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Do all cells of a plant contain chloroplasts?


If the answer is no, then how do plant cells tell whether they need to keep chloroplasts or not? What kind of signals are used, and how are chloroplasts eliminated?


Not all cells of the plant contain chloroplasts, but they all contain some form of plastid. When the plant is its development state, they contain proplastids which may turn into chloroplasts if the cells are exposed to light. Other forms of plastids may play a role in storing lipids, amylum or proteins and they form because there is a lack of light (these are present mostly in roots). Chloroplasts are not eliminated from the cell. Here you have a helpful wikipedia image:

This is a very general explanation though and you should look more into hormones and specific triggers for the formation of chloroplasts. Article talking about chloroplasts biogenesis


Plant cells

Plant cells have a distinct set of features and characteristics. They are different to the cells of organisms from other kingdoms of life.

The cells of plants are eukaryotic. A eukaryotic cell is any cell with a ‘true’ nucleus and organelles. This immediately separates plant cells from the cells of bacteria and archaea.

Animals and fungi also have eukaryotic cells. Plant cells have a unique set of organelles that distinguishes them from the cells of animals and fungi. The presence of organelles called chloroplasts, vacuoles and a cell wall are three key features of the cells of plants.

Plant cells are relatively large and can differ considerably within a plant. There is a large diversity of different types of cells found through stems, leaves and roots.


Do all cells of a plant contain chloroplasts? - Biology

What are chloroplasts?

Chloroplasts are unique structures found in plant cells that specialize in converting sunlight into energy that plants can use. This process is called photosynthesis.

Chloroplasts are considered organelles in plant cells. Organelles are special structures in cells that perform specific functions. The main function of the chloroplast is photosynthesis.

Chloroplast Structure

  • Outer membrane - The outside of the chloroplast is protected by a smooth outer membrane.
  • Inner membrane - Just inside the outer membrane is the inner membrane which controls which molecules can pass in and out of the chloroplast. The outer membrane, the inner membrane, and the fluid between them make up the chloroplast envelope.
  • Stroma - The stroma is the liquid inside the chloroplast where other structures such as the thylakoids float.
  • Thylakoids - Floating in the stroma is a collection of sacks containing chlorophyll called the thylakoids. The thylakoids are often arranged into stacks called granum as shown in the picture below. The granum are connected by disc-like structures called lamella.
  • Pigments - Pigments give the chloroplast and the plant its color. The most common pigment is chlorophyll which gives plants their green color. Chlorophyll helps to absorb energy from sunlight.
  • Other - Chloroplasts have their own DNA and ribosomes for making proteins from RNA.

Chloroplasts use photosynthesis to turn sunlight into food. The chlorophyll captures energy from light and stores it in a special molecule called ATP (which stands for adenosine triphosphate). Later, the ATP is combined with carbon dioxide and water to make sugars such as glucose that the plant can use as food.

Other functions of chloroplasts include fighting off diseases as part of the cell's immune system, storing energy for the cell, and making amino acids for the cell.


Chloroplast

Chloroplasts are the source of virtually all of the world's food and fuel and much of its oxygen supply, and as such life on Earth depends on them. They are a vital component of all photosynthetic cells in plants and algae, and are unique to them. What makes them so important is that they are the sites of photosynthesis, from the absorption of light by chlorophyll through to the production of the first simple sugars. It is chlorophyll that gives them their characteristic green color. They are present in all green-colored cells of a plant not only in leaves, but also in green stems and green parts of a fruit (for example, in an apple peel).

Chloroplasts are approximately 4 to 6 micrometers in diameter and shaped like a satellite dish with the concave face toward the light. This shape, together with their alignment along the inner surface of the cell, maximizes their ability to capture light. Depending on the plant species there can be as many as two hundred chloroplasts in a cell.

A chloroplast is enclosed by two membranes, which together are termed the Ȯnvelope." Inside are two distinct features: a complex organization of folded and interconnecting membranes, called the thylakoids, and a protein -rich fluid region called the stroma. The proteins and pigments (chlorophyll and carotenoids) involved in the light reactions of photosynthesis are located on the thylakoid membranes. The enzymes involved in the conversion of carbon dioxide to simple sugars (the ⋚rk reactions") are found in the stroma. Together these reactions convert carbon dioxide and water to sugars and oxygen.

