How to live with a legume

Peas, beans and other members of the legume family of plants can form friendly relationships (symbioses) with nitrogen fixing bacteria from the soil. Guided by the plant, the bacteria infect into the root and colonise plant organs called nodules, which supply sugars to the bacteria. Nodules also provide conditions that enable the bacteria to efficiently convert nitrogen gas (N2) into a form of nitrogen that plants can use to grow.

Endophytic bacteria (red) in surrounded by nitrogen-fixing bacteria in a nodule from the legume Lotus japonicas. Scale bar = 50 um. Image from Figure 1 by Zgadzaj et al (2015) (CC BY 4.0)

Endophytic bacteria (red) in surrounded by nitrogen-fixing bacteria (green) in a nodule from the legume Lotus japonicas. Scale bar = 50 um. Image from Figure 1 by Zgadzaj et al (2015) (Licenced under CC BY 4.0)

To set up a symbiosis, the plant and bacteria exchange signals to enable them to identify each other. The plants release molecules called flavonoids into the soil and, in return, the nitrogen-fixing bacteria produce molecules called Nod factors. These Nod factors activate signalling pathways that trigger many responses in the plant and allow the bacteria to enter. The bacteria need to produce the correct Nod factors to gain admittance and so most legumes are only able to team up with a few species of bacteria. Other bacterial molecules such as exopolysaccharides also play important roles in establishing the symbioses.

Although legumes choose their symbiotic partners carefully, other bacteria known as endophytes are able to infect and colonise nodules. Since these endophytic bacteria do not fix nitrogen, they do not appear to be beneficial to the plant and may take up room that could be filled with nitrogen fixing bacteria. However, we do not know exactly how the endophytes are able to gain access to the root.

In a paper published in PLOS Genetics earlier this year, a group of researchers led by Simona Radutoiu at Aarhus University, Denmark investigated how endophytic bacteria infect the nodules of a legume called Lotus japonicas (Zgadzaj et al. 2015). The researchers exposed the plants to a nitrogen-fixing bacterium called Mesorhizobium loti – which is able to form symbioses with L. japonicas – and a species of endophytic bacteria called Rhizobium mesoninicum strain KAW12.

Zgadzaj et al. found that R. mesonicum KAW12 alone is not able to induce the formation of nodules on L. japonicas. However, it is able to infect the nodules that form on the plant in the presence of M. loti. In these nodules, the nitrogen-fixing bacterium occupied most of the space, while the endophytic R. mesonicum KAW12 was confined to small areas. Further experiments showed that the ability of the endophyte to colonise the nodules depends on the signaling pathways in the plant that are triggered by Nod factors from the nitrogen-fixing bacterium.

Although the R. mesonicum KAW12 does not produce Nod factors, it does produce exopolysaccharides that might be recognized by the plant. Zgadzaj et al. found that exopolysaccharides produced by the endophyte promote its infection into nodules, while exopolysaccharides produced by the nitrogen-fixing bacterium restricted it.

Researchers have access to many different L. japonicus mutant plants that have defects in genes that control various stages of infection by nitrogen-fixing bacteria. The researchers used these plants to show that some of these genes also regulate which endophytic bacteria can enter the nodule.

Together, Zgadzaj et al.’s work demonstrates that legumes selectively regulate both the nitrogen-fixing and endophytic bacteria that are able to enter the nodule. In the field, symbioses between legume crop plants and nitrogen-fixing bacteria are often not as efficient as they could be, which can limit the growth of the plants. Therefore, these findings may aid efforts to improve the yields of legume crops in the future.

Reference: Zgadzaj, R, James, EK, Kelly, S, Kawaharada, Y, de Jonge, N, Jenson, DB, Madsen, LH, Radutoiu, S (2015) A legume genetic framework controls infection of nodules by symbiotic and endophytic bacteria. PLOS Genetics

Producing the perfect tomato

Image by regan76 (CC BY 2.0)

Image by regan76 via Flickr (CC BY 2.0)

This summer, I’ve been growing some vegetables in my garden. As a novice gardener, I selected some plants to grow on the basis of what is “easy to grow” rather than any other concern. Fortunately for me, one of my favourite foods happens to be the tomato, and tomato plants (Solanum lycopersicum) are very easy to grow even in small gardens like mine.

