Bulletin du Centre Franco-Japonais d'Histoire des Sciences (Kitakyushu-Paris), Vol. 7(2) : 65-77 (2013)
日仏科学史資料センター紀要

ISSN 1882-3548 (online), 1882-353X (CD-ROM)-Mini ReviewPioneering work of Anton Karsch (1822-1892) suggesting the rolefor intercellular space in plant tissue as the path for cell-cellcommunication during plant-pathogen interaction
Tomonori Kawano1,2,3, François Bouteau2,4, and Kiyoshi Moritaka1,2
1 Faculty and Graduate School of Environmental Engineering, The University of

Kitakyushu, Kitakyushu, Japan;
2 University of Florence LINV Kitakyushu Research Center (LINV@Kitakyushu),

Kitakyushu, Japan;
3 Université Paris Diderot, Sorbonne Paris Cité, Paris 7 Interdisciplinary Energy

Research Institute, 75103 Paris, France
4 Université Paris Diderot, Sorbonne Paris Cité, Institut des Energies de Demain (FRE3597),

75103 Paris, France.

(kawanotom@kitakyu-u.ac.jp)

Abstract
Recently, we have described in two independent articles that a pioneering work of Anton Karsch(1822-1892) who is known as a medical doctor (internist), an ecologist, a plant collector, amicrobiologist, an early cell biologist, and an philosopher. Anton Karsch, published in 1855, a worksuggesting the role for intercellular space in plant tissue as the paths for spread of pathogenic
microorganisms and also for cell-cell communication required for combatting the invading
pathogenic microorganisms. It is also noteworthy that the entrance of air-borne spores of pathogenic
fungus into the leafy tissue through the opening stomata which is recently studied by plant cellbiologists, has been already described by Karsch. This short article briefly introduces the key worksof Karsch from the view point by plant biologists of today.

T. Kawano et al. (2013) Pioneering work of Anton Karsch (1822-1892) suggesting the rolefor intercellular space in plant tissue as the path for cell-cell communication during
plant-pathogen interaction. (1822-1892). Bull. Cent. Fran. Jpn. Hist. Sci. Vol. 7(2): 65-77.

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Keywords: Anton Karsch, intercellular space, microscope, Phytophthora infestans, plant cell, plant
immunity, stomata, thing-in-itself (ding an sick)1. Introduction—Pieces of Westphalia
All truly wise thoughts have been thought already;
we must think them over again honestly
Johann Wolfgang von Goethe
In our life, we often face the situation that a newly invented idea has been already proposed
and tested by someone else in the past, in a similar or different form. In this short article, we describesuch story we experienced in our plant biological research finding and shocked by a similarity
between the recently proposed plant pathological model and a classical proposal.
Anton Karsch (formally, Anton Ferdinand Franz Karsch, but authored most of articles andbooks as Dr. Karsch; June, 19th, 1822—March, 15th, 1892) is known as (i) a medical doctor(internist), (ii) an ecologist, (iii) a plant collector, (iv) a microbiologist, (v) an early cell biologist,
and (vi) an philosopher born and lived in Germany. His life was dedicated to collect the naturalpieces of the region of Westphalia (Westfalen). The works of Karsch as a locally acted ecologist
based in the region of Westphalia is well recognized among the scholars and his book focusing on
the biota (especially flora) in Westphalia is still revived and available today (Fig. 1).
Recently, in two independent articles both in Japanese (Kawano, 2013) and in English(Kawano and Bouteau, 2013), we have introduced a series of works of Karsch documented in 1855.
The works of Karsch appeared as seven different articles in the first issue of the first volume of a
German journal of science and philosophy, “Natur und Offenbarung” (Nature and Revelation),widely covering various area including biology and philosophy. In fact, Karsch was one of four
founding editors of “Natur und Offenbarung” which continued for 36 years since February 1855.
Note that the launch of this interdisciplinary science journal in Germany covering astronomy,geology, electronic communication, botany, medicine and philosophy, actually precede those of“Nature” in United Kingdom (1869) and Science in United States (1880).
As we have obtained the first volume of “Natur und Offenbarung” in the city of Bonn inDecember, 2006, original copies of “Natur und Offenbarung” are preserved and circulated in themarket today. More conveniently, digitalized versions became partly available online (URL:

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Fig. 1. A book authored by Karsch (Flora der Provinz Westfalen) originally authored in 1856, but
recently reprinted simply by binding the photocopied images (Kessinger Publishing, LLC;
www.kessinger.net). (Top) Newly designed cover and original cover image. (Bottom) Snapshot of
the text, describing the family of Cruciferae now classified as Brassicaceae.

