Category Archives: development

Flying Duck Orchid

Caleana major off the Elvina Track, Ku-ring-gai Chase National Park, Australia Credit: Peter Woodard via Wikipedia

Today’s featured floral form is Caleana major, an orchid from Australia. It looks like a duck. It flies like a duck when the wind blows, but it’s just a flower. Why would an orchid develop such an elaborate costume? The answer is again pollination.

While this may look like yet another case of autotroph posing as heterotroph, it’s not the one you think. Caleana major’s flowers are designed to attract male sawflies. When the flies enter the larger ‘body’ portion of the flower, the ‘neck and head’ portion of the flower snaps closed behind them. For about a minute or so, the sawflies buzz around in a slight frenzy and become coated in pollen. This ensures that flower pollinates itself and any pollen remaining on the fly travels with it to the next flower.

Closed Flying Duck Orchid Credit: Peter Woodard via Wikipedia

The secret to this strategy is the sensitive ‘neck’ strap of the flower. This portion can sense when a fly has landed within the bottom part of the flower and trigger a response to have the ‘head’ snap closed. This trigger must also be reversed on a relatively short timescale to release the captive fly. He just needs enough time to be coated in pollen but none the worse for wear (unlike other carnivorous plants that intend on killing their insect victims with triggered mechanical responses).

This is an painting of Caleana major by Ferdinand Bauer, based on a drawing by him of material collected at Sydney in September 1803. It first appeared as Plate 8 in Stephan Endlicher’s 1838 Iconographia. It was scanned from Plate 13 of Mabberley, D. J. (1984) Jupiter Botanicus. via Wikipedia

There must be some interesting biochemistry underneath that response, not to mention the developmental gymnastics that must occur to make flowers that look like flying ducks. I’m not sure scientists will figure out these tricks because Caleana major cannot be cultivated outside its native environment. Because of its novel form and potential popularity with orchid enthusiasts, experienced growers have tried to grow it under greenhouse conditions, but with little success. It is speculated that a symbiosis with another microorganism in the soil of its native habitat is necessary for growth.

 

Johnna

References and Links:

http://en.wikipedia.org/wiki/Caleana_major

http://www.odditycentral.com/pics/what-the-quack-australias-amazing-flying-duck-orchid.html

http://gardenofeaden.blogspot.com/2013/11/the-flying-duck-orchid.html

http://www.friendsoflanecovenationalpark.org.au/Flowering/Flowers/Caleana_major.htm

http://nossa.org.au/tag/caleana-major/

http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Caleana~major

http://books.google.com/books?id=kUGL1TAaEtEC&pg=PA203&lpg=PA203&dq=Caleana+Major+pollination&source=bl&ots=bV-qtKkB8T&sig=-RSeg-ieBXJS428M6HdXHMuOOCY&hl=en&sa=X&ei=IehIVOWJBIi2yQT24IC4Cg&ved=0CF0Q6AEwDQ#v=onepage&q=Caleana%20Major%20pollination&f=false

http://books.google.com/books?id=SYvGAQAAQBAJ&pg=PA36&lpg=PA36&dq=Caleana+Major+pollination&source=bl&ots=fz35wIjm6P&sig=C-XAlmqySg2u2zznI5KzYcaCSa8&hl=en&sa=X&ei=U-hIVPi6N5epyASv_IHACA&ved=0CCYQ6AEwAjgK#v=onepage&q=Caleana%20Major%20pollination&f=false

 

Labor Day: Cotton

Happy Labor Day! I hope you are enjoying your day off of work or for those of you still on duty, I hope you are at least thankful for safe working conditions and reasonable pay. While there may not be an official botanical symbol of Labor Day, today’s post will feature cotton as the ultimate autotrophic symbol of work. So whether your collar is blue or white, even if you don’t have a collar at all, it’s probably still made of some cotton. So, take some time today to consider the labor of cotton in your life.

