#plastid

[theliteralbear]

[er-cryptid]

Plastid Differentiation

Patreon | Ko-fi

[tpointtechblog]

Plastids: Definition, Types, and Functions Explained

Plastid Definition

Plastids are double-membrane organelles found in plant cells and some protists. They are responsible for functions like photosynthesis (chloroplasts), storage (leucoplasts), and pigment synthesis (chromoplasts).

The plastid is a membrane-bound organelle that is present in the cells of plants, algae, and certain other eukaryotic creatures. The Greek word for plastid is plastós, which means "formed, molded" (plural "plastids").

These cyanobacteria are thought to be intracellular endosymbiotic. Examples include leucoplasts (non-pigmented plastids that can occasionally differentiate), chromoplasts (used for pigment production and storage), and chloroplasts (used for photosynthesis). Around 1.5 billion years ago, a cyanobiont (symbiotic cyanobacteria) belonging to the genus Gloeomargarita most likely had a role that resulted in permanent endosymbiosis in the Archaeplastida clade (including land plants, red algae, and green algae).

About 90–140 million years ago, photosynthetic Paulinella amoeboids had a later main endosymbiosis event. In the cells of algae, plants, and numerous other eukaryotic species, the plastid serves as a membrane-bound organelle. Plastids were discovered and named by E. Haeckel, but A. F. W. Schimper was the first to give them a clear description.

Plastids create and store crucial chemical compounds used by autotrophic eukaryotic cells. The types of pigments found in plastids, which are utilized in photosynthesis, define the color of the cell.

They have a common evolutionary ancestor and have a circular double-stranded DNA molecule with prokaryotic organisms. Another significant energy-transmitting cell organelle that is unique to plants is the plastid. Schimper gave these photosynthesis-related structures the name Plastids.

Chloroplasts are the sole organelles in all other living organisms that are capable of absorbing, converting, and conserving solar energy in the form of chemical energy. In actuality, photosynthesis either directly or indirectly transports chemical energy.

Plastids, which can be either colorless plastids, colored plastids, or proplastids, are present in nearly all cells in the plant body. The "PS-clade" (of the algae genera Prochlorococcus or Synechococcus) includes this plastid.

Many other species have also experienced secondary and tertiary endosymbiosis. Some organisms can sequester ingested plastids through a process known as kleptoplasty.

Plastids were originally identified and precisely defined by A. F. W. Schimper. The types of pigments found in plastids, which are employed in photosynthesis, define the color of the cell.

Additionally, they serve as the location of the production and storage of crucial chemicals utilized by autotrophic eukaryotic cells.

Plastids in Plant Cells: Definition, Types, and Their Role

Chloroplasts are plastids that have chlorophyll and can perform photosynthesis. Additionally, plastids may create fatty acids and terpenes, which can be employed as a starting point for the production of other compounds as well as collect products like starch.

For instance, palmitic acid, which is produced in the chloroplasts of the mesophyll tissue, is used by the epidermal cells to create the components of the plant cuticle and the epicuticular wax. Proplastids, which are present in the meristematic areas of the plant, are the ancestors of all plastids.

Though more mature chloroplasts may also do this, proplastids and juvenile chloroplasts often split through binary fission.

Depending on the role they serve in the cell, plasmids can take on a variety of different shapes.

The following variations may emerge from identical plastids (proplastids):

Green plastids used in photosynthesis are called chloroplasts.

Chromoplasts pigment production and storage in colored plastids.

During plant senescence, protoplasts control how the photosynthetic system is broken down.

Leucoplasts are colorless plastids that combine monoterpenes; they can occasionally develop into other, more specialized plastids.

Amyloplasts are capable of storing starch and recognizing gravity (for geotropism).

Elaioplasts are used to store fat.

Proteinoplasts are used to store and modify proteins.

Tannosomes are for producing and synthesizing polyphenols and tannins.

Plastids can distinguish or redifferentiate between these and other forms based on their morphology and function.

A 75–250 kilobase circular plastome is produced in several copies by each plastid. The number of genome copies per plastid varies; it can be over 1000 in rapidly proliferating cells, which typically include few plastids, or it can be 100 or less in mature cells, where plastid separations have resulted in a large number of plastids.

A hundred or so genes make proteins that regulate photosynthesis, plastid gene transcription and translation, ribosomal and transfer ribonucleic acids (rRNAs and tRNAs), and other biological processes in the plastome.

