Does the composition of the bacteria around the roots of the plant affect the plant?

Plants "whisper" to the soil: they secrete various substances from their roots and thus influence the composition of the bacteria in the soil that surrounds them. The scientists of the Weizmann Institute of Science recently showed that through the same soil bacteria, the soil also whispers back to the plants - and affects the plant's metabolism and the substances secreted from its roots. These findings, which were published in the scientific journal PNAS, may allow in the future to decipher the language of communication between plants and insects, and to use this language to increase the production of medicinal and other substances extracted from plants

Plants "whisper" to the soil: they secrete different substances from their roots and thus influence the composition of the bacteria in the soil that surrounds them. The scientists of the Weizmann Institute of Science recently showed that through the same soil bacteria, the soil also whispers back to the plants - and affects the plant's metabolism and the substances secreted from its roots. These findings, which were published in the scientific journal "Records of the American Academy of Sciences" (PNAS), may allow in the future to decipher the language of communication between plants and insects, and to use this language to increase the production of medicinal and other substances extracted from plants.

The narrow strip of soil around the roots of the plant is one of the most complex ecosystems on earth and is teeming with millions of bacteria and other tiny creatures. In order to find out if the composition of the bacteria around the roots of the plant affects the plant, the post-doctoral researcher Dr. Eliza Kornblum and other researchers, led by Prof. Assaf Aharoni from the Department of Plant and Environmental Sciences, split the roots of tomato plants in two, and grew them in a hydroponic system - growing on a substrate Water, no need for soil. In a series of experiments, the scientists placed one side of the split tomato roots in a jar with a soil solution that was gradually diluted more and more (each dilution changed the composition of the bacteria in the solution and reduced their diversity until creating solutions with a high, medium and low diversity of bacteria), and buried the other side in a jar with a solution Clean, landless.

The assumption was that if and when the bacteria in the soil solutions come into contact with the plant, it will be possible to find signs of this on both sides of the root system - both in the jars with the soil solutions and in the clean jars. Indeed, a week later, the researchers discovered, using high-resolution mass spectrometry, that the secretions of the roots on the "clean side" changed according to the composition and diversity of the soil bacteria on the "dirty side". For example, an increased presence of bacteria of the Bacillus species in the soil solution led to an increase in the production of sticky substances that trap insects, called acylsugars, on the "clean" side. Moreover, the changes in the composition of the bacteria in the soil affected the metabolism of the entire plant: they led to changes in the amount and distribution of more than 170 substances in the plant, as well as to a change in gene expression in the stem and roots.

"We showed that the messages of the soil bacteria travel long distances along the lines of communication in the plant, reprogram the metabolism and ultimately lead to changes in secretions from the roots," says Prof. Aharoni. "These secretions affect, apparently, in turn, the composition of soil bacteria."

To test how the bacterial messages travel within the plant, the scientists focused on a potential message subject: azelaic acid - an organic compound that apparently plays a role in the plant's defensive response. The scientists added azelaic acid to the soil on one side of the tomato roots, and wonder of wonders, they found molecules of this acid on the "clean" side as well. Also, they diagnosed changes in secretions from the roots caused by the azelaic acid. "Our goal is to decipher the chemical language in which the plants and the bacteria in the soil communicate with each other," says Dr. Kornblum. "Azelaic acid is probably one of the 'words' in this language."

Tomato roots. Right: Mass spectrometry imaging revealing the concentration and location of different chemicals (represented by different colors). This method helped the researchers track the secretions of the substances from the roots

Substances secreted from the roots of the plant strengthen its protective capacity, make it easier for it to absorb the nutrients and fulfill a series of other essential functions. A better understanding of how soil bacteria affect the secretion of these substances may allow scientists to help the plant become a better "farmer", that is, change its environment for the better. In addition, the ability to influence these secretions may serve the pharmaceutical, cosmetic and other industries that will be able to increase on demand the production of substances derived from plants. In fact, the institute's scientists recently demonstrated, under laboratory conditions, that a change in the chemical environment of plant roots allows the secretion of anti-cancer agents, such as paclitaxel and alkaloids extracted from the vinca plant, to increase.

Dr. Yonghui Dong, Dr. Jedrej Yaakov Szymanski, Dr. Sayantan Panda, Dr. Adam Gozviak, Dr. Hassan Masalha, Dr. Shagit Meir and Dr. Ilana Rogchev participated in the study.

The secretion of the substances from the roots "takes away" about 50% of the energy produced by the plant in the process of photosynthesis.

Asaf AharoniPlant and environmental sciencesAgricultureAgriculture and nutritionPlant resistance