“All work, even cotton spinning, is noble; work is alone noble … A life of ease is not for any man, nor for any god.” Thomas Carlyle

A cotton field in Texas Credit: Kimberly Vardeman via Wikimedia Commons

Cotton plants have been hard at work for thousands of years supplying us with fiber for clothing and other goods. Also, as far as agricultural products go, cotton has historically set the highest bar in terms of human labor commitment. Consequently, this plant fiber has come to be both the most commonplace fabric as well as the most economically polarizing material in history. It is both a virtuous product as well as a historical symbol of labor exploitation because of the physical demands of its production and processing. ‘High cotton’ is synonymous with prosperity and good times. ‘Picking cotton’ was the epitome of slave labor, tedious and toilsome.

So what exactly is cotton? Plants of the genus Gossypium are perennial shrubs that bloom creamy white flowers. These self-pollinating flowers turn pink later in the day after pollination and begin to form a boll structure at the base of the flower that will contain the mature seeds for the plant. Check out the video below for images of developing cotton flowers and bolls in different stages.*

In generic terms, the boll is the seed pod of the cotton plant. It’s basically like its fruit, but instead of making a juicy delicious flesh around its seeds, cotton plants make soft fluffy fibers. When the seeds begin to mature within the boll, the cells of the outer layer of the seed elongate and kick cellulose production into high gear along their cell walls. It is a precise process that follows a specific pattern for reinforcing the thin cells, but also includes a regular deviation producing kinks and curves. It is these ‘imperfections’ that allow fibers to hold together into long threads as they are spun and thus confer their economic value. Once seed development is complete and the bolls burst open, these elongated cells desiccate, leaving behind shells of thin fluffy fibers hiding the seeds.

Thousands of years of cultivation have yielded a number of agricultural practices that make cotton crops easier to manage. While cotton plants will live as perennials, they are grown as annual crops. In order to have more predictable cotton yields, the fields are typically irrigated; however, cotton has high drought and salinity tolerance. So, for return on water use, it is a good crop choice and thrives in areas with long hot growing seasons. Harvesting is done by mechanical pickers that twist the bolls off of the plant. By weight, the majority of the cotton harvest is the seed. Each boll can contain 24 – 45 seeds entangled in the fibers. Cottonseed is valuable in its own right as a source for oil as well as nutritional meal. The separation of the cotton seeds from the fiber requires an enormous amount of effort. This process is now efficiently handled by mechanized cotton gins. The lint fibers are then baled into 500 lb units, which are the raw materials for textile mills that will then spin the fibers together to form threads and skeins of fabric.

The average acre of cotton in the U.S. will yield about 1 1/3 bales of lint. This is a two-fold increase over cotton production in the 1950s, largely due to improvements in land use, varieties, and irrigation. The vast majority of cotton grown in the U.S. is transgenic. It has been genetically modified to be resistant to certain herbicides or pests or both. Research continues on this economically important crop to improve fiber yield and quality as well as confer disease and pest resistance. Plant scientists are also eager to further push the limits of drought tolerance in this species.

The production and initial processing of cotton is only the beginning when it comes to cotton’s economic impact. According to the National Cotton Council, a bale is enough to make 215 pairs of jeans or 1,217 men’s T-shirts or 313,600 $100 bills. Yes, cotton is literally money. The estimated contribution of the cotton industry to the U.S. is $27 billion.

Olympia Cotton Mills, South Carolina c.1903

Olympia Cotton Mills, South Carolina c.1903

 

So consider cotton this Labor Day, whether you are enjoying a day off or clocking in. It doesn’t matter if your collar is blue or white, it all comes back to green in the plant Gossypium hirsutum. Both the plant and its processing have come a long way.

 

 

 

 

Johnna

*Video by Janice Person. Also check out the links below from her blog. If you want to know more about cotton, it’s definitely the place to visit. A whole blog about cotton! You can also follow her on twitter @JPLovesCotton (see, she really does love cotton).

