The dangers of overcharging your plants

Foreground: iPhone battery, expanded due to short-circuit. By Mpt-matthew CC BY-SA 3.0


This is a non-scientist friendly article. Words preceded by   are defined when hovered over.

Engineers are constantly trying to make phone batteries more efficient and lighter, and they do so by packing together very thin layers of the metal lithium. The problem is that overcharging these batteries can lead to serious damage, even fires that have been in the news recently.

It turns out that nature has been dealing with a similar problem for a long time in the process of  photosynthesis, the source of energy for most life on our planet. Our food supply depends on photosynthesis being efficient, and so do some of our renewable materials. And in the effort to help feed billions more people, or to power our jets and cars with biofuels, scientists have been trying to figure out how to improve this process.

But capturing light is a dangerous business for plants. And in its latest study, published in the prestigious open-access journal, eLife (go to article), the Kramer lab has discovered that photosynthesis can often overcharge plants, potentially killing them.


Storing energy in different forms

To be able to perform photosynthesis,  chloroplaststhe tiny “solar panels” in plants – have to absorb light that has very high energy and convert it into usable forms that power the plant.


Dr. Kramer


Chloroplasts do this by using the light energy to strip electrons from water and store them in various compounds, similar to what happens when we charge batteries. But unlike batteries, plants have to store energy in different forms in order to perform different jobs. A much more fascinating picture!

The Kramer lab has been studying one of these forms of storing light energy, an electric field generated by the chloroplast. Stored across an ultra-thin membrane in the chloroplast, the field powers a process that makes ATP, an essential ‘energy currency’ needed by the plant to survive and grow.


Dangerous electric spikes

In this latest study, Geoffry Davis from Kramer’s group has discovered that too much of this electric field can cause huge problems, because it destabilizes the other parts of photosynthesis, which then end up self-destructing. 

“When the field gets too large, it makes some of the electrons move backwards from the way they should,” says Dr. David Kramer Hannah Distinguished Professor in Photosynthesis and Bioenergetics at the PRL. “This wastes energy, but even worse, if these electrons end up on special  chlorophyll molecules, they can transform oxygen from the air into a chemical that can damage or kill the plant. “


A depiction of the energy spikes. By the Kramer lab


Scientists have known for a while that this damaging chemical is a byproduct of photosynthesis, but they haven’t known the extent to which this is a major limitation on plant productivity. The reason is that plants have been studied in bits and pieces in the lab, isolated from the organism and its environment.

With that in mind, the Kramer group, through support from the U.S. Department of Energy (Basic Energy Sciences), has developed the technologies that allow them to study photosynthesis in living plants under the conditions they experience in the real world.

And these technologies have been yielding surprising insights. According to Geoffry, “When the leaves move in the wind or clouds go by, the light hitting the leaves can flicker very rapidly. These rapid changes cause very large spikes in the electric field, enough to cause a lot of damage.”

“Think about it: these changes in light conditions happen all the time in nature.”


Inefficient natural defenses

Plants can partially protect themselves from this electric overcharge, but they do this by shedding energy that would otherwise be used productively.

The result is that, out in the field, plants typically store only about 1% of the energy that they absorb as biomass that is suitable for human use. But it’s theoretically possible to store much more.


Geoffry Davis


Even worse, Geoffry says, the protective mechanisms are often too slow to protect against large spikes in electric field that happen when the light flickers.  

“We need plants that can respond more rapidly so they can protect themselves without losing production efficiency. We have been looking at a wide range of different plants that do a better job and also making mutations in plants to figure out what makes them more or less sensitive. This is giving us some important clues about how to proceed.”


Aiming to grow better plants

One of the collaborators on the team, Professor William Rutherford, sums up the study’s importance nicely: “There are many ways to kill a photosynthesizer with light, but this discovery is probably the most credible in terms of mechanism and physiological relevance. These big spikes in the electric field simply replace our hand-waving explanations…that is a big step forward.”

And increasing photosynthetic efficiency, even by a small percentage (say 1 or 2 percent), could dramatically increase crop yield. More importantly, such photosynthesis-related increases would not require additional fertilizer or other inputs, an improvement over the first Green Revolution due to it being intrinsically more sustainable.

Kramer emphasizes that we are going to have to find newer ways to sustain an expanding population. “There is not much more new arable land to use. So we are going to have to breed or create more efficient plants that use the resources better. And we’ve already tapped out a lot of the ‘easy’ ways to make plants more efficient.”

Kramer concludes, “Now we have to get into the engine of photosynthesis and figure out how to squeeze a few more horsepower out of it. This is a much harder problem, but that’s where the energy losses are.”

Additional collaborators include Atsuko Kanazawa, Mark Aurel Schöttler, Kaori Kohzuma, John E. Froehlich, A. William Rutherford, Mio Satoh-Cruz, Deepika Minhas, Stefanie Tietz,  and Amit Dhingra.

Updated 5/17/17: The article has been recommended in F1000Prime as being of special significance in its field.