Sport or chimera?

The gardens at the Rashtrapati Bhavan turned out to be more interesting than I had expected. One of the fun things was a bed of pansies around the base of a tree. The gardening staff have been putting out interesting crosses with the Viola tricolor base stock in recent years. Having seen the photos from the past years, I looked carefully at the bed. The featured photo was taken by The Family. You can see two different stalks of the same plant have flowers in two different colours (the one behind is closer to the wild V. tricolor) than the main subject of her photo. How often do you see two differently coloured flowers on the same plant? Not so often that one can ignore it, right?

How can that happen at all? In any organism, different genes can be activated or silenced as the animal grows. The patches of colour on cowhide, or the stripes on a tiger are the most visible example of this. Sometimes a cell mutates during development, and the mutant cell produces more daughter cells with the mutation. This is called a chimera. Some individuals have a patch of coloured skin visible on their body, sometimes called a birthmark. This is due to such a mutation in skin cells. These two things can happen to a plant as well. If the genes for a pigment are switched on or kept off during the development of a flower, then you might have two different colours of flowers on the same plant. These are called sports in botany.

So the pansies that we saw in that one bed in the gardens of the Rashtrapati Bhavan are sports, and chimeras. I wonder if the flowers give rise to seeds which will keep the colour of the flower it came from. If it does, then you can breed multiple cultivars from the same plant. In that case some seeds from this plant could give violet flowers, others white, a third set yellow, and yet another set of seeds could give that tricoloured flower that you see in the featured photo. Is this one of the methods that plant breeders use? Someone with more knowledge than me will have to answer that question.

Vegetable memories

We tend to think of memories in a fixed way; as pictures in our minds, snatches of sounds, less often smell and taste, or touch. So we are fascinated by stories of other species who share such long term memories, for example, that crows remember human faces. But we also have memories of another kind, which we are not aware of. Our immune system remembers past encounters with invasive proteins, and reacts to them. This is the basis of vaccines. Some of these immune memories last a lifetime, others disappear, and have to be reinforced from time to time.

I was fascinated to find that there is now a whole new branch of science which deals with memories in plants. Plants lack a nervous system, and have no adaptive immune system like ours. Still, gardeners and farmers have noticed for long that trees seem to be able to adapt to fighting off recurrent invasions of fungi, or recover faster from those insect infestations which occur over and over. Apparently plants can also remember extreme weather (at least cold, I haven’t seen anything about the more important adaptation to hot weather). It turns out that these memories are directly coded into each cell. Plants have arranged to use a whole set of ways of triggering or silencing genes in response to environment and other stresses to enable them to respond faster in future. It would be really interesting to know whether they can learn to adapt to heat, in response to our mistakes with the environment.