Think plants are dumb?

What is intelligence? Intelligence can be defined as the ability to perceive changes in one’s environment, to apply knowledge to manipulate their environment to suit oneself, and to think abstractly. If I were to ask if you thought plants were intelligent, most likely your response would be “most certainly not, they’re not animals”, or something along those lines. And in one sense you would be right, they are not animals. Gotcha. But…it is of course much easier for scientists to prove that animals can be intelligent, because they have obvious structures that we associate with intelligence, such as a brain, and a nervous system.  However, when considering plants, the criteria for intelligence are less clear.  So this raises two questions – are plants intelligent, and if not intelligence, what has allowed plants to adapt, survive and flourish in their various environments.

The question of plant intelligence raises the issue of whether plants are capable of feeling and adapting to their environment and manipulating it, which has led to the idea of plant neurobiology. This concept of plant neurobiology allows us to understand how plants perceive their environment and how they respond to those stimuli. This could give us ideas for the future on how to develop better ways to grow crops. One particular person who is well-known for his views and work on the concept of plant neurobiology and plant intelligence is Professor Anthony Trewavas. He proposed that plants must be intelligent, because of their ability to perceive their environment and manipulate it. He described plant intelligence as the interactions between the plant tissues of an individual plant, which appear to give evidence for a nervous system.

In recent years, there has been an increasing amount of evidence to suggest that plants do possess a type of nervous system. One example demonstrating this is Arabadopsis thaliana, model plant species in plant biology and genetics. Scientists have performed experiments that showed the reaction of the whole plant (under fluorescence imaging) to light being shone onto a single leaf of the plant. They noticed that the plant responded to the light by carrying out light-induced chemical reactions (photosynthesis continued in the dark). These findings suggested that the leaf sent electro-chemical signals to other leaves, causing them to start photosynthesising too, which can be compared to the nervous system in animals. Another experiment subjected Sterllaria seeds to dark or light conditions for more than a year, and the seeds showed some memory of the conditions they had experienced. Some argue that plants do have a brain and it could be located in the meristem near to where the signal has been given. Evidence for this can be found in the local meristem itself, where decisions are made – whether a plant will move its roots towards the nutrients or water, or whether it will moves its leaves towards the sun.

Plants have the ability to perceive changes of abiotic or biotic factors within an environment; therefore, they react in a certain way to counteract that change. Plants, like carnivorous plants, are capable of perceiving changes in their environment, through the use of sensory organs, which allow them to respond to environmental stimuli, such as light, gravity, and water. The plant’s response to a stimulus is called a tropism. Behaviour of carnivorous plants supports plant intelligence further.  Dionaea muscipula (Venus flytrap) has modified leaves which trap insects for the plant to digest. Inside the leaves, 6 tiny hairs act as triggers, and when they are touched, this triggers the trap to close, due to deformation of hair sensory cells. It is argued that D. muscipula must have some form of nervous system in order for this reaction to occur.

Venus flytrap (Photo credit)

 

Plants also have the ability to manipulate their environment. One way that they do this, is through changing soil pH. For example, in some areas where the soil is very low in nutrients, (particularly iron, which is necessary for plants to grow healthily), some plants excrete protons into the soil, which causes the pH of the soil to decrease. This increases the solubility of the iron molecules so the plants are able to take up the iron from the soil more easily.

However, you could easily argue that plants do not possess intelligence. The most obvious argument is that plants do not have a brain, so they cannot think or reason. Yes, plants are capable of detecting changes within their environment, but they simply respond to these changes naturally without making a conscious decision. Their responses are innate, built into their molecular structure. For example, if a plant is placed near a window, the leaves will turn to face the sun (positive phototropism). The plant shoots move towards the light, due to the secretion of the plant hormone auxin. The light causes auxins to be secreted at the dark side of the plant, causing the elongation of the plant cells on the dark side of the plant. This is simply a hormonal response, as the plant is simply reacting to the light stimulus. The theory of evolution will say that this shows that the plant has ‘learnt’ through the process of evolution that it needs to move to the light to survive. Tropisms allow plants to maximise their chances of survival. Plants with more favourable responses to stimuli can pass on their genes to future generations, thereby increasing the survival of their species. In place of a nervous system, plants use chemicals to convey messages. For example, the sagebrush secretes chemical signals, which warn surrounding sagebrush plants that there are pests nearby. This triggers the surrounding plants to produce leaves that are more resilient to pest attack. The ‘decision’ for the plant to produce these chemical signals is made at the cellular level of the plant. What’s more important, the plant would still produce the signal without other sagebrush plants around. This suggests that plants are pre-programmed to react this way, and that they are not aware of their surroundings.

