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Genes and history

25/9/2017

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Just recently the journal Nature published an article by a group who have sequenced a Chinese orchid Apostasia shenzhenica. This may seem a bit obscure as a subject, but it does throw some interesting light on the was that orchids as a whole have become what they are. It does not answer all the questions, but what it does do is give us a glimpse of how very small and simple changes can have a huge affect on the way in which a plant grows.

​Among the interesting aspects of the research that was reported were comparisons of gene activity when compared with other orchid species and plants which were not orchids, but share common genes. Like all species, some basic genes are so fundamental that they appear in virtually all species. One of these is the gene AGL12. This gene seems to be fundamental in producing roots associated with terrestrial growth, as we find in our native British species. The epiphytic species have lost this gene and produce their typical root forms from another genetic process. In a similar way, the gene associated with production of lateral roots, another thing epiphytes tend not to do, is ANR1 and also lacking except in the terrestrial species. The team who did the work also recognised that the nature of orchid seeds, that is having no endosperm, seemed to be traceable to a conserved gene group widely found in other plants.

​All of this work is based on automated systems and complicated statistical software, but it did surprise me that they had a little section on genome size estimation where they used this tremendous hammer to crack a nut. Estimating the genome size of the Apostasioideae as a group between 0.38pg and 5.96 pg. What was a surprise was that there is a very easy way of measuring the DNA mass of a cell by quantitatively dyeing it and then measuring the optical absorption, from which a simple calculation gives a figure in grams. I know this because I used to do it myself on cells and individual chromosomes. On second thoughts, it did take me a year to work out the details so that the results were reliable.

​Anyway, the paper was quite fascinating and gave an insight into how small genetic changes can have a profound phenotypic affect. For example, once symbiotic germination is established the need for an endosperm is lost, so the gene becomes redundant and then symbiotic germination is essential to the ecology of the plant.
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Autumn potting

1/9/2017

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At this time of year, when lots of people are thinking about starting the new school year, we are thinking about potting up our new season of plants. These are the ones which have been in pots for most of this year, getting used to the weather and developing strong roots. Because we try not to disturb the plants too much, if they are not being sent out they tend to be left to grow unhindered in their pots throughout the year. So usually by now they have some moss and an occasional weed in the pot with them. To make sure they have an unhindered growth in the spring repotting them clears out the weeds and lets us see what is going on with root development. This can sometimes take us by surprise and requires a larger pot in anticipation of next years growth. If they do go into bigger pots they have reached a size where they are too big to send through the post and will only appear at our plant fairs. We generally sell these larger plants at a very reasonable price and they are often either in bud, or even in flower by the time they get to their first plant fair. Some of these orchids not only look good as green plants, but have a spectacular flower as well. These seem to sell very quickly and only stay on the stand for a short time before being bought by a customer. A species of this type is the Pyramidal Orchid, which as one of our winter green species, has to have repotting timed quite carefully.

 Most of our native orchids grow throughout the summer and are dormant during the autumn and winter months and these can be repotted at anytime while they are dormant, a period of several months. Our winter green species, of which Pyramidal Orchids and Green Winged Orchids are two examples, are different in having a very short dormancy in late summer before growing leaves which will spend the winter flat against the ground waiting for spring. This means that repotting has to be clearly timed to avoid damaging the actively growing parts of the plant.

​So if you have orchids in pots that you want to rehouse, now is a good time to do it, the winter dormant species have more or less stopped growing and the winter green species have not restarted growing yet. Grab your John Innes number 2 and enjoy the late summer sun.
​
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    Author

    Dr Wilson Wall, grower of orchids. A scientist by inclination and training.

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