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Kurinji (Strobilanthes) and the quest for Plant Intelligence

Updated Jan 8, 2007: Selva, The Scientific Indian at Science Blogs linked to this post. Thanks a lot Selva Updated Jan 5, 2007: April Holladay of Wonderquest is featuring science related posts from this site on her site. This post on Plant Intelligence is currently featured. Thanks April for your generosity.
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2006 is the year of the Kurinji (Strobilanthes Kunthiana), the plant that flowers every 12 years! I had a chance to see the Kurinji blossom this year in Kodaikanal. The question arose in my mind, why 12 years? I wanted to write what i found before the end of the year. [Above picture from The Hindu newspaper]
Why does this phenomenon happen?

First, the simple answers:
1. Kurinji practices an evolutionary strategy known as predator satiation – If a lot of plants flower at the same time, it will be difficult for predators to obliterate all of them.

2. It appears the plants wait for a period of time to flower untill they have enough nutrients to
support seeding. In Kurinji’s case that time period happens to be 12 years.

I was not satisfied with this set of answers (paraphrased from Senthil Subramanian, see references below).

How do plants keep track of time and how do they know when to flower? The first part of the question is simply answered by saying plants have a mechanism to keep track of time and that is how they know. The second part turns out to be a lot tougher question to answer.

It turns out Scientists have been grappling with this question for a long time. In 1937, a Russian scientist hypothesized that there is a plant hormone called Florigen that is responsible for flowering. Scientists have been looking for it since then and it appears they may have found it. Hold on to this, we will come back to this.

We first need to understand some more about the plant clock. It appears that there are 2 aspects that the plant needs to keep track of – one is the day length and the other is the ability to remember the length of winter (cold temperatures) so that they can flower at the appropriate time in Spring. The day length is likely to be a simple counter whereas the length of winter is some type of cellular memory.

Scientists have isolated the day length counter gene called ELF4. Remembering the winter or simply duration of cold temperatures is a process known as Vernalization. By studying Vernalization, Scientists have identified the mechanisms that control vernalization and in the process explain how plants remember winter.

Coming back to Florigen, Scientists have found a mechanism in plants known as the CO/FT module (Constans is CO, Flowering Locus T is FT) that seems to be the elusive Florigen. It turns out that CO protein keeps getting accumulated and when it reaches a threshold level, it induces the transcription of the gene FT in the leaf and the FT mRna (messenger RNA) moves from leaf to shoot apex where flowering is triggered by the FT protein.

Coming back to Kurinji, this CO is getting accumulated over a 12 year period calculated by the clock gene and flowering starts. In Kurinji, another interesting thing happens, the plant dies immediately upon flowering. Scientists are working on isolating what they are calling as the death signal which gets generated containing the instructions for the plant to die. But why 12 years?

Could not come up with a clear cut answer to this. I have one potential explanation – that in the plant kingdom’s evolution from annuals to perennials, the 12 year plant is a pit stop!

During my research, i came across several amazing facts about plants –

a. Did you know that plants used Aspirin (Acetyl Salicylic Acid) in their rudiementary defense system?

b. Dodder plant uses its sense of smell.

And finally my quest was complete when i came across Tony Trewavas’s brilliant paper “Aspects of Plant Intelligence“. In fact, Trewavas uses Dodders as an example of plant intelligence. He didn’t know about its sense of smell when he wrote this paper. This is a must-read paper for people interested in knowing more about plants.

Notes & References:
1. Senthil Subramanian, Donald Danforth Plant Science Center, St. Louis, U.S.comes up with some great answers to explain Kurinji’s gregarious flowering.

2. Kurinji is not the only rare blooming plant. Our friend Morgen Jahnke at ITOTD has some more – The Titan Arum lily, the talipot palm..

3. How plants remember winter – Sibum Sung and Richard M Amasion explain how Vernalization works in this important paper.

4. How do plants keep time – A Science Daily report mentioning the discovery of the ELF4 gene that seems to be responsible.

5. The landmark paper that talks about the CO/FT module.

6. Arabidopsis Thaliana seems to be the plant kingdom equivalent of the fruit fly Drosophila Melanogaster.