References and Links:

http://en.wikiquote.org/wiki/Thomas_Carlyle

http://en.wikipedia.org/wiki/Cotton

http://en.wikipedia.org/wiki/Gossypium_hirsutum

http://janiceperson.com/cotton-101/

http://janiceperson.com/cotton/cotton-101-understanding-cotton-plant-video/

http://janiceperson.com/agriculture/ag-awareness/cotton-plant-cotton-field-pictorial/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1540163/pdf/hw1361.pdf

http://www.cotton.org/tech/physiology/cpt/plantphysiology/upload/CPT-Aug94-REPOP.pdf

http://www.cotton.org/edu/faq/index.cfm

http://www.cotton.org/pubs/cottoncounts/resources.cfm

http://www.cotton.org/pubs/cottoncounts/fieldtofabric/upload/Cotton-From-Field-to-Fabric-129k-PDF.pdf

http://www.cotton.org/pubs/cottoncounts/story/upload/The-Story-of-Cotton-Hi-Res-642k-PDF.pdf

http://www.cotton.org/foundation/reference-books/cotton-physiology/upload/COTTON-PHYSIOLOGY.pdf

http://www.spar.msstate.edu/class/EPP-2008/Chapter%201/Reading%20material/Temperature%20including%20Extremes/cotton_heat_Units1.pdf

http://janiceperson.com/cotton/a-million-bales-of-cotton-impact-from-one-small-town/

https://www.thefabricofourlives.com/

 

Let it Go: Abscission

Frozen

Up next in the Frozen series: Plants let it go! Here’s the Disney version in case you’ve been living under a rock for the past several months.

 

The cell walls grow thin in the zone tonight

No chlorophyll to be seen

The leaf is about to fall

Thanks to all the ethylene

In the winter weather those cells would have died

Wouldn’t have mattered how many genes I transcribed!

Turn them red, set them free,

I can’t move I’m just a tree

Breakdown, recycle, not just a show

But, here’s your show!

Let it go, let it go

Not holding on any more

Let it go, let it go

Away they fall, away they soar!

I don’t care

What they’re going to say

Let my limbs lay bare,

The cold never bothered me anyway!

It’s funny how abscission

Makes mincemeat of cell walls

And the genes that once controlled me

Can’t get to my leaves at all!

It’s time to see what I can do

Other organs can shed too

No petals, no flowers for me, I set them free!

Let them go, let them go

Already pollinated, that’s why!

Let them go, let them go

Useless now to me, so let them fly!

Here I stand

And here I’ll stay

I can’t move on!

My fruit flutters through the air onto the ground

My seeds spiraling on the wind all around

The next generation moving forward at last

But I’m never leaving

My roots hold me fast.

Let it go, let it go

It’s really better for me and my spawn

Let it go, let it go

That springtime form is gone!

Here I stand

In the light of day

I can’t move on,

I’m better at biochemistry anyway!

 

 

It’s hard to tell if plants have any inner emotional turmoil like the one Elsa had to fuel this song. However, it is safe to say that no matter how stoic they appear, there’s a lot going on inside them. Since they can’t move, plants have to roll with environmental changes using biochemistry and a flexible developmental program. Plants may not run away to the North Mountain, but they know how to ‘let it go’ when necessary. They do this in a process called abscission, a regulated way of shedding parts of themselves for the good of the plant or the next generation.

One of the most spectacular shows of abscission is the autumnal color change and shedding of leaves in deciduous trees. We call it ‘Fall’ because of the dramatic leaf drop before winter. Even though plants can take some measures to protect themselves from the cold, keeping some tissues over the winter requires too much energy of the plant. The trees do what they can to recycle the valuable contents of the leaf cells, which results in their colorful display. Then they coordinate a way to drop their leaves that doesn’t leave open wounds on the plant.

It’s not just letting loose of leaves before winter, abscission is an important plant process for other organs as well. Plants don’t need to waste their energy on maintaining flower petal tissue after they’ve already been pollinated. If seeds are on their way to forming, no need to keep the lush colorful tissues that can’t photosynthesize enough to support themselves. Further down the line, once fruit has formed to encapsulate the seeds, it must also be let go from the mother plant in order for the next generation to find a hospitable place to germinate. These examples represent normal developmental progessions for plant tissues, but sometimes plants have to improvise. When plant tissues become infected with bacteria, viruses, or fungi, they can kick the abscission process into high gear in the hopes that shedding the infected or damaged parts will prevent the death of the whole plant.

