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Sergio Pennazio

Publications and source records attributed to Sergio Pennazio.

9 recordsLinked to original sources
PubMedDate not supplied

The discovery of the chemical nature of the plant hormone auxin.

The concept of substances working as a chemical messenger among the plant tissues was guessed in the last quarter of the nineteenth century as a consequence of a series of observations and experiments concerning two important phenomena: the geotropism and the heliotropism. The work of Theophil Ciesielski, Charles and Francis Darwin, Julius von Sachs, Martinus Beijerinck and Julius Wiesner supplied the fundamental pillar to the modern plant physiology. Hans Fitting [1909] introduced the term "hormone", coined in 1902 to indicate a substance promoting chemical correlations among various organs of animals, in plant physiology for indicating a substance stimulating the development of the ovary of orchid flower. Paul Boysen-Jensen and Arpad Paál focused the occurrence of a growth substance that somehow regulated the positive curvature of oats coleoptiles, the distinctive feature of the phototropism. During the 1920s, a few Mitteleuropean botanists gave circumstantial evidence of such a substance before the Dutch physiologist Frits Went elaborated an experimental procedure for isolating it, and quantifying its physiological activity. Went's work crowned with success a half century of research and opened the door to the chemistry of the auxins. A next important step concerned the purification of sufficient amounts of substance for analytical purposes. Five years of attempts made by Hermann Dolk, Jan Haagen-Smit, F. Kögl and Kenneth Thimann had success and the "substance" was finally identified as indolacetic acid and named "auxin". This result delivered definitively the concept of plant growth from a secular mysticism and established a milestone in the modern plant physiology.

Indoleacetic Acids↗
PubMedDate not supplied

The culture of single plant cells: a historical view.

Plant tissue culture, introduced unsuccessfully at the beginning of the twentieth century by Haberlandt, received full confirmation in the late Thirties by the works of Gautheret and Nobécourt, thanks to the discovery of auxin. A further special improvement--the free cell culture--, already fore-told by Haberlandt, was successfully achieved towards the mid-1950s by several physiologists thanks to coconut milk (cytokinin). The English physiologist Frederick Steward (who grouped an excellent American team of research during his twenty years stay at the Cornell University in Ithaca) was able to obtain complete cell differentiation from single cells cultured in vitro and demonstrate the totipotence of plant cells at any stage of development. The historical meaning of the research of Steward's team, accomplished between 1958 and 1970, rests on the concept of plant hormones as regulators of gene activity. In other terms, organogenesis was conceived as an epigenetically controlled series of events in which plant genes were "switched on" or "switched off" by special biomolecules. Steward's research paved the way for molecular plant physiology and inspired future research on the relation between cell receptors and specific hormones.

Cell Culture Techniques↗
PubMedDate not supplied

Photosynthesis: a short history of some modern experimental approaches.

This paper presents a personal interpretation of a chapter of plant physiology beginning from the early 1930s to the early 1940s, when plant physiologists tried to find the missing link between the two (dark and light) phases of photosynthesis. As initially inferred by Richard Willstätter and Arthur Stoll in the 1910s, and then stated by Robert Emerson and William Arnold in 1932, the most accredited theory proposed that carbon dioxide must combine with chlorophyll in the dark. Successive light flashes activated the complex chlorophyll-carbon dioxide with oxygen evolution, and carbon dioxide was reduced to formaldehyde and successively polymerised into hexose. Arthur Stool in 1932 and Cornelius v. Niel in 1935 gave the first stroke to this theory suggesting that carbon dioxide must be reduced and assimilated by means of a process of water oxidation. Robert Hill showed the existence of an indissoluble link between the light phase, water oxidation and possibly oxygen evolution. Two physicists, Sam Ruben and Martin Kamen proposed the assembly of photosynthesis into a unitary process occurring as a sequence of several steps in the first 1940s. By utilising for the first time radioactive carbon (11C), they elaborated a new theory according to which carbon dioxide reduction was a repeated "cyclic" mechanism. This "heretical" view abolished the old, but still considered, theory of formaldehyde. Hill, Ruben and Kamen were able to exploit at best the possibility offered by a very advanced technology, thus confirming once again that ideas stand upon the powerful legs of technology.

Botany↗
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The contribution of plant biology to the concept of virus (1886-1917).

Between 1860 and 1880 the so-called "theory of the infective germ", which stated in final way that every infectious disease was produced by a living pathogen agent, achieved great consent. The criteria of determining the presence of infectious pathogens (fungi, bacteria, protozoa) were established by "Koch's postulate", a set of experimental procedures conceived for isolating and determining single pathogens. In the last quarter of the 19th century became however evident that the agents of severe infectious diseases could not be identified through the "postulates". These agents could not be seen in light microscopy nor cultured in vitro but could pass through the thin pores of filters which hold back cellular micro-organisms. This last characteristic became a selective method to recognise these peculiar agents, from then named "filterable viruses". Most microbiologists considered the filterable viruses as living micro-organisms because of their extraordinary capacity of in vivo proliferation, and the impossibility of pointing out their structures was due to limits of the experimental techniques. Between the end of the 19th century and 1917, four plant biologists suggested that the filterable viruses were complex chemical substances rather than cellular microorganisms. Their contribution, not appreciated by the contemporary colleagues, laid the foundation of the modern concept of virus.

Botany↗
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"Florigen ": an intriguing concept of plant biology.