However, these proteins only make up a small portion of the overall protein configuration required to create and maintain the structure and functionality of a certain kind of plastid. The vast majority of plastid proteins are converted by nuclear genes in plants, and the expression of plastid and nuclear genes is tightly controlled to govern the appropriate development of plastids in connection to cell differentiation.

The term "plastid nucleoids" refers to the massive protein-DNA complexes that are connected with the internal envelope membrane and contain plastid DNA. More than 10 copies of the plasmid DNA may be covered by a single nucleoid particle.

A specific nucleoid that is found in the plastid's center is present in the proplastid. Proplastids transform into chloroplasts, plastids switch from one kind to another, and nucleoids alter in shape, size, and placement inside the organelle.

It is thought that changes to the content and abundance of nucleoid proteins cause nucleoids to remodel. Several plastids, namely those involved in photosynthesis, have several interior membrane layers.

Structure

All green plastids, and all other plastids for that matter, are enclosed by two-unit membranes, with the outer and inner membranes being 7 nm thick and the periplastid gap between them being 8–10 nm thick.

The inner membrane of fully formed plastids does not exhibit any inward foldings, unlike mitochondria, although it participates actively in the transformation of proplastids becoming mature plastids.

The stroma, a liquid that fills the chloroplast and contains the highly organized membrane structures known as grana, is called the tonoplast. The stromatic fluid, in addition to grana, includes a variety of enzymes, plastid DNA, RNAs, and 70s ribosomes.

[onlinewebtrigger]

প্লাস্টিড কী? Plastid কাকে বলে? প্লাস্টিড কত প্রকার ও কি কি?

গ্রিক শব্দ Plastikas থেকে Plastid (প্লাস্টিড) শব্দের উৎপত্তি হয়েছে। প্লাস্টিডই হচ্ছে উদ্ভিদ দেহের সর্ববৃহৎ ক্ষুদ্রাঙ্গ বা অঙ্গাণু।

[ayraethazide]

Here's a diagram connecting various types of plastid together. Notice how a lot of the plastid types turn into chloroplasts in the light. Also included is some information on apicoplasts, another type of non-photosynthetic plastid with a vestigial cpDNA genome most similar to dinoflagellate algae.

Types of plastid by Ayraethazide is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

[stuffxthree-blog]

The Seeds of Inheritance

Biology Concepts – pollen, plastid inheritance, gymnosperms, angiosperms

I am coming to believe that plants are more complex than animals, even more complex than females. Female plants must be the most difficult things on Earth to understand!

Complete flowers have both anthers for pollen and pistils for egg 

fertilization. Incomplete flowers occur on dioecious plants, 

and have either the pistil (gynoecious) or the anther 

(androecious). Dioecious plants cannot self pollinate, unless 

they have both types of incomplete flowers, like coast

redwoods (see last picture).

Yes, thereare female plants. In the plant world, species can be monoecious (mono = one, and ecious = household) or dioecious (di = two). Monoecious plants have individuals that produce both male microgametophytes (pollen) and female megagametophytes (oocyctes or ovules). The individual dioecious plants are either androecious (pollen producing) or gynoecious (seed producing). It's okay to ask if a plant is female, but you still shouldn’t ask her age.

This isn’t even the tip of the tip of the iceberg when it comes to diversity in plant reproduction. There are also different ways to produce seeds. The gymnosperms have unenclosed seeds (gymno = naked, and sperm = seed). Gymnosperms include the conifers (cone producers), the cycads that we talked a little about a few weeks ago, and the gnetum plants. Gnetum plants live close to the equator around the globe and include the Ephedraspecies. It is from these plants that we get ephedrine and pseudoephedrine that work to relieve allergy and cold congestion.

The other type of seed plants is the angiosperms(angio = hidden). These are the flowering plants that have seeds encased in fruits or other structures that help to protect them and to encourage their dispersal.

One way that the gymnosperms and angiosperms differ is in how they inherit their plastid organelles. But even here there is a lot of overlap and exceptions; plants just keep getting more complex.

Gymnosperms have there seeds exposed on the scales

of the cones, while angiosperms have the protected

inside the fruit (except for strawberries).

Angiosperms have a maternal inheritance of chloroplast DNA (cpDNA), much like animals have maternal inheritance of mitochondrial DNA (mtDNA). The reasons for maternal inheritance of cpDNA elude me. For mitochondria, the theory is that damage to the sperm mitochondria would occur during the swim to the oocyte, so it would be smart to ban them from the egg.

