosperms (A)</p> Signup and view all the answers

Phloem translocation is significant from an agricultural perspective mainly because it affects which of the following?

<p>Crop yield and productivity (D)</p> Signup and view all the answers

What role does carbon partitioning serve in plants?

<p>Distribution of photosynthetic energy and carbon (D)</p> Signup and view all the answers

What is the location of phloem in relation to other vascular tissues in plants with secondary growth?

<p>On the outer side of both primary and secondary vascular tissues (B)</p> Signup and view all the answers

What is the primary sugar transported in the phloem?

<p>Sucrose (C)</p> Signup and view all the answers

Which of the following substances is contained in the phloem sap?

<p>Proteins (D)</p> Signup and view all the answers

In which species is photosynthate readily transferred from a partly defruited branch to a partly defoliated branch?

<p>Glycine max (B)</p> Signup and view all the answers

What is the most abundant substance transported in the phloem?

<p>Water (C)</p> Signup and view all the answers

Which of the following hormones has been found in sieve elements?

<p>Both B and C (C)</p> Signup and view all the answers

Which inorganic solute is relatively immobile in the phloem?

<p>Sulfur (D)</p> Signup and view all the answers

What types of proteins found in the phloem are involved in the sealing of wounded sieve elements?

<p>Filamentous P proteins (A)</p> Signup and view all the answers

Which of the following is NOT typically considered part of the phloem transport system?

<p>Lipids (D)</p> Signup and view all the answers

What is the process by which sugars are transported from mesophyll cells to sieve elements called?

<p>Sieve element loading (D)</p> Signup and view all the answers

Which structures are often regarded as a functional unit during the loading of sugars?

<p>Sieve elements and companion cells (C)</p> Signup and view all the answers

What is the first step in the import of sugars into sink cells?

<p>Sieve element unloading (B)</p> Signup and view all the answers

What term describes the transport of photosynthates from the sieve elements to sink cells?

<p>Phloem unloading (A)</p> Signup and view all the answers

Which process describes the movement of sugars from the source to the sink in plants?

<p>Translocation (D)</p> Signup and view all the answers

What term is used to describe the regulation of fixed carbon into various metabolic pathways?

<p>Carbon allocation (D)</p> Signup and view all the answers

After sieve element unloading, how are sugars transported to sink cells?

<p>Using short-distance transport pathways (A)</p> Signup and view all the answers

What happens to sugars in sink cells after they are imported?

<p>They may be stored or metabolized (B)</p> Signup and view all the answers

What is the term used to describe the differential distribution of photosynthates within a plant?

<p>Partitioning (D)</p> Signup and view all the answers

Which two factors determine sink strength?

<p>Sink size and sink activity (B)</p> Signup and view all the answers

What effect does cooling a sink tissue have on photosynthate transport?

<p>It inhibits activities requiring metabolic energy. (C)</p> Signup and view all the answers

Which of these activities can potentially limit the rate of uptake by a sink?

<p>Unloading from sieve elements (A)</p> Signup and view all the answers

What would likely happen if the size of a sink tissue is increased?

<p>Sink strength would increase. (B)</p> Signup and view all the answers

What is the role of acid invertase and sucrose synthase in photosynthate transport?

<p>They catalyze the first step in sucrose utilization. (B)</p> Signup and view all the answers

A mutant corn plant with a defective enzyme for starch synthesis would likely display what characteristic?

<p>Reduced transport to the kernels. (A)</p> Signup and view all the answers

Which of the following statements about sink activity is true?

<p>It includes the rate of uptake of photosynthates per unit weight. (C)</p> Signup and view all the answers

Flashcards

Translocation

The process of moving sugars and other organic molecules throughout a plant.

Photoassimilates

The main source of energy for plants, produced during photosynthesis.

Sinks

Organs or tissues that utilize or store sugars from the source.

Phloem

The tissue that conducts sugars and other organic molecules from the source to the sink.

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Sieve tube elements

Specialized cells in the phloem that transport sugars.

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Carbon partitioning

The process of distributing photosynthetic carbon between different parts of the plant.

