Mikhail Khristoforovich Chailakhyan: The fate of the scientist under the sign of florigen

ISSN 1021�4437, Russian Journal of Plant Physiology, 2012, Vol. 59, No. 4, pp. 443–450. © Pleiades Publishing, Ltd., 2012.Original Russian Text © G.A. Romanov, 2012, published in Fiziologiya Rastenii, 2012, Vol. 59, No. 4, pp. 483–490.

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Much has been written about Mikhail Khristo�forovich Chailakhyan and his main scientific discov�ery, florigen, including papers published in the Rus�sian Journal of Plant Physiology [1–4], but manyimportant details of his life and scientific researchremain largely unknown to a wide audience. Chaila�khyan is one of the most famous in the country andabroad national scientists, whose scientific foresight isbrilliantly confirmed and whose works, published stillin Soviet journals, are actively cited until now. Thisbrief biographical sketch shows how difficult was thefate of the outstanding scientist and his discovery evenin such seemingly “peaceful” field of science as plantphysiology.

Chailakhyan went to Moscow from Leningrad in1934, together with the Laboratory of Plant Biochem�istry and Physiology (LABIFR), in which he con�ducted research under the guidance of A.A. Richter.While still in Leningrad, Chailakhyan began the workon plant photoperiodic responses, as evidenced by hispublications in the early 1930s [5–7], and then con�tinued his research in the Timiryazev Institute of PlantPhysiology (Russian Academy of Sciences). Plantphotoperiodic responses have been earlier (in 1920)described in detail in the classical work of Gardner andAllard [8]; however, it remained unknown how plantssense the alternation of light and dark periods and howthey determine their durations. At the beginning, itseemed obvious that the plant recognizes these exter�nal signals by its most sensitive and movable part,namely, by its stem apex, which responses to these sig�nals by switching development from vegetative to

reproductive. This obviousness seemed to be con�firmed in experiments [9, 10], in which it was shownthat, in the ornamental plant Cosmos bipinnatus, thephotoperiodic stimulation of lateral branch apicesmay induce local flowering independently of the stateof the rest of the plant.

On the other hand, some facts appeared indicatingthat the sites of photoperiodic signal perception andthe sites of responses to them may be spatially sepa�rated. Rasumov [11], who studied tuberization in thephotoperiod�sensitive potato cultivar, was one of thefirst who draw attention to this fact. Therefore, withrespect to flowering the “obvious” point of view didnot seem indisputable any more. This prompted plantphysiologists to verify the hypothesis experimentally,the more so that by this time such work became quitefeasible. In 1934, the American scientist Knott pub�lished his results [12]; he has long studied the photo�periodism phenomenon and was proving in his earlyworks that just stem apex senses the day length [10].Later Knott performed his experiments on spinachand was forced to admit that, at least in this plant, thephotoperiod is recognized not only by the stem apexbut also by leaves. He determined the role of leaves inflowering as “hastening of the response”. Knottassumed with a caution that the involvement of spin�ach leaves in the acceleration of the plant response tophotoperiod favorable for reproductive developmentcould be related to “the production of some substance,or stimulus, that is transported to the growing point”[12]. It should be noted that in this paper among fiveworks cited by Knott two belonged to Russian scien�

Mikhail Khristoforovich Chailakhyan: The Fate of the Scientist under the Sign of Florigen

G. A. RomanovTimiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;

fax: 7 (499) 977�8018; e�mail: [email protected] October 3, 2011

Abstract—The more significant is a discovery made by the scientist, the greater influence it exerts on the fateof its author. The theory of florigen, a hormone of flowering, put forward by M.Kh. Chailakhyan in 1936 ini�tially was inconvenient for Soviet authorities and brought severe trials to the scientist. However, as distinctfrom many others, Chailakhyan did not deny his scientific beliefs but continued to defend them in spite ofharassment and threats. Later, on the contrary, this theory promoted the worldwide fame of its creator,although during Chailakhyan lifetime florigen has not been definitely identified chemically. Chailakhyan wasclose to the establishing of florigen protein nature, but even his long life was not enough to identify this elusivesubstance.