As well as in making sugars, chloroplasts are important in making other essential plant products, such as fats, oils, scents, and proteins. They can

Many pieces of evidence support the endosymbiotic theory. Chloroplasts, for example, contain deoxyribonucleic acid (DNA), the entire sequence of which has been determined in a number of species. Chloroplast DNA codes for a number of essential chloroplast proteins. Over time, large parts of the DNA of the original bacterium have found their way into the nucleus of the host cell, giving it control over many of the functions and features of the chloroplast. Genes involved in controlling the division, and hence "reproduction," of the chloroplast are now present in the nucleus. The composition of the DNA and the way in which it is translated resembles that of bacterial cells, adding further support to the endosymbiotic origin of chloroplasts.


Do all cells of a plant contain chloroplasts? - Biology

Name the part of the cell labelled A in the diagram.
  1. ? to control what enters and leaves the cell.
  2. ? to give the cell shape and support.
  3. ? to control reproduction in the cell.
  4. ? to control activities in the cell.
  1. ?
  2. ?
  3. ?
  4. ?
  1. ? Plant cells generally have a well-defined shape.
  2. ? Animal cells contain chlorophyll.
  3. ? Plant cells do not have cell walls.
  4. ? Animal cells are usually bigger than plant cells.
  1. ? control the activities of the cell.
  2. ? provide shape and support to the cell.
  3. ? organise the cell into tissues.
  4. ? control what enters and leaves the cell.
The green part of the cell labelled X in the diagram is known as The diagram shows a group of onion cells. The parts labelled A, B and C respectively are
  1. ? A = cell wall, B = cytoplasm, C = nucleus
  2. ? A = cell wall, B = cytoplasm, C = membrane
  3. ? A = cytoplasm, B = cell wall, C = nucleus
  4. ? A = nucleus, B = cell wall, C = cytoplasm
  1. ? Tissues form organs, and organs form systems.
  2. ? Cells form organs, and organs form tissues.
  3. ? Cells form tissue, and systems form organs.
  4. ? Cells form systems, and systems form organs.
  1. ? plant cells have a cell wall while animal cells do not.
  2. ? animal cells contain chloroplasts while plant cells do not.
  3. ? plant cells do not have a nucleus while animal cells do.
  4. ? plant cells have a cell membrane while animal cells do not.
  1. ? Animals can make their own food.
  2. ? Animals do not contain chlorophyll in their cells.
  3. ? Animals cannot carry out photosynthesis.
  4. ? The cells in animals do not contain cell walls.

The diagram shows a plant cell as seen under a microscope. Two of the labels are incorrect. What are they?
  1. ? Vacuole and chloroplast
  2. ? Vacuole and cytoplasm
  3. ? Nucleus and chloroplast
  4. ? Cell wall and cell membrane
The diagram shows a plant cell. Identify parts A and B.
  1. ? A = cell wall and B = nucleus.
  2. ? A = cell wall and B = cytoplasm.
  3. ? A = cell membrane and B = nucleus.
  4. ? A = vacuole and B = nucleus.
Look at the diagram of an animal cell. Select correct statement from the following about animal cells.

Differences between cell types: Organelles and their functions

All basic chemical and physiological functions – repair, growth, movement, immunity, communication, digestion – are carried out inside of cells, and the activities of cells depends on the activities of the structures within the cell (including the organelles). This means cells can convert energy from one form (which, depending on the cell type, can be in the form of light, sugar, or other compounds) into another. For example, cells can digest the building blocks of other organisms that it has eaten and used the released energy to build its own materials such as proteins, carbohydrates, and fats.

Most of the activities of a cell are carried out via the production of proteins. Proteins are large molecules that are made by specific organelles within the cell using the instructions contained within its genetic material (see our series on DNA: DNA I: The Genetic Material, DNA II: The Structure of DNA, DNA III: The Replication of DNA). Depending on the type of organism, specific organelles may or may not be present in a cell.

In addition to the plasma (cell) membrane, cytosol, ribosomes, and nucleus, the typical components of eukaryotic cells include: mitochondria, transport vesicles, endoplasmic reticulum, Golgi bodies, and lysosomes. In addition to these, photosynthetic (plant) cells will have a cell wall, chloroplasts, and a central vacuole.

Prokaryotic cells, however, do not contain any membrane-bound organelles. Instead, they can include plasmids, a cell wall, and in the case of photosynthetic prokaryotes, thylakoids. Table 1, below, lists the function of each type of organelle and which group of cells it is found in.

