The tobacco factory is open for business...

Science is always a numbers game.

The more experiments you do, the more data you get; the more data you have, the more likely you are to find something interesting; the more novel discoveries, the more papers you can write…and so on until that elusive permanent research position comes within reach. ‘Workaholism’ is a virus which spreads easily in labs and I fully admit to being susceptible. I would love to do never-ending series of experiments after experiments, cramming as many plants as possible into my growth cabinet and spending my weekends gleaning through hoards of accumulated data. It’s probably just as well for my mental health and wider interests that I can’t do this. The reason? I simply don’t have enough seed. My stocks of Striga gesnerioides, the parasitic plant that I study, are down to the last vial.

Those of you who have been following this blog for a while may recall that I had the same problem a few years back. In the end, I managed to solve it by getting hold of some tobacco, a very susceptible host for S. gesnerioides (the model host I use for my experiments, Arabidopsis, is so small that the attached Striga never progress to the flowering stage). So I am appalled to find myself in the same position again – but it’s not as though I haven’t been trying. One of the first things I did when I came off leave of absence was to sow some more tobacco and start the process again. When the first shoots came up, I relaxed – complacent with the thought that soon I would have an abundance of seed capsules to harvest. But it never happened. Weeks passed and nothing else appeared….I told myself not to panic, that Striga gesnerioides is notoriously slow to get going and reminded myself that it had taken a while last time. Eventually, after weeks turned to months, I did start to panic. Scrabbling through the soil, I found that the Striga had died underground – withered and black. My supervisor thinks I watered them too much: “They are very sensitive to getting wet!”

 Tobacco plants growing in rhizotrons (left): Tobacco root system infected with Striga gesnerioides 2 weeks ago (right).

So gone are the days when I could do any experiment I fancied. According to the weight of the remaining seed, I am down to my last 14 assays. I can’t afford to waste any more: after all – no seed, no experiments, no PhD. Therefore, I have taken to having a constant stock of tobacco growing in rhizotrons (root observation chambers). Each time I have done an infection as part of my normal experiments, I took the seed that remained at the end, opened up a tobacco rhizotron and applied them directly to the roots with a paintbrush. Infecting them in this way means that I can leave them for a week or two to make sure the Striga are firmly attached before transplanting them carefully into pots (all of different sizes, in case this makes a difference!).

This time, I certainly won’t be so heavy handed with the watering can. And there will be a lot more tobacco plants (going back to the numbers game). I have also given them all names, although it’s not as if I needed more motivation to take good care of them! So meet the team: Serenity, Dimitri, Artemis, Brent, Sentinel, Robert, Halo, Magic, Aristotle, Nighthawk, Angel and Destiny (no there is no explanation, other than that they were the first words I thought of when repotting them, apart from Robert who was named in honour of our summer research assistant). So far, they seem happy enough although I try not to let on how much I am counting on them. Last week, the first Striga shoots started to come up on Artemis, who appears very heavily infected indeed. But I’m not getting my hopes up yet – it could still all go horribly wrong, and so far, none of the others show any signs of the parasite.

Destiny, Robert, Artemis, Sentinel and Nighthawk.

Close up of Striga shoots on Artemis

On a more cheerful note, I have had one recent success. Until now, I have been having terrible trouble getting the S. gesnerioides seed that I do have to germinate properly: the maximum I ever reached was 30% germination. This was probably because I was using an artificial chemical called GR24, which is actually a germination stimulant for the related species Striga hermonthica. So I decided to take a step back to nature…. unlike S. hermonthica, which infects cereal crops such as maize, the original host for S. gesnerioides is cowpea. In their native soil, the parasite seeds germinate in response to chemicals naturally released by the cowpea roots (a handy trick to ensure they only germinate when a suitable host is present!). Although the exact chemical/s Striga responds to are unknown, this needn’t stop me from trying the same thing! Consequently, I have been growing cowpea hydroponically and taking samples from the liquid every few days. I was amazed at how well the cowpea took to it, given that the only support they had was a tube in a rack with the end sawn off. Even better, since using the cowpea extract, the germination rates have shot up to over 50%. It’s a good lesson in putting a problem back into the context it came from.

My super-hyrdroponic cowpea plants!

But it was over all too quickly – cowpea generation one have finally expired: after growing an exuberant display of twirling tendrils and straggly pods, they yellowed, shrivelled and died. But within those pods, they gave me all I needed to carry on and I planted the seeds for generation two last week.

Growing, harvesting and growing again: at the end of the day, it’s basically what continuing plant science, whatever the species you study, comes down to.

Thanks for reading! And if you have any suggestions for the next tobacco names, do get in touch…