Keywords: higher plants, florigen, flowering, hormonal theory, photoperiodism, FT proteins.

DOI: 10.1134/S1021443712040103

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tists, namely, the aforementioned paper of Rasumov[11] and also that of Tageeva [13], who proved thatphotosynthesis is not involved in the flowering induc�tion. There were no further Knott publications on thistopic; at least we do not know about them.

However, in parallel, this topic was actively investi�gated in the USSR, and in 1936 several publicationsappeared indicating the role of leaves in the perceptionof the photoperiodic signal. Three articles by Chaila�khyan should be acknowledged to be the most impor�tant ones. They were published in the most prominentin our country at that time scientific journal Dokladyof the Academy of Sciences of USSR [14–16]. Chaila�khyan performed his experiments mainly on chrysan�themum: this plant flowering was strongly acceleratedunder the short�day conditions. By using local plantillumination and the removal of some plant organs,Chailakhyan proved that just leaves are the mainorgans sensing the photoperiod. He proposed a quitematerialistic explanation for the uncoupling betweenthe sites of photoperiodic signal perception and plantresponse to this signal. In his papers, Chailakhyan for�mulated the idea of “florigen” as a hormonal com�pound produced in the leaves under the influence of afavorable photoperiod and then transported to thestem apex, inducing the conversion of the apical mer�istem from vegetative to generative (floral). Chaila�khyan wrote [16]: “… we may term this blossom form�ing or blossom hormone, more concisely, florigen,meaning “blossom�former”, which expresses the basicfunction of this substance in the vegetable organism.”

Thus, Chailakhyan found a good term for a sub�stance transferring a flowering signal from the leaf tothe apex. This term outlived its creator and became socommon in the world literature that many contempo�rary authors do not know about its origin and attributeits introduction in the scientific lexicon to other scien�tists (see for example [17]).

Thus, the photoperiod recognition by plants occursin their leaves, and some compact “biocalculator”functions in them, which permits for determination oflight period duration (later it was elucidated that theduration of the dark rather than light phase of the dayis important for the plant).

Chailakhyan not only established the sites of pho�toperiodic induction but also, still in the second half ofthe 1930s, conducted dozens of experiments to provethe presence of florigen in various plant species, itsproduction in the leaves, and determined the rate anddirection of its transport over the plant. As method�ological approaches, he used plant girdling and graft�ing, including interspecies grafts. As a result, Chaila�khyan came to the conclusion that florigen is a univer�sal substance; it has no specificity as to the type ofphotoperiod and plant species and is capable of long�distance movement along the phloem both up anddown the stem at the rate of about 2 cm/day.

In this Chailakhyan thought big: after recognizingof florigen as a new phytohormone, he came to the

general concept of hormonal regulation of plantgrowth and development. At that time, only a singlephytohormone, auxin, was known. In his experi�ments, Chailakhyan showed that properties of florigendrastically differ from those of auxin, i.e., florigen is acompound of the new type. Having formulated hishormonal theory of plant development [15, 16, 18],Chailakhyan foresaw the discovery of new phytohor�mones and their important role in the plant ontogeny.Thus, Chailakhyan was as if the successor of one of theclassics of plant biology J. Sachs, who developed, stillin the end of the XIX century, the idea about the exist�ence in plants of specific morphogenic substances,each of which induces the development of leaves,roots, or flowers [19]. Although this Sachs idea was notdirectly confirmed, it served as a prototype of themodern concepts for plant morphogenesis hormonalregulation initiated by the Chailakhyan theory (1936–1937).