Interactive Animation: The Structure of Animal Cells

Interactive Animation: The Structure of Plant Cells

Mitochondrion (plural: mitochondria)

The “power supplier” for the cell, generating most of the ATP used in cell processes through the conversion of nutrients into energy. Also involved in cell signaling, controlling the cell cycle and cell growth, and cellular differentiation. Found in all eukaryotes.

Chloroplasts

A chlorophyll-containing plastid responsible for converting sunlight and carbon dioxide into oxygen and sugar. Found in plants and algae.

Smooth Endoplasmic Reticulum

A series of sac-like membranes responsible for the synthesis and storage of lipids, phospholipids, and steroids, as well as the metabolism of carbohydrates.

Rough Endoplasmic Reticulum

A series of sac-like membranes studded with ribosomes, responsible for the synthesis and export of proteins

Golgi Apparatus

Functioning like a distribution center, the Golgi Apparatus gathers simple molecules and creates more complex molecules. Once created, those complex molecules are transported to other organelles, stored in vesicles, or exported from the cell.

Plasma Membrane

A layer of phospholipids and proteins that forms a barrier between the inside of the cell and the outside environment.

Found in plants, fungi, and some protists, a structure outside of the plasma membrane that provides strength, support, and protection.

A specialized compartment containing hydrolytic enzymes. The role of lysosomes is to digest sugars, proteins, and other “foods” a cell absorbs.

Nuclear Envelope

A double-membrane surrounding the nucleus. This membrane provides a barrier between the nucleus and the cytosol.

Similar to lysosomes, these contain enzymes used in a variety of reactions, including oxidation reactions. In plant seeds, peroxisomes convert stored fatty acids to carbohydrates, providing energy for germination. In plant leaves, they are involved in photorespiration.

A compartment used for storage of nutrients, water, and waste. In plants, the central vacuole plays an important role in providing structure.

A small spherical compartment composed of a lipid bilayer and internal fluid used to exchange cargo between organelles of the endomembrane system. Specialized vesicles play a variety of roles.

Otherwise known as intracellular fluid (ICF), the liquid matrix found within a cell that holds other organelles and allows intracellular processes to take place.

Cytoskeleton

A complex network of protein fibers that give the cell its shape. These fibers also play important roles in assisting vesicles and organelles to move around the cell, as well as the movement of chromosomes during cell division.

The protein builders of the cell. Ribosomes are responsible for constructing amino acids to build amino acid chains.

Where ribosomes are made inside the nucleus.

The production of ______ allows the cell to carry out most of its activities.


Vacuoles

Vacuoles are membrane-bound sacs that function in storage and transport. The membrane of a vacuole does not fuse with the membranes of other cellular components. Additionally, some agents such as enzymes within plant vacuoles break down macromolecules.

The Central Vacuole

Previously, we mentioned vacuoles as essential components of plant cells. If you look at Figure 2b, you will see that plant cells each have a large central vacuole that occupies most of the area of the cell. The central vacuole plays a key role in regulating the cell’s concentration of water in changing environmental conditions. Have you ever noticed that if you forget to water a plant for a few days, it wilts? That’s because as the water concentration in the soil becomes lower than the water concentration in the plant, water moves out of the central vacuoles and cytoplasm. As the central vacuole shrinks, it leaves the cell wall unsupported. This loss of support to the cell walls of plant cells results in the wilted appearance of the plant.

The central vacuole also supports the expansion of the cell. When the central vacuole holds more water, the cell gets larger without having to invest a lot of energy in synthesizing new cytoplasm. You can rescue wilted celery in your refrigerator using this process. Simply cut the end off the stalks and place them in a cup of water. Soon the celery will be stiff and crunchy again.

Figure 2. These figures show the major organelles and other cell components of (a) a typical animal cell and (b) a typical eukaryotic plant cell. The plant cell has a cell wall, chloroplasts, plastids, and a central vacuole—structures not found in animal cells. Plant cells do not have lysosomes or centrosomes.


Advances in chloroplast genome engineering

In the past century, desirable agronomic traits, including yield enhancement and resistance to pathogens or abiotic stress, were achieved by breeding cultivated crops with their wild relatives. As explained above, chloroplast genome sequences are very useful in the identification of closely related, breeding-compatible plant species. With the advent of modern biotechnology, desirable traits from unrelated species can now be readily introduced into commercial cultivars. Such genetically modified crops have revolutionized agriculture in the past two decades, dramatically reducing the use of chemical pesticides and herbicides while enhancing yield. For most commercial cultivars, herbicide- or insect-resistance genes are introduced into the nuclear genome. There are, however, a few limitations for nuclear transgenic plants, including low levels of expression (<1 % total soluble protein (TSP)) and potential escape of transgenes via pollen.

