Can we grow plants on Mars?

All the recent talk about the Mars One project got me thinking; what are these guys and gals going to eat? According to the website they’re planning on growing a lot of food within the habitation pods, but just how easy is it to cultivate plants on Mars?

First, the basics.

Mars

Can plants grow on this icy world? Image credit: NASA

An obvious problem is that Mars is very cold. It’s further than Earth from the Sun and it has a very thin atmosphere. A summer’s day at the Martian equator can reach 20°C but at night the temperature would fall to -73°C, killing even the most cold-tolerant of arctic plants.

Plants on Mars will have to be grown in heated greenhouses, with additional lighting to combat the lower light levels, which are around 50% of Earth’s light intensity. Liquid water can be obtained by melting the ice found in Martian soil, and carbon dioxide for photosynthesis makes up most of the Martian atmosphere (although the atmospheric pressure would have to be increased for both plant and human survival).

Yes yes, the basic necessities of plants are covered on Mars. BORING!

What about the nitty gritty details of growing plants on another planet? There are a lot of big unknowns, but we are slowly finding the answers to some of these questions.

Are plants able to grow on Martian soil?

The surface of Mars

The dusty soil on the Red Planet lacks reactive nitrogen, which plants need to grow. Image credit: NASA

Shipping tonnes of compost to the red planet would be expensive, so it’s better to grow plants on native Martian soil. Samples taken by Mars Pathfinder showed that the soil on Mars is sand-like, but does contain nearly all the essential nutrients that plants need to grow, with the exception of reactive nitrogen compounds like nitrate (NO3) and ammonium ions (NH4+), which are vital for plants to make proteins and DNA. On Earth, the majority of reactive nitrogen comes from rotting organic matter from dead plants and other organisms. Since there is no life on Mars, it makes sense that the soil is lacking these nutrients.

So is it possible to grow plants in this soil? Scientists from the Netherlands used simulated ‘Martian’ soil to find out. (Check out the paper here – open access).

NASA produced this Mars simulant soil using volcanic ash from Hawaii, which has little organic material, and treated it until it chemically and structurally resembled Martian soil. The researchers then used this soil to try and grow plants.They used 14 different species with small seeds so that the plants couldn’t rely on the nutrients stored inside the seed for growth.

All the plants germinated on the Mars soil simulant, and the researchers were amazed to find that despite the lack of reactive nitrogen, many of the plants grew better than those on nutrient poor Earth soil taken from a riverbed. The four crop plants in the study, tomato, rye, carrot and cress, survived well on the Mars soil simulant, which bodes well for growing plants on Mars in the future.

The simulant soil was a very close replica of Martian soil, but it did contain trace amounts of organic material because it came from Earth. Still, a colony on Mars could fertilise their soil with -ahem- human waste, so it is a promising start.

The problem of gravity

This is about to get a little Physics-y, but don’t worry, it’s simple enough even for me to understand!

The gravity on Mars is only around 38% of that which we experience on Earth. This means you weigh 62% less on Mars! (Click here to explore your weight around the solar system, but if you’re dieting, avoid travelling to the Sun…).

weightless

Science writer Mary Roach experiences weightlessness in a parabolic flight. Image credit: NASA

Gravity is really important for the movement of heat and gases. Cold air is denser than hot air, meaning a given volume of hot air weighs less than cooler air. The hot air rises and is replaced by dense cooler air, causing the air to move and circulate in a process known as convection.

At zero gravity everything weighs the same (nothing), so as Martian gravity is lower than Earth’s then the weights of hot and cold air will be more similar to each other. Convection on Mars will be reduced and the air will not circulate as much as on Earth.

This will limit the plant’s ability to take in CO2 for photosynthesis and release water through their leaves in the process of transpiration. Transpiration is important because it cools leaf surfaces much like sweating cools us down, but it is also the driving force behind the uptake of nutrients from the soil; as the water travels from the roots to the shoots it carries dissolved nutrients with it in solution.