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(http://books.google.co.jp/books?id=4_0GAAAAcAAJ&printsec=frontcover&hl=ja&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false).
A part of philosophical works (Karsch, 1855a-c) dealt with the idea of “thing-in-itself” (dingan sick) proposed by Arthur Schopenhauer (1788-1860), a German philosopher. Karsch was alsointerested by the use of microscopes which was surely considered as “new technology” at that time
and thus authored the articles entitled “microscopic form of life 1 and 2” (Mikroskopische
Lebensformen; Karsch, 1855d, e), “From the life of a gnat” (Aus dem Leben einer Mücke; Karsch,
1855f), presenting the drawings of microscopic structures of bacteria, protozoa, blood cells andinsects.
His interests also covered the behaviors of higher plants surrounded by pathogenic
microorganisms (Karsch, 1855g). In our recent articles a piece of Karsch’s works were comparedwith the recently proposed plant pathological model and suggested that both the classical and recent
works are indicative of the role for intercellular space in plant tissue as the paths for spread of
pathogenic microorganisms and also for cell-cell communication required for combatting theinvading pathogenic microorganisms.

2. Outbreak of plant diseases and plant responses
Historically, humans have long been suffered by the loss of crops due to the outbreak ofplant diseases. One of the symbolic incidents, known as Irish potato famine occurred in 19th century
and we can find out the remaining impact of the aforementioned incident even today. In 1997, Tony
Blair, British Prime Minister (terms, 1997-2007) has issued a statement on Irish potato famine
apologizing on behalf of the British authority for the first time in 1.5 centuries after the incidents(The Independent, Monday 02, June, 1997).
It is known that the Irish potato famine was caused by a single clonal genotype of
Phytophthora infestans, an oomycete that causes the serious potato disease known as late blight or
potato blight (Goodwin et al., 1994). Today, survey by Goodwin et al. (1994) revealed that a single
clonal lineage of Irish potato famine fungus dominated most populations worldwide. Therefore, P.
infestans is used as model plant pathogenic organism in the fields of phytopathology, and moregenerally, in physiology, cell biology, biochemistry and molecular biology of plant-microbe
interactions.
In 1983, Doke (Nagoya Univ., Japan) reported that the infection by P. infestans (late blight68

pathogen of potato) into potato tubers causes the generation of a member of reactive oxygen species(ROS), superoxide anion radicals (O2•-) at the host cells’ plasma membrane, in the incompatible
interactions (Doke, 1983a). This was the first report on the generation o ROS in plant-microbe
interaction which is specifically responsive to the attacks by pathogenic microorganisms. As his
work demonstrated that the members of ROS possibly function as the chemical signals required for
induction of hypersensitive responses as typified by host cell death and they are most likely
generated and released in the intercellular space, plant biologists and pathologists now consider the
space called apoplast (outside the cells) surrounded by multiple cells in plant tissue as one of the key
paths, or media of a series of reactions and/or events determining the behaviors and/or fate of theplant cells challenged by pathogens.
Following the first observation, Doke (1983b) further predicted that the recognition of plant
pathogens by plant cell surface leading to “oxidative burst” takes place on the interface (extracellularmatrix) of both the plant cells and pathogenic cells, based on the observation that treatments ofpotato tuber protoplasts with the cell wall preparation from P. infestans readily induce the ROS
production. This suggested that chemical components derived from pathogenic microorganisms (cellwall-derived elicitors) trigger the burst of ROS production in the apoplast in order to stimulate theplant defense mechanisms.

3. Medal of Honor with Purple Ribbon.
In November, 2006, from the hands of his majesty Emperor Akihito (the 125th Emperor ofJapan, a renowned marine biologist), the Medal of Honor with Purple Ribbon was handed to Prof.
Noriyuki Doke of Nagoya University for honoring his pioneering works (carried out since early
1980’s) leading to the discovery that members of ROS (especially superoxide anion, O2-) could be
produced from the plant tissues challenged by the pathogenic microorganisms (Yoshioka et al.,2008).
We understood that the honor was also given to the area of plant biology emphasizing the roleof extracellular (intercellular) communications by plant and microbial cells, which has markedly
developed in the last two decades.

4. Intercellular-space as the site of species-species contacts and recognition
followed by early signaling events.
To date, multiple roles of ROS have been proposed in direct microbicidal actions,69

strengthening of cell wall through oxidative cross-linking of glycoproteins, induction of intracellularsignaling pathway such as the synthesis and release of salicylic acid (SA), a stress-related and plant
defense-related phytohormone, and activation of mitogen-activated protein kinase (MAPK) cascade,or activation of systemic acquired resistance associated with systemic propagation of the oxidative
burst (Kawano et al., 1998, 2004). We have recently outlined the relationship between the roles of
ROS and behaviors of plant defense-related signaling molecules chiefly, of SA through the crosstalk
between intracellular and extracellular signaling events leading to long-distance spread of defense
signals (Yoshioka et al., 2008; Kawano and Bouteau, 2013). The production of ROS, mostly O2•-,hydrogen peroxide (H2O2), and hydroxyl radicals (HO•), at the cell surface is one of the earliest
events detectable during the incompatible interactions between plants and pathogens (Yoshioka et al.,2001) and also plant cellular recognition of exogenously applied SA (Kawano et al., 1998; Kawano
and Muto, 2000).