Brilliant achievements of the young head of thelaboratory (in 1936 Chailakhyan was only 34�year�old) played not only positive but also negative role inhis life, which often happened in our country. As wasmentioned earlier, in 1936 several papers were pub�lished about the localization of photoperiod signalperception: three papers of Chailakhyan as well asthose of Moshkov [20, 21] and Psarev [22]. Chaila�khyan and Moshkov worked with one and the sameplant species (Chrysanthemum) and started to work inone and same laboratory (LABIFR in Leningrad);they came to similar conclusions, with the differencethat the theory of plant development hormonal regu�lation and the term “florigen” were advanced byChailakhyan but not Moshkov. It is unknown underthe influence of which senses, but in the next 1937Moshkov reproached Chailakhyan in one of his publi�cations [23] that he borrowed his conclusions. Chaila�khyan rejected decisively and with a great dignity allthese accusations [24]; thereafter, Moshkov did notrepeat his reproaches, at least publicly. Another oppo�nent who negatively reacted to Chailakhyan publica�tions was the Academician N.G. Cholodny “himself”,the recognized leader of domestic plant hormonology[25]. The main criticism of Cholodny was that florigenis a too hypothetical substance and in fact the activeagent is one of the usual plastic substances movingfrom the leaf into the stem or the growth hormoneauxin. But in this case as well, in spite of a greatCholodny authority, Chailakhyan gave a detailed andreasoned response to all critical considerations [26].

However, disputes between scientists, although attimes quite hot, did not go beyond the academicianframework and in general were helpful for the searchfor the truth. Another thing was the attacks fromunprincipled team supporting the ignorant “people’sAcademician” Lysenko, who wanted to take leader�ship positions in science and to dismiss all dissidents.It is worth remembering that, since 1936–1937, thegeneral atmosphere in the country, in science in par�


MIKHAIL KHRISTOFOROVICH CHAILAKHYAN 445

ticular, was poisoned by mass repressions, widely prac�ticed betrayal and denunciation; Lysenko’s “Michurinagrobiology” was actively promoted; scientists�non�conformists were suspended from work, jailed, or shotas the “enemies of the nation”. Unfortunately, Chail�akhyan became unwillingly one of such scientific dis�sidents because he put forward his theory of plantdevelopment, regardless of already approved by theParty and Government “theory of phasic develop�ment” of the “people’s academician.” Chailakhyanposition was still complicated in the late 1930s by thefact that his chief and protector Academician Richter,the director of the Institute of Plant Physiology, RAS,who ventured to criticize the nonsense ideas ofLysenko and mocked them out, was slandered bycoworkers of this institute; they submitted a letter ofdenunciation to the newspaper “Pravda” (from July 26,1938) [27]. This letter was signed by Prof. A.I. Potapov(simultaneously NKVD member), PhD V.B. Katun�skii, A.A. Isakova, G.K. Samokhvalov, N.S. Petinov,and others. All these people were taken to the Institutepersonally by Richter, and some of them were evenconsidered as his pupils.

This letter seems to be inspired by Lysenko and hiscircle, as evidenced from its style and contents.Among other demagogic and unsubstantiated accusa�tions, it contained an item about the appearance at theInstitute “the hormonal theory of plant develop�ment.” Richter was accused as a supervisor in the sup�port of this “hormonal theory,” which “essentially is apoorly masked attempt to divert our scientific thoughtfrom advanced and progressive theory of plant phasicdevelopment rised by the Acad. T.D. Lysenko” [28].After publication of this letter in “Pravda,” corre�sponding measures were undertaken very rapidly. Inthe summer 1938, Richter was dismissed from theposition of the Institute director, and Chailakhyanceased to be the head of the laboratory. However,Chailakhyan managed to stay at the Institute and tocontinue his work because Academician N.A. Maxi�mov, who knew Chailakhyan well and consulted himbefore, was invited to the post of the Institute director.Maximov enrolled Chailakhyan in his laboratory ofplant growth and development, and Chailakhyan waseven able to defend his doctor thesis “The Role ofHormones in Plant Developmental Processes” in spiteof oppression from Lysenko and his proponents.

