Kiel Plant Center

Emese Eysholdt-Derzsó and Chen Lin - adaptations to flooding

Emese Eysholdt-Derzsó and Chen Lin are postdoctoral researchers in the group of Margret Sauter at the Botanical Institute at Kiel University. They are interested in understanding how plants adapt to flooding and how this can help identify flooding robust crops for a changing climate. Here they talk about their research on the regulation of root architecture in rice and Arabidopsis species in low oxygen environments.

Postdocs Chen Lin and Emese Eysholdt-Derzso in the lab

Chen Lin (left) and Emese Eysholdt-Derzsó (right) 

How do you define flooding in plants?

Emese:
Flooding refers to the submerging of a plant under water. It can be caused by environmental events such as hurricanes or be more seasonal in nature such as rivers flooding their banks into fields in springtime. I always like to highlight that flooding does not just mean extremely high-water levels that submerge plants under for example 5 m of water. Even a few centimetres of water is enough to flood a plant in the early stages of development in spring when it still very tiny. Here in Germany and Denmark this happens quite frequently in the spring when we have heavy rain fall. And even 1 cm is enough to cause significant damage to the plant that it cannot recover from. You can already see the damage done to crops in the early stages of their development in years where there has been a lot of rainfall in spring.

Chen:
In comparison areas such as Asia do experience huge floods with water levels rising by over a metre. As you can imagine flooding is a very diverse phenomenon and a serious problem for agriculture.

 

What changes does a plant experience during flooding?

Emese:
When the plant is submerged, it cannot effectively capture sunlight as it does normally so it cannot photosynthesise. But there is a huge variation in flooding environments. So how muddy or turbid the water is will influence how well light can diffuse through the water column and whether a plant can photosynthesise for example. In clear water some photosynthesis can still continue, and the plant can continue to produce some energy.

Chen:
A bigger problem than being able to photosynthesise is actually the significant decrease in gas exchange, or more specifically oxygen and carbon dioxide diffusion. Short term this is not so much of a problem, as the plant can draw on energy reserves. However, when these reserves run out the stress is considerable, and the plant can die. Depending on the species, the time frame of the flooding event also plays a role. Some plants are sensitive to flash floods which recede quite quickly while others can stay in the water for quite a long time. The rice that I study is called deep-water rice, which is tolerant to long-term submergence.,

 

Why are you interested in studying flooding?

Emese:
Due to climate change the frequency of flooding events is increasing. This is especially a problem in areas of Asia and South America. Crops are a major part of the GDP in these countries, and so environmental disasters, such as flooding, but also drought for example, that have a huge impact on the crop production also really impact their economy when they lose income due to crop damage and death. For a more sustainable agriculture, as well as for the benefit of people’s livelihoods and global food security, we believe we need to increase the number of flood resistant species being used as crops.

Chen:
I hope with our research we can contribute to understanding more about flooding stress in plants, and their adaptations. Long term hopefully our research can help improve flood sensitivity in plants.

Rice plants
Rice plants with adventitious root growth after 10-day submergence. Image: Chen Lin

What is the focus of your research?

Emese:
We want to understand how plants adapt to flooding, and what changes a plant goes through on a morphological, biochemical and genetic level during and after flooding. Specifically, we are studying how the root architecture changes under flooding conditions and under post submergence stress, as well as the underlying molecular mechanism. It was known that the root architecture changes when the plant is under stress generally, but not much is known about root adaptation in response to low oxygen environment.

Chen:
A plant generally has a main root and several lateral roots. Under stress, root types called adventitious roots or fibrous roots start to appear and grow. In cereals, adventitious roots are genetically formed at the node above the soil; however they only emerge when triggered by flooding events. The main root gets damaged during flooding and not enough nutrients and energy can be transported through the root, but these new roots are good at storing energy and taking up nutrition and oxygen for the plant. The newly generated adventitious roots, which grow very quickly, take the place of the original roots and can help the plant recover after the water has subsided. This is a crucial adaptation in rice, but also other species like barley and wheat.

