Jan van Helmont was one of the first scientists who found that the mass of a plant is not acquired from the soil it grows in. When he grew a 5 lb willow tree in 200 lb of soil for 4 years, he found that the tree gained 164 lb, while the soil was only reduced by 2 lb.
But van Helmont concluded that the plant gained its mass solely from the water he added & neglected the air, despite being the person to first isolate & describe carbon dioxide, which he assumed was a different form of air, in the mid-17th century.
In the second half of the 18th century, Joseph Priestley’s experiments with air put in place the next steppingstone toward the discovery of photosynthesis. At the time of his work, oxygen, carbon dioxide & nitric&nitrous oxide were all known but considered different forms of air.
Priestley investigated these ‘airs’ by isolating & filling an inverted beer glass with them. He then placed a burning candle, mouse or plant inside the glass, and observed the effect the different ‘airs’ had on the object.
Among other things he found that air could be ‘damaged’ by animals breathing in it, turning it toxic. Since this meant that all air in the Earth’s atmosphere should be toxic at one point, killing all life on Earth, he reasoned that there must be a mechanism to ‘repair’ the air.
Indeed, he found that placing a mouse in one of his beer glasses containing air that had been ‘damaged’ by another animal breathing in it, would kill the added mouse, or extinguish a burning candle. He performed his key experiment in 1771.
He prepared two glasses, both containing ‘damaged air’, produced by mice breathing in it until they died. Then he added a mouse to one, or a mouse & a mint plant to the other glass. And while the lone mouse quickly died, the mouse in the presence of the mint plant lived happily.
Priestley concluded that plants can ‘repair’ ‘damaged air’, and this is the mechanisms evolved in nature that enables life on earth by 'purifying' the air after it was damaged by the breathing animals.
In 1779, Jan Ingenhousz repeated Priestley’s experiment, but additionally placed one glass in the dark, & one in sunlight, demonstrating that sunlight is necessary for a plant to ‘repair’ air, while the plant also ‘damages’ air in the dark, but less than it ‘repairs’ it in light.
So Ingenhousz had correctly described the plant as giving off carbon dioxide at night, while producing oxygen at day. He even managed to visualize the latter, by observing aquatic plants, and noting that little bubbled formed along green tissue while in the sunlight.
In the mid-19th century Julius Sachs added that the result of this light-reaction is the accumulation of sugar as starch, which eventually led to the description of photosynthesis by Charles Barnes in his 1893 article ‘On the food of green plants’.
Ironically, in the articles he discusses the names #photosynthesis or #photosyntax for the process, eventually deciding that photosyntax is the preferred term that should be used. Quite evidently a conclusion not everybody agreed on.
Further reading: Jane Hill - Early Pioneers of Photosynthesis Research doi.org/10.1007/978-94…
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Ethylene is a gaseous #phytohormone with a wide range of roles from plant development to immunity. Ernest Starling in 1905 defined a hormone as mobile chemical messenger synthesized by a multicellular organism, that has physiological activity distant from the site of synthesis.
The effect of ethylene on plants was first noted in the 1900s, when it leaked from illumination gas used in lamps and affected plants nearby. But it was Dimitry Neljubow, who in a series of experiments identified ethlyene as the active substance in the illumination gas in 1905.
#PlantScienceClassics #17: The Mildew Resistance Locus O (MLO). 80 years ago Rudolf Freisleben & Alfred Lein created the first powdery mildew resistant barley plant. 30yrs ago the gene was mapped, 25yrs ago cloned-yet it's mode of action remains a mystery. doi.org/10.1007/BF0148…
Powdery mildew is a fungal disease of many crop plants, most prominently maybe barley and wheat, where outbreaks can reduce grain quality & yield, and ruin complete harvests. Visible are the fluffy patches formed by the fungus (Blumeria graminis f. sp. hordei).
Freisleben used radiation-induced mutagenesis to create the barley 𝘮𝘭𝘰 mutant, which showed full resistant to this pathogen. A massive agricultural breakthrough!
See also Classic #2, to read about how Emmy Stein has developed this technique in 1921:
#PlantScienceClassics #16: A linkage map of Arabidopsis thaliana. In 1983 the legendary Maarten Koornneef published a genetic map of A. thaliana, the basis for genetic work & an important contribution towards the acceptance of Arabidopsis as plant model. doi.org/10.1093/oxford…
In the early 1980s scientists finally adopted A. thaliana as model plant. At this point, several mutants were available, but their positions in the genome were mostly unknown. This was years before genome sequences became available,&genetic maps were still based on recombination.
Arabidopsis pioneer György Rédei did linkage analyses with 14 loci in the 1960s, but his genetic map from 1965 suggested 6 linkage groups – 1 more than chromosomes. Curiously, A. D. McKelvie created another map in parallel - & found 4 groups, 1 less than chromosomes.
#PlantScienceClassics #15 #PlantScienceFails #1: The auxin-independent (axi) Nicotiana tabacum lines. In 1992 Richard Walden et al. (specifically co-worker Inge Czaja) published activation-tagged axi protoplasts @ScienceMagazine that could divide&grow in the absence of any auxin!
The development of plant transformation in the early 1980s (classics #6&13) was inspirational for many scientists. Among them was Richard Walden, who teamed up with plant transformation pioneers Barbara & Thomas Hohn to leverage this advance to develop the “Agroinfection" method.
He then joined the next transformation pioneer, Jeff Schell, to develop more such tools. Their first was Activation-Tagging: 4 CaMV 35S enhancers (classic#9) were placed at the RB of the T-DNA. That way, they would overexpress the plant gene next to which the T-DNA was inserted.
#PlantScienceClassics #14: Mendelian inheritance. In 1866 Gregor Mendel published his work on dominant/recessive trait inheritance in peas, establishing the hereditary rules on which modern genetics is based. But nobody cared,& his scientific career ended. biodiversitylibrary.org/page/48299076
Mendel had always been interested in nature, and grew/kept and observed plants and bees in his parent’s garden. He later decided to become a monk and teacher. However, he failed teacher’s exam in 1850 & 1856, & eventually settled on being a monk and substitute teacher.
He satisfied his curiosity as a naturalist by keeping and observing plants and bees in the monastery garden, and eventually became interested in how traits are determined through generations. So he started to conduct crossing experiments with mice with grey or white fur.
Do you know Daisy Roulland-Dussoix? She is one of the discoverers of restriction enzymes, who’s findings paved the way for the development of recombinant DNA and cloning technologies. Accordingly, the finding was rewarded with a #NobelPrize. But the prize didn’t go to her... 🧵👇
Daisy Roulland-Dussoix worked with Werner Arber to study the mechanism for the observed host-specificity of λ Phages. It was known from an important 1953 paper (Bertani & Weigle) that phages, that had replicated in a certain E. coli strain, could only re-infect the same strain.
Roulland-Dussoix & Arber showed that host-specificity is linked with the phage’s DNA. Using phages carrying radiolabeled DNA, they showed that progeny with 2 parental DNA strands retained specificity, while progeny with newly synthesized daughter strands could adapt to new hosts.