Engineering the introduction of foreign genes into the chloroplast genome addresses both of these concerns. Just two copies of transgenes are typically introduced into the nuclear genome, whereas up to 10,000 transgene copies have been engineered into the chloroplast genome of each plant cell, resulting in extremely high levels of foreign gene expression (>70 % TSP) [122]. Most importantly, chloroplast genomes are maternally inherited in most cultivated crops, minimizing or eliminating transgene escape via pollen [123].

The basic process of chloroplast engineering is explained in Fig. 3a, b. Chloroplast genome engineering is accomplished by integrating foreign genes into intergenic spacer regions without disrupting the native chloroplast genes (Fig. 3a). Two chloroplast genes are used as flanking sequences to facilitate integration of transgene cassettes. Transgene cassettes include a selectable marker gene and gene(s) of interest, both regulated by chloroplast gene promoters and untranslated regions (UTRs Fig. 3a). Chloroplast genome sequences are essential to build transgene cassettes because they provide both flanking and regulatory sequences. Transgene cassettes that are inserted into bacterial plasmids are called chloroplast vectors and they are bombarded into plant cells using gold particles and a gene gun (Fig. 3b). Because of the presence of chloroplast DNA in the nuclear or mitochondrial genome, transgene cassettes may integrate via homologous or non-homologous recombination events but any transgenes that are integrated within the nuclear or mitochondrial genome will not be expressed because chloroplast regulatory sequences are not functional in other genomes. If such integration occurs, the transgenes could be easily identified by evaluation of their integration site and eliminated [124].

Basic process of chloroplast genetic engineering, diversity in intergenic spacer regions, and impact of transgene integration (endogenous versus heterologous genome sequences). a Complexity of heterologous sequence integration into intergenic spacer regions between lettuce and tobacco. The schematic diagram represents recombination between the tobacco transplastomic genome and the lettuce transformation vector [128]. Purple bars represent unique lettuce intron sequence the green bar represents unique tobacco intron sequence black bars are exon regions blue regions are looped out sequence. The expression cassette comprises: promoters (P), leader sequence (L), gene of interest (GOI), terminators (T), and selectable marker gene (SMG). IG intergenic spacer region. b Basic process of chloroplast genetic engineering. Gene delivery is performed by bombardment with gold microparticles coated with chloroplast vectors, followed by three rounds of selection to achieve homoplasmy. After confirmation of transgene integration, plants are grown in the greenhouse to increase biomass. Chloroplast transgenes are maternally inherited without Mendelian segregation of introduced traits. c Comparison of 21 of the most variable intergenic spacer regions among Solanaceae chloroplast genomes. Atr Atropa, Pot potato, Tob tobacco, Tom tomato. *Tier 1, **tier 2, and ***tier 3 regions reported in the paper by Shaw et al. [250]. Plotted values were converted from percentage identity to sequence divergence on a scale from 0 to 1 as shown on the Y-axis these values demonstrate a wide range of sequence divergence in different regions. Nucleotide sequences were determined by a bridging shotgun method and genome annotation was performed using the Dual Organellar GenoMe Annotator [13]. d, e Decrease in the expression of transgenes regulated by heterologous psbA promoters and untranslated regions (UTRs) engineered via tobacco chloroplast genomes. When the lettuce (La) psbA regulatory region was used in tobacco (Na) chloroplasts or vice versa, transgene expression is dramatically reduced. d Accumulation of a cholera toxin B subunit (CTB) and proinsulin (Pins) fusion protein (CP) was quantified by densitometry and e anthrax protective antigen (PA) accumulation was estimated by enzyme-linked immunosorbent assay (ELISA). Total leaf protein (TLP) or total soluble protein (TSP) data are presented as a function of light exposure and developmental stage. The order of young, mature, and old is different in d and e because of the accumulation of more CTB-Pins in older leaves and PA in mature leaves [128]. Young (top five), mature (fully grown), and old (bottom three) leaves were fully expanded and were cut from plants grown in the greenhouse for 8–10 weeks