Another argument against plant intelligence is plants’ lack of a true nervous system. Some plants do have sensory hairs, like Mimosa pudica, which has tiny hair-like projections on its leaves. Once these hairs are touched, this triggers the leaves to close up, acting as a defense mechanism. This is as a result of rapid long-distance signalling . The plant appears dead, so it is preventing its predator from eating it. This increases its chances of survival and maintaining genetic diversity.

Mimosa pudica (Photo credit)

If a systematic approach is used, you could say that plants can’t be classified as intelligent. Although they do have systems which allow them to conduct chemical signals across from one part of the plant to another, they do not have a proper nervous system with a brain. As a result, they cannot think, or reason. Plants show that they are unable to choose where their seeds land and germinate – it is random. However, just because plants may not be considered intelligent in the way humans are, does not mean that they are not productive – they still need to regulate their metabolic and developmental processes in order to maintain function. However, this regulation does not mean that a plant has thought about any of the processes it is involved in. Plants have a built-in ability to adapt to changes in their environment. Some plants have shown to be resilient against drought, extreme soil salt concentration, flooding, and fire. Their ability to survive maximises their chances for successful reproduction, therefore allowing their genes to be passed onto future generations.

The scientific community (and perhaps my readers) remain divided as to whether plants can be considered intelligent, and this is likely to remain the case. However, the concepts of plant intelligence and neurobiology could raise awareness of what plants are capable of, when placed into challenging situations; and this can allow us to find ways of utilising plants’ amazing features which make them the most successful species on the planet.

So the verdict is…I’ll leave that to you to decide.

#plantsgotskills

Extra reading:

Chakrabarti, B. K. and Dutta, O. (2002) An electrical network model of plant intelligence. Indian Journal of Physiology

Firn, R. (2004) Plant Intelligence: an Alternative Point of View. Annals of Botany 93

Gill, V. (2010) Plants ‘can think and remember’ BBC. 14 July 2010. 12 February 2012 <http://www.bbc.co.uk/news/10598926>

Hodick, D. and Sievers, A. (1988) The action potential of Dionaea muscipula Ellis. Planta 174

Struik, P. C.; Yin, X. and Meinke, H. (2008) Persepctive Plant Neurobiology and Green Plant Intelligence: science, metaphors and nonsense. Journal of the Sciences of Food and Agriculture 88

Taiz, L. And Zeiger, E. (2010) Plant Physiology 5^th Edition Online. Sinauer Association, U.S.A. 12 February 2012 <http://5e.plantphys.net/article.php?ch=3&id=289

Trewavas, A. (2004) Aspects of Plant Intelligence: an Answer to Firn. Annals of Botany 93

Trewavas, A (2005) Green plants as intelligent organisms. Trends Plant Sci 10

Let them eat meat – it’s as easy as 1, 2, 3

If you think plants weren’t smart then you would be wrong.

Counting numbers is something we do on a regular basis, how much change for a cup of coffee, calculating how much time we have between meetings, counting the number of days until payday.

But imagine if you had to count numbers so that you could eat. Venus flytraps (Dionaea muscipula) do just that. A group in Germany led by Jennifer Böhm and Rainer Hedrich recently published a paper looking at the mechanism behind mealtime for the popular carnivorous plant. What they really wanted to know was how did the venus flytrap know when to kick-start the glands that produced the digestive juices once its prey had been trapped. What was the mechanism responsible for this?

In areas of infertile, nutrient-poor soils, carnivorous plants thrive. The reason? They feed solely on insects and other small animals. The anatomy of a venus flytrap is pretty simple, yet does a very effective job at capturing and digesting flesh. The trap itself is actually a modified leaf, with a hinged middle, which would act like the central vein of a normal leaf. The edges of the modified leaf (trap) end in spikes which interlock with each other when the trap closes.

A carnivorous beauty. Tiny hairs are present on the inner surface of the trap. Touching these stimulate action potentials which trigger the trap to close and produce digestive juices (Photo credit).

A starving flytrap will release a smell much like a fruity cocktail. This attracts numerous insects and small animals (frogs have even been known to succumb to the venus flytrap). When an unsuspecting fly lands on the trap, its movement triggers tiny hairs present on the inner epidermis of the trap.

A wasp caught in the hinges (Photo credit).

