Conservation and Sustainable Use of the Biosphere - WBGU

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Conservation and Sustainable Use of the Biosphere - WBGU

38 D The use of genetic and species diversity

Box D 1.3-2

Arabidopsis: The story of the wallflower that

became a queen

Arabidopsis thaliana – Thale cress – is one of 141 cruciferae

in Germany’s flora, small, unremarkable flowers that occur

on poor, dry sandy soils. Arabidopsis is neither particularly

pretty nor rare and is just one of many pioneer plants in the

open soil.

The career of Arabidopsis began when the Frankfurt

botanist Laibach (1943) discovered that this species had an

unusually diverse growth habit that was apparently genetically

determined. There are high and low flower panicles,

ones with more or fewer branches, early and late blooming

individuals, those with hair and those without. Because of

the short time from germination to formation of seed and

the high variability of its structure, Arabidopsis was highly

suitable for genetic investigations at a time when the

genetic code had not yet been discovered. Around 20 years

later Dr Röbbelen (Göttingen) and Dr Kranz (Frankfurt)

began a seed collection (1963) that initially served for crossbreeding

experiments, but later provided the basis for physiological

and molecular experiments. The move into molecular

biology meant diminishing interest in the diversity present

in nature. Most of today’s experiments are conducted

on just a few wild genotypes.

Its molecular career began in the 1980s when Koorneef

et al (1983) produced the first genetic map of Arabidopsis.

When it was also found that the genome of Arabidopsis

could be transformed by agro-bacteria and that this species

contained the smallest genome of all known plant species,

Arabidopis began its triumphal march at the head of all

other model plants. There were not just new physiological

experiments, such as experiments on changed sugar levels

(Schulze et al, 1991), but also futuristic experiments in

which polyhydroxybutanoic acid – a biodegradable plastics

feedstock – was synthesized in the chloroplasts of Arabidopsis

(Nawrath et al, 1994). Currently experiments are

being conducted to saturate the genome by mutation on the

basis of insertion of agro-bacterium T-DNA.This allows for

the swift identification of genes that are involved in certain

physiological processes (Walden et al, 1991).

These physiological experiments led in 1996 to the Arabidopsis

Genome Initiative in which it was decided to

sequence the entire genome of Arabidopsis by the year

2000 and deposit it in a public database. Thus, Arabidopsis

would be the first flowering plant for which the entire

genome is known. After much molecular preparatory work

on the fine structure of the genome, in October 1998 the

complete map of the 4th chromosome was published

(Meinke et al, 1998). Within 20 years this species therefore

rose from a once obscure weed to a member of the ‘Modern

Genetic Model Organisms’.

But why is that so important? With the knowledge of the

genome of one tough survivor species we have available all

of the information about the genes that are necessary for

the functioning of a plant. Past experience with other organisms

suggests that great similarities with other plant species

can be expected. By researching Arabidopsis we know the

genes that cause certain processes such as drought resistance,

saline resistance and heavy metal resistance. This

would be a breakthrough in breeding research. In addition

to the resistances, the hormonal metabolic processes are

also attracting attention, particularly the steroids. Many of

these plant hormones are similar to those that occur in the

human body. And so Arabidopsis becomes important medically.

There is one bitter note: a large pharmaceutical company

has gathered up the knowledge about the genetic

structure of Arabidopsis as published on the internet and

with great speed has sequenced the large majority of the

rest of the genome – probably with the aim of patenting it.

Thus, the success and the profit from the groundwork of scientists

is lost to them.

From an ecological standpoint Arabidopsis is probably

just a ‘queen for a day’, because it is already clear that it

does not represent all plant functions. It is a relatively specialized

organism that, for example, has no mycorrhiza and,

because of its short life span, can survive without any mechanisms

to defend itself against predators or disease. This

species is a master of survival that focuses on swift mutation

and high reproductive rates, with the mutations surviving on

sandy sites where there is little competition. And so it is

clear already that to understand the interaction between

pathogens and mycorrhiza, further species need to be

sequenced.

tion merely bans trade in these species and so cannot

provide comprehensive protection (Section D 3.4).

Worldwide, at least 34,000 species are under threat

(WCMC, 1992), and national protective provisions

only cover some of these. Other international conservation

conventions, such as the Ramsar Convention

on wetlands, only focus on particular habitats.

The Convention on Biological Diversity could build

an important bridge here (Section I 3).

D 1.3.3

Species not currently being used: genetic

resources for the future

If we do not include the used or crop plants, the true

ornamental plants and the protected species from the

total, then around 175,000 species remain that are not

subject to use by humankind and have not received

attention under protective efforts thus far. It is this

group of species for which the Convention on Biological

Diversity is so important (Section I 3).

D 1.3.3.1

Medicinal plants

Some of the species belonging to this relatively large

residual group of species not currently in use will be

used with some degree of probability at some point

in the future as genetic resources, eg to extract certain

pharmaceuticals (Section D 3.3). So far, only

around 5,000 plant species have been examined systematically

for potential active substances. However,

there are indications that with the advent of new

biotechnological procedures, dependence on natural