Interesting article from:
Ove Nilsson is Professor of Plant Reproduction Biology at the Ume Plant Science Centre. His field of research is plant biotechnology - and he has a special interest in trees, particularly the poplar. But his discoveries can be applied to all plants.
"In the early 20th century, biologists had gained certain insights into why some plants flower in the spring and others in the autumn. But that was about it."
Professor Nilsson tells the exciting story of the race to discover the mechanisms behind flowering. Apparently, two camps were formed. One was convinced that flowering was governed by temperature - that plants sensed the warmth in the spring and the cooling-off in the autumn. The other camp claimed that it had to do with how long the day was. But this theory meant that plants had to be able to sense the quantity of light in some way, that the days were getting longer or shorter. This in turn required some kind of built-in gauge of time, a clock... (Link to question 33, Nilsson4).
Around a hundred years ago, people realised that plants are able to gauge the length of the day via their green leaves, causing the shoots to form flower buds. In other words, some kind of signal must go from the leaves to the tips of the shoots, though the exact nature of this signal was a mystery.
Grafting leaves from plants that had been light-stimulated to flower onto plants that had not started to flower caused the whole recipient plant to flower. This implied that some substance must have spread from the grafted leaves to the rest of the plant and initiated flowering there too.
In the 1930s the Russian biologist Chailakyan called this mystical substance florigen and thought it must be a universal substance because he could many plant species reacted to this kind of grafting. The substance spread flowering, but nobody could understand what it was. Some type of sugar molecule? A hormone?
Biochemists tried in vain to extract the substance. They found nothing and were forced to conclude that either a number of different substances are involved or that they had so far been looking for the wrong type of substance.
In May 2005, Ove Nilsson showed that the second explanation was the right one - he had found the flower-initiating substance that Chailakyan predicted 70 years ago.
"We discovered that the genes that determine when flowering occurs are active in the leaves, not in the tips of the shoots where the actual flower opens. The gene that we found produces signal molecules that are conveyed from the leaves to the tips of the shoots, where they control the formation of proteins that in turn are responsible for the actual flowering."
This signal molecule is neither a sugar molecule nor a protein, but a type of messenger RNA (mRNA), a tiny piece of the genetic material that controls the formation of proteins. The point in time at which flowering occurs is thus pre-programmed in plants' genetic code in the same way as when humans and other animals reach sexual maturity.
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