These hairs then convert the mechanical stimulation to an electrical excitation, otherwise known as an action potential. The trap shuts once two action potentials have been fired within approximately 30 seconds, caging in the insect. As the trapped insect continues to struggle, inevitably more hairs are triggered. As many as 60 action potentials per hour can be fired. Böhm and her group observed that after 3 action potentials were fired, the level of calcium within the cytoplasm (of the plant cells) increased. This then stimulated the expression of the touch hormone jasmonic acid. The jasmonic acid signalling pathway is usually used as a defense mechanism in a non-carnivorous plant when it is wounded. However, in carnivorous plants, the pathway stimulates the production of digestive enzymes by switching on certain transcription factors (proteins that control gene activity). Effectively, the closed trap turns into a green stomach and the insect is mercilessly broken down into its basic molecules, e.g. carbon, nitrogen, phosphorus etc., which are absorbed by glands in the trap. Also, digestion of prey increases production of a specific transporter which allows for greater uptake of sodium, which in turn is important in regulating the nutrient uptake channels found in the glands. The group also noted that the flytrap seemed to regulate the amount of digestive juices secreted into the trap by how many action potentials had been fired. The flytrap could potentially use this as a clue to the size of its prey, so it wouldn’t over-flood its trap therefore conserving as much energy as possible.

More research is going into sequencing the genome of the venus flytrap to understand how these carnivorous traits have developed, and how they can thrive in nutrient-poor environments. Maybe from that we can take what information we know about nutrient uptake in carnivorous plants and transfer that to other plants. Or do we risk creating Frankenstein plants?

Who knows. All I know is that you won’t find out if you don’t try.

#tryscience

Link to journal paper:

Böhm J., Scherzer S., Krol E., Kreuzer I., von Meyer K., Lorey C., Mueller T. D., Shabala L., Monte I., Solano R., Al-Rasheid K. A. S., Rennenberg H., Shabala S., Neher E. and Hedrich R. (2016) The venus flytrap Dionaea muscipula counts prey-induced action potentials to induce sodium uptake. Current Biology 26, 286-295

http://www.sciencedirect.com/science/article/pii/S0960982215015018

 

 

What’s that smell?

On the 1st February, I had the privilege of seeing the titan arum lily flowering at the Adelaide Botanic Gardens. I was prepared to get a waft of something similar to rotting flesh, but maybe the flower decided not to shower us with its best quite yet.

Six quirky facts about the titan arum lily:

•  Amorphophallus titanum, commonly known as ‘the stinky flower’, is endemic to island of Sumatra in Western Indonesia. The Indonesian word for the plant is bunga bangkai which literally translates as ‘flower’ ‘corpse, cadaver, carrion’. A pretty descriptive name. The chemicals released from the spadix have been tested, and the results show that the flower’s smell is a result of the production of chemicals like isovaleric acid (sweaty socks), trimethylamine (rotting fish) and indole (like human feaces). These smells attract insects, flies and carrion beetles, and they act as pollinators.

• The reason why people flock to see the flowering of the titan arum is the rarity of its flowering. A first-time bloomer won’t flower until between 7-10 years old. After the first flower, some plants might not bloom for another 7-10 years, though others may bloom every 2-3 years. The plant must replenish energy spent from flowering, so every year that it doesn’t flower it sends up a leaf shoot.

Non-flowering titan arum – the plant sends up a single leaf with a large surface area to maximise photosynthesis. [Photo credit Olivia Cousins, Adelaide Botanic Gardens]

• Once the flowering has started, it will only last for 24-36 hours. The blooming generally starts overnight, as that is when the pollinating insects are most active.

Flowering titan arum – the burgundy sheath wrapping the base of the inflorescence (flowering structure) is called the spathe, and it protects the female flowers which sit towards the base of the spadix (spike). The male flowers cover the spadix from the base upwards. [Photo credit Olivia Cousins, Adelaide Botanic Gardens]

• It holds the record for having the largest unbranched inflorescence (flowering structure), reaching over 3m in some cases!

• Sir David Attenborough actually coined the name ‘titan arum’ in his documentary The Private Life of Plants.

• The titan arum is classed as vulnerable due to the increasing rate of deforestation. There are over 170 different species of titan arum, so efforts are continuously being made to try to cultivate titan arums in glasshouses and botanic gardens to ensure conservation of the species.

A celebrity of the plant world, it needs 7 years to get ready for its dramatic red carpet event.

#naturefreaks

Winter is coming – time to leaf

Seeing all the beautiful colours of the trees against the backdrop of a swirling autumnal sky, made me want to recap on why some plants lose their leaves in such a kaleidoscopic fashion.

Leaves act as mini factories for plant food production. When light hits the leaf surface, it becomes part of an essential chemical reaction. When carbon dioxide and water are combined with energy from light, the result is glucose (sugar) and oxygen. Chloroplasts within leaf cells are responsible for this reaction. The plant uses up the glucose, but the oxygen is released into the atmosphere.

Simple photosynthesis equation.

