Beijing, China – In 1875, the renowned scientist Charles Darwin proposed in his book Insectivorous Plants that “certain plants of the genus Saxifragus may be carnivorous.”
This hypothesis, which Darwin formulated after observing plants of the genus Saxifragus
with sticky glandular hairs, remained a mystery due to the lack of the necessary testing techniques.
For a long time, no one was able to test it. It was only after about a century and a half that its validity was officially confirmed.
The study provides a definitive answer
In this context, a joint research team of scientists from China and the United States announced
on the 5th of this month, in the prestigious scientific journal Nature Communications,
their confirmation that Saxifraga candelabrum (known as the candelabrum saxifrag,
which grows in the rocky mountainous regions of the Qinghai-Tibet Plateau
and the Hengduan Mountains in China) is a true carnivorous plant.
They also confirmed its ability to attract, trap, and digest insects using digestive enzymes.
Furthermore, it absorbs their nutrients.
The research team explained that this study provides a definitive answer to Darwin long-standing hypothesis.
They indicated that the findings suggest the possibility of predation not only
in other previously overlooked saxifrag species, but also in many other flowering plants.
Predation criteria and field tests
Carnivorous plants are not simply those that occasionally capture insects; to be classified as such, a plant must not only attract and capture its prey,
but also break it down using digestive enzymes and absorb the resulting nutrients.
For this reason, plants that capture insects without demonstrating the ability to digest and absorb them are classified as “primitive carnivores.”
To investigate the predation hypothesis of Saxifraga fortunei, the research team conducted a multifaceted examination of this plant,
which is characterized by dense, red, sticky glandular hairs on its stems and flowers. These hairs facilitate the capture of small insects.
The presence of insects attached to the glandular hairs
Field studies and analysis of herbarium samples collected between 1888 and 2016 revealed insects attached to glandular hairs in 43 out of 45 samples examined.
Furthermore, insect attraction experiments showed that flowers attracted greater numbers when their appearance was concealed
while their fragrance was allowed to permeate. This was compared to concealing the fragrance and relying solely on the visual appearance.
Attractant compounds such as beta-myrcene and eucalyptol were detected in the flower’s fragrance.
This confirms that insect trapping was not purely accidental but rather the result of a polarizing activity by the plant.
Biological and genetic evidence for the digestive mechanism
To resolve the issue of digestion, researchers examined the activity of the enzyme phosphatase (a digestive enzyme common in carnivorous plants).
Its presence was clearly confirmed in the glandular hairs of Saxphraga fortunii, while it was completely absent in closely related non-carnivorous species.
To confirm nutrient absorption, fruit flies were fed a radioactive nitrogen isotope (15N) and presented to the plants.
In this experiment, they observed a significant increase in nitrogen concentration within the vascular tissues of Saxphraga fortunii.
Meanwhile, its concentration remained stable in the non-carnivorous control species.
Decoding the plant genome
Interestingly, the nitrogen absorbed is concentrated most abundantly in the flowers, followed by the leaves and then the roots. Studies explain this by suggesting that the saprophytic plant,
which flowers only once in its lifetime, directs nitrogen obtained from prey to its reproductive organs. This aims to maximize reproductive efficiency.
Furthermore, sequencing the plant’s genome and comparing it to known carnivorous plants has confirmed evidence of convergent evolution. The genes responsible for food attraction, digestion,
and absorption have evolved identically across different plant lineages. This supports the independent evolution of insectivory in angiosperms and validates Darwin’s historical perspective.
