The advent of spring always feels impulsive, arriving overnight in an unconstrained force of petals and leaves. A few days past the first bud, we suddenly exist in our awakened, stunning environment. It has an annual familiarity, but at the same time, it feels so foreign from the elongated grays of winter. There are adequate words to dictate our visual experience, but we often fail in finding the right expression for our emotive response. D.H. Lawrence addressed the feeling in his poetry:
And I, what fountain of fire am I among
This leaping combustion of spring? My spirit is tossed
About like a shadow buffeted in the throng
Of flames, a shadow that's gone astray, and is lost.
-excerpt from ‘The Enkindled Spring’
D.H. Lawrence, Amores (1916)
To reign in this ‘leaping combustion’ a bit, I investigated a small history of the science behind the flowering season, and what I found was an arduous tale of scientists chasing after the explanation of the opening bud.
Plant physiology was not a rigorous academic study until Julius von Sachs began his pioneering lab in nineteenth century Germany. By illuminating the leaves of the morning glory, he could induce flowering at the end of a shoot which he enclosed in a light-proof box. In 1865, he hypothesized that a physical substance traveled slowly from the light-exposed leaf to the apex of the stem, triggering the flower cascade. There was still a great mystery as to why plants only flowered at particular times of the year. In 1920, Wightman Garner and Henry Allard expanded our understanding with the concept of photoperiodism, whereby the plant detects the change of seasons as the day-length shifts.
The Armenian-Russian scientist, Mikhail Chailakhyan, applied von Sachs theory in his plant grafting experiments of the 1930’s. Taking the leaves of plants exposed to a controlled number of hours of light, he could induce flowering by grafting them onto other plants, even those of differing species. He hypothesized that the flower-inducing substance was a universal hormone to be known as ‘florigen’. The term florigen stuck, but the substance was remarkably elusive for the next seventy years.
With the advent of molecular biology, the story accelerated in the late twentieth century. Two genes: constans (CO) and flowering locus T (FT) proved to be critical in the night length regulation of flowering. Finally, a Swedish lab published a study that established FT messenger RNA (mRNA) to be the long-distance molecule that traveled from leaf to shoot apex. Their finding was published in Science magazine and called one of the most important scientific discoveries of 2005. Well, it was, until the paper was retracted.
As it turned out, the data were flawed and it is actually the FT protein (not the preceding mRNA) that is taking the long trip. Green fluorescent protein was the key molecular tool used to finalize the story. One hundred and forty years after von Sachs proposed his idea, Corbesier and collegues at Max Planck Institute grafted leaves containing an FT-GFP fusion protein to stems without the molecule. They then tracked the fluorescent molecule as it crossed the graft junction and traveled to the apex where flowering ensued.
Looking back on the life of Julius von Sachs, there were many complexities to his character that make the history of florigen somewhat tragic. His commitment to research had him working by 4 am and then continuing for fifteen hour periods. He later admitted that he paid for each of his published books with ill-health in his later years. In the end, Sachs not only had problems with his physical health but he developed a dark-side that alienated him from his contemporaries. At first a Darwin-enthusiast, he changed his position of support to one of fierce criticism. His assistant, Karl Goebel, wrote, “The latter part of his life found him a lonely man who had estranged many of his friends by bitter and sometimes even unjust criticisms.” Ironically, Sachs himself attributed much of his unhappiness to a lack of sunshine in the winter months:
“there are no signs of blossoms …I should not complain, liking as I do to take things
as they come, but unfortunately I cannot live without sunshine and the lack of it
makes me ill."
Kanzan blossoms at night (Mott, 2013)Sources:
[1] "Sachs, Julius von." Complete Dictionary of Scientific Biography. 2008. Encyclopedia.com. 20 May. 2013.
[2] Romanov GA Mikhail Khristoforovich Chailakhyan: The fate of the scientist under the sign of florigen. Russian Journal of Plant Physiology 59:443-450.
[3]Corbesier L, Vincent C, Jang S, Fornara F, Fan Q, Searle I, Giakountis A, Farrona S, Gissot L, Turnbull C, Coupland G (2007) FT Protein Movement Contributes to Long-Distance Signaling in Floral Induction of Arabidopsis. Science 316:1030-1033.
[4] Julius Sachs, by Professor K. Goebel in Flora (1897). Archived here.
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