Scientists in Leipzig, Germany have discovered that, if threatened by parasites, barberry plants will sacrifice their own seeds depending upon the chance of survival. This, they said, suggests plants can make complex decisions.

Scientists from the Helmholtz Center for Environmental Research (UFZ) and the University of Göttingen concluded that a study of the barberry, which is able to abort its own seeds to prevent parasite infestation, has yielded the first ecological evidence of complex behaviour in plants. They said their findings indicate that this species has a structural memory, is able to differentiate between internal and external conditions and anticipate future risks.

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Last year, researchers at the John Innes Centre in Norwich improved understanding of plant behaviour, revealing that plants do complex sums to ration energy stored during the day in order to make it through the night.  

The barberry, a shrub widely distributed throughout Europe, was compared with another plant from the same family. Dr. Harald Auge, a biologist at the UFZ , gave a brief account of the study; "A highly specialized species of tephritid fruit fly, whose larvae actually feed on the seeds of the native Barberry, was found to have a tenfold higher population density on its new host plant, the Oregon grape" which was used for comparison. This led scientists to examine the seeds of the Barberry more closely. Approximately 2000 berries were collected from different regions of Germany and examined for signs of piercing, the method by which the fruit fly lays its eggs.

The scientists discovered that the barberry, which often has two seeds in its fruit, can stop the development of one, effectively aborting the infested seed, which means the parasitic fly larvae dies with it, saving the second seed in the berry.

When analysing the seeds, the scientists came across a surprising discovery. Dr. Katrin M. Meyer, who worked on the study, explained that "The seeds of the infested fruits are not always aborted, but rather it depends on how many seeds there are in the berries".

In 75 percent of cases where there were two seeds in a berry, the plant aborted the infected seed, but this only happened in 5 percent of cases where berries contained a single seed.

Dr. Hans-Hermann Thulke from the UFZ elaborated on the scientists' conclusions, "If the Barberry aborts a fruit with only one infested seed, then the entire fruit would be lost. Instead it appears to 'speculate' that the larva could die naturally, which is a possibility. Slight chances are better than none at all. This anticipative behaviour, whereby anticipated losses and outer conditions are weighed up, very much surprised us. The message of our study is therefore that plant intelligence is entering the realms of ecological possibility."

But how does the Barberry know what is in store for it after the tephritid fruit fly has punctured a berry? It is still unclear as to how the plant processes information and how this complex behaviour was able to develop over the course of evolution. The Oregon grape – the closely related species studied by the UFZ researchers – has been living in Europe for some 200 years with the risk of being infested by the tephritid fruit fly and yet it has not developed a comparable defence strategy.

These new insights shed some light on the underestimated abilities of plants, but the UFZ researchers said that for the time being they raise more questions than they answer.