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Carbon allocation

The process of turning photoassimilates into either sucrose or starch

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Bundle sheath

The outer layer of cells that surrounds bundles of xylem and phloem in vascular plants.

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What are sieve tube elements?

Specialized cells in the phloem, responsible for transporting sugars throughout the plant. These cells are interconnected by sieve plates, which allow for easy passage of sugars.

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What is P-protein?

A protein found in the sieve tube elements of most angiosperms. It plays a crucial role in sealing off damaged sieve elements, preventing leakage and maintaining efficient sugar transport.

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What is girdling?

A process where the phloem tissue is removed from a stem, interrupting the flow of sugars and nutrients. This technique demonstrates that the phloem is responsible for transporting sugars.

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What are phloem parenchyma cells?

A type of parenchyma cell found in the phloem tissue. These cells store and release food molecules, helping to regulate the supply of sugars to various parts of the plant.

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What are sieve plates?

Small, thickened areas on the cell walls of sieve tube elements. These areas have numerous small pores that allow for the passage of sugars and other molecules between adjacent cells.

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What is translocation?

The process of transporting sugars and other organic molecules throughout the plant. It occurs primarily through the phloem tissue.

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What are companion cells?

Cells in the phloem that are closely associated with sieve tube elements. They provide support and metabolically support the sieve tube elements, ensuring efficient sugar transport.

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What is the vascular cambium?

The vascular cambium is a layer of cells that separates the xylem and phloem tissue. It is responsible for producing new xylem and phloem cells.

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Transfer cells in xylem

Specialized xylem parenchyma cells with numerous plasmodesmata connecting them to surrounding cells. They facilitate the movement of solutes in the xylem.

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Sap

The fluid found in the phloem, containing sugars and other organic molecules.

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Source

Any part of a plant that exports sugars or other organic molecules, like mature leaves.

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Translocation in phloem

The process of moving sugars and other organic molecules from sources to sinks within a plant.

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Companion cells

Cells in the vascular bundle that are connected to sieve tube members via plasmodesmata. They help regulate the movement of sugars in the phloem.

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Intermediary cells

Cells that have many plasmodesmata connecting them to surrounding cells, particularly to the bundle sheath cells, facilitating the efficient transport of sugars.

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Bundle sheath cells

The outer layer of cells surrounding bundles of xylem and phloem in vascular plants. These cells play a vital role in regulating the movement of sugars.

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What is partitioning?

The process of distributing photosynthates within a plant, determining the amount of sugars allocated to different parts.

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What is sink strength?

The amount of sugars a sink can take up, depending on its size and activity.

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What is sink size?

The total weight of a sink tissue.

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What is sink activity?

The rate at which a sink takes up sugars per unit weight.

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How does temperature affect sink activity?

Cooling a sink tissue can reduce its metabolic activity, leading to slower sugar transport.

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How does enzyme deficiency affect sink activity?

A mutant with a defective starch synthesis enzyme transports less sugar to its kernels.

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What is the role of acid invertase and sucrose synthase?

These enzymes are involved in the first step of sucrose utilization, potentially playing a role in sink strength.

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Is the relationship between these enzymes and sink strength proven?

The relationship between these enzymes and sink strength is still being investigated.

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Phloem loading

The movement of sugars from the mesophyll cells to the sieve elements of the smallest veins in a leaf. This is a short distance transport.

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Sieve element unloading

The process where sugars exit the sieve elements of the sink tissues. It's the opposite of loading.

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Short-distance transport (sink tissues)

After sieve element unloading, sugars move to cells in the sink via a short-distance transport pathway.

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Storage and metabolism in sink cells

The process of how sugars are stored or utilized in the sink cells; the final step of translocation.

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Photosynthesis allocation

The process of regulating the distribution of photosynthetic carbon into different metabolic pathways within a plant.

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What is translocation in plants?

The process by which plants move essential materials, like sugars and amino acids, from sources (like leaves) to sinks (like roots or fruits).

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What is the most common sugar transported in phloem?

The main type of sugar transported throughout a plant, typically reaching high concentrations in the phloem.

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What are P-proteins and what is their function?

