{"id":194,"date":"2013-06-24T15:40:38","date_gmt":"2013-06-24T13:40:38","guid":{"rendered":"http:\/\/wp.unil.ch\/geldnerlab\/?page_id=194"},"modified":"2013-07-17T12:40:45","modified_gmt":"2013-07-17T10:40:45","slug":"classics","status":"publish","type":"page","link":"https:\/\/wp.unil.ch\/geldnerlab\/publications\/classics\/","title":{"rendered":"Classics of Casparian Strip Research"},"content":{"rendered":"

According to my old boss, Gerd J\u00fcrgens, \u201cclassic papers\u201d are those that everybody cites and nobody reads (while \u201cneo classics\u201d would be those that everybody reads and nobody cites . . .). One of the main reason for this discrepancy between citation and reading of the classics (besides laziness and lack of time) is certainly the unfortunate tendency of our predecessors to write about science in their respective mother tongues, before the victory march of our new Latin \u2013 English. This prevents most scientists in the world from diving into the treasure chest of anatomical and physiological literature of the 19th<\/sup> and 20th<\/sup> century, written in German or French or Italian or Dutch . . . Not all of those authors were giants – although some certainly were, commanding an incredible power of observation and very sharp reasoning. I am fortunate enough to read German and French, which opens a big part of this treasure chest to me and I just wanted to share with you those papers that I found most inspiring to read:<\/p>\n

Robert Caspary<\/strong> (1865)<\/p>\n

Bemerkungen \u00fcber die Schutzscheide und die Bildung des Stammes und der Wurzel\u00a0<\/i>Transl.: \u201cRemarks on the protective sheath and the formation of stem and root\u201d<\/a><\/p>\n

\"Captura<\/a><\/p>\n

This is the work that gave rise to one of the few examples in plant biology in which a botanical structure was named after its discoverer. The reasons for this are unclear to me. Caspary himself referred to the Casparian strips simply as the walls or bands of the \u201cprotective sheath\u201d (\u201cSchutzscheide\u201d), as he called the endodermis (this name, ironically, did not catch on). Kroemer (1903) already called the structure \u201cCaspary\u2019s strips\u201d, while Rufz de Lavison (1910) calls them \u201csuberised frames\u201d \u2013 so there might have been some German-French conflict there . . . The work of Caspary is more difficult to read than the work of Kroemer. This is partially because of the nomenclature that is already much more modern in Kroemer\u2019s work and easier to understand. Another reason, however, is that Caspary drives the complexity and length of German sentence structure to insane heights. There are several instance where sentences go over more than half a printed page. This, together with the strange insistence of Germans to put the verb right at the end of sentences, leads to awe-inspiring constructions. Here is an example of a rather short sentence, the only one in this entirely anatomical work in which Caspary speculates on the function of the endodermis (I attempt to keep the German syntax): \u201cThat such a greatly thickened, poreless cell layer that is joint together without extracellular spaces and which surrounds the body of the vascular bundle as a tube, is especially difficult to permeate for gases and liquids, can be assumed.\u201d<\/i> Original: \u201cDass eine so stark verdickte, porenlose, ohne Zwischenzellr\u00e4ume an einander schliessende Zellschicht, die den Gef\u00e4ssb\u00fcndelk\u00f6rper als Rohr umgiebt, in ganz besonderer Weise f\u00fcr Gase und Fl\u00fcssigkeiten schwer durchdringlich oder ganz undurchdringlich ist, l\u00e4sst sich vermuthen.\u201d<\/i><\/p>\n

As I understand Caspary\u2019s work, it was mainly concerned with clearly defining the endodermis as a cell type in its own right, delineating it from other cell types. It was especially important for Caspary to distinguish the endodermis from the Cambium\/pericycle as he insists several times that the endodermis is not a \u201clignified secondary growth ring\u201d or a \u201clignified cambial sheet\u201d (\u201cverholzter Verdickungsring\u201d), which was apparently assumed by some authors of the time. If I understood correctly, the origin of the different stem\/root tissues from either apical or radial meristems was still a matter of debate and Caspary (rightly) insisted that the endodermis is formed from the apical meristem, before the formation of a cambium and that it also takes no part in forming the cambium later on.<\/p>\n

Caspary, as Kroemer, is personal and confrontative, but what I like in Kroemer becomes a bit too much in Caspary\u2019s work for our modern taste. Caspary is especially worked up about a colleague, cited as Sanio, which he repeatedly faults for his logic, his forgetfulness, his self-contradictions, exaggerated claims and generally wrong understanding of plant anatomy. I assume the colleague was Carl Gustav Sanio, which must have been quite a prolific botanist, since he named a lot of plant species and apparently has even a fern species named after him. Interestingly, Sanio also worked in K\u00f6nigsberg at the same time as Caspary. I don\u2019t dare to imagine the working atmosphere at this place!<\/p>\n

Karl Kroemer<\/strong> (1903)<\/p>\n

Wurzelhaut, Hypodermis und Endodermis der Angiospermenwurzel (<\/i>Transl.: \u201cRootskin (Epidermis), Hypodermis and Endodermis of Angiosperm roots\u201d)<\/a><\/p>\n