The abscission process creates an area of tissue designated the abscission zone, in which the cells take on distinctive characteristics. These cells are smaller and have an extensive network of endoplasmic reticulum and Golgi membranes with connections to the plasma membrane. The specialized cells of the abscission zone acquire the ability to respond to certain triggers to induce cell separation. These triggers can be a combination of environmental (ex. defense proteins induced upon infection) and internal (ex. the plant hormone ethylene) stimuli. When these triggers are perceived, the cells of the abscission zone up-regulate enzymes that breakdown the cell walls making cell separation easier. Ultimately, the abscission zone cells that remain on the main body of the plant differentiate into a protective layer so there is no open wound on the plant. The abscission process requires the coordinated activity of a large number of genes that must straddle the intersections of developmental pathways and environmental sensory integration.

Plant scientists are still working out the details, but the confluence of so many processes during abscission makes it a difficult problem to attack. However, understanding the abscission process remains a high-priority pursuit in the world of plant science. Agriculturally and horticulturally important plants have been heavily selected with respect to their abscission properties over many generations. In some cases, preventing early abscission may increase yields of certain crops (think- use those leaves longer, don’t drop them). Slowing down or halting the abscission process is also important for aesthetic reasons (keep those flowers and leaves around longer). Facilitating the abscission process may be equally useful and aesthetically pleasing. If plants could be engineered to abscise sooner or more completely, harvests would be easier because fruit would require less force to remove from the plant.

Consider the case of the gardenia- a striking example of a plant that needs to learn to let it go. It is perhaps the most perfect garden shrub- beautiful white blooms that coordinate with any background palette and a lovely scent. However, the blooms past their prime are truly one of the most pitiful sights in the botanical world- shriveled and brown and hanging on for dear life many days longer than anyone would care to look upon them. I’m not sure what inner turmoil is raging within this species, but biochemically, the processes of programmed cell death within the petals and their abscission from the plant are not coordinated in a way that is pleasing to the eye. If there were a gardenia variety that timed these processes more closely with one another, then gardeners would not be forced to look at the crumpled brown blooms.

 

 

Johnna

References and Links:

http://en.wikipedia.org/wiki/Abscission

http://lifeofplant.blogspot.com/2011/03/leaf-abscission.html

http://www.loyno.edu/lucec/natural-history-writings/abscission-reason-why-leaves-fall

http://www.ncbi.nlm.nih.gov/pubmed/24151306

http://www.ncbi.nlm.nih.gov/pubmed/24138310

http://www.ncbi.nlm.nih.gov/pubmed/23265318

http://www.ncbi.nlm.nih.gov/pubmed/12221970

http://www.ncbi.nlm.nih.gov/pubmed/11402180

http://jxb.oxfordjournals.org/content/48/4/821.full.pdf

http://www.plantcell.org/content/15/10/2296.abstract

For the First Time in Forever: Vernalization

Frozen

Next up in the Frozen series… we’re talking about flowering for the first time in ‘forever’ (really, just after winter). Here’s the Disney version for your reference.

FRIGIDA’s gone, so’s FLC

Winter is over? Can it be?

We need to transcribe a thousand different genes

For months we’ve waited in dormancy

Halted all pluripotency

Finally, it’s time to make some scenes!

There’ll be actual real live flowers

It’ll be totally great

I’m so ready for this activated state!

‘Cause for the first time in forever

There’ll be flow’ring, there’ll be growth

For the first time in forever

Translating AP1 and LFY both!

It must be the gibberellic acid

There’s active meristematic zones

‘Cause for the first time in forever

FLC is gone

I can’t wait to bloom, everyone!

What if I meet… the one?

This Spring imagine me petals and all,

Fetchingly vining up the wall

My flowers a delicately shaped vase

Ooh! I suddenly see him buzzing by

A striped pollinator that can fly

I’m gonna shove some pollen in his face!

But then we trade pollen and nectar

Which is completely strange

Not like when FLC is in detectable range

For the first time in forever

There’ll be flowers, there’ll be sun

For the first time in forever

I’ll be making AP1

And I know it is totally crazy

Excitement over meristems

But for the first time in forever

There’s activity in them

[FLC:]

Don’t let them out, don’t turn them on

Winter could still go on and on and on

Repress, turn off, it’s not time to grow,

Make one wrong move and get killed by snow

[FLC:] Is it only for today?

