Melbourne: Australian researchers have found that a `yellowbox` eucalyptus tree was able to control the smell of its leaves from one side of the tree to the other in a bid to protect itself against predation.
The new finding published in online journal BMC Plant Biology, answers a 20-year-old mystery of a eucalyptus tree in a sheep paddock at Yeoval, New South Wales.
The tree which was centre of the study was almost totally defoliated by insects in 1990, with only one branch left completely untouched, ABC News has reported.
According to lead author Amanda Padovan, a doctoral student at Australian National University`s Research School of Biology, their study showed the Eucalyptus Melliodora commonly known as `yellowbox` was able to control which leaves are attacked by predators by alterations in its genes.
She said that the tree, which is estimated to be 75 years old, has developed this ability known as "genetic mosaicism" as a survival mechanism.
"If an insect outbreak occurs then a part of the plant won`t be eaten and therefore it will still be able to grow and reproduce," she said.
The research team collected leaves from both sides of the tree and through gene sequencing found there were 10 genes that contained differences between the leaves from each side.
She added that one of the main defences the eucalyptus uses against predation is its distinctive smell, which is the result of a "cocktail of terpene oils", including monoterpenes and sesquiterpenes, and formylated phloroglucinol compounds or FPCs that make animals nauseous.
The gene sequencing revealed that leaves were predation-resistant with five fewer monoterpenes and nine fewer sesquiterpenes than the leaves that were "tastier".
However the concentration of FPCs and the remaining monoterpenes was far higher.
As a result, Padovan said, the leaves on the part of the tree that was not eaten had a strong eucalyptus smell whereas the leaves that were attractive to the insects had a stronger florally smell.
She added that the impact on vertebrates such as Koalas is similar as feeding experiments in the laboratory show Koalas reject the same leaves as the insects.
"Trees can`t get up and walk away from unfavourable conditions and so we believe this genetic mosaicism is a way for trees to survive changing conditions throughout their life," she said.
She added that all trees have the ability to acquire mutations in their stem cells, however mutation must be favourable - in this case the mutation lead to resistance against feeding - to allow an entire branch to develop.