But cpDNA is much more passive, they do not have to do a huge amount of work to get to the ovule of the pollinated plant. The pollen tube grows down to the ovule and delivers the sperm cells right to the egg. There must be some other reason, but I don’t know what it might be.

However, there seem to be more exceptions in angiosperm inheritance of cpDNA than there is in animal mtDNA. A few families of plants, like alfalfa (Medicago sativa) and kiwi fruit vine (Actinidia deliciosa), have a strict paternal inheritance of cpDNA.  This is odd since, the angiosperms have a couple of mechanisms for keeping the plastids out of the male gametes.

Every plant species has a distinct pollen shape, which

is why you can be allergic to some plants and not

others. But each pollen grain has the vegetative cell

that becomes the sperms cells and the tube cell. The

tube usually grows from the side that rests on the

fertilized stigma.

The pollengrain contains a few different kinds of cells. There are one or more generative cells; these are the reproductive cells of the pollen. There will also be many non-vegetative cells as well. The generative cell has two nuclei. One will divide to become the two sperm cells, while the other will form the tube cell to deliver the  sperms cells to the ovule.

In many species, when the generative nucleus divides to form sperm, the plastids are partitioned off, and are not included in the sperm cells. This works to ensure maternal inheritance. In other species, the sperm cells may include plastids, but these quickly degenerate and are not delivered to the ovule. Somehow, the alfalfa plants have overcome these mechanisms and even invented a new one to eliminate or exclude the plastids from the ovule, giving strict paternal inheritance.

Going beyond the alfalfa and kiwi fruit ability to preserve their paternal plastids is the fact that a full 20% of angiosperms can show (but don’t have to show), bipaternal inheritance of cpDNA. This is called potential bipaternal plastid inheritance (PBPI) and is controlled by a male gametic trait, called of all things - PBPI trait! Therefore, the fairly strict maternal inheritance of mtDNA in animals (blue mussels excepted) is not matched by cpDNA in angiosperms.

But it gets weirder. The angiosperm exception is normal for the gymnosperm. Gymnosperms tend to have paternal inheritance patterns for cpDNA. This difference is important to note, since scientists often try to use cpDNA inheritance patterns to track seed movements around the world and through evolutionary time, just like human populations are often tracked using mitochondrial ancestry and inheritance.

But this must be frustrating, because there are also exceptions in the paternal inheritance pattern in gymosperms. The Chinese fir (Cunninghamia lanceolata), which isn’t a fir, is native to Asia but was brought to America in the 1800’s. Remember that before molecular biology, most taxonomic classifications were made on just the morphology (shape and look) of an organism, and its grouping and name were based on how it compared to other organisms. Names often get stuck in the language and are hard to change, so many of the misnomers persist.

Godzilla, or Gojira, always seemed surprised when

the other monster grabbed his tail. Here it happens

to be a giant wolfman. Everybody cashed in on the

werewolf brand; I am surprised Abbott and Costello

aren’t in that picture somewhere.

Consider this, we now know that the Japanese pronunciation for the big green movie monster is “go-zeer-a” or “go-jeer-a,” as it was a portmanteau of the Japanese words for gorilla and whale. But when it came to America, it was just assumed that the name was mispronounced in English and that it was supposed to be “god-zill-a.” We know it is wrong, but the wrong name still survives; it's what you get used to that sticks around.

But back to the Chinese fir. This gymnosperm is a conifer that can grown 150 feet tall, but flaunts its individuality by having a maternal inheritance pattern for cpDNA – much more angiosperm-like behavior than gymnosperm. And this is even odder because the Chinese fir is an older gymnosperm, a much more distant relative to the angiosperms than many gymnosperms that have a strict paternal cpDNA inheritance.

Gymnosperms that show maternal cpDNA inheritance are rare, or just less studied, so one might assume that paternal cpDNA inheritance is fairly strict – wrong. Many gymnosperms have bipaternal inheritance patterns of plastids, so the mechanism might be different from angiosperms, but is no more consistent than that of the flowering plants.

Finally, there is the issue of crossbreeding. In this animal mtDNA and plant cpDNA seem to be similar. Whatever the dominant form of inheritance is seen in natural breedings, the numbers get screwed up when cross breeding occurs. We saw that paternal inheritance of mtDNA in mice was much likely in the mating of different species (interspecific breeding).

