Name: how plant cells build a new wall
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 1 min 59 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-4

The Phragmoplast

Plant cells are enclosed by a rigid cell wall, making it difficult for cells to divide by contracting from the outside. Hence, plant cells divide by forming a new cell wall between the two daughter nuclei in an &#8220;inside out&#8221; fashion. A specialized structure in plants called the phragmoplast guides the new cell wall formation.
The plane of cell division, which is the future site of cell wall formation, is marked by a preprophase band made up of microtubules and actin filaments that forms during the G1 phase of the cell cycle. The preprophase band assembles at the cell cortex and disappears at the beginning of the M phase.
During mitosis, chromosomes separate and start moving to opposite poles. At the poles, the nuclear envelope forms around the separated chromosomes and the spindles start to disappear. The remaining microtubules of the mitotic spindle form the phragmoplast.
The phragmoplast microtubules are polar, with plus ends near the equatorial plane, and minus ends near the poles.
Golgi bodies secrete small vesicles that are carried by motor proteins along the microtubules to the cell center. These vesicles are filled with polysaccharides and glycoproteins, two important components required for new cell wall synthesis. The fusion of vesicles forms a disc-like structure called an early cell plate.
The phragmoplast microtubules are successfully regenerated at the free margins of the cell plate, enabling the phragmoplast to extend the plate laterally. The new cell plate joins with the mother cell walls at the site that was marked by the preprophase band before the M phase. The plasma membrane fuses with the cell plate and a new cell wall is formed, separating the two daughter cells.

the phragmoplast

Cell division is essential for organismal growth and development. In animal cells, the central spindle and its associated proteins form the midbody, a structure that has an essential role in cytokinesis. In plants, the central spindle, along with the microtubules, actin, and other cell components, matures into the phragmoplast, which is necessary for cytokinesis. Unlike the stationary midbody, the phragmoplast expands centrifugally, eventually leading to the formation of the new cell wall.
The mature phragmoplast is donut-shaped and contains an outer leading region, a middle transition zone, and an inner lagging region. In the leading region, new microtubules are assembled continuously. Microtubule nucleation is initiated by the &#947;-tubulin ring complex (&#947;-TuRC), which contains six subunits&#8212;GCP1 to GCP6. However, &#947;-TuRC cannot directly interact with the microtubules; therefore, augmin, a microtubule-interacting protein complex, mediates the recruitment of &#947;-TuRC to the microtubules. The microtubules present in the phragmoplast act as tracks for transporting the secretory vesicles produced by the nearby Golgi body.
In the middle transition zone, the vesicles initially transition into tubule-like structures and then interconnect to form an intertwined tubular network. The continuous addition of secretory vesicles results in the outward growth of the tubular network until it meets with the parental cell membrane. The vesicle membranes are used to form the plasma membrane of the daughter cells, while the biomolecules present in the vesicles are used to build the cell plate present between the two daughter cells&#8217; membranes.
In the lagging region, the microtubules depolymerize, leaving behind the mature portion of the cell plate. The fully formed cell plate subsequently develops into the cell wall that separates the two daughter cells. The polymerization of microtubules at the leading end and the depolymerization of the microtubules at the lagging region cause the outward expansion of the phragmoplast and the cell plate until the latter joins with the parent cell wall. Failure in phragmoplast functions can result in multinucleated cells and embryonic lethal phenotypes.

Cell division is essential for organismal growth and development. In animal cells, the central spindle and its associated proteins form the midbody, a ...

Education

JoVE Core

Molecular Biology

Unit 2

Cell Division

KEY TERMS AND CONCEPTS

how plant cells build a new wall

Plant cells build a new wall during cytokinesis with help from the phragmoplast. This plant structure forms from the central spindle and related cell parts as the cell finishes dividing. In animal cells, the comparable structure is the midbody, but in plants the phragmoplast expands outward to guide new wall formation.

The mature phragmoplast has a donut-like shape. It has an outer leading region, a middle transition zone, and an inner lagging region. New microtubules are assembled continuously in the leading region. Microtubule nucleation begins with the gamma-tubulin ring complex, or gamma-TuRC, which contains six subunits called GCP1 through GCP6. Because gamma-TuRC cannot attach to microtubules on its own, augmin, a microtubule-interacting protein complex, helps recruit it to the microtubules.

The microtubules in the phragmoplast act as tracks for secretory vesicles from the nearby Golgi body. In the middle transition zone, these vesicles first change into tubule-like structures. They then connect to form an intertwined tubular network. As more vesicles are added, the network grows outward until it reaches the parental cell membrane.