The beginning of Great Patriotic War pushed to thebackground all scientific controversies. The buildingof the Institute in Moscow was essentially empty. Atthis time Chailakhyan worked in Yerevan, taking thepositions of professor, the head of the Department ofPlant Physiology and Anatomy of the Yerevan StateUniversity, and the head of the Department of PlantPhysiology and Microbiology of the Armenian Agri�cultural Institute. In parallel, it performed defenseorders to find raw material sources of vitamin C andsome others. Just how successful was the work ofChailakhyan in Armenia can be judged from the fact

that in 1945 he was awarded the Order of the Red Starand the medal “For Valiant Labor in the Great Patri�otic War of 1941–1945”. He was also elected a Corre�sponding Member of the Armenian SSR Academy ofSciences.

At the end of the war (1944), Maximov restoredChailakhyan as a head of the laboratory at the Instituteof Plant Physiology (RAS), and he renewed his exper�iments on florigen studying. It seemed as if scientificlife was getting better, but here the new misfortunecame: the notorious August 1948 VASKhNIL (LeninAll�Union Academy of Agricultural Sciences) session.Stubborn Chailakhyan with his theory is again amongunwanted, and the previous scenario repeats: Chaila�khyan is dismissed from the position of the head of thelaboratory with laboratory liquidation, he is excludedfrom the members of Scientific Council, and he is nowhas no right to guide graduate students. However,Chailakhyan is not expelled from the Institute becauseMaximov enrolls him in his laboratory of plant growthand development again.

After the death of Maximov in 1952, A.L. Kursanov(academician in future) was invited to the post of theDirector of the Institute. Kursanov had the courage tore�appoint Chailakhyan as the head of the same labo�ratory of plant growth and development, and this wasat the beginning of 1953 when Stalin was still alive andLysenko still dominated. At last, administrative shockscame to the end for Chailakhyan, and he remained inthis position until 1988, i.e., for 35 years.

This period of Chailakhyan life was the period offruitful scientific research: the size of his laboratoryincreased, the subject of its research expanded. How�ever, the main focus of the work remained, as it was,the study of plant flowering (Fig. 1). In the 1950–1960s, new phytohormones were discovered one afteranother; to the mid�60s, already five hormones areknown that determine the most important aspects ofplant life. They are called “classic” hormones. Chai�lakhyan is again right, no one is challenging him inearnest relative his general concept of hormonal regu�lation of plant development. However, among thesehormones there is no one that could reasonably becalled florigen. Initially, great hopes were placed togibberellins, which were capable of inducing floweringin many long�day plants. However, in short�day plantsgibberellins as a rule only enhanced growth but did notinduce flowering [29]. Chailakhyan modifies his the�ory: he postulates that florigen is a bicomponent com�pound including both gibberellins (which are deficientin long�day plants under short day) and hypotheticanthesins (which are deficient in short�day plantsunder long day). It remained only to determine themolecular structure of anthesins, and the secret of flo�rigen will be deciphered. However, in spite of enor�mous efforts to extract and identify florigen (anthesin)made in the laboratory of Chailakhyan and in manyother laboratories in different countries, the attemptsto detect and isolate this mysterious substance failed.

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Against this background, the criticism of the theoryof florigen was developed newly, fortunately, withoutadministrative consequences. Under the pressure of“Lysenkoism”, some of those, who have recently putforward very similar ideas and even challenged Chai�lakhyan priority in his discoveries (Moshkov, forexample), became active critics. In particular, Rasu�mov and Moshkov published in 1961 the monographsglorifying “scientific” work and achievements ofLysenko and using the quotes from the classics ofMarxism–Leninism [30, 31] as arguments. In thechapter “The theory of plant phasic development –the leading concept of Michurin biology”, Rasumov[30] wrote “ the real existence of the flowering hor�mone has not been proven. It remains only the hypo�thetical compound and serves mainly for the conve�nience of explanation of complex processes of plantdevelopment.” As to Moshkov, he completely deniedconclusions (including his own) on the photoperiodicinduction in plants of flower�producing compounds[31]. He somehow related this very materialistichypothesis with Lenin’s definition for philosophicalidealism. Note that “Lysenkoites” constantly tried tostick the label idealism to the theory of florigen, com�paring it with flogiston theory rejected by the modernscience. Evidently, Chailakhyan was bitterly awarethat former supporters of his ideas, whose scientific

results he cited repeatedly, became his ideologicalopponents. But even in this situation, Chailakhyancontinued to respect his opponents and their opinions.For instance, Moshkov and Rasumov continued tovisit Chailakhyan laboratory and even participate inthe laboratory seminars.

In the world science, the theory of florigen contin�ued to play a leading role for explanation of photope�riodic regulation of plant flowering, although not all ofthe major experts in this field were in agreement withit. Failures in florigen molecular identificationbrought to life alternative theories of plant flowering,true, much more reasonable than the “theories” ofLysenko and his proponents. Thus, some researchers(F. Lona, D. von Denffer, A. Lang, and others)believed that flowering inhibitors rather than flowerinducers (florigens) control the process of flowering.Other researchers (L. Evans, G. Bernier, R. Sachs, andothers) were of the view that not hypothetical universalflorigen but species�specific complex comprisingalready known hormones and/or metabolites inducesflowering [29, 32]. Chailakhyan and his coworkers putmore and more experiments to prove the correctnessof his ideas. In this period, they showed that the extractfrom the leaves of short�day tobacco induced to flow�ering could induce flowering of another short�day spe�cies (Chenopodium rubrum) under non�inductive con�

Fig. 1. M.Kh. Chailakhyan with his coworkers (V.N. Lozhnikova and L.P. Khlopenkova) in the greenhouse of the TimiryazevInstitute of Plant Physiology, RAS (1970).



ditions, i.e., this extract manifested the properties ofanthesin [33, 34]. Great interest was also evidence thattobacco scion induced to flowering could stimulatetuberization in the potato rootstock [35]. However,even these findings were not able to ultimately con�vince the scientific community in the existence of flo�rigen.

In 1988, Chailakhyan published a comprehensivemonograph ”The Regulation of Higher Plant Flower�ing” [29], summing the results of his long studies ofplant flowering physiology. By this time, Chailakhyanwas a recognized leader in this area (Fig. 2). He wasthe author of more than 500 scientific papers (includ�ing ten fundamental monographs), Academician ofthe Academy of Sciences of USSR and ArmenianSSR, the member of the Academy of Natural Sciences“Leopoldina”, a Corresponding Member of theAmerican Society of Plant Physiologists and Ameri�can Botanical Society, a Honorary Doctor of the Uni�versity of Rostock (Germany), a Honorary Member ofthe Bulgarian Botanical Society, the Indian Society ofPlant Physiologists, and International Plant Growth

Substance Association; he was awarded two Orders ofLenin, Orders of the Red Banner of Labor and Octo�ber Revolution, the medal of the International PlantGrowth Substance Association [36]. In more then20 chapters of his fundamental work, Chailakhyanreflected the current state of the flowering problem,focusing special attention to the nature of endogenousfactors that cause plant flowering.

This book conclusively proved the existence of flo�rigen and gave an idea about many features of its for�mation and functioning. The only thing lacking in thisbook was the molecular characterization of florigen;however, in that time, nobody in the world could givesuch characteristic.

A specific compound produced in the leaves inresponse to favorable photoperiod and transported tothe apical meristem was identified only in 2005–2007[37–41], i.e., in many years after the death of Chaila�khyan. For its detection, the combined efforts ofgenetics, biochemists, and plant physiologists wereneeded. To the surprise of many researchers, this com�pound was not a small molecule like a usual phytohor�

Fig. 2. Collective photo of the staff of the Laboratory of Plant Growth and Development and foreign guests at the TimiryazevInstitute of Plant Physiology, RAS (1982).Sitting from left to right: Jan Krekule (Czechoslovakia), Anton Lang (United States), M.Kh. Chailakhyan, Folke Skoog (UnitedStates), and Philip Wareing (Great Britain).