[FT:] It seems like Spring today!

[FLC:] It’s agony to wait

[FT:] It’s agony to wait

[FLC:] The VRNs are saying open up the gate

[FT:] The gate

[FT:] For the first time in forever

[FLC:] Don’t turn them on, don’t let them out

[FT:] I’m getting what I’ve waited for

[FLC:] Be the regulator the plant needs about

[FT:] A chance to change my stagnant world

[FLC:] Repress

[FT:] A chance to pollinate!

[FLC:] Repress, turn off, don’t let them out

I know it all ends in autumn,

So it has to start today

‘Cause for the first time in forever

For the first time in forever

Nothing’s in my way!

Flowering is important for plants because it’s how they reproduce. So, they need to have ways of ensuring that this process occurs under conditions that are most favorable for seed production. Plant species solve this problem in a variety of ways. Some annual plants avoid harsh conditions altogether and complete their life cycle within a single warm growing season. Others must find ways of going dormant during the freezing winter months and wait out the season until spring comes back. Plants integrate information on both day-length and duration of cold temperatures so they are not fooled into flowering on a random warm day in winter.

Under any conditions, the transition to flowering requires an elaborate set of gene expression changes so that cells achieve the proper developmental fate. The perennials and winter annual plants that require a cold period of dormancy prior to the flowering transition have an extra layer of regulation to ensure the transition occurs at the right time. Plants accomplish this with a set of gene regulators, some promoting the floral transition and others repressing it. These tiered layers of control allow for seemingly binary (on/off) switches to become a way of fine-tuning the development of flowers in these plants.

It’s not unlike the opposing personalities of Anna and Elsa in the movie Frozen. The gene FLC functions to keep plants from flowering, while genes like AP1, SOC1, FT, and LEAFY turn on genes to promote flower production. In perennials and winter annual plants, FRIGIDA serves to keep plants from flowering through the work of FLC until a certain amount of winter temperatures have passed. The genes VIN3, VRN1 and VRN2 act to let the plants know that enough winter weather has occurred and the hold on flower development (via FLC and FRI) can be let go. The way that the repression system works is also an interesting case. It’s not that these proteins physically block transcription of certain genes; these repressors leave covalent marks on the genome and the histone proteins whose job it is to organize the DNA within the cell nucleus. It takes some effort on the part of the activators to undo these marks to subsequently turn on the necessary genes.

Major players controlling flowering in plants. Pointed arrows mean activation or promotion, while blocked lines indicate repression.

Major players controlling flowering in plants. Pointed arrows mean activation or promotion of the next downstream thing, while blocked lines indicate repression of the next step in the pathway.

It’s interesting to note that all of the genes mentioned in the above paragraph are gene transcription regulators of one variety of another. This highlights a continuing theme in how pathways for development or environmental acclimation are controlled. There are a small set of regulators which control sets of other genes that are also regulators or that actually do the necessary biochemical work. These regulators work together to integrate environmental information (in this case-temperature, light, day-length) and keep developmental programs in check. Scientists tend to identify these factors pretty early in their investigations of these big questions, usually because mutants in these important regulators have obvious defects in the process of interest.

However, I have to admit, this drives me crazy as a biochemist. I want to know what’s going on beyond the nucleus in these processes. Sure, we may know a lot about what conditions turn these regulators and other genes on and off, but we know very little about the physical mechanisms by which plants sense the winter temperatures and time how long they’ve persisted. What is the actual ‘winter sensor’ in plants? How is it different from the cold sensor that plants use for cold acclimation on the timescale of hours or just a few days? How does this winter sensor differ among varieties with different ‘chill requirements’ before they flower and make fruit in the spring?* These components remain a mystery, but one that plant scientists are furtively working to solve.

Vernalization (the plant biology word of the day) is the acquired ability of a plant to flower after a cold season. For our perennials and winter annual plants, the passing of sufficient winter (as measured by the mysterious ‘winter sensor’ and regulated by VIN3, VRN1, VRN2, and FRI) gives these plants the ability to burst forth in flowers in the spring. Even though these regulators have a protective role for the plants in keeping them from trying to flower in the freezing winter, once their control is finally released, the flurry of activity associated with flower development is akin to a grand celebration after what seems like a lifetime of seclusion. Upon flowering, it’s all about reproduction. When it comes to plants, there’s not even a pretense of modesty; they have no problems trading pollen grains with a pollinator they have just met.