The vesicle membranes become the plasma membrane of the daughter cells. The materials inside the vesicles help build the cell plate between the two daughter-cell membranes. In the lagging region, the microtubules break down, leaving the mature part of the cell plate behind. The finished cell plate then develops into the cell wall that separates the two daughter cells.

This outward growth depends on microtubules being built at the leading end and broken down at the lagging end. If phragmoplast function fails, cells can become multinucleated. It can also lead to embryonic lethal phenotypes.

How Plant Cells Build a New Wall

mitosis and cytokinesis

Mitosis and Cytokinesis Stages

Mitosis and cytokinesis are the two main steps of cell division. Mitosis is the process that divides the nucleus, while cytokinesis splits the rest of the cell. During mitosis, the cell’s genetic material is separated into two sets. This helps form two new nuclei with the same genetic information. Cytokinesis then completes division by separating the cytoplasm, which creates two daughter cells. These stages work together to make cell division possible in growing and repairing tissues.

duplication of chromatin structure

Chromatin Rebuilding During DNA Replication

Chromatin rebuilding during DNA replication helps cells copy DNA and pass on chromosome structure to daughter cells. During cell division, the genome must be disrupted and then reassembled across the whole chromosome. This process allows chromatin to be inherited, rebuilt, and maintained in new cells. The basic unit of chromatin is the nucleosome. A nucleosome contains DNA wrapped around an octamer of histone proteins, with short linker DNA between neighboring nucleosomes. The histone proteins...

cohesins

Cohesins in Meiosis and Genetic Disorders

Cohesin protein complexes act like molecular glue that keeps sister chromatids together. They are important in both mitosis and meiosis. In mitosis, cohesin complexes are removed from chromosomes before anaphase begins. Meiosis has two rounds of chromosome separation. Meiosis I separates homologous chromosomes, while Meiosis II separates sister chromatids. This process produces four daughter cells. The Meiosis I cohesin complex is made of four subunits: Smc1, Smc3, Rec8, and Scc3. Rec8...

condensins

How Condensins Shape Mitotic Chromosomes

Condensins shape chromosomes during mitosis, the stage when a cell divides. These large protein complexes use ATP, the cell’s energy molecule, to help turn loose post-interphase DNA into compact, separate chromosomes. They organize and segregate chromosomal DNA so it can be passed on correctly. Plant and animal cells contain two condensin complexes: condensin I and condensin II. Each complex has five subunits. Two are SMC, or Structural Maintenance of Chromosomes, subunits. One is a kleisin...

the mitotic spindle

How the Mitotic Spindle Separates Chromosomes

The mitotic spindle is a microtubule-based structure that helps separate chromosomes during cell division. It forms in eukaryotic cells and moves sister chromatids to opposite ends of the parent cell. This leaves each new cell nucleus with the correct genetic material. A bipolar spindle has two poles, and that shape is important for chromosome segregation. In many animal cells, two centrosomes are present when mitosis begins. Each centrosome helps organize a circular set of microtubules at one...

centrosome duplication

Centrosome Duplication in the Cell Cycle

Centrosome duplication is a key part of the animal cell cycle. The centrosome is the main microtubule organizing center, or MTOC, in animal cells. It contains two cylindrical centrioles at its core. Each centriole has nine sets of three microtubules held together by proteins. The two centrioles sit at right angles and are surrounded by the pericentriolar matrix, or PCM, a shapeless protein cloud. Duplication starts early in the cell cycle so each daughter cell can receive a centrosome after...

microtubule instability

Microtubule Growth and Shrinkage

Microtubules are hollow, cylindrical filaments in the cell. They are about 25 nm wide and can range from 200 nm to 25 μm in length. Their main building blocks are GTP-bound tubulin subunits that form αβ-heterodimers, which then assemble into protofilaments. These protofilaments join by lateral bonds to create stable microtubule cylinders. Microtubules are highly dynamic because they repeatedly assemble and break down. They can even grow on one end while shrinking on the other at the same time.

spindle assembly

How the Mitotic Spindle Forms

The mitotic spindle forms through centrosome-mediated, chromatin-mediated, and microtubule-mediated pathways. These pathways often work at the same time. Together, they build a strong spindle apparatus for cell division. In most cells, centrosomes are the main sites where microtubules begin to grow. During the G2 to prophase transition, centrosomes mature and make more microtubules. The growing microtubules extend from both centrosomes, and their plus-ends search for chromosomes by attaching...