For culinary purposes, we generally treat the tomato as a vegetable, but it is in fact a fruit. The tomato plant comes from the Andes in South America where it grows as a vine (1). It is not certain when the plant was first cultivated but it was already being grown in Southern Mexico by 500 BC. At this time, the fruits were about the same size as cherry tomatoes and likely to be yellow in colour.

Today, tomato plants are grown across the world and produce fruits of various sizes and in a range of colours from yellow to red. The spread of tomatoes around the globe started in the early 1500s when the Spanish conquered South America (1). The Spanish took tomatoes to back to their colonies in the Caribbean and to Europe. Tomatoes quickly proved to be a hit in Southern Europe and were soon incorporated into the local cuisines. However, it took longer for tomatoes to catch on in Britain because, at first, many people thought that the fruits were poisonous due to their resemblance to the fruits of deadly nightshade, which belongs to the same plant family as tomato and potato (Solanaceae). Eventually, the British realised what they had been missing, and by the mid 1700s, S. lycopersicum was grown widely in Britain and in North America (1).

While writing this article, a fellow train passenger asked me “why do the tomatoes from my garden taste better than ones from the supermarket?” The answer is that the flavour of the fruit is influenced by when it is picked. Ideally, a tomato should stay on the vine until it ripens as this maximises its sweetness. However, soon after they ripen they become too soft and go off (over-ripen). This is not a problem if you are growing tomatoes in your garden, but for commercial growers that need to transport large quantities of tomatoes over long distances this is a big issue. As a result, most commercially grown tomatoes are picked and transported when they are still green (not ripe). When the tomatoes near their destination they are treated with a plant hormone called ethylene, which causes them to ripen. This enables consumers in many countries to eat fresh tomatoes all year round, but unfortunately also means that the fruits are less sweet than they could be.

The demand for sweeter tomatoes has led to tomatoes that are ripened “on the vine” becoming increasingly popular “premium” products. These tomatoes are removed from the plant along with a section of the vine so that the tomatoes can still gain flavour and sweetness from it.

Another possible solution is to develop tomato varieties whose fruits have a longer shelf life once they ripen. In the 1990s, researchers in the US developed a genetically modified tomato variety – called Flavr Savr – that was missing an enzyme that normally causes the fruit to over-ripen (2). This meant that the fruits could be left on the tomato plants until they ripened and then transported long distances without compromising their shelf life. The tomatoes were initially popular but the company the developed them ran into financial difficulties so the tomatoes ceased to be produced in 1997. A similar tomato variety was also developed in Europe and products containing these tomatoes were sold in UK shops until a scare over the safety of GM food in 1998 led to public opposition and the supermarkets withdrew the products (2).

More recently, a group of UK researchers have developed another variety of tomato that also have a longer shelf life than normal tomatoes (3). These tomatoes have been genetically modified to contain genes that increase the production of pigments called anthrocyanins so that the skin and flesh of the tomatoes are deep purple. The researchers were interested in these anthrocyanins because they have been reported to have health benefits and, indeed, the purple tomatoes increased the life expectancy of cancer prone mice. However, the researchers also noticed that the anthrocyanins slowed down the over-ripening process and made the tomatoes less susceptible to a fungal disease (3). Purple tomatoes are now being produced in Canada so that the tomato juice can be used in further experiments to assess the potential health benefits (4). It is possible that the tomatoes might be licenced for commercial production in some countries within the next few years.

Note: Apologies for the long gap since my previous post. Over the summer I’ve experienced a spell of “writer’s block” and so I decided to give myself a “blogging” break. I spent much of the summer reading fiction books and gardening and now feel it’s the right time to get back into a more regular blogging routine. I’m aiming to post every other week for the next few months. As ever, I’m always interested to hear from anyone who would like to write a guest post.


