Tiny highways in leaves could lead to more productive crops

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Scientists have found that some plants have ten times more communication channels inside their leaves than other plants, which they think is a crucial factor in determining photosynthetic efficiency.

PhD student Florence Danila showing plasmodesmata. Taken at the AMMRF (ANU)

These highways, called plasmodesmata, are microscopic structures that pass through plant cell walls. They are so small that it is possible to fit more than 25,000 plasmodesmata in the diameter of a human hair.

“Plasmodesmata transport small molecules or metabolites, such as sugar molecules, in the same way roads transport cars. Just like in a city, having more roads mean that cars can travel faster, while less roads result in traffic jams,” said ANU PhD student Florence Danila, whose project at the ARC Centre of Excellence for Translational Photosynthesis, has resulted in these findings.

“We found that plants that are able to produce more food, like corn, have ten times more plasmodesmata than less efficient plants, and that they have a very special role allowing the flux of metabolites” she said.

Two biochemical pathway processes, C3 and C4 photosynthesis, are used by plants to fix carbon using sunlight. Food crops that use C4 photosynthesis include maize and sorghum, while rice and wheat use the less efficient and ancient C3 pathway.

“Our findings are ground-breaking and extremely exciting because this is the first systematic comparison of plasmodesmata in an extensive number of C3 and C4 species, including some of the most important food crops such as wheat, sorghum and rice,“ said ANU Professor Susanne von Caemmerer, Deputy Director at the ARC Excellence for Translational Photosynthesis and one of the authors of this study.

Understanding the differences between these two pathways is crucial, because it may permit the conversion of C3 plants, like rice into the more productive C4 plants, and help solve one of the biggest challenges of the 21st century: how to feed the ever growing world population.

Scientists have known of the existence of plasmodesmata for a long time but these structures are so small, that early researchers found it very challenging to explore and study them.

Florence’s project made it possible to capture these elusive structures, by developing an innovative methodology that combines scanning electron microscopy (SEM) and three dimensional (3D) immunolocalisation by confocal microscopy.

It is a painstaking process – some species take 2-3 months to be processed, which includes; making the leaf transparent by removing pigments and lipids, and digesting the cell wall enough to make them permeable to stains. This permits to count the clusters of diminutive plasmodesmata by making them visible.

“I have been very lucky, because I have had an ideal team of people taking part in the project, scientists who are world experts in microscopy, C4 photosynthesis and metabolites,” Danila said.

“This is a very important set of data for projects that aim to engineer the C4 photosynthesis pathway into C3 crops, but it is also very important for crop modelling and to help unravel one of the unsolved mysteries of plant evolution; why and how some plants evolved the more efficient C4 photosynthesis pathway,” said ANU Professor Robert Furbank, CoETP Director.

This work was recently published in the Journal of Experimental Botany. It was partly funded by the Australian Research Council (ARC) Centre of Excellence for Translational Photosynthesis (CoETP), the International Rice Research Institute (IRRI) and ANU. The investigation took place at the Australian Microscopy and Microanalysis Research Facility (AMMRF) at ANU in collaboration with the Microscopy Centre at CSIRO.

For Interview contact:

Florence Danila

PhD student Centre of Excellence for Translational Photosynthesis

Phone: +61 2 6125 9353

E-mail: Florence.Danila@anu.edu.au

 

Media Contact:

Natalia Bateman

Communications Officer, ARC Centre of Excellence for Translational Photosynthesis

Phone: +61 02 6125 1703 m. 0401 083 380

E-mail: communications@photosynthesis.org.au

 

Publication Details

Florence R Danila, William Paul Quick, Rosemary G White, Steven Kelly, Susanne von Caemmerer, Robert T Furbank; 2018. Multiple mechanisms for enhanced plasmodesmata density in disparate subtypes of C4 grasses, Journal of Experimental Botany, , erx456, https://doi.org/10.1093/jxb/erx456