5. A work by Karsch in 1855 emphasizing the possible role of intercellular spaceand stomata as the path of pathogen entrance and the path of intercellularcommunication
In the middle of 19th century, P. infestans was also described under the name of Botrytis
infestans (Cline, 2006). A classical study describing the interaction between B. infestans and potato
leaves (Karsch, 1855g), has suggested that apoplastic space, as such in the leafy tissues, is the key
path to the cell-to-cell communication within plants, thus the events of pathogenic invasion andresultant plant responses through this path are of great importance. Note that the terms related to“intercellular space” and “communication” were used in this early study (underlined words in Fig.
2a). The authors were impressed by frequent uses of such modern scientific terms in the journal
published in 19th century.
Followings are original German text (A) and its translation to English (B), stating that theimportance of intercellular space during the early phase of pathogen attacks and also at the phase ofpathogenic propagation and disperse:(A) Zwischen den einzelnen Parenchymzellen, zumal da, wo mehre Zellen zusammenstoßen,
zeigen sich eckige oder rundliche, mit Luft gefüllte Räume, (Interzellularräume) die, im Zellgewebe
des Blattes zerstreut, mit einander communizieren und dadurch ein vielfach verschlungenes Nets vonKanälchen (die sogenannten Interzellulargänge) bilden.

(B) Between the parenchymal cells, especially where several cells meet, square or roundair-filled spaces (intercellular spaces) can be found, being scattered in the tissues of the leaf,
70communicate with each other and thus forming the tangled nets of small channels (called
Interzellulargänge ).
Today, stomata in the epidermis of terrestrial plants are known to be pivotal for (i) CO2
absorption, (ii) transpirational water loss, and (iii) entry of pathogens (Zhang et al., 2008). The workby Karsch clearly pointed out the importance of stomata for potential points of entry for pathogenic
microorganisms into plants.

Fig. 2. Snapshots of text and illustrations by A. Karsch (1855g, pp. 65-66). (a) Importance ofintercellular space and communication between the plant cells during plant-microbe interaction was
pointed. Two key words, interzellularräume (intercellular space) and communiziren (tocommunicate) are underlined. (b) Leaf anatomy highlighting the stomatal aperture and intercellular
network as the path of late potato blight infection and outbreak.

6. Controls in stomatal aperture as the point of plant defense and pathogenic
counter defense
Since the stomata on the leaves connect the internal environment in the plants and the aerial
environment surrounding plants through gas exchange, it is natural to relate the air-borne entry offungal spores and the gating behavior of stomata. As suggested by Karsch (see Fig. 2b), stomata
have long been considered as the gates for entry and further spread of pathogenic microbes. To our71knowledge today, roles of stomata in plant defense mechanism so called plant innate immunity
against foliar diseases is now documented (Melotto et al., 2006, 2008).
Upon attacks by pathogens or treatments with elicitors — pathogen-derived molecules which
trigger a series of defense-related reactions in plants — such as chitosan, stomatal closure is rapidly
induced as examined in tomato (Solanum lycopersicum L.) and Asiatic dayflower (Commelina
communis) (Lee et al., 1999). By doing this, plants might limit the chance of further fungal invasion
through stomata (Mori et al., 2001).
Note that Asiatic dayflower is one of the best materials for microscopic observation of
stomatal behaviors. Fig. 3 shows a typical image of highly populated stomata on epidermis peeledout of the leaf of Asiatic dayflower for demonstration in our laboratory.

Fig. 3. Stomata on the epidermis of Asiatic dayflower observations under a stereomicroscope(SMZ645; Nikon, Tokyo, Japan). Arrow, typical stoma.

According to the model reported by Lee et al. (1999), additions of elicitors are resulted ingeneration of ROS and in turn, stomatal closure is stimulated by ROS. There are two distinct enzyme
models for apoplastic generation of O2•- upon treatment of model plant cells (tobacco BY-2 cells)with chitosan oligomers and chitin oligomers involving extracellular peroxidase and NADPH