  1. Wikipedia: Tomato (retrieved 14/09/15)
  2. Wikipedia: Flav Savr (retrieved 14/09/15)
  3. Zhang et al. (2013) Anthocyanins Double the Shelf Life of Tomatoes by Delaying Overripening and Reducing Susceptibility to Gray Mold
  4. BBC News “Genetically-modified purple tomatoes heading for shops” by David Shukman, Jan 2014 (retrieved 14/09/15)

The (un)natural history of maize

Image by Spiritia licensed under CC BY-SA 3.0 via Wikimedia Commons

Image by Spiritia licensed under CC BY-SA 3.0 via Wikimedia Commons

As a PhD student, I once scared some work colleagues by making popcorn during a tea break (in the kitchen, not the lab, I hasten to add). They did not expect to hear the microwave making a series of “popping” noises, and for a few moments, I think they were genuinely worried that the microwave might explode.

Popcorn is made from heating the grains (kernels) of the plant maize until they explode, or “pop”. Also known by its latin name Zea mays ssp. mays, maize is the second most important crop plant in the world behind rice and is widely used in many human foods, as well as for animal feed and to make biofuels. It has many characteristics that make it useful to humans. Maize produces large kernels with high starch content (except for the varieties that are grown to make sweetcorn). The case surrounding a kernel is firm, but soft enough to allow us to grind these kernels to make cornflour. Also, harvesting the crop is relatively easy because the kernels stay on the cob even when ripe.

Maize belongs to the grass family (Poaceae) of flowering plants. The seeds of most of the grasses typically fall off the plant when they ripen to allow them to be scattered in the environment. Since maize kernels stay on the cob, it relies on humans to harvest the grains and sow them for the following season. So how did maize come to be so dependent on us?

To answer this question we must look to the origins of this crop in South America. Maize was domesticated from a wild grass called teosinte (Zea mays ssp. parviglumis). Archeological and genetic evidence suggests that farmers in the Balsas river valley of Mexico were the first to selectively breed teosinte about 9000 years ago. The people would have had to work hard to produce food from teosinte as each cob produces fewer kernels than modern maize. Also, these kernels are much smaller, fall off the plant when ripe, and have hard cases that would have made grinding difficult.

Teosinte versus maize. (A-B) The The female (left) and male (flowers) of teosinte (A) and maize (B). (C) Teosinte kernel (left) and maize kernel (right). (D) A comparison of teosinte on the left, maize on the right and the F1 of maize and teosinte in the middle. Image credits: (D) John Doebley, Department of Genetics, University of Wisconsin–Madison; all other images, Sarah Hake. (CC BY 4.0)

Teosinte versus maize. (A-B) The The female (left) and male (flowers) of teosinte (A) and maize (B). (C) Teosinte kernel (left) and maize kernel (right). (D) A comparison of teosinte on the left, maize on the right and the F1 of maize and teosinte in the middle. Image credits: (D) John Doebley, Department of Genetics, University of Wisconsin–Madison; all other images, Sarah Hake. (CC BY 4.0)

The domestication of teosinte also led to some other changes in physical characteristics. For example, teosinte plants have many branches, but in maize these branches are shortened and the leaves wrap around the cob to protect the kernels from birds, insects and other pests. Teosinte is adapted to life in tropical regions where the length of the day and night vary little throughout the year. If it is grown in more temperate regions – where the days become longer in summer – the plants flower later. Flowering time in modern maize is less sensitive to day length, which has allowed maize to be grown in much wider areas (including the UK).

In the 1970’s, George Beadle – who won a Nobel prize in 1958 for his work on the fungus Neurospora – became the first person to cross breed modern maize and teosinte. He then cross bred the offspring (known as the F1 generation) with each other and studied the characteristics of the next (F2) generation. Most of the characteristics of these F2 plants were intermediate between maize and teosinte, but some plants had features that were more like the teosinte or maize parent. Based on the frequency of these features in the F2 plants, Beadle argued that most of the differences between teosinte and modern maize may be accounted for by just 5 gene positions (loci). Further experiments by other scientists have backed up this idea and identified the roles some of these loci have played in domestication. For example, the gene locus tga is responsible for the harder coat of teosinte kernels, which appears to be due to differences in the proteins produced by this locus in teosinte and maize. Another locus, called tb1, is involved in stem branching and its activity is regulated differently in teosinte and maize.

The five gene loci suggested by Beadle illustrate how dramatic changes in a plant can happen with relatively few genetic changes. However, these loci are not the only regions of the genome that differ between teosinte and maize. Analysis of whole genome sequences from multiple teosinte and maize plants suggests that nearly 500 regions of the genome have been subject to selection. Some of these regions do not contain genes, and many of the genes identified in these regions show differences in their levels of activity. This suggests that changes in gene regulation have played an important role in the development of modern maize.