\"kroemer\"<\/a><\/p>\n

Published in Bibliotheca Botanica<\/i> this \u201cpaper\u201d is actually a whole book, published by Dr. Kroemer, who worked as an \u201cAssistant\u201d for Prof. Meyer in Marburg (interestingly, Prof. Meyer is not author on this work, so some Germans maybe weren\u2019t all that hierarchical?). It\u2019s a massive work that was probably many years in the making, covering the comparative anatomical development of all major dermal cell layers in angiosperm roots. The chapters on the endodermis start with a very good and critical review of what has been done in the 19th<\/sup> century since the discovery of Caspary. I love the way the work of colleagues is discussed by Kroemer (and generally by authors of this time). It is personal, opinionated, argumentative and confrontational, but it makes it so much clearer what the author believes himself and which claims of his colleagues he accepts and which one he refutes and why. It makes you wonder whether our way of writing hasn\u2019t become too detached and polite at times.<\/p>\n

The data on the endodermis is essentially a very careful description of the anatomical development of the endodermis, going back and forth between many different plant species \u2013 always attempting to use the comparison to either reveal general features or to use an extreme case to reveal something that would be otherwise not observable. The descriptions are based on careful use of histochemical stains whose specificities and limitations Kroemer discusses at great detail in the beginning. Based on these studies Kroemer concludes that: \u201c3. dass der Streifen Reaktionen gibt, die man gew\u00f6hnlich als Holzreaktionen bezeichnet, dass dagegen eine Kutisierung des Streifens mit Sicherheit nicht nachzuweisen ist.\u201d<\/i> My translation: \u201c3. that the strip displays (color) reactions that would be generally considered (color) reactions of wood, a suberisation of the strip, by contrast, cannot be demonstrated with any certainty.\u201d<\/i> This essentially means that Kroemer concluded that the \u201cCasparian strip is made of lignin and not suberin\u201d, 109 years before our paper on Arabidopsis (Naseer et al., PNAS, 2012). Sometimes science doesn\u2019t move very fast . . .<\/p>\n

Kroemer also did an amazing description and classification of the different stages of endodermal development, defining \u201cembryonic\u201d, \u201cprimary\u201d, \u201csecondary\u201d and \u201ctertiary\u201d stages of endodermal development, which has been later used in variants by many other authors. If there is anything unsatisfying in this work than it is its complete absence of physiology. This wouldn\u2019t be so bad, if there wasn’t a very long discussion at the end of the paper, trying to make a point about endodermal function from this purely anatomical description. Apparently, other people in the department of Prof. Meyer worked on physiological experiments. I am not aware whether this became ever published (but see the work of de Rufz de Lavison below, published 7 years later).<\/p>\n

Jean de Rufz de Lavison<\/strong> (1910)<\/p>\n

Du mode de penetration de quelques sels dans la plante vivante
\n<\/i>Transl.: \u201cAbout the penetration of some salts into the living plants\u201d<\/a><\/p>\n

\"Rufz<\/a><\/p>\n

I don\u2019t know how old the author was when he wrote this paper, but I also imagine him very young, because of his very direct, nearly blunt way of writing, his particular way of describing his methods and his way of citing. Rufz de Lavison extensively uses the first person, even more than usually done at that time. The author with his strange name of a French noble family doesn\u2019t mention any title or position on the title page, but mentions at the end that the work was done at the Sorbonne, in the laboratory of Prof. Gaston Bonnier, who appears to have been an influential botanist at his time (see wiki entry<\/a>). The author makes a short introduction in which he challenges the idea that plants lack the ability to select the nutrients that will be transported to the shoot. Here is how he formulates his question (my translation): \u201cI wondered whether it would indeed be possible that a salt would penetrate a plant by following only the cellulose. Actually, I felt that the suberised frames of the endodermis would interrupt the continuity of the cellulose in the root.\u00a0 . . .\u00a0 I have tried to experimentally address this question for some salts.\u201d\u00a0Original: \u201cJe me suis demand\u00e9 s\u2019il \u00e9tait possible qu\u2019un sel p\u00e9n\u00e9tr\u00e2t dans la plante, en suivant uniquement de la cellulose. Il me semblait, en effet, que les cadres sub\u00e9ris\u00e9s de l\u2019endoderme interrompaient la continuit\u00e9 de la cellulose dans la racine. … J\u2019ai essay\u00e9 de r\u00e9soudre exp\u00e9rimantalement cette question pour quelques sels.\u201d<\/i><\/p>\n

The experiments he does are very simple: Using salts that can easily be detected, he treats plant roots with different salt solutions and looks whether there is no penetration into the cells themselves. If the salt isn\u2019t taken up by the protoplast, he uses it (in his case iron sulfate) to visualize the block of uptake at the level of the endodermis. The important difference to earlier experiment was the awareness of Rufz de Lavison that the plants needed to stay alive during the treatment (he was an early live-imager!). His way of assessing whether he uses too much of a given salt was very simple indeed – he gently squeezed the roots; if they had become soft, they were discarded. Only conditions were the roots remained turgescent were considered as being instructive.<\/p>\n

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