Introduction
Among the greenhouse gases, carbon dioxide (CO₂) is one of the most critical contributors to global warming. 💭
The most fundamental way to reduce it is to increase the Earth’s carbon sinks — things like planting trees and expanding ecosystems that can naturally store carbon.
✋ Wait, what is a Carbon Sink?
A carbon sink refers to any material or system that absorbs and stores carbon. Minerals, oceans, and photosynthetic organisms like plants and algae all act as carbon sinks.
But as CO₂ levels keep rising, it’s hard to even imagine how many trees we would need to plant to make a real difference. 🌳 That’s why biologists came up with another idea which is developing “special trees” 🌲 that can absorb far more CO₂ than normal ones.
“To absorb more CO₂, something has to get faster — but what?”
For a tree to absorb more CO₂, photosynthesis has to happen faster.
Photosynthesis has two main stages:
- the light-dependent reactions, which require sunlight, and
- the light-independent reactions (or dark reactions), where the Calvin Cycle occurs.
This is where CO₂, a one-carbon compound, is converted into a six-carbon sugar molecule, glucose. Here, CO₂ binds with a five-carbon molecule called RuBP to form a six-carbon compound. The enzyme that helps them “stick together” is called Rubisco.
🧬 The most abundant enzyme on Earth? Rubisco!
Surprisingly, Rubisco is the most abundant enzyme on the planet. It’s crucial for producing glucose through photosynthesis and provides the foundation of energy for almost all living organisms that cannot generate their own.
🦥 Rubisco — the “sloth” of enzymes
Despite its importance, Rubisco has one big flaw: it’s slow. Its reaction rate is low, meaning it can’t process CO₂ fast enough. In other words, the slower Rubisco works, the slower CO₂ in the atmosphere is converted into biomass — making carbon fixation inefficient. So you might wonder:
“Why not just make Rubisco work faster?” 🤷
Exactly! That’s what researchers initially tried. In general, increasing the amount of enzyme can boost the rate of reaction (the enzyme-substrate complex formation). So, scientists first focused on increasing the amount of Rubisco in plants.
🗝️ The key to photosynthetic speed = efficiency!
When Rubisco levels increased, the reaction rate did rise a bit — but not enough. Rubisco reacts not only with CO₂ but also with oxygen, which produces toxic by-products like phosphoglycolate. This triggers a photorespiration process that consumes ATP/NADH and releases CO₂, ultimately lowering net photosynthetic efficiency. So researchers shifted their focus from quantity to efficiency — realizing that by improving photosynthetic efficiency, they could increase the rate of photosynthesis ⬆️ and the amount of carbon fixed per unit time ⬆️.
🌿 So how can photosynthetic efficiency be improved?
The key is to relocate the photorespiration pathway so that it happens within the chloroplast instead of across multiple organelles. Normally, photorespiration takes a long, energy-consuming detour:
Chloroplast → Peroxisome → Mitochondrion → back to Chloroplast.
During this process, CO₂ and energy are lost.
So researchers asked:
🧐 “If photorespiration starts and ends in the chloroplast,
why not keep it all inside in the first place?”
That simple question led them to introduce chloroplast-targeted enzymes. These enzymes help detoxify CO₂ or reroute the photorespiratory pathway entirely inside the chloroplast, minimizing carbon and energy loss and speeding up the reintegration of carbon into the Calvin Cycle. This results in a higher net photosynthetic rate.
⚡ The Booster Gene (BSTR) that “genetically boosts” photosynthesis
Another approach involves a “booster gene” called BSTR, discovered only recently. This gene is tied to a mechanism known as non-photochemical quenching (NPQ). When plants are exposed to intense sunlight, the light energy absorbed can exceed what the photosynthetic electron transport chain can handle, causing reactive oxygen species (ROS) and leading to photodamage. To protect themselves, plants intentionally release excess energy as heat which is called NPQ. But NPQ must turn on and off rapidly, like a light switch. If it doesn’t, plants end up wasting energy even when sunlight isn’t too strong, lowering photosynthetic efficiency.
For years, scientists focused only on genes that directly regulate NPQ. But it turns out, the real control lies with another gene called BSTR located farther away in the genome. BSTR produces a “megaphone-like” protein that amplifies the NPQ control signal. By increasing BSTR gene expression, it’s like giving the plant 100 loudspeakers instead of one. Hence, the “NPQ on/off” signals are transmitted much faster, allowing plants to adjust quickly to changing light conditions and greatly enhance photosynthetic efficiency.
🌱 Closing Thoughts
When we hear the term GMO, we often tend to think of it negatively. I’m the same. I usually try to choose Non-GMO foods whenever I can, and I know many people feel the same way.
However, Genetically Modified Organisms aren’t created just to make things cheaper or easier to produce. Around the world, scientists are working together to develop plants and trees that can absorb more carbon dioxide and increase biomass more efficiently, all in hopes of contributing to solutions for the climate crisis.
As someone deeply interested in this field, I found this topic especially fascinating to explore. I’ll be back soon with another exciting topic to share with you! :)
[This following article is translated version of the post uploaded on NEWNEEK]
Photo credit: Arnaud Mesureur from Unsplash
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