Getting to the Root of the Problem

Common wisdom has it that carrots are rich in vitamin A and tomatoes contain large amounts of lycopene, but reality is much more complicated: Plants contain thousands of substances called secondary metabolites. Their name notwithstanding, these substances are not secondary at all; they are involved in a host of vital processes, including gene control and interaction with the environment. Their functions include attracting pollinating insects and defending the plant against pests or too much sunlight. Luckily for humans, many of these substances also contribute to our health.

In the past few years, much effort has gone into identifying, mapping and monitoring secondary plant metabolites. Scientists use an approach called metabolomics: obtaining a general profile of various metabolites in a biological sample. This approach might help develop plants with a high concentration of metabolites that are useful for humans, or plants that are capable of fighting off pests more efficiently. Metabolic profiles make it possible to identify the genes and biochemical pathways involved in the production of these metabolites, and to increase or decrease the activity of these genes on demand. But despite the rapid progress in metabolomics technologies, scientists have until now had to make do with metabolic profiles of plants at a low resolution: They could determine the total quantity of metabolites in a particular plant tissue or organ, but not exactly in which types of cell these metabolites were found.

Weizmann Institute scientists, using an advanced metabolomics system, have now managed to increase this resolution substantially, determining the metabolic profiles of various cell types in plant roots. The study, reported in the Proceedings of the National Academy of Sciences, USA, was performed by Prof. Asaph Aharoni of the Institute’s Plant Sciences Department and his team: Drs. Arieh Moussaieff, Ilana Rogachev and Sergey Malitsky, and Merav Yativ, in collaboration with colleagues in Israel and abroad.

The scientists grew five types of plants, marking with a fluorescent dye particular cell types in their roots. They then sorted the root cells with the help of the fluorescent marker.

The study produced a comprehensive profile that revealed hundreds of substances, including those derived from three main chemical classes, distributed among different types of root cells. One of these groups, composed of a specific set of di-peptides, has been identified in roots for the first time. An analysis of the findings has also overturned an intuitive assumption: Metabolites were not necessarily found in the same cells that expressed the genes involved in their production. Apparently plants have a mechanism for moving substances to target areas.

Aharoni intends to increase the resolution of metabolic profiles even further, focusing on a particular group of root metabolites: plant hormones. A detailed mapping of materials in this group in root cells will make it possible, among other goals, to gain a better understanding of root development and growth, and to reveal how the root helps regulate the plant’s environment by releasing hormones into the surrounding soil.

 

Prof. Asaph Aharoni's research is supported by the Clore Center for Biological Physics; the Kahn Family Research Center for Systems Biology of the Human Cell; the Tom and Sondra Rykoff Family Foundation; Roberto and Renata Ruhman, Brazil; the Adelis Foundation; the Leona M. and Harry B. Helmsley Charitable Trust; the Minna James Heineman Stiftun; and the Raymond Burton Plant Genome Research Fund. Prof. Aharoni is the incumbent of the Peter J. Cohn Professorial Chair.