We are all explorers and the need for exploration drives us to discover uncharted territories, including the mysteries of far-away galaxies and the edges of the known universe, whereas few of us know that the lawn under our feet is still full of unfathomable mysteries. A group of researchers from the JU Department of Plant Physiology and Biochemistry is working to shed more light on this issue. Their research aims to answer an apparently trivial question: how plants become green?
If you are fond of Italian or French cuisine you must be familiar with asparagus – once a hard-to-get ingredient of gourmet dishes, now available in every major supermarket. Yet, things may become a bit more complicated when you are about to get it from the shelf. Which to choose: white or green? In fact, these two entirely different vegetables are produced by the very same plant. It’s activation of different sets of genes which, under the cover of darkness, turns Dr Jekyll into sinister Mr Hyde. Indeed, darkness plays a key role in this incredible transformation. Although plants have no eyes, they constantly watch the world around them with photoreceptors, similar to those present in human retina. Thanks to them, plants are capable of “seeing” colours, as well as the intensity and even the direction of light rays.
So when the lights go out, plants can sense it and act accordingly. The lack of light makes photosynthesis impossible, which means that plants are unable to initiate the process during which the immense power of the Sun allows them to produce sugar, which is used as a source of nutrition and a building material for leaves, stems, roots, and branches. Hence, lack of light means hunger, to which angiosperms (fruit-producing plants) quickly react by tightening their belts and introducing a stricter management of resources. The sinister Mr Hyde isn’t mad – he is extremely rational and determined to survive. And that’s why asparagus shoots buried underground are white – chlorophyll (the green pigment) isn’t worth producing if photosynthesis cannot be performed anyway. Quick growth turns out much more important – under natural conditions, the prolonged lack of light usually means that the plant is buried underground, so it does its best to make its way to the surface. Leaves are useless for this task – they would only impede growth and could get damaged in the process. This explains, for instance, the characteristic shape of sprouts of potatoes kept in the cellar. Observation of these phenomena has led plant researchers co coin the terms skotomorphogenesis – development in darkness and photomorphogenesis – development under exposure to light.
Like a clockwork
So what would happen if a plant that has developed in darkness, finally gets access to light? This means the beginning of a difficult and dangerous transformation known as de-etiolation or greening. To make it possible for leaves to develop, it’s necessary to activate certain genes and proteins in a proper sequence. At the same time, the activity of other proteins, for instance those responsible for quick growth of the stem, becomes hindered, whereas pigments, such as chlorophyll and carotenoids (yellow and orange pigments supporting photosynthesis), are accumulated and photosynthetic complexes, molecular power plants of cells, are assembled. Everything has to run like clockwork. Hence, there arises the question how the biosynthesis of both types of pigments and the production of proteins are coordinated. It turns out that the whole plant works like a corporation, run by a well-qualified board consisting of regulatory proteins that optimise and manage the work of other proteins.
During the greening process pigments are quickly accumulated – cotyledons become vividly green.
As these proteins – like most managers – perform a number of tasks simultaneously, it is worth analysing their actions in order to learn which of them influence the developmental processes. What is the easiest way to do this? The answer is: by getting rid of one of them and observing what happens. The worth of individual employees becomes apparent when one of them vanishes. Everything starts falling apart without a good manager. And so it does without a protein regulator. By growing a mutated plant lacking one of regulatory proteins, researchers can check which processes of greening became disrupted, and, consequently, what were the responsibilities and qualifications of the fired staff member of the protein corporation.
In this way, the Jagiellonian University researchers are investigating the role of another two protein managers supervising the work of other proteins and ensuring the well-balanced production of various types of pigments. Their are also studying the activity of a key angiosperm protein, which, under exposure to light, converts the material accumulated in darkness into a very important ingredient used to produce chlorophyll. The protein functions similarly to a financial department officer, who carefully reads through invoices and orders, signs them and forwards them. These actions initiate the process involving other staff, which finally leads to a certain action, e.g, a money transfer. So the JU biologists are checking whether the activities of the biochemical accountant trigger other, previously unknown, processes important for the greening of plants.
What doesn’t make you stronger, kills you
Another interesting phenomenon is the fading of chlorophyll under the influence of light. This is because the green pigment, indispensible for the process of photosynthesis, is also a dangerous substance – in the presence of light it can initiate the development of harmful, reactive forms of oxygen, which destroy everything that comes in their way. For plants, light is not only the source of vital energy, but also a threat. Like an excessive electric current which can damage an electric circuit, excessive light damages cells, which may weaken or even kill a plant. This problem is especially important at the initial stages of plant development. For a seedling even a little stress can prove deadly. Yet, the plant is not completely defenceless – while still in darkness, it prepares a whole set of defensive measures, especially antioxidants. How effective are they? How much light can a plant bear? How does it deal with stress? These are some of the key questions addressed by the researchers from the Jagiellonian University Department of Plant Physiology and Biochemistry, who are investigating how plants’ defensive mechanisms are shaped and what can be done to support the greening process.
The research on greening is funded from the National Science Centre grant UMO-2013/10/E/NZ3/00748.
Original text by Dr hab. Beata Myśliwa-Kurdziel and Dr Paweł Jedynak: www.nauka.uj.edu.pl.
