Ultrafast imaging tech unlocks 'impossible' pathway in photosynthesis for new clean fuels

Yet, despite decades of scientific inquiry, photosynthesis still has secrets to tell. In a groundbreaking endeavor, an international team led by the University of Cambridge has ventured into uncharted territory, peering into the core of photosynthetic processes with unprecedented precision.

Their weapon of choice? Ultrafast imaging, capable of capturing the fleeting moments unfolding within a millionth of a second. This cutting-edge technology has illuminated a previously unseen pathway, emerging in the earliest stages of photosynthesis. 

Interesting Engineering (IE) reached out to Dr. Jenny Zhang at Cambridge's Yusuf Hamied Department of Chemistry, who coordinated the research, to delve into how this discovery could challenge our current understanding of photosynthesis and assist in ushering in novel routes for renewable energy. 

Unlocking the impossible: electrons' power in early photosynthesis

During photosynthesis, plants use sunlight to convert carbon dioxide and water into energy-rich molecules. A critical aspect of this process (an oxidation-reduction reaction) is the transfer of electrons, like tiny particles carrying energy.

"We have discovered a new way to steal electrons from photosynthesis using artificial electron shuttles," Zhang told IE. 

"The spot at which the electron can be stolen is at the earliest step of photosynthesis possible - this is highly desirable because, at this time point, the electrons are highly energetic and more useful than if we steal the electrons at later time points." 

To elaborate, think of it as capturing the electrons at their most powerful and useful state. By capturing them at this early stage, scientists maximize the energy that can be harvested and utilized.

Zhang emphasized that this achievement is a significant milestone, as extracting electrons from such an early stage was previously considered impossible. "It turns out that this pathway had been there all along, but no one had detected it," she commented.

Ultrafast tech 'opened the black box of photosynthesis a bit further'

"We had to use a highly sophisticated technique – ultra-fast spectroscopy - to 'see' how energy is transferred in living photosynthetic cells at very fast (picosecond) time frames to help us with this discovery."

To give an idea of how short a period of time is involved here, one picosecond is equal to one trillionth of a second, or 0.000000000001 seconds (10^-12). Think about the blink of an eye, which happens relatively quickly. Well, a picosecond is about a million times faster than that. It's a tiny fraction of a second that humans can't perceive with our own senses.

At first, Zhang and her colleagues aimed to investigate how ring-shaped molecules called quinones (which occur as biological pigments) could 'steal' electrons from photosynthesis. Quinones are commonly found in nature and can easily accept and release electrons. Little did the researchers know that they were about to unearth an entirely new photosynthetic electron transfer pathway.

"No one had properly studied how this molecule interplays with photosynthetic machineries at such an early point of photosynthesis: we thought we were just using a new technique to confirm what we already knew," revealed Zhang in an earlier press release. 

"Instead, we found a whole new pathway and opened the black box of photosynthesis a bit further."

The scientists found that the protein structure responsible for the initial chemical reactions in photosynthesis is permeable, or 'leaky,' allowing electrons to escape. They could observe and track this movement in real-time by utilizing ultrafast spectroscopy.

"Since the electrons from photosynthesis are dispersed through the whole system, that means we can access them," stated co-first author Dr. Laura Wey who performed the work in the Department of Biochemistry and is now based at the University of Turku, Finland.

"The fact that we can steal them at an earlier process is mind-blowing. At first, we thought we'd made a mistake: it took a while for us to convince ourselves that we'd done it," expressed Zhang.

Paving the way for novel renewables and crop resilience

In addition to extracting charges at an earlier stage of photosynthesis, which can help enhance the production of clean fuels from solar energy, the ability to control photosynthesis could make crops more resilient to intense sunlight.

While specific benefits of controlling photosynthesis for making crops more resilient to intense sunlight were not discussed in the interview, mitigating the impacts of rising temperatures on plants comes to mind — at least in the context of climate change.

For instance, extreme heat events like heat waves are becoming more frequent and intense globally, negatively affecting crop growth and productivity. By manipulating photosynthesis, scientists could develop more heat-tolerant crops, allowing them to maintain optimal photosynthetic activity even under stressful conditions. Ultimately, this could safeguard crop yields and ensure food security.

It's worth considering that controlling photosynthesis may have broader implications for plant health, resource efficiency, and overall crop performance. That said, further research and exploration are needed to uncover the full range of advantages this ability could bring concerning climate change and sustainable agriculture.

Now, "we need to find better [electron] shuttles" 

When questioned about her motivation to "hack" photosynthesis, Zhang explained that this goal, shared by many, is to find better methods for converting solar energy into chemical energy. "Doing this may provide a greener way of producing chemicals and fuels, helping us on our journey for fossil-free clean growth," she said. 

"Currently, the major alternative on the market for generating fossil-free clean fuels is via bioenergy. This route relies on agricultural crops, is highly inefficient, and places large pressures on land use (competes with food production and decreases biodiversity)," Zhang highlighted. 

"By re-wiring photosynthesis occurring in photosynthetic cells such as cyanobacteria, we can potentially mitigate these problems and provide more efficient, less land-demanding options for producing green chemicals/fuels," she added. 

Further, when prompted about the limitations of her team's research, including challenges to taking the discovery forward, Zhang revealed the need to find better electron shuttles— i.e., ones that can steal the electrons from photosynthesis while retaining the high energy of the electrons. 

"We need to find better shuttles that will be compatible with the living systems so that they can be used for a long time without side effects, she concluded. 

On a closing note, as the world grapples with the need for climate change solutions, endeavors like this offer a glimmer of hope. They remind us that tireless exploration and relentless curiosity are essential if we are to inch closer to realizing a future where clean energy flows abundantly and the echoes of our carbon footprint fade away. It's a future where the intricate workings of nature harmonize with human ingenuity.