A number of economically important agricultural crops, like wheat, cabbage, carrots and most fruit trees, have vernalization requirements for flowering. Understanding how this process works is critical for getting the most out of these plants where they are grown and expanding the arable ranges for these crops. It may be some time before plant biologists make a Honeycrisp apple tree I can grow in Louisiana, but even modest adjustments to vernalization requirements to staple crops like wheat may be needed to accommodate predicted climate changes.

For more on how plants remember winter, check out this post over at The Quiet Branches.

Johnna

*This is why apple trees (with varieties requiring 400 – 1000 chill hours) don’t flower efficiently and produce fruit in a place as far south as Baton Rouge, LA (~200 – 300 chill hours), but figs (requiring only 100 – 200 chill hours) do.

References and Links:

http://www.azlyrics.com/lyrics/idinamenzel/forthefirsttimeinforever.html

http://en.wikipedia.org/wiki/Vernalization

http://www.newphytologist.org/app/webroot/img/upload/files/amasino.pdf

http://www.plantcell.org/content/16/10/2553.full

https://www.jic.ac.uk/staff/caroline-dean/vernalization.htm

http://plantcellbiology.masters.grkraj.org/html/Plant_Growth_And_Development11-Physiology_Of_Vernalization.htm

http://www.weigelworld.org/research/projects/floweringtimes

http://www.pnas.org.libezp.lib.lsu.edu/content/111/27/10001.abstract

http://www.ndsu.edu/pubweb/~mcclean/plsc731/homework/kim-et-al-vernalization-winter-%20and-the-timing-of-flowering-in-plants.pdf

Do you want to make a plastid?

FrozenNext up in the Frozen series… Do you want to make a plastid? Here’s the snowman version from Frozen for your reference.

Plant cells…

Do you want to make a plastid?

Come on, differentiate

Time to photosynthesize

Special things to metabolize

C’mon they need a fate

Those used to be proplastids

And now they’re not

We hope genetics tells us why!

Do you want to make a plastid?

It doesn’t have to be a chloroplast

Do you want to make a plastid?

Some grana stacks green and tall?

I think some development is overdue…

Environment gives you cues

From the nucleus transcription calls!

(Induce there GLKs)

It gets a bit confusing

All these proteins whizzing by

Translocation…

TIC, TOC, TIC, TOC, TIC, TOC

Chromoplasts get lots of color

With all these carotenoids

Amyloplasts store starches

For all the tissues underground!

Do you want to make a plastid?

It could even be a tannosome

Yes, etioplasts are in there

In the dark since who knows when

Shine the light to start,

The nucleus is there for them,

No longer inside meristems,

Time for some changes to begin!

They do so many functions,

Biochemistry

What can’t plastids do?

Do you want to make a plastid?


Well, if you are a plant cell, the answer to that refrain is always, “Yes!” Plastids are specialized organelles in plants that perform a wide array of specialized biochemistry. The most well-known and recognized of these are chloroplasts. These subcellular compartments are packed full of the thylakoid membranes and enzymes necessary to convert light into sugars. Chloroplasts perform other important biochemical reactions including the synthesis of starches and fatty acids as well as the assimilation of nitrogen into amino acids.

The chloroplast by User:Miguelsierra, adapted by User:Vossman via Wikipedia

There are other types of plastids made in plant cells for other specialized purposes. There are chromoplasts, which are full of carotenoid and other pigments giving them distinctive colors. The cells of tomato flesh, carrots and rose petals contain this type of plastid. Of course, pigments don’t do much good in root tissues. You may not find chloroplasts or chromoplasts there, but they do contain leucoplasts (loosely defined as non-green plastids used for storage of starches and oils). Storage-type plastids aren’t relegated to the roots. Recently other types of plastids have been identified, which specialize in the synthesis and storage of distinctive metabolites. Tannosomes have recently been characterized as specialists in tannin storage. A phenyloplast was also recently described in vanilla fruit as the storage location for vanillin precursor metabolites. In fact, the range of biochemical specialization that plastids perform strains their traditional nomenclature and definitions. As scientists learn more about them, the divisions between traditional types seems to blur. It seems that plants can make them as specialized as they need to be along a gradient of biochemical functions.