Hake, S and Ross-Ibarra, J (2015) The natural history of model organisms: Genetic, evolutionary and plant breeding insights from the domestication of maize. eLife 4:e05861. DOI:

The precious pods of the vanilla orchid

By H. Zell licensed under CC BY-SA 3.0  via Wikimedia Commons.

By H. Zell licensed under CC BY-SA 3.0 via Wikimedia Commons.

At the mention of “vanilla”, the first things I think of are ice cream, cake and other tasty foods. Next, I think of the little bottles of vanilla extract or flavouring that I often use when baking. In turn, that makes me think of the brown, shrivelled vanilla pods I have occasionally used in particular recipes. Vanilla is a popular ingredient in many foods and perfumes, but where does it come from?

The answer lies in an orchid called Vanilla planifola (also known as flat-leaved vanilla), which originates from Mexico. The Totonac people of Mexico were the first to cultivate vanilla. In their mythology, this plant was born when Princess Xanat—whose father had forbidden her from marrying a mortal—fled to the forest with her human lover. The lovers were captured and killed, and it is said that the vine of the first vanilla plant grew from the ground where their blood landed (2).

This myth reflects how highly vanilla was prized in the Totonac culture. Flat-leaved vanilla is a climbing vine and its delicate greenish-yellow flowers give rise to vanilla pods that contain hundreds of tiny seeds (2). The pods take about 6-9 months to mature on the vine, and then they are harvested, dried and fermented to produce the distinctive vanilla flavour (1), so it easy to understand how the pods became precious to the Totonacs.

Vanilla also became popular with the the Aztecs after they invaded Totonac lands. When the Spanish arrived in South America and reached the Aztec leader Montezuma, the Aztecs believed that their creator had returned and presented gifts, including their favourite drink, which was made from cocoa beans (chocolatl) (1). This drink contained vanilla and other various flavours that were previously unknown to the Spanish. Not surprisingly, vanilla soon became popular across Europe.

The Spanish kept tight control of vanilla production until the early 1800s, when French entrepreneurs shipped vanilla plants to the Islands of Réunion and Mauritious in the Southern Indian Ocean (2). The early attempts to grow flat-leaved vanilla outside of South America were not successful because the vanilla flowers, which only last one day, were missing their natural pollinators. In 1841, a 12-year old slave called Edmond Albius developed a simple and efficient hand-pollination method using a small pointed stick (2). By 1898, Madagascar, Réunion, and the Cooris Islands produced about 80% of the world’s vanilla (2).

Two other species of vanilla orchid—V. tahitensis and V. pompona—are also cultivated to produce vanilla, but the majority of the world’s supply comes from flat-leaved vanilla (3). Today, the main producers are Madagascar and other islands in the Indian Ocean, and Indonesia. The flowers are still pollinated by hand and, since the production process is so labour-intensive, vanilla is the second most expensive spice in the world behind saffron (2).

Vanilla contains more than 250 active ingredients, but the main one that is responsible for its distinctive flavour is called vanillin. Vanilla is so expensive–and the flavour is so popular–that many of the vanilla-flavoured food products we eat are made from artificially-made vanillin. Currently, most vanillin is produced by converting a naturally occurring organic compound called guaiacol, but researchers are also developing methods to produce vanillin from other sources, for example, from a structural molecule found in most plants called lignin. Another possibility may be to use a soil bacterium to convert a compound found in sugar beet pulp, wheat/maize bran and other agricultural waste products into vanillin (4). Unfortunately, I’ve struggled to find out more about this research because much of the published literature appears to be behind paywalls (grr!).

Whatever methods we use to make vanillin, the demand for “real” vanilla in premium foods is likely to sustain the livelihoods of the people that cultivate flat-leaved vanilla for some time yet!

Flat-leaved vanilla is the Organism of the Month. Apologies for the delay in publishing this post, it has taken me longer to finish than planned due to a combination of a family holiday, illness and the demands of my growing garden!

