Scientists from the Wageningen University Laboratory of Plant Physiology and
an international team of scientists have discovered a new group of plant
hormones, the so-called strigolactones.
This group of chemicals is known to be involved in the interaction between
plants and their environment. The scientists have now proven that
strigolactones, as hormones, are also crucial for the branching of plants.
The discovery will soon be published in Nature and is of great importance
for innovations in agriculture. Examples include the development of cut
flowers or tomato plants with more or fewer branches. These crops are of
major economic and social importance worldwide.

The growth and development of plants is largely controlled by plant
hormones. Plants produce these chemicals themselves, thus controlling the
growth and development of roots and stems, for example. A number of plant
hormones, such as auxins, giberellins and cytokinins, were discovered by
scientists decades ago. Now a new group of hormones has been found: The
so-called strigolactones.

Previous research by institutes including Wageningen UR has shown that
strigolactones plays a major part in the interaction between plants and
their environment. As plants cannot move, they commonly use their own
chemicals to control the environment as best as they can.

Strigolactones are of major importance to the interaction between plants and
symbiotic fungi, for example. These fungi live in a symbiotic relationship
with plants, lthat is mutually beneficial. They transport minerals from the
soil to the plant, while the plant gives the fungi sugars ?in return?.

Unfortunately, the strigolactones have also been ?hijacked? by harmful
organisms: They help seeds of parasitic plants to germinate when plant roots
are in the vicinity. The seedlings of the parasite attach to the root of the
plant and use the plant?s nutrients for their own growth and reproduction.
Unlike the symbiotic fungi, however, they do not give anything in return. On
the contrary, the parasitism often causes the host plant to die, eventually.

The international research team consisting of French, Australian and Dutch
scientists, coordinated in France, found mutants of pea that were branching
without restraint. It turned out that these pea plants were not capable of
producing strigolactones. When the plants were administered strigolactones,
the unrestrained branching stopped. The same effect occurred in an entirely
different plant, thale cress. The mutant plants also caused a significant
lower germination of the parasitic plant seeds and induced less interaction
with symbiotic fungi.

The scientists also showed that a specific ?receptor reaction? for the
strigolactones occurs in plants, a phenomenon that is characteristic for
plant hormones. Although some previously discovered plants with unrestrained
branching turned out to be producing strigolactones themselves, their
receptor connection was disturbed: Strigolactones administered from the
outside could not stop the uncontrolled branching.
It has also been shown that the plants are capable of transporting
strigolactones internally and that the chemicals work at very low
concentrations, two other typical characteristics of plant hormones.

The importance of this discovery of a new group of plant hormones is
emphasised by the fact that Nature is publishing an article by a Japanese
team in the same issue in which similar results are presented. It is
expected that this new knowledge will be applied in agriculture and
horticulture, for example in breeding and the development of branching
regulators.

Cut flower varieties and potted plants with either more or less branching
may have special ornamental value, while crops with more or less branching
may be beneficial in cultivation. Tomato plants in which less branching
occurs can benefit the greenhouse horticulture, for instance.

Plant breeding and greenhouse horticulture are key agricultural industries
in the Netherlands and strongly focussed on innovation.
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