One of the challenges of creating chloroplast transgenic (transplastomic) plants is the elimination of all untransformed copies (>10,000 per cell) of the native chloroplast genome and replacing them with transformed genomes that contain integrated transgene cassettes. The absence of the native chloroplast genome and the presence of only the modified genomes is referred to as the homoplasmic state, which is typically achieved after two or three rounds of selection (Fig. 3b). The most effective selectable marker used is the aadA gene, which confers resistance to streptomycin and spectinomycin. These antibiotics bind specifically to chloroplast ribosomes and disrupt protein synthesis without interfering with any other cellular process. Efforts to transform the chloroplast genome of cereal crops have been mostly unsuccessful. This could be due to the instability of chloroplast DNA in the mature leaves of cereals [47] or to a requirement for better selectable markers [125].

Table 2 provides the first global, comprehensive summary of the power of chloroplast genetic engineering, utilizing valuable information generated by the sequencing of chloroplast genomes described in previous sections. This table includes the most complete list of chloroplast genomes that have been engineered for enhanced agronomic traits or the production of different bio-products, including biopolymers, industrial enzymes, biopharmaceuticals, and vaccines. Within Table 2, transgenes are grouped according to their functions and are organized according to their site of integration. The efficiency of transgene expression is also included in Table 2, providing important information about the regulatory sequences used to express the transgenes.


Types of Plastids

Plastids are organelles that function primarily in nutrient synthesis and storage of biological molecules. While there are different types of plastids specialized to fill specific roles, plastids share some common characteristics. They are located in the cell cytoplasm and are surrounded by a double lipid membrane. Plastids also have their own DNA and can replicate independently from the rest of the cell. Some plastids contain pigments and are colorful, while others lack pigments and are colorless. Plastids develop from immature, undifferentiated cells called proplastids. Proplastids mature into four types of specialized plastids: chloroplasts, chromoplasts, gerontoplasts, and leucoplasts.

    These green plastids are responsible for photosynthesis and energy production through glucose synthesis. They contain chlorophyll, a green pigment that absorbs light energy. Chloroplasts are commonly found in specialized cells called guard cells located in plant leaves and stems. Guard cells open and close tiny pores called stomata to allow for gas exchange required for photosynthesis.
  • Chromoplasts: These colorful plastids are responsible for cartenoid pigment production and storage. Carotenoids produce red, yellow, and orange pigments. Chromoplasts are primarily located in ripened fruit, flowers, roots, and leaves of angiosperms. They are responsible for tissue coloration in plants, which serves to attract pollinators. Some chloroplasts found in unripened fruit convert to chromoplasts as the fruit matures. This change of color from green to a carotenoid color indicates that the fruit is ripe. Leaf color change in fall is due to loss of the green pigment chlorophyll, which reveals the underlying carotenoid coloration of the leaves. Amyloplasts can also be converted to chromoplasts by first transitioning to amylochromoplasts (plastids containing starch and carotenoids) and then to chromoplasts.
  • Gerontoplasts: These plastids develop from the degradation of chloroplasts, which occurs when plant cells die. In the process, chlorophyll is broken down in chloroplasts leaving only cartotenoid pigments in the resulting gerontoplast cells.
  • Leucoplasts: These plastids lack color and function to store nutrients.

Cell Biology of the Chloroplast Symbiosis in Sacoglossan Sea Slugs

Sidney K. Pierce , Nicholas E. Curtis , in International Review of Cell and Molecular Biology , 2012

Abstract

Chloroplasts removed from their species of origin may survive for various periods and even photosynthesize in foreign cells. One of the best studied and impressively long, naturally occurring examples of chloroplast persistence, and function inside foreign cells are the algal chloroplasts taken up by specialized cells of certain sacoglossan sea slugs, a phenomenon called chloroplast symbiosis or kleptoplasty. Among sacoglossan species, kleptoplastic associations vary widely in length and function, with some animals immediately digesting chloroplasts, while others maintain functional plastids for over 10 months. Kleptoplasty is a complex process in long-term associations, and research on this topic has focused on a variety of aspects including plastid uptake and digestive physiology of the sea slugs, the longevity and maintenance of symbiotic associations, biochemical interactions between captured algal plastids and slug cells, and the role of horizontal gene transfers between the sea slug and algal food sources. Although the biochemistry underlying chloroplast symbiosis has been extensively examined in only a few slug species, it is obvious that the mechanisms vary from species to species. In this chapter, we examine those mechanisms from early discoveries to the most current research.