Scientist Chen Lin with rice plant in the lab
Chen prepares a rice sample in the lab. Image: Chen Lin

What plant species are you specifically studying in connection to flooding adaptations?

Emese:
I am working with Arabidopsis thaliana which, as a model organism, is easy to handle, grows quickly and it is ideal for understanding the underlying molecular mechanisms. Clearly this is not a plant well known being flood tolerant, but it is a good system to study different traits.

Chen:
I am studying rice. Rice is also relatively easy to handle so we can use it as a crop model to study mechanisms. There are many different cultured rice varieties, but only a few cultivars that are generally used widely in modern agriculture. The general association is that rice likes to be, or copes well with being flooded. But actually, it depends very much on the cultivar – there are many dry land rice cultivars, for example, that do not like to be flooded. We are studying a deep-water rice that grows next to rivers and through evolution has evolved to be extremely tolerant of flooding. A variety of adaptive traits have been described in rice, but many of these can also be identified in other crops like barley and wheat. Once we identify the underlying genes and pathways, we hope we can search for homologs in other crops and wild type species that may be more suited for agriculture.

 

How are you studying these traits in the lab?

Chen:
In the lab I use a simplified set up. This consist of a 1 m cylinder in which we can put the plant stem and can easily observe the root growth and angle. A mixture of water and different solutions is added to induce adventitious root growth.

Emese:
In the lab we put Arabidopsis seedlings into air-tight containers which creates a controlled low oxygen environment much like that which they would experience when submerged. We then can observe the roots clearly to see how they behave.

Plants in transparent boxes on the left. Scientist studies box on the right.

The Arabidopsis seedlings are kept in air-tight containers (left), making them easy to observe (right). Images: Christian Urban, Kiel University.

What have you found out so far?

Emese:
We have already shown, for example, that low oxygen levels result in the arrest of lateral and primary root growth and triggers the development of adventitious roots. Furthermore, the primary root bends  in a certain direction which we refer to as ‘root bending’. The developmental and growth change we see in root architecture under low oxygen stress is controlled by a complex cross talk and feedback loops of plant hormones, genes and transcription factors. We focussed on plant specific transcription factors known as group VII Ethylene Response Factors (ERFVIIs). We were able to show that beside the root arrest caused by energy deprivation, plants evolved a genetically controlled mechanism to readjust root growth in response to low oxygen stress in an ERFVII-dependent and –independent manner. Additionally, we could provide evidence on the cross talk of ERFVII transcription factors with hormonal metabolism and biosynthesis which all together set the pace of root growth under low oxygen stress.

Chen:
Our experiments have shown that the rapid induction of adventitious roots is important for plant survival as is the angle at which it grows. The deeper the flood water the less oxygen the plant has, so the angle and position the root grows will dictate how much oxygen the root can take up. Our results also show that the blue part of the light spectrum is the most important factor that influences the angle of the adventitious root. In addition, red light and gravity also control the root angle to some extent.

 seedlings showing root bending
Oxygen deficiency causes the Arapidopsis root to bend . The seedling on the left has been grown under normal oxygen conditions (control). In contrast, the seedling on the right has been grown under normal oxygen conditions alternativing with oxygen deficient conditions. The arrows indicate the position of the root tip at the time the plant experienced a switch to oxygen deficient (1) or to normal (2) conditions. Images: Emese Eysholdt-Derzsó

What’s next?

Chen:
Several wild type rice species are very tolerant of flooding. We would like to find the genetic mechanisms underlying these adaptive traits, as Emese has done in Arabidopsis, and use this knowledge to find the corresponding genes in other rice and crop species. Ultimately, once these genes have been identified we could use transgenic models in the lab to understand better how flooding effects plants, and traditional breeding methods to develop more robust crops for the future.

 

Links:

Pflanzen gegen Staunässe schützen. Press Release from the University of Kiel.

Flooding adaptation project page, Sauter group.