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mone but a small protein called in arabidopsis Flower�ing Locus T (FT). It was proven that, in a completeagreement with the theory of florigen, this protein issynthesized in the leaves in response to photoperiodfavorable for flowering and then moves along thephloem to the stem apex where, in combination withthe FD transcription factor of bZIP�type, it activatesthe genes of floral meristem identity. Proteins of FT�type were found in various plant species (arabidopsis,rice, tomato, rape, pumpkin, and others); their actionturned out to be species�unspecific, i.e., expression ofFT of one species stimulated flowering of the recipientplant of another species. In correspondence with allthese characteristics, we can conclude that FT pro�teins are plant protein hormones, flowering inducers[42, 43].

The establishment of the molecular nature of flori�gen is, without doubt, one of the most importantadvances of the XXI century biology. However, it isworth mentioning that the discovery of proteins�flori�gens could be much earlier, still during the lifetime ofChailakhyan. It was in his laboratory, the analysis ofproteins appearing in photoperiodically sensitiveplants in response to different photoperiodic regimesstarted. The results of these studies performed on Rud�beckia bicolor were published in the beginning of 1991[44]. It was established that, at long day favorable for

flowering, new proteins with a low molecular weight(about 27 kD, Fig. 3, the right gel, the fourth track)appeared. In several days, similar low�molecular pro�teins were detected in the stem apices (Fig. 3, left gel,the fifth track). From the top of present�day knowl�edge, it seems likely that Chailakhyan and his col�leagues were the first to observe the induction of FT�like protein (florigen) in the leaves under favorablephotoperiod with subsequent (after a certain lag�period) stem apex response to florigen inflow from theleaves. The authors concluded the article ([44], p. 14)by the words: “It should be especially noted that thesame protein lacking under short day conditions – theprotein with a molecular weight of 27 kD – appearedunder the influence of photoperiodic induction in dif�ferent organs (leaves and stem apices). Such facts havenot been clarified in other investigations… It may behypothesized that the appearance of this protein isdirectly associated with synthesis of flowering hor�mones under the influence of photoperiodic induc�tion”.

Thus, in 55 years after suggestion of the theory offlorigen and long research, Chailakhyan could first seehis florigen de facto as protein bands on the gel andwas very close to give an adequate interpretation ofthese results [44]. However, death in 1991 preventedhim from the completion of the search for flowering

кД (а) (b)

94

63

45

17.8

12.9

130

104100918380

726258

3731

28272221181412

1 2 3 4 5

kD kD

1 2 3 4 5

93

57

43

32

27

83

Fig. 3. Radioautography of 35S�labeled proteins from stem apices (a) and leaves (b) of Rudbeckia bicolor after electrophoretic sep�aration in the gradient (10–20%) PAAG after Laemmli.(1) Non�inductive short day; (2–5) after induction with long day (LD): (2) 2LD; (3) 4 LD; (4) 8 LD; (5) 18 LD. The numberson the left – molecular weights of marker proteins in kD; the numbers on the right – molecular weights of detected R. bicolorproteins [44].



hormone. This was done much later by other research�ers [37–41], who put the glorious molecular point inthe long florigen history. Henceforth there is no doubtthat Chailakhyan was right in his conceptions and thatflorigen really exists (may be also in several molecularforms – see R. King paper in this issue of RussianJournal of Plant Physiology), while the term “flori�gen” will always be the best memory of an outstandingscientist, the plant physiologist AcademicianM.Kh. Chailakhyan.

ACKNOWLEDMENTS

The author is grateful to Vl.V. Kuznetsov,N.P. Aksenova, T.N. Konstantinova, and E.L. Milyaevafor valuable advice and comments and to V.N. Lozhni�kova for providing documents from personal archives.

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Documents

Mikhail Khristoforovich Chailakhyan: The fate of the scientist under the sign of florigen