Message travels in the plant cytoplasm, but how?

All the cells in a plant are connected with each other by means of thin cytoplasmic threads. Academy professor Yrjö Helariutta is determined to find out what kind of messages the cytoplasm delivers to the roots and how this signaling is mediated.

Yrjö Helariutta

Yrjö Helariutta studies plants and tries to find out how the roots receive information from neighbouring cells, for example, or from the whole plant itself.

– The cytoplasm inside plant cells is known to extend uninterrupted from one cell to another. The cells are connected via openings known as plasmodesmata. The cytoplasm extends through these openings as thin strands, so all the plant’s cells are connected by the cytoplasm - unless, of course, communication is somehow interrupted, Helariutta says.

Plasmodesmata are especially copious in the phloem, a layer of cells located immediately under the bark. In the phloem, liquids flow from the upper part of the plant towards the roots. The plasmodesmata are anything but simple holes in the cell wall that enable molecules to travel from one cell to another. Transport through the plasmodesmata is regulated, but exactly how this occurs remains unclear despite the long history of plant research and the essential role plants play in life on Earth.

– We still lack a comprehensive analysis of the signalling that takes place in the cytoplasm. We don't know, for example, what role the cytoplasmic messages play in the development of the phloem or what signals travel to the root system. In fact, the structure of the plasmodesmata and the regulation of their function largely remain unstudied, says Helariutta.

More than just lumps

Messages from one plant cell to another are transmitted via plasmodesmata or structures closely related to them, i.e. sieve plates with multiple holes. Messages may also be stopped by a polysaccharide known as callose, which can clog the plasmodesmata and sieve plate holes. Under a microscope, callose looks like a lump of used chewing gum, but does not emerge haphazardly.

– The production of callose is very subtly mediated, or at least that's what we understood when we found some suitable mutants amongst our selection of mouse-ear cress, i.e. Arabidopsis thaliana. Apparently some of the plants produced too much callose, which led to unusual structures in the roots.

The Helariutta group has genetically controlled the amount of callose in the plasmodesmata. Using this knowledge, they can halt callose production in specific cells whenever they want. Afterwards they can observe the effects the callose has in cell-to-cell signalling and plant development.

Helariutta is now an Academy professor of the Academy of Finland. In addition, he received a five-year EUR 2.4 million grant from the European Research Council (ERC).

Research Database TUHAT: Yrjö Helariutta »»

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Text: Elina Raukko
Photo: Veikko Somerpuro
University of Helsinki, digital communications

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