Types of plastids by Mariana Ruiz Villarreal LadyofHats via Wikipedia

Plant cells have definitely capitalized on the versatility of the plastid organelle structure to ensure dedicated locations for all manner of biochemical reactions and/or storage of their products. This is no small task. It requires the coordination of genes in two different genomes (that of the plant cell nucleus as well as a small genome in the plastid), trafficking of proteins throughout the cell, sensing of environmental cues, and synchronization with the overall plant developmental program. It’s enough to make any project manager run out of color-coded post-its and lose track of scheduled task times. Here are the highlights:

First of all, plastids do not exist in their mature forms in plant seeds and developing meristem tissues, but as immature and developmentally-flexible proplastids. These proplastids may not be special biochemists in their own right, but they have the potential to become any kind of plastid the plant cell needs. Consequently, proplastids have to know whether they are inside a root cell, petal cell or leaf cell. This means that plastid differentiation (aka development to maturity) must be coordinated with the development of the rest of the plant. Scientists are beginning to learn more about how this works, but this research is difficult since we’re talking about tiny, unremarkable pro-organelles within small portions of tissue. It’s a universal rule of cell biology that studying on small things is much more difficult than studying large things. Genetics has provided some new insights as to which genes have control over this developmental process. Transcription factors like the Golden-like (GLK) family of proteins have been identified as major players in this process, turning on suites of other genes to trigger proplastid development into mature plastids.

Of course, a lot of plant cell and plastid development is tied to environmental cues like light intensity. For example, plants can develop up to a point in darkness, but that doesn’t mean those cells have the same mature chloroplasts present in light-grown plants. Dark-grown plant cells contain plastids termed etioplasts, which are somewhat more differentiated than proplastids but not quite chloroplasts. Upon illumination, etioplasts quickly whip up thylakoid membranes and the photosynthetic machinery and get to the work of photosynthesis.

Plastid development and maintenance requires a large protein migration within plant cells. While plastid genomes make a number of their proteins, they do not make all of their resident proteins. Many essential proteins must come from genes transcribed in the plant cell nucleus and translated in the cytoplasm or endoplasmic reticulum. Thus, plant cells have an elaborate system of trafficking proteins to the proper cellular destination. This is true for all kinds of eukaryotic cells, but plant cells have extra organelles to distinguish among relative to animal cells. For those proteins with final destinations in the chloroplast, they have signals within their sequences that target them there. When they arrive at the chloroplast, they must pass through the surrounding double membranes using the Translocon of Outer Chloroplast Membrane (TOC) and the Translocon of Inner Chloroplast Membrane (TIC). In addition to the large influx of proteins that must be deposited upon initial development, the nucleus continues to provide essential proteins to the chloroplasts throughout their lifetime. It’s a constant flurry of activity maintained by two-way communication between the nucleus and chloroplast such that each organelle knows the biochemical status of the other.

Development into a mature plastid type isn’t the end of the line. There is still some developmental plasticity allowing certain plastids to convert into other plastid types. I’ve mentioned before that chloroplasts convert to chromoplasts in ripening fruit, as can be seen in the characteristic color change of green, unripe fruits into bright yellows, oranges and reds. Chloroplasts also provide the starting point for the development of other plastids specializing in storage of certain biomolecules. Plant cells also have ways of recycling the valuable contents of their plastids when cells and tissues reach the end of their lives (think autumn leaf color-change). As you might expect, this process requires more changes in gene transcription, protein synthesis and membrane structure orchestrated by the cell nucleus in response to more environmental and developmental cues.

Finally, proplastids and plastids of all types have ways of replicating themselves within plant cells. In this way, as plant cells divide each new daughter cell will contain roughly equal numbers of plastids. It wouldn’t be very good if a certain cell line within a tissue ran out of plastids. As much as plastids rely on the nucleus to full development and function, the nucleus cannot spontaneously create plastids from nothing. This wrinkle adds another layer of complexity to plastid biology. It means plastids must have some way of dividing themselves within the cells, and when plant cells divide, they must have some way of equally segregating the multiple plastids between the two new cells.