In temperate regions, as the days become shorter and colder, the levels of light are not sufficient enough for plants to photosynthesise. One way many plant species have of adapting to this environmental change is to slow down or halt photosynthesis during winter months. One by one, leaves start to shut down their chloroplast factories; no more sugar is being made. Plants are able to live off sugars they have already stored away.

Chlorophyll is a green pigment which resides in the chloroplasts, and is necessary in helping to create glucose from carbon dioxide and light. Other pigments, such as carotenoids and anthocyanins, are also present in leaves, but they are usually masked by chlorophyll. However, when the chloroplasts begin to shut down, chlorophyll is no longer being produced in order to save the plant’s precious energy. The oranges and yellows result from higher levels of carotenoids, whereas anthocyanins are responsible for the red hues.

Autumn leaves showing different pigments – anthocyanins (reds) and carotenoids (yellow/orange). [Picture credit Olivia Cousins]

Cell layers start to build up between the leaf and stem, slowing down the transport of sugars, water and nutrients in and out of the leaf. Once the final cell layer, called the abscission layer, is formed, the leaf drops off. It results in a clean break, and entry to the leaf stem is sealed shut, preventing excessive sap loss. Formation of the abscission layer can also act as infection prevention. Leaf cells are filled with water and can be susceptible to freezing, particularly thin leaves, e.g. maple leaves. Freezing inevitably kills the leaf , causing the leaf to wither and fall away from the stem, leaving an open wound. This wound becomes an easy pathway for infection and could cost the plant it’s limb, or its life.

However, some trees don’t fully lose their leaves, even when chlorophyll production has stopped. For example, oaks and beeches don’t fully form their abscission layers until much later, so although many of their leaves freeze over and die, they remain on the branches until new leaf growth pushes them off in spring. This phenomenon is known as marcescence.

Beech leaves showing marcescence.

The lengths plants will go to in order to protect themselves is fascinating, and yet there is still more that remains to be uncovered. If we can understand the processes that drive plants to photosynthesise, then maybe we can use it to improve photosynthesis of crops, increasing growth and yield. It’s one way to save agriculture.

Winter is coming, but new discoveries might just be around the corner.

Tulip Mania

The Spring Equinox has come and gone, which means only one thing. Spring has finally come! If you hadn’t already noticed the crocuses and daffodils popping up everywhere, when you start to see the splashes of red, orange, pink and purple which signal the arrival of the tulip, you’ll know. Speaking of riotous colours, have you ever wondered why tulips have crazy colours and patterns?

A lot of tulips are susceptible to a plant virus, called Tulip Breaking Virus. This virus infects the tulip bulbs before they come into flower. So when tulips flower, the petals show a variety of colour changes, stripes, flames and streaks.  Infected tulips are then called ‘broken’ tulips. The intensity of these colour changes will depend on the age of the tulip bulb before it has sprouted, or the age of the flower when first infected, as well as the variety of tulip. There are two strains of the virus: Severe Tulip Breaking Virus and Mild Tulip Breaking Virus. Severe Tulip Breaking Virus will cause either full or light breaking. This means that the virus has stopped production of anthocyanin, a pigment found in the petals (and sometimes leaves) which results in red, purple or blue colouring. Lack of anthocyanin usually results in streaking and feathery patterns on the petals. Infection with Mild Tulip Breaking Virus causes an excess of anthocyanin production, resulting in petals with darker streaks, flecks or swirls. Although these colour changes and patterns make tulips more desirable, most ‘broken’ tulip lines no longer exist. This is because, over a period of time and tulip generations, the viral infection will cause the plant to slowly die, unable to pass on genetic information to future tulip generations.

‘Broken’ tulip

‘Broken’ Tulip Absalon

Two of the most famous ‘broken’ tulips were the Semper Augustus and the Viceroy. They were grown during the Dutch Golden Age, when the prices of tulip bulbs rose rapidly, as demand grew. This period in time was also known as ‘Tulip Mania’. The public coveted these ‘broken’ tulips because they looked exotic, flamboyant and extravagant. As a result, the prices of these prized bulbs rose even further. Unfortunately these tulip lines don’t exist anymore.

Semper Augustus Tulip from 17th Century

A couple of the ways in which growers try to protect their tulips against this viral disease is by adding mineral oils to the soil, and spraying the tulips with insecticides. Spraying helps to deter aphids, which have been proven to help in the transmission of the virus. The aphids colonise the tulips and feed off the tulip sap, and at the same time the virus is transferred from the aphids’ saliva into the plant. These tulips are then stuck in a cycle of disease, but despite their vulnerability produce some of the most beautiful displays of colour.