The passionflower vine can grow to be 10 meters high

and is the source of the passion fruit that I enjoy so

much. The fruit protects the fertilized seeds that

probably have paternal cpDNA, since most of the

varieties we eat are hybrids of different species.

In plants, this also holds, and may even be more discrepant. Take the passion flowers  (family Passiflora) for instance. Intraspecific breeding (same species) showed the maternal cpDNA inheritance one might expect. But in interspecific crosses the inheritance was 100% paternal. This must represent some attempt to limit the genetic diversity of the organellar genomes, but I leave it to you to explain the reason for it.

The similarity between mitochondrial and plastid inheritance in hybrids brings up another issue – what about mitochondrial inheritance patterns in plants?

It turns out that most plants that have been studied for mtDNA inheritance have a maternal inheritance pattern, just like animals. Amazingly, this includes the gymnosperms, most of which have paternal inheritance of cpDNA. But even some plants with maternal cpDNA patterns can pass on paternal mitochondria. An example of this is the banana - tomorrow morning you can feel like a rebel for garnishing your cornflakes with such an outlaw fruit.

However, the reason would be different. Remember that sperm have their mitochondria in their tails, and in most animals, this is not included in what enters the egg or is degraded just after entering. But few plants have flagellar sperm (like the cycads we talked about before). The sperm mtDNA is not exposed to anymore oxygen radical damage than the ovule mtDNA, yet there is most often uniparental, maternal inheritance.

Coastal redwoods can reach up to 110 meters

(360 ft) tall, but their roots may only go 6 ft.

underground. What's holding this tree in place?

It has two different types of leaves, and has male

and female branches and flowers, but all its

mitochondria and chloroplasts come from one

place, its father.

The interesting cases are those like the gymnosperms; paternal cpDNA, but maternal mtDNA. Once again, the plants are much more complex and intricate in their behaviors than animals, as two separate mechanisms for organellar retention and degradation must be at work in these plants. But even here there can be exceptions. The coast redwood (Sequoia sempervirens) has normal gymnosperm (paternal) inheritance of cpDNA, but it also has paternal inheritance of mtDNA! And the Chinese fir, which breaks the rules and is a gymnosperm with maternal inheritance of cpDNA, also makes itself exceptional in that it has paternal inheritance of mtDNA! Very confusing.

So mitochondria and chloroplasts both work in energy production, both evolved through endosymbiosis, both have single, circular chromosomes (with exceptions), and both have uniparental inheritance patterns (with exceptions). Next week, let’s look a behavior that is different in these two organelles.

For more information or classroom activities on monoecious/dioecious plants, angiosperms, gymnosperms, or plastid inheritance, see:

Monoecious/dioecious –

http://www.saylorplants.com/SaylorPlants/Ref_Info/Dioecious2w.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEkQFjAA&url=http%3A%2F%2Foklahoma4h.okstate.edu%2Flitol%2Ffile%2Fothers%2Fenrichment%2F4h500.pdf&ei=aXvKT4TuMIeC2wW1q4HaCw&usg=AFQjCNGyz1D_o5uVX0nMrNa2VpjchuJHgw

http://botany.csdl.tamu.edu/FLORA/Wilson/pp/s99/flowers.htm

http://www.oakleafgardening.com/glossary-terms/hermaphrodite-monoecious-dioecious/

http://www.bushmansfriend.co.nz/dioecious-plants-xidc18308.html

Angiosperms –

http://www.ehow.com/info_8462298_classroom-activities-angiosperms.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CHIQFjAI&url=http%3A%2F%2Fwww.burpeehomegardens.com%2Fpdf%2FBHC10538-BurpeeICanGrow-PlantClassification.pdf&ei=vn3KT5-dNMnW2gXOjc3ZCw&usg=AFQjCNH5IaI0aDUM1qd4wj_tVEaF-o8-jw

http://alex.state.al.us/lesson_view.php?id=24127

http://www.teachervision.fen.com/seeds/printable/28684.html

http://beckyboop.wordpress.com/2011/04/05/flowering-plants-lesson-plan/

https://www.google.com/#hl=en&sclient=psy-ab&q=gymnosperms+and+angiosperms&oq=gymnosperm&aq=1&aqi=g4&aql=&gs_l=serp.1.1.0l4.50243.54373.3.55834.20.16.1.1.1.13.328.3452.0j9j6j1.16.0...0.0.2xyYaWj6zCc&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=9d6464494833eb73&biw=1689&bih=895

