How to grow tomatoes without the corresponding plant

Seven years ago, a colleague gave Lucas van der Zee (34) an idea that would define his career. The then master’s student biosystems engineering sat in a Wageningen lecture hall listening to the latest techniques in tomato cultivation. Outside of his studies, he had just read about cultured meat – something that fitted in seamlessly with his background in the climate movement. “I thought growing meat was a really cool idea,” he says. “And then I thought: if you can grow meat from cells, could that also be possible for fruits such as tomatoes?”

Without wasting much time, he took “some papers about this” on holiday and discovered that hardly anyone worldwide was working on lab fruits. Only NASA had tried to grow plant-less tomatoes for space missions in the 1990s. However, Van der Zee did not want to feed astronauts, but the growing world population. “So I took the plunge, went to my professor and asked if I could do a little experiment in the lab.”

That “little experiment” grew from a master’s thesis to a doctoral research project. Van der Zee is now a third-year PhD candidate. He recently published an opinion piece with colleagues about his method of growing tomatoes without plants – a technique whose fruits could be more climate-resilient and environmentally friendly, according to the article.

The idea is to bring some agriculture in so that agricultural land can be used more sustainably – for example by growing plants less intensively or returning a piece of land to nature. Tomatoes serve as a model species here, just like mice do in medical research. So if you can grow a tomato without a plant efficiently and sustainably, the method can later be applied to different fruits.

In addition to the possible benefits for nature, the research also offers another opportunity: being less influenced by production shortages. We will see this more often due to climate change, says Van der Zee. “If you can predict that harvests will turn out poorly, you can intervene with this technology. For example, you could produce 5 percent of the citrus or cocoa fruits in the lab instead of importing them.”

Upright in a clear gel

In his small lab in Wageningen, Van der Zee opens a refrigerator in which rows of round, transparent containers are neatly next to each other. Each container is the size of a saucer and contains about ten tomato flowers. At the place where the flower normally turns into a stem and then into the rest of the plant, they stick upright in a transparent gel.

Some flowers are still closed, others have already grown and are open. Small green tomatoes can even be seen in a few containers. In theory, these are the result of the four-step process of growing a lab tomato: first making a shoot from seed or stem cells, immediately growing a flower from it, pollinating the flower and finally growing a fruit.

In practice, however, the flowers here are cut from plants; the first two steps of the process take place at Utrecht University. This way, scientists can investigate and improve all steps simultaneously. Van der Zee is responsible for the final steps: finding an efficient way to pollinate the flower and grow a fruit that grows to the same size as on a normal plant. “We still see that those fruits remain very small,” he says. He wants to find a solution for that. “They now grow about three times as fast as at the start of my PhD, but still half as fast as on the plant.”

Before a tomato can develop, there must first be a small shoot that immediately forms a flower. That sounds simple, but it is quite a challenge. Normally a young plant does not produce flowers, just as young animals cannot yet reproduce. To circumvent this, the researchers switch on a gene in the plant that produces a special protein. In a mature plant, that protein stimulates flower formation. “We make the plant immediately mature artificially,” Van der Zee explains.

This step has already been achieved in the lab, but it is technically complex, which means that not every grower can easily apply it. “High-tech is sometimes quite problematic,” says Van der Zee. “My idea is that as a scientist you should make technologies as low-tech as possible, so that small companies can also benefit from them.” That is why Van der Zee devised a method in which the tomatoes do not have to be genetically modified. Instead of switching on the gene, researchers – and later producers – can provide the required protein directly to the plant. The protein thus stimulates flower formation and then disappears again.

To make the technique even more accessible, Van der Zee also wants to work on a method that no longer requires completely sterile laboratory conditions. In addition, in the final phase of his PhD research, he plans to analyze the flavor and contents of the cultivated fruits to demonstrate that they are equivalent to fruits that have grown naturally.

Sugar nourishes the flowers

But even if all that succeeds, one major issue remains: how sustainable is the method really? “You see many articles that immediately want to claim that this is more sustainable – but we don’t actually know that yet,” says Van der Zee and he emphasizes: “It could be more sustainable.” The bottleneck is in the nutrition of the mini plants. Normally tomatoes get their energy from photosynthesis, but in Van der Zee’s refrigerator the ‘plants’ have no leaves and obviously lack sunlight. That is why the flowers are given sugar as a nutrient. However, that sugar has to come from somewhere. “If it just comes from sugar beets or sugar cane, you won’t make much progress in terms of sustainability,” Van der Zee explains.

A possible solution comes from researchers in California, with whom Van der Zee is in contact. They are working on a way to make sugar entirely in the lab, from CO₂ and electricity. This has not yet been achieved in practice, but major steps are being taken, and according to Van der Zee this could become a “huge revolution”. With artificial photosynthesis, researchers could not only provide lab tomatoes with nutrition, but also create bioplastics, medicines and countless other products.

While this research is still in full development in the US, Van der Zee notices that his work is attracting increasing interest in the Netherlands. Other researchers want to replicate his experiments, investors approach him and a young German even wanted to set up a company with him. “I didn’t feel like doing that yet, so it didn’t happen,” he smiles.

“It gives a lot of satisfaction when a new protocol works. I am proud of that, but I can also be very disappointed when something goes wrong – and a lot goes wrong,” he adds, laughing. “That really keeps me awake and I try to compensate and work harder.”

Whether all that hard work pays off and we see cultivated fruits in stores in the future depends on finding a truly sustainable, applicable method. “If a whole group of scientists starts working on it, something could be available in eight to ten years,” says Van der Zee. “But if I remain the only one, it could take twenty years – or it may never work.”

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