Ute Krämer: Chasing up the mechanisms of herbal metal-eaters

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Biochemist Dr. Ute Krämer has her eyes on plants which have developed a distinct appetite for metal.

01.06.2006  - 

Ute Krämer is not a scientist who had her career planned-out from the outset. Ten years ago in Oxford, England, and somewhat by accident, the biochemist discovered her specialty: Plants that can pull heavy metals from the soil in high concentrations and enrich them in their leaves. Since then, the 36-year-old has contributed crucially to the understanding of the biochemical processes behind these metal-munching plants. Step by step, the natural-sciences researcher has smoothed the way to a means of cleaning metal-contaminated soils in a natural way.

As a child growing up in Weserbergland in Lower Saxony, she never imagined that she would become a researcher. "Back then, those things were off in the distance", she remembers today. However, Ute Krämer knew that, above all, biology and chemistry were the subjects that inspired her most. After her Abitur, the German high-school diploma, she was intent on a studying biochemistry in Hanover. But, on arriving, she did not feel comfortable. Swatting-up on the basics was not her passion. "I learn faster and better if I go tooth and nail into a problem", she says. With her interests kindled and brimming with ambition to become a researcher, she went to Oxford with a scholarship, following her intermediate diploma. During the search for an interesting graduation subject, the young student finally found what she was looking for: "In the interview, my future doctoral advisor told me about plants which grow on metal-contaminated soil and can enrich these metals. I was immediately curious."

Plants with a distinct appetite for metal

To date, there are approximately 400 known plant types that are able to prosper on strongly metalliferous soils, and to store the highly poisonous materials in their leaves. The majority of these metal hyperaccumulators, has a hunger for nickel. Others have developed a preference for cobalt, copper, manganese, zinc or cadmium. Some plants can accumulate up to four per cent of their dry weight in metal. How they can survive such high doses in their metabolism at all is not yet completely understood, but it’s a highly-complex procedure: The roots of the plants must not only extract the metals from the soil but also distribute them to other plant organs, absorb them into their xylem, the water conducting tissue of plants, and then deposit them in the vacuole, a water-filled storage space in the leaves. Whilst in Oxford, during her dissertation under J. Andrew C Smith at the Department of Plant Sciences, Ute Krämer gave the first account of the biochemical mechanisms used by the plants: Apparently there are clearly increased quantities of molecules of an amino acid, called histidin, which pacjage the metal ions absorbed by the roots in such a way that they are detoxified and therefore able to be transported through the xylem in high quantities into the leaves. This discovery was a success for the young researcher, resulting in her first paper in the renowned science magazine Nature. "I would have never have thought that I could enjoy my time in the laboratory so much", she remembers today of her time in England.

Highly motivated, Ute Krämer decided to continue her work in the US. With the assistance of a scholarship of the German Academic Exchange Services (DAAD), the young German went to Rutgers University in New Brunswick, New Jersey. "Somewhat differently to Germany, there are strict laws covering the cleaning of poisoned soil in the US, giving plant research in this area a higher value", says Krämer. There, her prejudices regarding the US were immediately challenged: "The Americans can work unbelievably productively and purposefully." For Krämer personally, the traveling proved worthwhile: With two first-authored publications, the time spent there smoothed the way for her future career.

BioFuture boosted career in science

Ute Krämer eventually found herself back in Germany, despite her enthusiasm for the research conditions overseas. In 2000, not long after her return, the Biochemist won the BioFuture competition initiated by the Federal Ministry for Education and Research (BMBF), as one of the few plant researchers among the winners. With the BioFuture funds, paid over five years, she was able to begin her own working group at the Max-Planck Institute for Molecular Plant Physiology in Golm, and get further into the thick of the factors influencing the metal-tolerance of plants. "It was thanks to the BioFuture funding that I was able to continue this kind of research at all. Without this program my scientific career in would have ended some time ago", she says.

At that time, as today, the Biochemist has key genes in her sights. As a plant model, Krämer uses Arabidopsis Halleri, a plant with a marked appetite for zinc. Genetically, it’s 94% identical to another model plant- the common wall-cress Aradopsis Thaliana - whose genome has been completely encoded for some years. "Using this plant, we don’t need to begin from scratch as we can apply tried and tested methods, and we can align both plants and search for crucial genes", she says. Already, Krämer and her team have discovered some potentially interesting genes. Apparently, there are the blueprints for proteins saved that play an important role in the metal tolerance of Arabidopsis Halleri. Two proteins are of interest above all: One transports zinc ions into the cell vacuoles inside and, in so doing, detoxifies the metal ions. The other ensures that the zinc and cadmium ions are able to get out of individual cells, thereby probably aiding both the decontamination of the metals and the transport of the metal ions from the root into parts of the plant above-ground.

In the past five years the researchers have also developed important tools to directly determine the participation of genes which carry the blueprints for these transporter proteins. In the three to five years of intensive efforts to come, Krämer is hoping to determine whether these genes have actually a key role to play and whether the extreme abilities of Arabidopsis Halleri can be reduced to a few genes.

A long way to employment as a soil cleaner

However, if this hurdle can be cleared, then the proper work will have only just begun. Despite the extremely high metal concentrations in the leaves, Arabidopsis Halleri can only produce a small biomass and this would rule out commercial use as a soil cleaner. For that reason, the researchers intend to employ a trick and transfer the metal-corrosive and metal-storing characteristics of Arabidopsis Halleri to plants that can produce much more biomass. “So far, using current methods, it’s possible to double the abilities of a normal plant. The application will begin to be of commercial interest at the tenfold range, better still, however, would be about 100 times the capabilities", explains Krämer. For some soils, this could already be sufficient. In many other places, however, one plant will be of lesser value: ultimately, different metal-eaters will be needed for soils contaminated with different metals.

Such methods are understandably of economical interest, particularly for countries with large amounts of contaminated agricultural land, which must be detoxified in order to contain the substantial risk it poses to public health: for example India, China and Poland. In Germany, there is less interest at present – there being no appropriate legal framework for this type of soil cleaning and no economic need to use contaminated land for agriculture. For this reason, the financial resources in this area of plant research are not being abundantly sown. Ute Krämer is therefore trying to closely co-operate with as many different groups of researchers working on similar topics as possible. "With limited means, it’s the best way to get the knowledge levels going", she says.

But her focused attention is not limited to the application of her research results. "Firstly, we have to better understand just how nature ticks, and only then we will be able to develop an approach for cleaning soil," thinks Krämer. Very little is predictable in science, a fact that the researcher loves: "We never know where the journey will end, and so there’s always the chance of one day creating an application that’s undreamt-of today”.