To find out more, a daredevil research team from Osaka took to the skies to investigate the effect of gravity on plants. They strapped strawberry plants, lights and sensors into an aeroplane and took 28 parabolic reduced gravity flights used to train astronauts, measuring transpiration and photosynthesis rates in both doubled gravity (2g) while the plane ascended and at near zero gravity during the periods of weightlessness. (The paper can be found here behind a paywall).

In zero gravity plant transpiration decreased by 46% and there was 20% less photosynthesis than there was under normal gravity conditions. Interestingly, the opposite was true of the high gravity periods; plants increased their transpiration by 32% and their photosynthesis by 7%. This shows that gravity plays a major role in regulating plant transpiration and photosynthesis, so the reduced gravity on Mars may have a negative impact on plants, limiting their growth, nutrient uptake and temperature regulation.

Is it safe?

According to a recent MIT study (freely available here), growing crops on Mars isn’t as idyllic as it sounds. In fact, oxygen levels will shoot up as the plants mature and increase photosynthesis, posing a huge risk for fires. Oxygen venting systems are not currently well enough developed to keep the concentration at a safe level without venting nitrogen, which is needed to maintain the air pressure needed to breathe, so it would seem the choice is either suffocate or possibly burn to death.

Add to that the other unknowns described above, and it looks like a Mars colonisation attempt would need a lot of new technology and further research before anyone blasts off.

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Parasitic plants: Stealing food and genes

 Is it a mushroom? Is it a toadstool? No! It’s Helosis cayennensis, a plant!

Helosis is not your average plant.

Instead of photosynthesising to produce its own food, Helosis grows as a parasite on the roots of trees, stealing water and nutrients from its host. It spends most of its life underground, erupting only to flower in the mushroom-like inflorescences you can see above.

Helosis cayennensis is just one of around 4100 species of parasitic plant. They all produce haustoria, special threadlike organs that penetrate the host plant like a fungus to steal its sap.

There are two main types of parasitic plant:

  • Facultative parasites that are able to photosynthesise and live independently without a host, but can exploit other plants when available.
  • Obligate parasites like Helosis, which typically lack chlorophyll and exploit their host plants for the nutrients they need for survival.

Obligate parasites are the freakier of the bunch. They often don’t have leaves or roots, just a stem, their parasitic haustorium and eventually some flowers.

Parasitic plants steal DNA

The ‘corpse flower’ Rafflesia arnoldii is famous for producing the world’s largest flowers, which stink of rotting meat. It’s also an obligate parasite with no leaves, roots or stem, absorbing everything it needs to make these gigantic 1m flowers from its host, the Tetrastigma vine.

Rafflesia

Parasitic plant Rafflesia arnoldii produces the world’s largest flower, which smells of rotting meat! Image credit: Wikimedia

But that’s not all it steals.

In 2012, a team studying Rafflesia cantleyi and its host Tetrastigma rafflesiae found something strange in their DNA. Just looking at the two plants is enough to show they are distantly related, but for certain genes Rafflesia‘s DNA sequence closely resembled its host. The only possible explanation was that Rafflesia had stolen Tetrastigma‘s genes.

The researchers found that Rafflesia had acquired 49 genes from its host in a process called ‘horizontal gene transfer’. This is best known in bacteria, which can pass useful genes, for example those encoding antibiotic resistance, to other individuals in a colony.

Horizontal gene transfer is very rare in multi-cellular organisms. Interestingly, Tetrastigma did not have any of Rafflesia‘s genes. This suggests that the parasite benefits from stealing its host’s DNA, possibly by camouflaging it from the host plant which would otherwise mount a defensive immune response against it. This has also been seen in a malaria parasite (Plasmodium vivax), which has acquired human genes involved in the immune system (e.g. Interleukin-1 genes) that might help it to manipulate or evade the immune response and persist in the body.

Click here to read the Rafflesia paper (open access).

Parasitic plants and hosts exchange mRNA

When a cell wants to express a particular gene, the DNA sequence is transcribed into a messenger RNA (mRNA) sequence before being translated into its corresponding protein. mRNA was believed to be highly unstable, but recent research has found that it can be exchanged between parasitic plants and their hosts as a possible means of communication.

