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28 Pesticide Outlook Fe b r u a ry 2001 DOI: 10.1039/b100805f

This journal is The Roya l Society o f C hemistry 2001

IntroductionP robenazole (3-allyloxy-1,2-benzisothiazole-1,1-oxide) (Figure

) is a prot ecta nt developed by M eiji Seika Ka isha Ltd. for

ice blast control. Oryzemate, containing probenazole, has

een widely used against blast by Japanese farmers since

975 because it provides good, long-lasting control, when

pplied on a pa ddy f ield or in a seedling box . After applic-

tion to rice plants, probenazole is absorbed by the roo ts,

hen systemically transferred to the w hole pla nt, almo st

ompletely controlling leaf blast fo r 4070 days a fter applic-

tion. Despite extensive use over many years no development

f resistance in the target fungus has been observed.

ctivation of the natural plant diseasedefence systemMost plants have the ability to escape invasion of pathogens

y using defence systems, even if t hey do not ha ve a specific

isease resistance gene. There is a delicate relationship be-

ween plant and pathogen. When environmental conditions

such a s temperature and humidity are fa vourable for the

atho gen, the patho gen can easily invade the plant. When

he defence system of the plant functions effectively, on the

ther hand, the plant can overcome pathogen attack.Our studies show that probenazole activates the disease

efence system of a plant an unusual mode of action fo r a

isease control chemical, previously unre p o rted. By activat ing

he plant defence system, probenazole a lters the bala nce of the

lantpathogen relationship in favour of the plant.

Non-fungicidal protectionOur experiments on the effect of probenazole on the blast

ungus have shown:

it does not have any fungicidal activity against the

fungus

it is not changed to a fungicidal substance within the

rice plant tissue or in a n environment such a s padd y

water

q it does not reduce virulence of the fungus

q it does not inhibit biosynthesis of fungal melanin

pigment, w hich is essential fo r penetra tion o f the fungus

into t he plant tissue

Hence, although probenazole gives excellent control of

blast , i t and i ts metabo l ites do not a f f ect the grow th or

infectivity of the blast fungus.

Activation of defence-relatedphenylpropanoid pathwayActivities of enzymes in the phenylpropano id pat hw ay, such

as phenylalanine ammo nia-lyase, peroxida se and po ly-

phenoloxida se, a re enhan ced in rice plants treat ed with

probenazole, especially in plants inoculated with the blast

fungus after probenazole application (Iwata et al., 1980).

The phenylpropanoid pathway plays an important role in

the plant defence system; when the plant is being infectedlignin is synthesised and acts a s a physical ba rrier a gainst

pathogen invasion, and a phytoalexin w ith antimicrobial

activity is produced. These contribute to the limitation of

pathogen invasion in the plant tissue. Our results show that

probenazole activates the phenylpropanoid pathw ay and

thereby enhances the defence response in the plant.

Accumulation of fungicidal substancesWe found th at fungicida l substa nces accumulat e within t he

tissue of t he treated a nd inoculat ed rice leaf. Since proben-

azole and its metabolites do not have any fungicidal activity,

w e thought tha t these substa nces originated from the riceplant. They w ere identified a s hydroxy unsaturated fa tty

acids derived from -linolenic a cid (Shimura et al., 1983).

We also proposed a biosynthesis pathw ay of these hydroxyl

unsaturated fa tty a cids as follows: -linolenic acid cut off by

phospholipase A2 f rom phospholipid in cell plasma membrane

is peroxidized into hydroperoxylinolenic acids by lipoxyge-

nase ; then the hydro peroxides a re ra pid ly reduced to

hydro xides (Figure 2). Activities of b oth enzymes in the rice

leaf were enhanced when the plant was inoculated with a

resistant-reaction-inducing, incompatible race of the blast

fungus, suggesting participation of both enzymes in defence

response. The hydro peroxide synthesis for ms part of t he

octadecanoid (18-carbon) pathway by which the plant

hormone jasmonic acid, an endogenous elicitor of defence

PROBENAZOLE A PLANT DEFENCE ACTIVATOR

Michiaki Iwata from the Meiji Seika Kaisha Ltd. Pharmaceutical Research Centre in Yokohama in Japan

discusses the mode of action of probenazole, a leading agent for the control of rice blast

RICE BLAST CONTROL

Figure 1. Structure of probenazole

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30 Pesticide Outlook Fe b r u a ry 2001

RICE BLAST CONTROL

Our conclusion on the mode of action of probenazole is

hat it prevents the invasion of pa thogen by inducing many

efence genes through the signal transduction pathway

(Figure 3).

he futureSeveral chemicals that activate the defence system of plants

ike have now been reported. Benzo(1,2,3)thiadiazole-7-arbothioic acid S-methyl ester (acibenzolar-S-methyl) (Figure

), induces systemic acquired resistance (Friedrich et al.,

996) which is one of the natural defence systems of plants.

This compound ha s been intro duced commercial ly by

Novartis for control of a range of plant diseases. The modes

f action of probenazole and acibenzolar-S-methyl are not

he same, because expression o f th e RPR1gene is induced

y a cibenzolar-S-methyl, but t hat of t he PBZ1gene is not.

Plant activat ors, such as probenazole and a cibenzolar-S-

methyl, usually do no t ha ve biocidal activity, ha ve good

nvironmental safety, are good protectants, a ct aga inst a

ide range of plant pathogens (fungi, bacteria and viruses),

nd ha ve a low risk of development o f pa thogen resista nce.

t is expected tha t plant activators w ill occupy a major position

s agrochemicals for controlling diseases and insects early in

he 21st century.

References

Doke, N. (1983) Involvement of superoxide anion generation inthe hypersensitive response of potato tuber tissues to infectionw ith an incompatible race of Phytophthora i nfestansand to thehyphal w all components. Physiol ogical Plant Pathology23,345357.

Friedrich, L.; Law ton , K.; R uess, W.; M asner, P.; Specker, N .; R ella,M . G .; M eier, B.; D incher, S.; Staub , T.; Uknes, S.; