Ethylene: Nobel Prize Controversy
It is always fascinating how a small hydrocarbon or 2 carbon containing alkene has huge impact on plants. Yes, you gussed it right. It’s Ethylene. First gaseous compound discovered as hormone. It has specific roles in fruit ripening, cell elongation, senescence, seed germination, leaf abscission, defense response and so on.
According to the definition of hormone, it should have two characteristics. Biosynthesized in a small amount by multi cellular organism and work on a distant place from the synthesis site. This classical definition for hormone was provided by Ernest Starling at 1905. Ethylene fulfills both requirement as a hormone. In addition, it can diffues and affect surrounding plants. We may consider it as pheromone in that case.
The initial discovery of ethylene is nothing but accidental observation like penicillin. In 1858, George Fahnestock observed that leaking illuminating gas are causing damage to the plants at greenhouse. During that time illuminating gas was used almost everywhere and supplied by underground pipes. So, gas distributors, plant growers, general people- everyone was concerned to know the real causative agent behind this incidence.
In 1901, Dimitry Neljubow identified the causative agent as ethylene. He showed that ethylene has triple resposne effect on etiolated pea seedlings. This result was replicated for different species by different labs around the world. That’s how it was established as ethylene sensitive bio-assay.
It’s true that Neljubow showed the biological effect for ethylene. But, to fullfil the criteria as a hormone, it should be synthesized by plant itself. Until then, there was no report of ethylene production by plants. Interestingly, in 1910, Herbert Cousins observed that fungus causing damage to oranges followed by release of a particular gas, which eventually causes the ripening of banana. This was a critical point, First, the unknown function, involvement in fruit ripening, of ethylene was observed. Secondly, the gas produced during fungus infection could be either from oranges or fungus. This puzzle was solved by the discovery of Richard Gane in 1934. Through quantitative chemical method, he showed that apples syntheszied ethylene. But, synthesis of ethylene in apples and claim it as a plant hormone was not sufficient. Initially the concept of ethylene as plant hormone was rejected by many groups around the globe. On the following year, Gane provided evidences for other plants also. This is how the last piece of puzzle, biosynthesis of ethylene by plants, was solved to establish ethylene as first gaseous plant hormone.
If we think about ethylene, it’s more than a phytohormone. Because it can be produced by a particular plants and work on the same plant or neighbouring plants also. That means it can work as signaling molecule and we can consider it as pheromone.
Interestingly, Nobel Prize in Physiology or Medicine 1998 was awarded jointly to Robert F. Furchgott, Louis J. Ignarro and Ferid Murad “for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system”. With due respect to their discovery, “endogenously produced gas” acts as a “signalling molecule” and has capability to “penetrate the membranes” and “regulates the function of other cells” are totally fulfilled by ethylene, gaseous plant hromone discovered almost more than 60 year ago.
In 1901, Dimitry Neljubow showed the biological effect of ethylene and in 1934, Richard Gane showed that ethylene was produced by plants. And, if we follow the progress of ethylene research further, endogenously produced ethylene regulates many basic plant processes, ranging from seed germination to senescence. The most important agronomic property is the role of ethylene as inducer of fruit ripening and as a mediator of defense responses in plant pathogenesis.
Biosynthetic enzymes of ethylene have been isolated and characterized biochemically. The genes that encode these enzymes have been cloned, and their regulation has been described. The ethylene receptor has been identifed, and the ethylene signal transduction pathway is being elucidated in detail. These discoveries serve as the basis for biotechnological applications, for example, the genetic engineering of fruits whose ripening can be controlled and whose spoilage is, thereby, prevented. The discovery of ethylene as an endogenous signal molecule should be recognized as the first demonstration — by plant biologists — that a gas can serve as a signal molecule in the organism and that this constitutes an entirely new principle for signaling in biological systems. (Source: Hans Kende, Plant Biology and The Nobel Prize)
This controversial Nobel Prize award was really frustrating for plant scientists as ethylene was known as gaseous signaling molecule or phytohormone or pheromone for long time.