The team investigated the obligate parasitic plant dodder (Cuscata) growing on two hosts, Arabidopsis (the lab rat of the plant kingdom) and tomato. Dodder produces a network of tangled yellow stems that wrap around host plants and can cause significant damage to crops if left untreated.

Amazingly, the researchers found that huge amounts of mRNA was exchanged between dodder and its hosts. Almost half of the expressed Arabiodopsis genome was found in the parasite! Unlike the Rafflesia gene stealing above, around a quarter of dodder’s mRNA sequences were also found in Arabidopsis, showing for the first time that large amounts of mRNA could be exchanged between species in both directions.

Why is this important? Well, it’s known that mRNAs are able to transmit information within a single plant by moving between cells, so the researchers suggest that parasites could use these molecules to monitor the host plant or manipulate it for its own gain.

It’s possible that the mRNAs move passively from host to parasite, but the fact that parasite mRNAs are moving into the host cell too suggests that they are actively moved by the plants for meaningful communication. What are these plants talking about? With around 45% of Arabidopsis‘ mRNA sequences present in dodder it’s hard to decode the message, but hopefully science will soon be able to answer that question.

(Original paper is here, behind a paywall).


If you enjoyed this post, please feel free to leave a comment below or on Twitter (you can find me at @JoseSci)! Thanks!

Desert race for life

The record for the oldest living plant goes to a Great Basin Bristlecone Pine (Pinus longaeva), which lived to be over 5000 years old. Quite impressive, but all it’s managed to do is not die. Boring! What about the plants living life in the fast lane?

If you sift through the dusty soils of the North American deserts you’ll find a secret garden waiting to leap into bloom. Each square metre contains tens or even hundreds of thousands of tiny seeds all hoping for one thing: rain.

These are the desert ephemerals, the Ferraris of the plant kingdom that can complete their life cycle from seed to seed in just a few short days or weeks.


Chinchweed - Pectis papposa

Chinchweed flowers brighten up the desert. Image credit: Stan Shebs

Cinchweed (Pectis papposa) can germinate, grow and set seed in just four to six weeks, covering the desert with beautiful yellow flowers after the summer rains. Its fragrant leaves and seeds were used by native Americans as a condiment for cooking.


Desert ephemerals are a type of annual plant, which grow, reproduce and die back within a single growing season. Seeds of annuals are dispersed and remain dormant in the earth, poised to take advantage of the perfect growing conditions.

Instead of being slow growing like many desert plants, ephemerals spring up during the short wet season to dominate other species. They are not well adapted to dry conditions, so instead of wasting time growing into huge plants they stay small and reproduce rapidly to produce seeds.

Seeds are a lot more resistant to long periods of drought because they have an ultra slow metabolism, so don’t require water. The dry conditions in deserts prevent rotting, so the seeds may remain in the soil for many years if necessary.


This super cute tiny grass is called six-weeks grama (Bouteloua barbata). Its short stature helps it to quickly flower and produce hundreds of lightweight seeds.

Boutelouabarbata

Teeny tiny flowers of six-weeks grama. Image credit: Matt Lavin

Boutelouabarbataplant

Speedy growth means short stature. Image credit: Jacopo Werther 

 

 

 

 

 

 

 

 

 


Desert ephemerals may not stick around, but they have several important roles to play even after they’re dead. The dry plant material covers a lot of ground, preventing the arid soil from being too badly eroded by the wind. Their seeds are a nutritious lifeline for rodents and insects living in the harsh desert environment long after they’re dead. Not bad for a few weeks work.


 The real winner of the speedy life cycle contest has to be Plantago ovata, the desert Indianwheat. It races through life in just 2-3 weeks!

Plantagoovata

Plantago ovata, possibly the speediest flowering plant. Image credit: Stan Shebs


So there you have it. Desert ephemerals win the incredible plant race for life, often providing a stunning floral display in an otherwise pretty barren landscape.

Want to know more? Let Sir David Attenborough show you the desert in bloom.

 

P.S. If you’re into plant science, you’ve probably heard of another desert ephemeral without knowing it; Arabidopsis thaliana, the model plant!

Five weird and wonderful types of pollination

There’s more to pollination than bees. Plants are sneaky. They’ll use anyone or anything to get what they want. From treats to treachery and imprisonment, here are some of their most uncommon pollination tricks.