attachment of sister chromatids

Kinetochore-Microtubule Binding in Mitosis

Kinetochore-microtubule binding helps chromosomes line up and separate during mitosis. After the nuclear envelope breaks down, condensed chromosomes are exposed to the bipolar microtubules of the mitotic spindle. The kinetochore is a large, disc-shaped protein complex at the centromere region of each sister chromatid, and it serves as the microtubule binding site. Usually, the plus-end of a single microtubule inserts into the kinetochore. In some cases, a kinetochore first makes lateral...

forces acting on chromosomes

Chromosome Movement During Mitosis

Chromosome movement during mitosis depends on several small forces that act at different times and positions in the cell. In prometaphase, these forces help chromosomes move to the equatorial plane and line up at the metaphase plate. Because the forces change with location and stage, chromosome behavior also changes as mitosis continues. Microtubules and motor proteins create two main kinds of force on chromosomes: poleward force and anti-poleward force, also called polar-ejection force.

separation of sister chromatids

Anaphase Start and Chromatid Release

Anaphase starts when sister chromatids are released from one another and pulled toward opposite spindle poles. Before that happens, cohesion along the chromosomal arms is reduced from prophase to metaphase, which helps the sister chromatids resolve. A residual cohesin link still holds them together until the metaphase-to-anaphase transition. This leftover connection helps prevent early separation and reduces the risk of aneuploidy, or the wrong number of chromosomes, in daughter cells. At the...

the spindle assembly checkpoint

How Cells Safeguard Chromosome Separation

The spindle assembly checkpoint helps cells safeguard chromosome separation during anaphase. It acts as a molecular surveillance system. The checkpoint checks whether the steps needed for chromosome segregation are complete before the cell moves on. Many proteins work together to control this checkpoint. If mutations affect these proteins, a cell may enter anaphase too early. Chromosomes can then separate before the needed steps are finished. When this happens, the daughter cells may receive...

anaphase a and b

Chromatid Movement by Microtubule Forces

Chromatid movement during anaphase depends on microtubule forces at the spindle. Kinetochore microtubules grow from the spindle poles, and their plus ends attach to kinetochores on sister chromatids. The kinetochore protein complex Ndc80 makes low-affinity links with the microtubule plus end.

the contractile ring

How Cells Build the Contractile Ring

Contractile rings are built from microfilaments and help separate daughter cells during cytokinesis. This ring forms as the cell cycle moves forward, but the exact timing and coordination with other cell cycle events are still not fully understood. RhoA, a small GTPase in the Ras superfamily, controls contractile ring assembly and function. The inactive form of RhoA is bound to GDP. A guanine nucleotide exchange factor, or Rho-GEF, is located in the cortex region, where the next cell division...

determining the plane of cell division

How Cells Set the Division Plane

How cells set the division plane during cell division affects daughter cell size and, in many cases, cell fate. The plane of division is perpendicular to the plane of chromosome segregation. Different organisms use different cues to place it, based on their shape and needs. In animal cells, the cleavage furrow forms along the division plane from the cell cortex, the area just below the plasma membrane. The mitotic spindle is the main guide for this position. If the spindle axis changes, the...

Plant cells build a new wall during cytokinesis with help from the phragmoplast. This plant structure forms from the central spindle and related cell parts as the cell finishes dividing. In animal cells, the comparable structure is the midbody, but in plants the phragmoplast expands outward to guide new wall formation. The mature phragmoplast has a donut-like shape. It has an outer leading region, a middle transition zone, and an inner lagging region. New microtubules are assembled...

distribution of cytoplasmic content

How Organelles Are Split During Cytokinesis

Cytokinesis splits a cell’s chromosomes and organelles into two daughter cells. Before cell division, organelles grow and divide. They cannot be made from scratch, so each daughter cell must inherit at least one copy to survive. Many details of this organelle sorting process are still not fully known. The cytoplasm contains organelles, salts, proteins, and water. Small organelles such as peroxisomes and lysosomes can be shared by simple diffusion. Because cells contain many copies of these...

anaphase promoting complex

APC Activates Chromosome Separation

The anaphase-promoting complex, or APC, helps control cell cycle progression by destroying specific proteins at the right time. These proteins are tagged with ubiquitin by ubiquitin ligases and then broken down by the proteasome. The SCF (Skp1/Cullin/F-box) complex and APC are two major ubiquitin ligases involved in this process. SCF stays active throughout the cell cycle, but APC turns on during the metaphase-to-anaphase transition. APC becomes active when Cdc20 or Cdh1 binds to it. These...

key terms and concepts

Learn how the phragmoplast helps plant cells complete cytokinesis, guide vesicles, and form the new cell plate and cell wall.

How Plant Cells Build a New Wall | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

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New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS1-4.

Characteristics of Life

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HS-LS1-1

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Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

HS-LS1-2

How Plant Cells Build a New Wall

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