Gymnosperms –

www.clt.astate.edu/mhuss/Lab%20Exercise%2011.doc

http://faculty.unlv.edu/landau/gymnosperms.htm

http://www.gardenbuildingsdirect.co.uk/Article/gymnosperms

http://alex.state.al.us/lesson_view.php?id=24115

http://sfr.psu.edu/youth/sftrc/lesson-plans/forestry/6-8/gymnosperms

http://academic.kellogg.edu/herbrandsonc/bio111/gymnosperms.htm

http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/seed%20plants/seed%20plants.htm

http://www.msnucleus.org/membership/html/k-6/lc/plants/5/lcp5_5a.html

Plastid inheritance -

http://www.ncbi.nlm.nih.gov/pubmed/20052516

http://www.amjbot.org/content/94/1/42.full

http://www.generationcp.org/plantbreeding/index.php?id=015

http://www.clivias.com/Articles/Article016.htm

[stuffxthree-blog]

When Is A Chloroplast Not A Chloroplast?

Biology concepts – gravitropism, plastid, chloroplast, chromoplast, amyloplast, leucoplast, malaria parasite

Believe it or not, the way plant roots know to grow into the dirt is related to photosynthesis! “How can this be?” you ask. Well, let’s talk about it.

The cells in the tips of the plant rootlet respond positively to gravity, called gravitropism(the older word for it is geotropism). If you lay a growing plant on its side, the roots will respond by growing (turning) toward the gravity within 10 minutes. The mechanism for this stimulation involves tension and a plant hormone called auxin.

Auxin is a growth hormone that gets redirected

in the growing plant root. The statoliths settle

and trigger the hormone to some cells more than

others. Auxin means ”to grow” in Greek, but in

some cases, like in gravitropism of roots, it

actually inhibits growth.

The rootcap (the cells at the tip of the root) have some specialized cells called statocyte (stat = position, and cyte = cell). Inside the statocytes are dense granules called statoliths (lith = stone). The statoliths are made of densely packed starch and are a specialized type of organelle called an amyloplast, which is used in many plant cells for storing carbohydrate in the form of starch (amylo = starch). The statoliths are denser than the cytoplasm of the cell; they don’t just float around, they settle out according to gravity.

Since the statoliths are connected to the membrane of the cell by the cytoskeletal actin molecules, so when they settle toward gravity, some cells in the membrane are stretched and some are compressed. This tension signals the cells to change the number of receptors for the growth control hormone auxin. More tension (more stretch) causes the auxin to move away, toward cells that are under less tension. Auxin prevents cell enlargement and cell division, so those root tip cells on the bottom receive more inhibition. Those on top enlarge more and divide more, so the root turns down. If the root is already vertical, the tension is equal in all directions, and the growth is equal in all directions – the root gets thicker and longer.

Gravitropism is related to photosynthesis in that both mechanisms involve chloroplasts, sort of. Root cells don’t perform photosynthesis, they are underground, so they don’t have chloroplasts. But they do have the amyloplastid statoliths, and these are related to chloroplasts.

Both amyloplasts and chloroplasts are specialized versions of the plant organelle called the plastid. We asked last week about what defines a plant cell – maybe the plastid is it. All plant cells have some plastids, but in different plant cells they may take different forms, including chloroplasts, chromoplasts, leucoplasts, amyloplasts, elaioplasts, or proteinoplasts, but they all start out as proplastids (pro = early and plastos = form in Greek).

Proplastids are in every new plant cell. From there

they can differentiate into other forms, including

the chloroplast. Other plastids are used for storage

or biochemical production. We will talk about statoliths

again when we discuss proprioception.

When acell divides, each daughter gets its share of proplastids, and then depending on the chemical signals that the daughter cell receives, the proplastid will differentiate (from latin, means to make separate) into the types of plastids that the cell needs. A proplastid can become any type of plastid, and from time to time can change between forms as the plant cell requires. Think of it as a sort of stem cell inside a plant cell – if the cell happens to be in the stem of the plant, it could be a stem cell inside a stem cell!

Proplastids become etioplasts, chloroplasts or leucoplasts. The etioplast is a sort of pre-chloroplast; a chloroplast without chlorophyll. It is waiting to be stimulated by light energy before it decides to spend all the energy it requires to make the chlorophyll. The old science fair project about growing bean plants in the dark demonstrates the etioplasts. The plants are white when grown in the dark, but bring them into the light and they soon green up. The sunlight stimulates the etioplasts to make chlorophyll, become full-fledged chloroplasts and start photosynthesizing.