Pollen blast

Axinaea affinis

A flower of Axinaea affinis, showing “bellows” style stamens. Image source: Dellinger et al., 2014, Current Biology.

Birds passing this Axinaea flower are in for a treat. Its stamens (pollen-producing organs) are attached to what looks like a delicious yellow berry. These eye-catching appendages are full of sugar, so the bird hops down to peck off a tasty treat.

Of course, the plant has a reason for producing these energetically expensive snacks. These appendages are made of spongy material, full of air. The black sticks are the anthers where the pollen is produced. In this flower they’re hollow with a pore at the far end.

When a bird’s beak clamps down on the spongy appendages, the air inside is squeezed out through the anther like a bellows, blasting the bird with a face-full of pollen, which is carried to the next plant when the bird moves on.

 

Imprisoning pollinators

The giant Amazon water lily (Victoria amazonica) is an amazing plant. Its leaves can reach over 2.5 metres across and its beautiful flowers are over 30cm wide, but they live for just two days.

On its first evening the magnificent bloom opens, revealing white petals scented like pineapple. Beetles are attracted to the flower not just for its fragrance, but for the heat that the flower provides; around 10°C higher than the surrounding air. The flowers are female on the first night, and as the beetles enter they transfer any pollen they’re carrying onto the stigma.

In the morning the flower gets sneaky, trapping the basking beetles inside.

 

During the day the lily flower turns pink and becomes male, showering the scrabbling beetles inside with pollen. On the second evening, the flower opens once more, this time without scent or heat. The pollen-dusted beetles leave to search for another white flower, and the pollination continues.

 

Cologne for bees

Male_Euglossa_sp

A beautiful male Euglossa bee. Image from Wikipedia

The bucket orchids (Coryanthes sp.) produce aromatic oils for one purpose; it’s cologne for bees. Males euglossid bees collect the esters and other fragrant chemicals from the flower to impress the ladies, but in their excitement and jostling they often fall into the water-filled bucket of the flower. Their wet wings and the slippery sides make their escape almost impossible, except through an escape tunnel with bee-sized footholds. Handy.

You can see the escape spout in this Coryanthes alborosea flower on the left. Image from Wikipedia.

You can see the escape spout in this Coryanthes alborosea flower on the left. Image from Wikipedia.

The escape tunnel of bucket orchids is very narrow. Bees take around 30 minutes to carefully climb out to safety, but not before being adorned with a pollinium, an aggregated mass of pollen grains. On their next dip into a bucket orchid, the pollinium rubs off onto the stigma inside the entrance to the escape tunnel.

The scent droplets produced by the plant dry up by the time the bees have escaped the flower, which encourages the bee to visit another flower the next time it wants to apply cologne.

 

Fatal figs

There are around 750-850 species of figs (Ficus), each with its own species of pollinating fig wasp. Each is totally dependent on the other for successful reproduction. I’ll explain, but first, step away from any fig-based foods you might be eating.

A cross section of a fig

A cross section of a fig. Image from Wikipedia.

A fig fruit is a synconium, a bulbous stem containing hundreds or thousands of flowers, completely enclosed but for a narrow ostiole (hole) that only allows a specific species of fig wasp to enter. Female fig wasps crawl into the ostiole when they are ready to lay their eggs. The passage is so narrow that the wasp usually loses its wings and antennae, so she is doomed to die within.

(Some of the figs we eat come from sterile species that don’t require wasps. Others, however, do have… deceased occupants).

The fig contains three types of flowers; male, short female and long female. The wasp lays its eggs in the short female flowers, but it can’t reach down into the base of the longer females. Instead, these flowers are pollinated with the pollen the adult female carried from her original host fig and develop into seeds.

fig with wasps

A fig with its wasp inhabitants. Image from Wikipedia

When the larvae hatch they feed on their host short female flower until mature, receiving a coating of pollen from the male flowers as they move within the fig. The adult males are wingless and have two important jobs to do. First, they mate with the females. Next, they chew a hole out of the fig through which the females can escape. Then they die.

