A day in the life of a plant scientist

 

Check out my Storify post for an insight into the day-to-day world of science (and what it’s like to be a PhD student at the University of Bristol!)

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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.

Carrots and beta-carotene

Still waiting for your carrot-induced night vision to kick in? You might have a long wait.

The myth that carrots help you see in the dark began during World War II to try and hide the rapid improvement of British radar. We needed an explanation for why our pilots could suddenly take down enemy planes in the dead of night, so propaganda posters were produced spreading the line that carrots could help you to see during the blackouts.

Unfortunately carrots can’t improve a healthy person’s night vision, but you can see why the enemy might have been fooled. Carrots are rich in the orange-red coloured pigment beta-carotene, which our bodies convert into vitamin A to use in vision.

betaCARROTene

Beta-CARROTene! Geddit?! Image mutilated from originals on Wikipedia here and here.

 

Beta-carotene 

Plants use chlorophyll to harvest light energy for photosynthesis, the process by which they convert carbon dioxide and water into sugars (and oxygen). Chlorophyll isn’t brilliant at soaking up the blue wavelengths of light, so beta-carotene steps in alongside it to mop up the blue and indigo rays. When we eat it, beta-carotene is broken down into retinal, one of the vitamin A compounds. It lets us see blue light at pretty similar wavelengths to those it absorbs in plants.

photosynthesis spectrum

Beta-carotene and other carotenoids help plants absorb blue light at 450-570nm wavelengths. Image adapted from Wikipedia

 

Antioxidant effect

Photosynthesis is performed by reaction centres in plant cells called photosystems. As well as light harvesting, beta-carotene can be added to these complexes for its antioxidant properties. If too much light reaches photosystems, they can produce highly reactive singlet oxygen molecules. Singlet oxygen can cause a lot of damage to cells, but beta-carotene is able to quench its effects before DNA, proteins and lipids are adversely affected. Whilst we don’t photosynthesise, our cells can be the victims of chemically reactive damaging compounds produced by our metabolism. Luckily beta-carotene from our diet retains its antioxidant effects, helping to prevent cell damage and cancer. That’s a better reason than “night vision” to eat your veg!

Pretty colours

tomato

Beta-carotene gives tomatoes their red colour. Source: Scott Bauer, Wikipedia

Plants use beta-carotene to produce beautifully colourful flowers to entice pollinators and fruits for other hungry animals to distribute their seeds. To that end, apricots, sweet peppers and tomatoes are all very high in beta-carotene.

It’s not altogether clear why root vegetables like carrots and sweet potatoes are so rich in beta-carotene, since none of the above benefits seem to apply.

 

Use in GM

Many people living in the developing world do not have access to foods containing enough beta-carotene. They become deficient in vitamin A, which can lead to blindness and death in extreme cases.

Golden_Rice

Golden rice has been engineered to produce beta-carotene in its grains. Source: Wikipedia

Now, genetic modification (GM) of food is a complicated topic that I don’t want to get into in this post, but there is a fairly famous crop specifically designed to target vitamin A deficiency. Golden Rice has been engineered to produce beta-carotene in the rice grains by adding one gene from maize (corn) and another from Erwinia, a type of bacterium. The proteins encoded by these two genes work together to produce beta-carotene.

Maybe it can’t help you see in the dark,  but beta-carotene is vital for healthy vision and cancer-preventing antioxidant effects. Keep munching those carrots.

What’s all this then?

Hi, I’m Sarah Jose and I’m in my second year of a PhD in plant sciences at the University of Bristol.

I’m sitting here writing because I want to tell the world about how AWESOME plants are! There are a lot of blogs out there about human-y subjects like medicine and psychology, but I want to get into how plants can do all the fantastic things that we take for granted.

I love writing about science (both academically and in the “real world”), so I started this blog to start some conversations about fantastic plant research. I’m talking to non-scientists about what has been found and why it’s great. 

A bit about my work

I should probably add a bit about my research so far, since it’s unlikely to be published for me to blog about any time soon!

I am looking into the link between the development of the microscopic pores on the leaves (known as stomata) and the waxy surfaces of the plant. Stomata let CO2 into the leaf fOpen and closed barley stomataor photosynthesis, but whilst open they let water escape. Plants have to open and close these pores to balance having enough CO2 with not dehydrating too much. The waxy surfaces on leaves help by not letting water escape from anywhere else. A few genes have been found that affect both the amount of wax and the amount of stomata that a plant produces, and I want to find out exactly what’s going on!

Why is this important? We’re going to need to feed a lot more people in the future, growing more crops in less land using less water. If we can understand how and why different types of leaf wax affect stomata development and water loss from plants, we can apply this to crops in the real world. This might mean genetically modifying plants to produce different types of leaf wax, but it might also be as simple as finding new waxy types of plants grown by conventional plant breeders.

barley

Keep in touch

If you enjoy an article, please leave a comment. If not, leave one to say what you disagree with. Whether you are a plant nerd like me or an accidental stumbler into my path, stay for a while and lets talk plants!

I tweet about science-y things: @JoseSci

I write about the environment and research at the University of Bristol for the Cabot Institute blog. You can find highlights on my Around the Web page above.