Spray-on drought resistance for plants

The Earth’s climate is predicted to heat up over the coming years, and droughts are expected to become more common. They’re a big problem already for some farmers, costing thirty billion dollars every year. But can science help? The answer is possibly, thanks to a new spray-on treatment - called “opabactin” - that artificially activates a plants’ natural drought responses. The idea would be to use it to prepare plants before disaster strikes, making them more resilient when the worst happens. To find out how it works, Phil Sansom met up with Cambridge University plant scientist Jim Rowe, who wasn’t part of the research but works on similar aspects of how plants grow…

Jim - So they've made a new chemical that activates the plant's own drought stress responses. When you spray the plants with this chemical they stay greener for longer when you then stress them.

Phil - What is this chemical?

Jim - So actually what they did was they took an existing chemical that occurs in plants that's actually a plant hormone called abscisic acid. And they then looked at the molecule it binds to, which we call a receptor. They looked at lots of different chemicals and designed a new one that binds the receptor even more strongly than abscisic acid.

Phil - So it does something similar to something that actually exists in nature already?

Jim - Yeah, yeah. So we would call this a hormone analogue. Plants normally under drought stress and stressful conditions will produce this hormone, abscisic acid. And this basically will tell the rest of the plant: water is scarce. We need to look after it and try and survive this.

Phil - Now call me crazy: I knew animals had hormones. I didn't realise plants had hormones too!

Jim - Yeah, yeah, and they do a lot of similar things to animal hormones. So they might control the way that plants grow and develop; stress responses such as drought; or response to pathogens; or response to being eaten.

Phil - Now tell me, how does abscisic acid work?

Jim - Abscisic acid is, we think, mostly made in the leaves. What it does is it will close the small holes in the leaves, that are called stomata, to help the plant lose less water in response to drought. It can also control the way that the plant grows and develops under stress. So for instance, a small amount of abscisic acid will stop plant roots growing sideways and make them grow down to try and get to deeper water.

Phil - It just does loads of different things that help it when there's not much water?

Jim - Yeah. It has a whole-plant effect and does lots of different things in lots of different places.

Phil - That's amazing!

Jim - Yeah, yeah I think so too.

Phil - So does this new compound work in exactly the same way?

Jim - It's hitting the same receptors that abscisic acid is. It won't happen in exactly the same way, quite possibly, because there may be other signals that would normally happen in the case of a drought. But it's mostly activating the same response.

Phil - Are there any downsides for a plant if you give it all these drought responses?

Jim - Yeah, yeah there are. It takes quite a lot of resources and investment to protect yourself from these stresses. And so if you're shuttling all your resources to protection, you might get short and stunted plants.

Phil - But it's worth it?

Jim - If a drought is coming along, then yes.

Phil - So this must be useful when there are actual droughts out in the world.

Jim - I think that's what the authors are hoping. Obviously this hasn't been tried outside yet and it's mostly early days, but this sort of approach could lead to much higher yields in water-poor years. Drought is one of the leading causes of crop loss globally, and the trouble is, whereas we can protect the weather next week, we might not know that in a year's time there's going to be a massive drought.

Phil - Yeah. And next week even is a bit of a toss-up. Do you think in theory, you could just spray this on your crops, how long would it protect them for?

Jim - The initial work in the paper shows that if you spray a high concentration you will maintain an abscisic acid-like response for five days. Now I don't know how long after that it would carry on doing it but that, the idea that you spray it before the drought and you get the plants prepping first, might make a big difference in survival later on.

Phil - And will this work for any plants?

Jim - It will certainly work for the crop plants that they've tried it on. I think it will work for most plants because water relations are so integral to colonising land. Abscisic acid seems to have evolved a long time ago so nearly all plants respond to abscisic acid.

Phil - Just like they'll respond to this new thing?

Jim - Exactly.