  1. Laws, B (2010) Fifty plants that changed the course of history. David and Charles
  2. Wikipedia: Vanilla (retrieved 16/07/15)
  3. Schmitt et al. (2015) Highly selective generation of vanillin by anodic degradation of lignin: a combined approach of electrochemistry and product isolation by adsorption. Beilstein Journal of Organic Chemistry.
  4. Greener Industry Vanillin (retrieved 16/07/15)

Negative but not useless: the results of a GM wheat field trial

Image by by Bluemoose (CC-BY-SA-3.0) via Wikimedia Commons

Image by by Bluemoose (CC-BY-SA-3.0) via Wikimedia Commons

Last week it was reported that a GM wheat variety that was found to deter aphids in laboratory tests failed to do the same in field trials (1). Some opponents of GM technology have called the trial a “waste of over £1 million of public money” and said that the trial “confirms the simple fact that when GM tries to outwit nature, nature adapts in response” (2). Are these fair criticisms?

The GM wheat variety—which was developed by researchers at Rothamstead Research in the UK—can make an insect pheromone called (E)-β-farnesene. This pheromone is normally produced by aphids when they are under threat to warn other aphids so they disperse. Some of the natural predators of aphids (e.g. parasitic wasps) are also able to detect this pheromone and are attracted by it.

(E)-β-farnesene and other insect pheromones have the potential to be used in agriculture as an alternative to pesticides, which typically kill beneficial insects too. However, the pheromones evaporate easily at normal temperatures and break down quickly, so application of synthetically made pheromones in fields is costly and technically challenging (1). Therefore, genetically engineering plants to produce the pheromone themselves could be more effective.

To enable the wheat plants to produce (E)-β-farnesene, the researchers introduced the genes that encode two enzymes called farnesyl diphosphate synthase and (E)-β-farnesene synthase, which modify molecules found naturally in the wheat plants. Laboratory tests found that the (E)-β-farnesene produced by these plants deterred three species of aphids and also increased the foraging behavior of a species of parasitic wasp called Aphidius ervi that preys on aphids. Based on these promising results, a field trial was carried out in 2012/3.

Why were the wheat plants able to deter insects in the laboratory but not in the field? The conditions in the environment could have played a role: both summers of the field trial were cold and wet, and researchers observed that the populations of aphids and parasitic wasps in both years were low, well below the threshold levels of infestation that would be reached before farmers would spray the crop with pesticides.

Also, the way in which the wheat plants produced the pheromone is perhaps not ideal. Aphids only produce the pheromone when threatened, but the GM wheat variety produced (E)-β-farnesene all the time. In the field, this could have led to the aphids becoming used to the pheromone—like how fishermen become accustomed to the strong smell of fish—so that the pheromone ceased to act as a deterrent. Therefore, developing different varieties that only make the pheromone at particular points in time (e.g. during aphid attacks) may be more effective.

The researchers have shown that it is possible to produce GM wheat that can make an insect pheromone. Although this variety is ineffective at deterring aphids in the field, it provides useful insights that could be used to develop better varieties in future, or may inform other approaches to deter aphids from attacking crops. “Negative” results are very common in scientific research because it is impossible to be sure of the results of an experiment before you have tried it. Therefore, this field trial was not “a waste of money”, but a normal step in research.

While I agree that “nature adapts” to finds ways around human technologies, this does not mean that we should completely give up on GM technology. After all, we haven’t stopped trying to develop new antibiotics just because some bacteria have developed resistance to some of the existing ones. Our problems with antibiotic resistant bacteria have been exacerbated by the over-use of antibiotics, which have placed bacteria under stronger selection pressures to develop resistance. Similarly, growing a limited number of crop varieties in monocultures places selection pressures on pests to develop resistance to our attempts to deter, or kill them. Using a mixture of different technologies and farming practices is likely to be much more effective in improving crop yields in the long-term. Even if they never make it to market, GM crop varieties are useful for scientific research, which will inform our efforts to improve agriculture in future.