This is a photomicrograph of the plastids of a

red flower petal. The chromoplasts hold the

xanthocyanin pigments, but we see it as a

continuous color because they are so small.

If the proplastid does not differentiate toward a chloroplast pathway (etioplast too) then it will become a leucoplast (leuko = white). The leucoplasts don’t have color; they become specialized for the storage of plant materials. If they store starch, they are called amyloplasts. Lipid storing leucoplasts are called elaioplasts, while protein storing plastids are called proteinoplasts. Each type serves a crucial purpose in the cells they inhabit, and they can all interchange, depending on the conditions the plant cell finds itself in.

Even more important, leucoplasts that are not serving as storage organelles have biosynthetic functions. They work in the production of fatty acids and amino acids. Amino acids link together to from proteins, so their synthesis is very important for plants. Plants must manufacture every amino acid it needs, whereas we get many of ours in our diet. There are even some amino acids that humans can’t make, called the essential amino acids. Of the twenty common amino acids, nine of them must be taken in through our diet, and some people with pathologies can’t make up to seven more. Plants don’t have this luxury; all their amino acids must be made on site. Good thing they have leucoplasts.

There is one other type of plastid that we haven’t talked about, the one that is important for the Autumn tourist trade. Etioplasts and chloroplasts can differentiate into chromoplasts, organelles that store pigments (colored molecules) other than chlorophyll. Chlorophyll provides energy through photosynthesis, but they also have a cost. The old saying, “It takes money to make money” applies to plants as well. It takes energy to make chlorophyll, so it only pays to make chlorophyll when there is ample sunlight to put through photosynthesis. When the days get shorter, the profit margin for producing chlorophyll goes down, so the plant just stops making it.

Twin females were imaged after a lifetime of smoking or non-smoking.   

Can you guess who was exposed to the oxygen radicals in cigarette

smoke her whole adult life?

The oxygen produced in plant cells during photosynthesis can damage many molecules; oxygen likes to react with other compounds and steal or donate electrons. This oxidative damage can wreak havoc with the cells, just look at the face of a long time smoker – the damage and aging process from the oxidants in cigarette smoke will be evident. The chromoplast pigments, like carotenoids (oranges and yellows) and xanthocyanins (reds and purples), can serve as antioxidants, and protect the other cell structures from the damaging effects of oxygen.

So the chloroplasts lose their chlorophyll in autumn and could be called leucoplasts, but the chromoplasts still have the pigments that had been masked by the greater number of chlorophyll molecules. The trees turn magnificent colors and bring people from the cities to stay in bed and breakfasts, and to purchase handmade scarves and way too much maple syrup and apple butter. Economy and biology are so often interrelated.

Plastids are the quintescential plant organelles – no plant cell is without them in some form (well O.K., there is one exception, we’ll talk about that next week). But that still doesn’t mean that they define a plant cell. Remember that algae are not plants, but they have chloroplasts, and chloroplasts are one type of plastid. There is even a bigger exception in this area; some of the apicomplexans.

Certain protozoal organisms, including the malaria parasite (Plasmodium falciparum) contain an organelle called an apicoplast. P. facliparum or its ancestor obtained an algae cell by secondary endosymbiosis (the primary endosymbiotic event was the algae taking in a cyanobacterium), so the apicoplast has a four, not two, membrane system.

The apicoplast of the malaria parasite is of plastid

origin, but it undergoes some unplant-like changes

during cell division. Image D with the branched

apicoplast is my favorite. Those in panel F will

grow to look the one in panel A.

The apicoplast does not perform photosynthesis; we aren’t exactly sure what it does – but it is crucial for the survival of the parasite. It is located in the front of the parasite (in the direction it moves and invades cells) and is always close to the nucleus and the mitochondrion. This suggests some role(s) in energy production and molecule synthesis.

There is evidence that the apicoplast works in fatty acid and heme synthesis, like the leucoplast or in the production of ubiquinones that are important for the electron transfer chain in the mitochondria. There is also evidence that it is involved in FeS cluster production, like the hydrogenosomeand mitosome. Both of these pieces of evidence show the interelationships of the endosymbiosed organelles and the connection between energy production and energy use. Whatever their functions are, if you destroy or inhibit it the malaria bug dies. As such, it has been a popular target for anti-malarial drugs.