The females, coated with pollen, then emerge from the fig to find a new place to lay their eggs.

 

Tidal transfers

Zostera_marina

Zostera marina‘s tiny flowers release and capture pollen underwater. Image source: Wikipedia

We’ve seen plants trick-or-treating animals into carrying their pollen, but what happens when a plant spends its entire life underwater?

Zostera (eelgrass) is a seagrass, a true flowering plant. It employs a little known type of pollen dispersal called hydrophily. Its tiny male flowers release streams of pollen into the surrounding water, which have a few special adaptations for life under the sea.

It takes time to find another receptive flower without dedicated pollinator-transport, so eelgrass pollen has the same density as water, allowing it to drift in the current for days without floating or sinking.

Zostera pollen is elongated. While spherical pollen must be directly upstream of the female flower to pollinate it, longer thread-like pollen grains can be caught in the flow and eddies of water around the plant and eventually swirl into place on the female flower.

 

Over to you

Competition for pollinators has led to plants exploiting a huge range of animals, as well as wind and water. Do you know of any weird and wonderful kinds of pollination? Let me know in the comments below, or message me on Twitter @JoseSci!

Arabidopsis, the darling of plant science

arabidopsis

Arabidopsis thaliana, the lab rat of plants

Plant scientists are obsessed with a little weed called Arabidopsis.

On the surface it’s a strange plant to study; it’s not grown for food nor to feed animals, it’s not ecologically important and its flowers are, frankly, boring. Yet tens of thousands of researchers around the world dedicate their careers to discovering everything there is to know about thale cress, Arabidopsis thaliana.

This little weed is more than it seems. Like rats, E. coli and fruit flies, Arabidopsis is a model organism. Scientists study model organisms to learn their basic biology, which can be extrapolated into other related species. Arabidopsis can tell us a lot about crop plants, many of which are notoriously difficult to study. It’s even given us an insight into human diseases!

What makes Arabidopsis a good model plant?

Arabidopsis is a weed, which is great for research because it’ll pretty much grow anywhere, from soil to Petri dishes to liquid nutrient solutions. The mature plants are only about 5-10cm in diameter, so you can grow hundreds of them in a typical growth chamber. Best of all, it’s fast growing, going from seed to (irritatingly small) seed in just 6 weeks.

arabseeds

Arabidopsis seeds are tiny!

What really separates Arabidopsis from the crowd is its tiny genome. It has around 27,500 genes encoded within a genome of 125 million bases (letters) of DNA. Contrast this with the huge genomes of crop plants like barley (30,000 genes, 5.1 billion bases) and wheat (96,000 genes, 17.1 billion bases) and it’s easy to understand how Arabidopsis was the first plant to have its genome sequenced, way back in 2000 (a year before the Human Genome Project was completed). Since then, fantastic genetic resources have been developed in Arabidopsis, leading to a revolution in plant science.

Arabidopsis’ impact

By deciding to focus on Arabidopsis, scientists around the world were able to share knowledge and rapidly build upon new ideas. Many people, including myself, believe that this had led to a much broader and deeper understanding of plant biology than we could ever have achieved otherwise.

One way to understand the function of a gene is to stop it from working properly and look at the effect on the plant. The Arabidopsis genome sequence has allowed scientists to develop huge libraries of “mutants”, plants deficient in every single known gene. We knew the basic processes of plants from work done on crops over 100 years ago, but didn’t really understand the details. By working backwards from the mutants, we are able to discover which genes are responsible.

dna alignment

Genes from different species have some changes. The less closely related they are, the more different they are likely to be. Image produced in ApE.

The next stage is to translate the knowledge gained in weedy little Arabidopsis into more useful plants, like crop plants. Even though they look so different, almost all the genes you find in Arabidopsis are present in all flowering plants.

barley

Barley in a growth cabinet

Using the new genome sequences of plants like wheat and barley, it’s easy to search for Arabidopsis genes in these crops. It’s a bit like Google. Stick the letters in and it’ll give you the best matches. Different plants usually have a few changes in the sequence of a gene, but the best match is usually the gene you’re looking for.