These are proteins found in sieve tube elements, crucial for sealing off damaged areas and preventing leakage.

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What is the plasticity of the translocation pathway?

The movement of sugars in the phloem is flexible and can adapt to changes in the plant's needs. For example, if the upper leaves are removed, lower leaves can take over the job of supplying sugars to the upper parts of the plant.

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Can sugars be transported between different branches?

Some plants can move sugars from one branch to another, even if they are different branches with different functions. This shows how flexible the translocation system can be.

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What are some examples of other materials transported in the phloem?

Hormones, which are crucial for regulating plant growth and development, travel throughout the plant via the phloem.

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What are examples of inorganic solutes, and how do they move within the plant?

Solutes that move in the phloem include potassium, magnesium, phosphate, and chloride, but nitrates, calcium, sulfur, and iron are relatively immobile.

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Study Notes

Introduction to Translocation in Phloem

  • Translocation is the movement of assimilates (products of photosynthesis) from source leaves to sink tissues where they are stored or metabolized
  • Phloem is the vascular tissue responsible for translocation
  • Phloem bundles are often surrounded by a bundle sheath, which isolates the veins from the intercellular spaces in the leaf
  • Carbon partitioning is the efficient distribution of photosynthetic energy throughout the plant
  • Carbon allocation is the conversion of photoassimilates to sucrose or starch
  • Phloem translocation affects crop yield, herbicide effectiveness, and plant productivity

Pathways of Translocation

  • Phloem is generally found on the outer side of primary and secondary vascular tissues
  • Sieve elements: conduct sugars throughout the plant
    • Sieve tube elements (angiosperms)
    • Sieve cells (gymnosperms)
  • Companion cells: involved in metabolic functions
  • Fibers and sclereids provide support and protection
  • Phloem removal (girdling) experiments show photosynthates move through phloem
  • Water and other inorganic molecules are also transported through the phloem

Companion Cells and Sieve Elements

  • Each sieve tube element is associated with one or more companion cells
  • Companion cells are connected to sieve elements by plasmodesmata
  • Companion cells take over some of the metabolic functions of sieve elements
  • Companion cells contain mitochondria, which provide energy (ATP) to sieve elements
  • Three distinct companion cell types exist in mature, exporting leaves:
    • Ordinary companion cells
    • Transfer cells
    • Intermediary cells

Materials Translocated in Phloem

  • Sucrose is the primary transported sugar
  • Amino acids, hormones, and some inorganic ions are also transported
  • Concentrations of sucrose can range from 0.3 to 0.9 M

Rates of Movement

  • Translocation rates can be measured as velocity or mass transfer rate
  • Mass transfer rates (grams per hour per cm²) are preferred to measure velocity through sieve elements

Pressure-Flow Model of Translocation

  • Phloem translocation is generally explained by the pressure-flow model
  • The model proposes a pressure gradient between source and sink driven by osmotic pressure
  • Phloem loading leads to a lower solute potential and higher turgor pressure at the source
  • Phloem unloading results in higher solute potential and lower turgor pressure at the sink
  • Water moves from high water potential (source) to low water potential (sink)

Phloem Loading and Unloading

  • Phloem loading occurs in mature source leaves
  • Triose phosphate, formed by photosynthesis, is converted to sucrose
  • Sucrose moves from mesophyll cells to sieve elements
  • Sieve element loading concentrates sucrose and other solutes in sieve elements
  • Sieve element unloading occurs in sink tissue
  • Unloading to sink cells is the reverse of the processes in source tissues

Factors Affecting Sink Strength

  • Sink strength is a function of sink size and sink activity
  • Sink size is the total weight of sink tissue and sink activity is the rate of photosynthate uptake per unit sink weight
  • Sink strength affects translocation patterns
  • Cooling a sink tissue inhibits activities that require metabolic energy and slows down the speed of transport.

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CRP 201 Lecture Note 7 Translocation in Phloem PDF

Description

This quiz explores the process of translocation in phloem, detailing the movement of assimilates from source leaves to sink tissues. It covers the structure and function of phloem, including sieve elements and companion cells, as well as the impact of translocation on crop yield and plant productivity.

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