  1. Bruce, TJA, Aradottir, BGI, Smart, LE, Martin, JL, Caulfield, JC, Doherty, A, Sparkers, CA, Woodcock, CM, Birkett, MA, Napier, JA, Jones HD and Pickett, JA (2015) The first crop plant geneticallyengineered to release an insectpheromone for defence. Scientific Reports.
  2. BBC News: UK GM wheat ‘does not repel pests’ by Claire Marshall

Dog rose: more mother than father

Image by Anemone Projectors via Wikimedia Commons (CC BY-SA 2.0)

Image by Anemone Projectors via Wikimedia Commons (CC BY-SA 2.0)

In the UK at this time of year, you may well see pink or white flowers that belong to a prickly shrub called the dog rose (Rosa canina) peeking out of a hedgerow. Later in the summer these flowers will be replaced with orange-red fruits called rosehips, which can be used to make a variety of food products including syrup, tea and marmalade. Rosehips are a rich source of vitamin C, and during WWII, British schoolchildren were actively encouraged to forage for them (1).

The dog rose—which is native to Europe, North Africa and western Asia—also has medicinal properties and was used in many traditional remedies. The seeds contain a diuretic, its leaves contain a laxative, and the plant was even used to treat rabid dog bites. Roses also feature in other aspects of human culture. For example, the flowers of the dog rose and other wild roses inspired the stylized roses in medieval heraldry (e.g. the Tudor rose). The pleasant scent of rose flowers means they have been popular ingredients in perfumes for centuries, and cultivated “ornamental” roses are found in many gardens.

Cuttings of ornamental roses are often grafted onto established dog rose root systems to generate healthy and uniform-looking plants for gardens, therefore there is a lot of interest in understanding dog rose genetics. Like our genetic information, the DNA of the dog rose is arranged into structures called chromosomes. We have two sets of 23 chromosomes (one set inherited from each parent when an egg and sperm cell fuse). Dog roses, on the other hand, have five sets of seven chromosomes (35 in total) and only one set comes from the male parent (Figure 1). This is possible because dog roses and their close relatives make egg and sperm cells in a slightly different way to most other organisms.

Egg and sperm cells are made in a type of cell division called meiosis. During meiosis in humans and most other organisms, each chromosome pairs up with the matching (but not necessarily identical) chromosome from the other set. These chromosome pairs are separated before the cell divides to make daughter cells with half the number of chromosomes.

However, since dog roses have 5 sets of chromosomes, it is not possible for all of them to pair up. Instead, only two sets of chromosomes (14 in total) form pairs (Figure 1; reference 2). These “bivalent” chromosomes are then divided equally between the daughter cells. In the female part of the flower, the remaining 21 “univalent” chromosomes join one of the sets of bivalent chromosomes to make an egg cell with 28 chromosomes. However, in the pollen, the 21 chromosomes are left out of the daughter cells to make sperm that only have 7 bivalent chromosomes.

Figure 1: Meiosis in dog roses. Sperm cells with 7 chromosomes are produced in the pollen and egg cells with 28 chromosomes are produced in the female part of the flower. Fusion of an egg and sperm cell produces an embryo with the full number of chromosomes (35). The chromosomes that form pairs (bivalent) are highlighted in pink. Image by Ritz et al. (2011) licensed under CC BY 2.0.

Figure 1: Meiosis in dog roses. Sperm cells with 7 chromosomes are produced in the pollen and egg cells with 28 chromosomes are produced in the female part of the flower. Fusion of an egg and sperm cell produces an embryo with the full number of chromosomes (35). The chromosomes that form pairs (bivalent) are highlighted in pink. Image by Ritz et al. (2011) licensed under CC BY 2.0.

Research suggests that it is usually the same two sets of chromosomes that pair up during meiosis (3). This might be because the other chromosomes are not similar enough to be able to form pairs. It is also possible that these chromosomes are capable of pairing up, but are prevented from doing so by a control system within the cell. Therefore, over many generations, the genes contained within the univalent chromosomes are likely to become more different to their gene copies on the bivalent chromosomes—which are mixed and rearranged when they pair up during meiosis.

The chromosomes in dog roses appear to have originated from different ancestral species of rose. This suggests that the extra sets of chromosomes are the result of the production of hybrids (when members of two different species reproduce). Hybrids are often sterile (i.e. mules) because the genetic material they inherit from the two parent species is too different to allow the different sets of chromosomes to pair up properly in meiosis. However, this problem can be avoided by duplicating all of the chromosomes so those from each species can pair up separately. For example, durum wheat—which has 28 chromosomes—originated from two grass species that normally have two sets of seven chromosomes each.

