Inside the cells of seemingly static plants are vibrant populations of motile organelles. Hundreds of mitochondria, energy providers of the cell, move about on their own individual journeys, and interact with each other as they go. They take small steps to explore their local cellular area, and use ‘highways’ in the cell (filaments made of actin protein) to travel over long distances quickly. Although this motion has been well characterised over the years, the mystery still remains: Why does the plant invest energy in moving these powerhouses around?

On the surface, plant mitochondria have an impossible task. On one hand, it is good for them to meet up. They can fuse and exchange mitochondrial DNA (mtDNA), proteins, and other chemicals, in an ongoing collaboration that is important for the plant. When this sharing is compromised, for example by mutations in the machinery responsible, plants grow less rapidly and less green, and may be sterile and experience other problems. On the other hand, it is good for mitochondria to stay apart. An even spread of mitochondria through the cell ensures an even supply of energy, limits the local buildup of damaging chemicals, and allows mitochondria to meet up with other cellular machinery. We thought that mitochondrial movement might be a way of getting the best of both worlds — allowing occasional meetups but also keeping mitochondria well spread in the cell. But to explore this idea we needed to understand both how real plant mitochondria move, and how different types of motion could help resolve this tradeoff.

How do we delve into these communities within plant cells? Let’s start with how mitochondria move. In our lab at the University of Birmingham (our group is based at the University of Bergen but we are international!), we use live-cell laser microscopy to watch mitochondria in seedlings of Arabidopsis, a favourite plant for laboratory experiments. Prof. David Logan, who has shaped the field of plant mitochondrial dynamics, made and kindly provided us with a line of plants with fluorescent proteins attached to their mitochondria. From this, we can take videos of mitochondrial dynamics, like the time lapse below from a single cell in the hypocotyl (early stem).