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oxidase, respectively (Kawano et al., 2000). In addition to elicitors, perception of multiple
pathogen-associated molecular patterns (designated as PAMPs) of bacterial origins, including
flagellin, lipopolysaccharide and elongation factor Tu, reportedly induce closure of stomata inepidermal peels of Arabidopsis leaves (Melotto et al., 2006). Since perception of PAMPs is the signthat plants are dangered by the risk of infection, members of PAMPs such as flg22 derived frombacterial flagellin, emergently interferes with naturally occurring light-induced stomatal opening, byinhibiting the inward K+ channels of guard cells that mediate K+ uptake during stomatal opening(Zhang et al., 2008). The PAMP-triggered stomatal response involving K+ channel regulation isdependent on signaling via cognate PAMP receptors and a heterotrimeric G-protein (Zhang et al.,2008).
Interestingly, for the purpose of enhanced penetration into the leaves by pathogenic microbes,
some plant pathogens such as Pseudomonas syringae pv. tomato DC3000 (Zeng et al., 2011) and thecausal agent of grapevine downy mildew, Plasmopara viticola (Allègre et al., 2007), are known to
produce some host-specific toxins which eventually open the stomatal cells. Such pathogen-derived
toxins include fusicoccin which irreversibly stimulates plant H+ ATPases (Eun and Lee, 2000) andcoronatine produced by several pathogenic strains of Pseudomonas syringae, which antagonizes
PAMPs-mediated plant immunity (Lee et al., 2013). For an instance, coronatine suppresses theinhibitory actions of flg22 on both inward K+ currents and stomatal opening. This indicates theinterplay between plant and pathogen in the regulation of plant ion channels.
As above, pathogen-derived molecules are involved in plant defense and counter defense. In
addition, plants possess the mechanisms for minimizing the chance of pathogenic penetration
through stomata via production of phytohormones, chiefly the action of SA is comparable with thatof elicitors. It has been reported that stomatal closure is induced after application of SA, adefense-related plant hormone, to epidermal peels of Commelina communis L. (Lee, 1998), Vicia
faba L. (Manthe et al., 1992; Mori et al., 2001) and Arabidopsis thaliana (Khokon et al., 2011). The
mechanism responding to pathogen-derived elicitors may be involved in the resistance at the site of
infection, while the mechanism responding to SA may be important for minimizing the chance offurther spread of pathogens (Mori et al., 2001).
Importantly, Mori et al. (2001) has shown the evidence in support of the involvement of
peroxidase-mediated O2•- generation and secondarily induced calcium signaling in the earlysignaling phase of SA-induced stomatal closure in Vicia faba. Moreover, the SA-induced stomatalclosure in Vicia faba and Arabidopsis thaliana was reportedly inhibited by pre-treatment withscavengers of ROS such as catalase and superoxide dismutase (SOD), and an pharmacologicalinhibitor of peroxidase, suggesting the involvement of peroxidase-mediated production of
extracellular ROS during the action of SA leading to stomatal closure (Mori et al., 2001, Khokon etal., 2011). Contrarily, pharmacological inhibition of NADPH oxidase (respiratory burst oxidase73homologs, RBOHs) nor mutation of atrbohD and atrbohF showed no inhibition on the SA-induced
stomatal closures (Khokon et al., 2011). This suggests that, unlike the action of abscisic acid
(Marinosend et al., 2011; Suzuki et al., 2011) and chitin oligomers (Kawano et al., 2000) stimulating
the oxidative burst via activation of NADPH oxidase, the peroxidase-dependent mechanism is solely
responsible for the rapid stomatal regulation by SA. As expected, SA-induced stomatalclosure-mediated defense could be counteracted by aforementioned pathogen-derived toxins such as
coronatine produced by Pseudomonas syringae pv. tomato DC3000 (Tsai et al., 2011).

As discussed above, the view proposed by Karsch is still hotly studied by plant biologist of
today.

7. Conclusion
In this short article, we described a story we experienced in our plant biological researchfinding and shocked by a similarity between the recently proposed plant pathological model and aclassical proposal. A pioneering work of Anton Karsch published in 1855 firstly suggested the rolefor intercellular space in plant tissue as the paths for spread of pathogenic microorganisms and also
for cell-cell communication required for combatting the invading pathogenic microorganisms.

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植物‐病原間相互作用における細胞間コミュニケーションのための経路としての植物組織中の細胞間隙の役割を示唆する Anton Karsch (1822-1892)の先駆的研究要約
19 世紀のドイツで活躍した Anton Karsch (1822-1892) は、医師（内科医）、生態学者、植物収集
家、微生物学者、初期の細胞生物学者として知られ、さらに哲学分野においても著述を残している。最
近、我々は、Karsch による植物分野での先駆的研究に関する２つの独立した論文を執筆した。Karschは、1855 年に、植物に感染する病原微生物の侵入やその後の拡散に対して植物が採り得る防御反応における細胞間コミュニケーションのための経路として、植物組織中の「細胞間隙」が果たす重要な役割について示唆する研究を発表している。近年の植物細胞生物学者が研究対象としている、気孔の開閉制御を介した、病原性カビの浮遊胞子の葉組織への侵入防止機構が、19 世紀の Karsch によって描写されていることは注目に値する。本論文では、今日の植物生物学者からの視点から見て重要な研究の源流としての Karsch の仕事を簡潔に紹介する。

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