How some Plants Can Live in Salt, and How to Make Crops That Way

As an evil mad scientist, my favorite pastime is to make elaborate schemes to conduct widespread evil using SCIENCE! Unfortunately, I can only bullshit physics defying inventions into existence when the plot needs it. Which it doesn’t at the moment, so I have to use real science and research for now. All the protagonists I usually fight will be off on a big alien invasion crossover arc for the next month or so. ¹For how often I try to kill them, it’s probably a good thing they’re around to do that. I can’t conquer the world if it gets bulldozed to make a hyperspace bypass, can I?

You may have heard that at the end of the Punic Wars, the Romans salted the earth around the razed city of Carthage. Thanks to that, Carthaginian farmers couldn’t grow crops there. ²It’s actually pretty unlikely that this happened, but it’s a funny meme so whatever

How does that work? Why do the plants care if some angry Italians salt their pasta before harvest instead of before boiling? The reason is that plants are lazy.

• Osmosis
• The Saltiest Plants
• Making Crops Salt Tolerant

Osmosis

Imagine you have a magical filter that water can go through but salt dissolved in that water can’t, otherwise known as the cell membrane. There is water on both sides of the membrane, but the inside of the cell is a bit saltier. When the saltiness on either side is different, water automatically moves across the membrane until the salt:water ratio is the same on either side. It’s a bit like how air will rush in on its own to fill a vacuum. ³Don’t ask why this happens. That’s a whole other thing, physics in particular, and this is a biology article. Just do what all self respecting biologists do and take the physical phenomenon on face value while pretending that math doesn’t exist.

You might have wondered how trees can get water into their roots. It’s not like they have a heart or other pump they can use to suck the water up their trunks. Instead, they exploit osmosis to move water for free. 

Plants just put more salt inside the root cells than is in the soil. Then osmosis will make water enter their roots. Then the plant opens microscopic holes called stomata to let water evaporate out of their leaves. Water is then drawn up the stem through capillary action to replace it. 

Well, this osmosis trick only works if there is more salt in the roots than in the soil. Most plants can tolerate a bit of salt. If the soil gets a little saltier, the plant just moves even more salt into its roots using active transport.⁴Active transport is done by molecular machines made of protein that use energy to pump ions across membranes (Cowan 1965). 

But eventually the plant reaches the point where putting any more salt in its roots would kill it. Active transport costs energy so can only go so far before salt starts piling up inside cells. Too much dissolved sodium chloride can start to mess with the chemistry the plant uses to survive. But soil has no such weakness. You can keep adding salt until there’s more salt than dirt.

The Saltiest Plants

So what do you do if you happen to live in a place where the dirt is really salty? Maybe climate change has desertified the region. Maybe you live near a salt mine that contaminated the soil. Maybe the fresh water in the region to be mixed with sea water by rising sea levels. Or maybe the Italian mafia has finally had enough of your kale and pineapple pizza nonsense and hired a hitman to pour salt on your trendy kale garden.

There are some extremophile plants that can live in very salty soil. They have a number of physical adaptations that allow them to survive and gather water despite the high salt concentration.  

One adaptation are special cells in the roots that use active transport to constantly pump excess salt out. They also widen the casparian band⁵which is like a filter around the core of the root that stops any toxins from going further into the plant. Have you ever noticed the circle around the center of a carrot? That’s it. Though a carrot’s casparian band isn’t particularly powerful and enhance the root endodermis. This helps desalinate the water the roots collect and stop water from moving backwards (Hameed et al 2010).

Some of the traits we associate with desert plants are also used by saline plants. Even ones that live in brackish marshlands with lots of water. Fundamentally, a salty environment is still going to draw water away from a region of lesser salinity, drying out the plant.

One of these adaptations is increased succulence (thiccness) in root and stem. An example of a succulent plant would be Aloe vera. Cactuses also have the right idea here. Thiccer stems and leaves means a better surface to volume ratio and increased storage for water. They also thicken the epidermis (skin) and coat it with a waxy layer to seal it off. (Hameed et al 2010). 

Genetically Engineering Salt Tolerant Crops

We could modify crops to be salt tolerant by giving them these anatomical traits. This could allow us to utilize salty soil that would otherwise be useless, and even water crops using salty water. This would be phenomenally useful in parts of the world without access to fresh water.

They wouldn’t even have to be weird xenofruits. Just make some changes to your kale’s roots, stem, and biochemistry. Before you know it will grow with its normal horrible, bitter taste no matter how much salt gets poured on it.