"Florigen" is the name that Mikhail Chailakhyan coined in 1937 for the putative hormone regulating flowering. At this concept, plant physiologists arrived following early research concerning the effects of temperature and day length on the transition from vegetative to reproductive stages of plants. The existence of florigen was postulated on the experimental backgrounds involving i) the response of plants to inductive conditions; ii) transmission of a flowering stimulus by grafting; iii) extraction of this stimulus from induced plants. This experimental results showed the existence of florigen at least as concept because they always failed to offer the experimental evidence of its chemical existence. The myth of florigen persisted as long as the end of the Seventies, when physiologists began to consider flowering as a complex process in which various classes of hormones might variously interplay.

Botany↗
PubMedDate not supplied

Mineral nutrition of plants: a short history of plant physiology.

The development of the knowledge on the mineral nutrition of plants begins between the 17th and 18th centuries when some European naturalists gave the first experimental evidences of what had been empirically known for about two millennia. The works of Hales and Ingenhousz were of absolute importance in relation to the transport of water and solutes, and assimilation of "fixed air" (carbon dioxide), respectively. The early chemistry introduced by Lavoisier benefited the first physiologists Senebier and De Saussure to reject the "theory of humus", which imposed the soil as the unique source of carbon. During the first half of the 19th century, Sprengel and Liebig investigated on the problems related to some indispensable mineral salts, while Boussingault and Ville attempted to prove the nitrogen fixation from air without giving any convincing evidence. Liebig was the pioneer of the agricultural chemistry: he epitomised the knowledge of that period by imposing the so-called "law of the minima", already acknowledged by Sprengel, and patronised the use of mineral fertilisers in Europe by devising several formulas of mineral manure. He, however, did not recognise the needs of external supplies of nitrogen salts for the crops, in open dispute with the English school of Lawes and Gilbert, who were instead convinced assertors of such needs. At the end of the 19th century Hellriegel showed that leguminous plants presenting peculiar nodules on their roots could really fix the gaseous nitrogen. From these nodules Beijerinck and Prazmowski isolated for the first time some bacteria which were recognised as the real agents fixing nitrogen. This discovery was of fundamental importance for plant nutrition, only second to the discovery of photosynthesis. Another basic contribution came from early research of Sachs on plants grown on aqueous solutions: these techniques allowed to impose the concept of "essential elements", which was fixed as a principle by Arnon and Stout in 1939. This principle benefited further research concerning the effects of states of deficiency on plant growth and development through investigation on the anatomical, histologic and biochemical nutritional disorders of plants.

Biology↗
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Air and the origin of the experimental plant physiology.

It is well known that oxygen and carbon dioxide are two chemicals which enter the plant metabolism as nutrients. The bases of this nowadays obvious statement were placed in the 18th century by means of the works of ingenious naturalists such as Robert Boyle, Stephen Hales, Joseph Priestley, Jam Ingenhousz, Lazzaro Spallanzani and Theodore De Saussure. Till the end of the 17th century, the atmospheric air was considered as an ineffable spirit, the function of which was of physical nature. Boyle was the first naturalist to admit the possibility that respiration were an exchange of vapours occurring in the blood. Stephen Hales realised that air could be fixed by plants under the influence of solar light. Priestley showed that plants could regenerate the bad air making it breathable. Ingenhousz demonstrated that the green parts of plants performed the complete purification of air only under the influence of the light. Spallanzani discovered that plants respire and guessed that the good air (oxygen) originated from the fixed air (carbon dioxide). Finally, Theodore De Saussure showed that plants were able to adsorb carbon dioxide and to release oxygen in a proportional air. All these discoveries benefited of the results coming from investigations of scholars of the so-called "pneumatic chemistry" (Boyle himself, George Ernst Stahl, Joseph Black, Priestley himself, and many more others. But among all the eminent scientists above mentioned stands out the genius of Antoine Laurent Lavoisier, who revolutionised the chemistry of the 18th century ferrying it towards the modern chemistry.

Air↗
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The origin of phage virology.

The history of bacteriophage (phage) had its start in 1915, when Twort isolated an unusual filterable and infectious agent from excrete of patients struck by diarrhoea; this discovery was followed by an analogous, and probably independent, finding of d'Hérelle in 1917. For several years phage research made scant progress but great attention was paid to the question of phage nature, which saw the contrast between d'Hérelle and Bordet's views (living against chemical nature, respectively). This situation changed with the independent discovery of lysogeny, in 1925, thanks to Bordet and Bail: this phenomenon was considered of genetical origin, a view that Wollman interpreted by assimilating the properties of phage to those of gene (according to a previous idea of Muller). In the 1930s, Burnet's work opened a new era by demonstrating the occurrence of several species of phages and their antigenic property. In the same period, the physical and chemical characteristics of these viruses were disclosed thanks, in particular, to the work of Schlesinger, who first demonstrated that a virus (phage) was constituted of nucleoproteins. The peculiarity of phage was finally shown after the invention of electron microscope: H. Ruska, in 1940, and Anderson and Luria in the next years, obtained the first images of tailed phages, a finding that strongly helped the investigation on the first steps of the infection process. The decisive impulse to phage virology came from Delbrück, a physicist who entered biology giving it a new arrangement. The so-called "phage group" assembled brilliant minds (Luria, Hershey and Delbrück himself, and later a dozen of other scientists): this group faced three fundamental questions of phage virology, i.e., the mechanisms of attack, multiplication and lysis. In ten years' time, phage virology became an integrant part of molecular biology, also thanks to the discovery of the genetical properties of DNA: in such scientific context, Delbrück, Luria and Hershey's works emerged for the absolute excellence of their results, which led such scientists to Nobel prize. Lysogeny was however neglected by the phage group: this singular property shared by bacteria and phages was instead investigated by Lwoff's group, in Paris, and explained in its fundamental features during the 1950s. The "phage's saga" has gone on being an important division of molecular biology till today, and its history is far from being over.

Bacteriophages↗