One of the amazing things about plants is how flexible
their development is compared with animals. You can take two plants of the same
species, even with exactly the same genetic code, but put them in different
conditions and they can end up looking completely different. Whereas for
animals, their development is much less sensitive to the environment and pretty much determined by their DNA sequence. It’s one of the things that
makes plants so interesting to study – and also why it is so important to
include all the appropriate controls when doing experiments with them!
A couple of weeks ago, I posted about my current seed crisis
and my ongoing struggle to obtain enough seed of the parasitic weed I study,
Striga gesnerioides, to finish my PhD. To do this, I grew some tobacco seedlings
as these are very sysceptible to Striga: my hope was that the parasite would
infect them well enough to produce an abundance of flowering shoots that would
eventually form seed pods. Unfortuantely, the few parasite shoots that did appear withered and died – despite me following my supervisors
instructions from when they did it before a few years ago “and it worked
perectly”. At this point, I was at the
stage where my seed supplies were so low, I was having to seriously cut down the number
of experiments I could do. So for round two, I couldn’t take any more chances.
The growth cabinet I used in the first attempt, Conviron
Number 502, is set to mimic a temperate British climate, with short days at
25 degrees. However, Striga gesnerioides is actually native to Sub-Saharan Africa,
where it devastates cowpea crops. I reasoned that it was more than likely that they would fare better
in a slightly more tropical climate. So this time, half my Striga-infected
tobacco ‘babies’ went in Conviron 502 and the other half went to joint the rice
plants in our tropical walk-in growth chamber. Up to that point, they had been
treated exactly the same.
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| Unhappy looking tobacco plants in Conviron 502 |
So what happened? After only a week or two, the two sets of
tobacco looked almost like different species. Those in Convrion 502 were small and
squat, with dark green leaves, almost dwarfed by their pots. On the other hand,
those in the tropical walk in grew vigorously and probably would have kept
going if they had been in bigger containers. As for the Striga…..it was no
contest. At first lots of parasite shoots appeared on both sets of plants,
putting me in hope of a super-abundant harvest. But the ones in 502 were weak
and weedy, flopping over the side of the pot or withering away as before. Meanwhile, the Striga shoots in the tropical cabinet stood up as straight as
soldiers with a healthy purple flush to their stems. And they just kept on
coming….whenever I felt down, I would go and run my hands over the surface of the
soil, delighting in the feel of their buds forcing their way upwards.
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| Much happier tobacco plants growing in the simulated tropics - they are even flowering! |
Over the weeks that followed, I visited almost every day,
agonising over whether I was giving them too much or too little water. I was
paranoid that I would somehow kill them all off. But the Striga shoots stayed
healthy and in time produced quite a wonderful display of tiny purple flowers.
Eventually this colourful show came to an end, the petals fell to the ground,
and the seed pods began to swell. And finally the moment I had waited so long for -
the pods started to mature, turning jet black, indicating that they were
ripe. It was a happy day last week when I delicately cut the first shoots,
taking great care not to agitate the seed pods too much, causing them to burst
open. After months of trying, my first harvest at last!
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| Not again! Withered, dead Striga shoots |
There is still a long way to go - the seed pods have to dry
out for a few weeks in the 30 degree incubator - and this first harvest is
unlikely to see me through to the end of my PhD. But I already have the latest
generation of tobacco seedlings coming through ...in fact, I have quite a
conveyor belt operation now, with new tobacco seedlings constantly moving along the system to make sure I always have new Striga- infected hosts
coming along!
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That's better! A beautifully infected tobacco plant with lots of flowering Striga shoots
Photograph by James Bradley
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Plants can be frustratingly complex at times, but that does
make them fascinating to study. The more we find out about their molecular
systems, the more layers of control, regulation and interplay we discover.
Which simply means there will surely be no end to the legions of PhD students
stepping up to these challenges!