You probably wouldn’t want to do this with a carrot or other root vegetable since, y’know, most of these changes affect the roots. Unless you are someone who would like their carrots to be waxier, tougher, and even taste a bit saltier. It might be an acquired taste.

Did you know that kale, collard greens, Brussels sprouts, cabbage, Savoy cabbage, cauliflower, broccoli, Chinese broccoli, and German turnips are all just different cultivars of the same species? Even though they’re barely recognizable as being in the same genus, let alone species, they’re still very close genetically (Stansell et al 2018). Brassica oleracea was originally just a small scrub adapted to grow in Europe’s limestone sea cliffs and nowhere else. 

Brassicrops were spread across Eurasia by humans and grown by different diverse peoples. All those different cultivars came from people breeding to exaggerate different parts such as leaves, flowers, buds, or roots. It’s like how you wouldn’t think that a chihuahua, dachshund, pug, and great Dane are all the same species just from looking at them. 

The Original B. oleracea was a salt and lime tolerant plant (Snogerup et al 1990). However, its many varieties have since lost that ability. They should have greater potential to regain tolerance than crops with no genetic history as extremophiles.

Though so far attempts to do this through selective breeding have yielded poor results. But there is a lot of promising work being done to genetically engineer salt tolerance back into Brassicrops (Zhang et al 2014).

Another great candidate is quinoa. As it turns out, quinoa is already a salt tolerant plant. It even has specialized cells on their leaves and stems that excess salt can be pumped into known as bladder cells. 

However, quinoa hasn’t found much popularity outside of South America beyond being a trendy superfood. So none of the advanced plant breeders in developed countries have bothered touching quinoa.⁶Though there are efforts to bring quinoa up to modern standards. And to splice some of its salt tolerant adaptations into other crops (López-Marqués 2020). As of yet, none of quinoa’s cultivars can compete with imports of highly productive dent corn, wheat, or rice despite its salt tolerance. 

Monologuing about my evil plan

Just imagine it; I could use my REsalinator⁷It’s just, like, a dump truck full of salt to salt the earth in all the farms surrounding San Francisco. All the farmer’s crops will die and the new age hippies will go hungry and desperate. Then I sell them my genetically engineered salt tolerant kale and quinoa and make MILLIONS! 

Then, to reach NEW UNPRECEDENTED LEVELS OF UNSPEAKABLE EVIL, I’ll use that money to lobby the government to make the ancient and basic practice of replanting your own seeds illegal so farmers have to keep buying them from me just to survive! MWAHAHAHA!

Citations

Cowan, I.R. 1965. Transport of water in the soil-plant-atmosphere system. J. Applied Ecol. 2: 221-39.

Hameed, M. Basra, S. Naz, N. & Al-Qurainy, F. Anatomical adaptations of Cynodon dactylon (L.) Pers., from the salt range Pakistan, to salinity stress. I. Root and stem anatomy. Pak. J. Bot. 2010; 42: 279-289. 

López-Marqués, R. Nørrevang, A. Ache, P. Moog, M. & Visintainer, D. Wendt, T. Østerberg, J. Dockter, C. Jørgensen, M. Salvador, A. et al. 2020. Prospects for the accelerated improvement of the resilient crop quinoa. J. Exp. Bot. 71/18. Available from: DOI:10.1093/jxb/eraa285 https://www.researchgate.net/publication/342846773_Prospects_for_the_accelerated_improvement_of_the_resilient_crop_quinoa 

Stansell, Z. Hyma, K. Fresnedo-Ramírez, J. Sun, Q. Mitchell, S. Björkman, T. & Hua, J. 2018. Genotyping-by-sequencing of Brassica oleracea vegetables reveals unique phylogenetic patterns, population structure and domestication footprints. Hort. Res. 5: 38. Available from: https://doi.org/10.1038/s41438-018-0040-3 

Snogerup, S., Gustafsson, M., & Roland Von Bothmer. (1990). Brassica sect. Brassica (Brassicaceae) I. Taxonomy and Variation. Willdenowia, 19(2), 271–365. http://www.jstor.org/stable/3996645Zhang, X. Lu, G. Long, W. Zou, X. Li, F. & Nishio, T. Recent progress in drought and salt tolerance studies in Brassica crops. Breed. Sci. 2014; 64(1): 60–73. Available from: https://doi.org/10.1270/jsbbs.64.60