Malaria parasites cured of their apicoplasts (cured means freed of) do not die right away. They just can’t invade any new cells and therefore can’t complete their life cycle. This is why anti-apicoplast drugs may be a boon to malaria treatment. The biosynthetic pathways in the apicoplast are the targets of four recent drugs, but the primary way to stop malaria remains the mosquito net. There is strong hope that a new vaccine, called RTS,S is a light at the end of the tunnel for this killer of millions.

The melanosome and the plastid have more in common.

The very rudimentary eye of some dinoflagellates

(dinos = rotating, and flagellum = whip) has a melanin-like

molecule in the pigment cup and the structure is called a

melanosome. However, it is of plastid orgin. The picture

above is of Polykrikos herdmanae. It has 8 transverse flagella,

as well as the pigmented eyespot to detect light sources.

One final thought on the plastid – an addition to the exception of melanosomes. We discussed a few weeks ago that melanosomes were the only organelles that could move from cell to cell. Well, that isn’t exactly so. I held off on adding the plastid to that list until we had discussed what a plastid was.

A 2012 study at Rutgers University tested whether plastids and mitochondria could move between plant cells. There results showed that entire plastid genomes could be seen in recipient cells, and the fact that the whole chromosome passed indicated that the plastid was probably moving from cell to cell intact. But there was no movement of the mitochondria, so it is a plastid (and melanosome) specific event.  The researchers hypothesize that this may be a way for plant cells to repopulate damaged cells with working organelles. As such, it would be similar to how mammalian stem cells can move mitochondria into damaged cells during tissue repair. But that is another story.

We have repeatedly talked about how the mitochondrion and plastid can replicate on their own and then are portioned out to the daughter cells when a parent divides. Can it really be that simple? I’ll bet there is a definite mechanism, and I bet that mechanism has exceptions. Let’s look into this next time.

Gregory Thyssena,Zora Svaba, and Pal Maligaa (2012). Cell-to-cell movement of plastids in plants Proc Natl Acad Sci U S A. , 109 (7) DOI: 10.1073/pnas.1114297109

For more information or classroom activties on plastids, gravitropism, or Plasmodium falciparum see:

Plastids –

http://teachersnetwork.org/ntol/lessons/plantcell/index.htm

http://pubs.acs.org/doi/abs/10.1021/ed074p1176A

http://theclassroomguide.com/category/sixth-grade-science-lessons/

http://sln.fi.edu/qa97/biology/cells/cell4.html

http://www.bcb.uwc.ac.za/Sci_Ed/grade10/cells/plastids.htm

http://www.nature.com/scitable/topicpage/the-origin-of-plastids-14125758

http://www.pnas.org/content/109/7/2439.full

http://library.thinkquest.org/27819/ch3_9.shtml

http://www.sivabio.50webs.com/plastids.htm

http://www2.mcdaniel.edu/Biology/botf99/cellstructure/plastids.html

http://www2.mcdaniel.edu/Biology/botf99/cellstructure/plastids.html

Gravitropism –

http://herbarium.desu.edu/pfk/page8/page9/page9.html

http://www.sciencebuddies.org/science-fair-projects/Classroom_Activity_Teacher_RootsGravity.shtml

http://www.sciencebuddies.org/science-fair-projects/project_ideas/PlantBio_p034.shtml

http://oldintranet.puhinui.school.nz/Topics/Plants/Ecosystem_Space/xpt1.html

http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/gravitropism/rootgrav/graviroot.html

http://www.nature.com/emboj/journal/v18/n8/abs/7591633a.html

207.62.235.67/case/biol215/docs/roots_gravity.pdf

Plasmodium falciparum –

http://www.yourgenome.org/teachers/managingmalaria.shtml

www.cpet.ufl.edu/icore/.../PDF/Malaria%20classroom%20activity.pdf

http://malaria.wellcome.ac.uk/doc_WTD023865.html

http://www.parasitesinhumans.org/plasmodium-falciparum-malaria.html

http://bioweb.uwlax.edu/bio203/s2007/augustin_laur/

http://www.icp.ucl.ac.be/~opperd/parasites/ancient_dna.html

http://www.tulane.edu/~wiser/malaria/cmb.html

http://www.searo.who.int/en/Section10/Section21/Section340_4269.htm

http://emedicine.medscape.com/article/221134-overview