Basically, plastids are a lot of work for plant cells to make and maintain. However, these high-maintenance organelles are worth it given the biochemical rewards they offer. Scientists are only beginning to understand how plants make, maintain and recycle their plastids. Pieces of the complex system are studied by plant biologists all over the world and will likely keep them busy for many years to come.

 

Johnna

 

References and Links:

http://www.disneyclips.com/lyrics/frozenlyrics2.html

http://en.wikipedia.org/wiki/Plastid

http://link.springer.com/book/10.1007%2F978-3-540-75376-6

http://www.springer.com/life+sciences/plant+sciences/book/978-94-007-5723-3

http://www.uoguelph.ca/~itetlow/publications/assets/pdf/BY008-03-60-125.pdf

http://pcp.oxfordjournals.org/content/51/10/1601.long

http://www.ncbi.nlm.nih.gov/pubmed/23851381

http://www.ncbi.nlm.nih.gov/pubmed/23876238

http://journal.frontiersin.org/Journal/10.3389/fpls.2014.00124/abstract

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-313X.2002.01390.x/full

http://aobblog.com/2013/09/announcing-brand-new-cellular-organelle-tannosome/

http://www.ncbi.nlm.nih.gov/pubmed/24683183

May Bouquet: Alstroemeria

April showers have brought May flowers… to the blog. Today’s post is part of a May Bouquet series focused on flowers one might find in a bouquet. Y’know, leading up to Mother’s Day next Sunday. Think of these posts as daily reminders with wonderful suggestions on ways to honor the mothers in your lives.

Alstroemeria aurea ‘Saturne’ in southern Tasmania, Australia Credit: JJ Harrison via Wikipedia

Today we’ll have a look at the flower prevalent in many mixed-flower bouquets whose name you never learned- alstroemeria or Lily of the Incas. There are numerous species and cultivars, but they are native to South America. The different cultivars sport a variety of bloom sizes and markings. Alstroemeria are far more popular as cut flowers than garden plants, but they can be safely grown outdoors in USDA hardiness zones 8 – 11. They may tolerate the southern part of Zone 7 if the bulbs or rhizomes are adequately protected with layers of mulch during the winter months. Everyone else will just have to enjoy them as cut flowers or be prepared to host them indoors during winter.

Alstroemeria aurea in southern Tasmania, Australia Credit: JJ Harrison via Wikipedia

The pictures provide ample evidence as to why alstroemeria are popular cut flowers. They come in all colors and have beautiful spot patterns on the petals. Take a closer look at some of the flowers. There is a method to the madness when it comes to the spot pattern for many alstromeria blooms. Notice how (at least for these varieties) only three of the petals have the spotted pattern, two on the top half of the flower and one on the bottom? How do you think the flowers know their orientation and produce those markings?

Alstroemeria magnifica Credit: Pato Novoa via Wikipedia

Well, the truth involves knowing a little bit more about plant flower development. You’re not really looking at a flower with six true petals. Only three of them are petals (the ones with the spots). The other three are derived from tissue that would normally be sepals (special leaves at the base of most flowers that appear to hold the buds and blossoms together). In the case of alstroemeria blossoms, the sepals follow a developmental program that makes them look more like petals than leaves. Of course, botany has a name for this situation- tepals (when the sepals and petals cannot really be distinguished from one another as flower components in the perianth). If you would like an even closer look, check out this link with stunning photos and microscopic images of alstroemeria flowers.

The main parts of a mature flower Credit: Mariana Ruiz LadyofHats via Wikipedia

Alstroemeria pelegrina L. Credit: Pato Novoa via Wikipedia

Johnna

References and Links:

http://en.wikipedia.org/wiki/Alstroemeria

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a436

http://kindsofornamentalplants.blogspot.com/2012/05/alstroemeria-lily-of-incas.html

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artoct08/bj-peru.html

http://en.wikipedia.org/wiki/Tepal

http://en.wikipedia.org/wiki/Perianth