Although many plant species have more than two sets of chromosomes, the dog rose and its close relatives are some of the only plants known to inherit unequal numbers of chromosomes from their male and female parents. The next challenge for researchers is to understand how this process works at a molecular level. In the meantime, it gives me another reason to admire the dog rose as I pass by…


  1. Laws (2010) Fifty plants that changed the course of history. David and Charles.
  2. Ritz, CM, Köhhnen, I, Groth, M, Theiβen, and Wissemann, V (2011) To be or not to be the odd one out – Allele-specific transcription in pentaploid dogroses (Rosa L sect. Caninae (DC.) Ser) BMC Plant Biology
  3. Lim, KY, Werlemark, G, Matyasek, R, Bringloe, JB, Sieber, V, El Mokadem, H, Meynet, J, Hemming, J, Leithc, AR and Roberts, AV (2005) Evolutionary implciations of permanent odd polyploidy in the stable sexual, pentaploid of Rosa canina L. Heridity

The surprise potatoes

One of the potato plants I found in my garden. Two shoots and plenty of roots are growing from the tuber. Growing from the stems are several long white structures called stolens from which new tubers will grow later in the year.

A few weeks ago, I found some potato plants growing in the garden of my new home. The plants were completely surrounded by weeds but—after I nearly stabbed one with a garden fork—I realized what they must be when I noticed that the stems were growing from buried potatoes. Apparently, the previous occupants missed some of their crop when they harvested their potatoes last year.

Potato (Solanum tuberosum) is the world’s fourth most important food crop (behind rice, maize and wheat) and is grown across the globe in areas with temperate and sub-tropical climates. It belongs to the nightshade family of flowering plants, which also includes other crop species such as tomato, aubergine (also called eggplant) and chilli pepper (1).

Potatoes produce flowers that are either white, pink, red purple or blue, depending on the variety. These flowers can go on to produce small green fruits that look a bit like cherry tomatoes and each contain about 300 seeds (2). However, these fruits—like most of the rest of the plant—are poisonous because they contain the toxin solanine and several other glycoalkaloids.

The part of the plant that we call “a potato” is a structure known as a tuber, which is produced from the stems of the plant to store starch and other nutrients underground. The tubers of cultivated potatoes are safe to eat because they contain very little solanine compared to the rest of the plant. Solanine levels increase if the potatoes start to turn green, which can happen in response to light exposure, physical damage and as the tubers age (2).

The tubers allow potato plants to survive for several years (known as perennial). At the end of the growing season, the stems die back leaving just the tubers in the soil, which can produce new stems the next year. Since each individual tuber is able to produce a fully independent plant that can produce many more tubers, over successive years a single potato plant can effectively produce an army of clones. We exploit this ability in agriculture and most of the potatoes we eat are grown from tubers.

Finding the potato plants in my garden presented me with a bit of a dilemma: I was reluctant to throw them away, but I had no idea how to care for them. Aided by some advice from friends I decided to move the plants to “potato bags” (plastic bag designed for growing potatoes in that you fill with compost). This freed up the vegetable patch for the vegetables I had originally planned to grow and should make it easier for me to harvest the new tubers at the end of the season.

The potatoes survived their move and are now thriving in the bags.

The potatoes survived their move and are now thriving in the bags.

Some of my new neighbours spotted my potato bags and I told them about how I had found the plants. They have an allotment and—concerned that my surprise plants may not produce many potatoes—they popped around a few days later to give me a few of their own seed potatoes (Thank you!). Seed potatoes are tubers that are grown with the intention of using them to grow potatoes as opposed to being eaten. They are carefully grown and regularly monitored to be sure that they are disease free. In the UK, most seed potatoes are grown in Scotland where the cold winters kill pests and the wind deters aphids from attacking the plants and spreading plant viruses.

So, I now have two small sets of potato plants to care for over the summer and into autumn. When the foliage starts to turn yellow they will be ready to harvest, and hopefully I will have some tasty homegrown potatoes to eat this winter.

Potato is the Organism of the Month on Plant Scientist. To see the organisms featured in previous months click here.


1. Kew: Solanum tuberosum (potato) (retrieved 03/06/15)

2. Wikipedia: potato (retrieved 03/06/15)