From there it’s a matter of silencing the gene you have identified in your chosen crop plant to see if it has the same impact as it did in Arabidopsis. If so, you’ve just improved our understanding of an economically important crop species.

The future of Arabidopsis

Genome sequencing is becoming increasingly cheap and easy. Will we still need Arabidopsis in a world of species-specific genomes? I’d argue yes, at least for a decade or two yet. It is still comparatively very difficult to work with crop plants directly. We don’t yet have full libraries of mutants so Arabidopsis plays a vital first step in gene identification. A full understanding of genes in the model plant would make it a lot more easy to investigate their functions in crop species. Future research areas like synthetic plant biology are predicted to be developed in Arabidopsis too.

Arabidopsis thaliana is the backbone of plant science. Its genetic resources have led to great leaps in our understanding of plant biology, focussing research and enabling translation into crop plants.

Weeds are flowers too, once you get to know them – A. A. Milne

Do plants get cancer?

Spend all day in the sun and you run the risk of developing skin cancer, yet plants seem to bask in UV rays without a care.

Truth is, plants can develop tumours. Unregulated cell division occurs in plants just like animals, so why don’t we ever hear of a plant dying of cancer?

Types of plant cancer

Infections can cause tumours in plants, in a similar way to the HPV virus causing cervical cancer in humans.

The bacterium Agrobacterium tumefaciens causes tumours called crown galls in many species of plant. The bacterium inserts its own DNA into the plant and messes up its growth hormones (auxin and cytokinin), creating a Agrobacterium-friendly tumour where it can live happily ever after. It’s rarely fatal but can cause some yield loss in perennial crops like fruit trees because gall production steals energy that could have been used to make more delicious apples or cherries.

cornsmutwiki

The corn smut fungus is a delicacy in Mexico. Source: wikipedia.

Fungi like Ustilago maydis can produce tumours in a similar way. U. maydis causes corn smut, turning ears of corn into the strangely grey and deformed Mexican delicacy known as huitlacoche.

Geminiviruses cause tumours by directly interfering with cell replication in plants.

Although it’s uncommon, certain types of plants are quite prone to spontaneous tumours too. In a fun twist of fate, tobacco (Nicotiana) plants are particularly prone to developing cancer; when two species cross-breed with each other, the resulting offspring often develop tumours because of hormone regulation problems.

How to grow a tumour

Plant tumours share some similarities with human cancers. Plant tumours are disorganised lumps of cells, similar to human cancers. They are often caused by problems with levels of the hormones auxin and cytokinin. Fluctuations in hormones like oestrogen can lead to cancer in humans too.

crowngallwiki

Agrobacterium tumefaciens causes crown galls to develop. Source: Wikipedia.

Cell replication is strictly regulated in animals and plants by genes that are amazingly similar in both groups. Auxin and cytokinins, as well as human hormones like oestrogen, can interact with these cell cycle genes. When the hormones are out of balance, cells can start to multiply out of control.

These cell cycle genes can mutate and stop functioning properly, causing cancers in animals. Plants are less likely to fall victim to these random mutations because they have many copies of most cell cycle genes, so another version can take over if one is put out of action.

Plants also have a few other fail safes to protect themselves from potential cancerous cells:

  • Regeneration. Brain tumours are one of the deadliest human cancers, with an 85% mortality rate after five years. The brain is such a vital organ that we cannot survive without it, but plants can regrow any damaged organs reducing the impact of a tumour.
  • Totipotency. Plant cells are totipotent, which means they can develop into any cell type. If too many cells are produced in a leaf they can be incorporated into a normal structure. Each cell will be smaller than normal to maintain roughly the correct leaf shape overall.
  • Containment. Plant cells are contained within a cell wall. Cancer cells can’t squeeze into neighbouring tissues, so the tumour is restricted to one area. Plant veins are different to humans too; only water and things dissolved within it can move through the vascular system. Tumour cells can’t cause new tumours elsewhere.

There are really two main stages to developing cancer; the cells go wrong then spread throughout the body. Infections, unstable hormones and plain old mutations can cause plant cells to override regulation and begin to divide, but cell walls and a dynamic body plan means plants are able to stop tumours from spreading uncontrollably or doing too much damage.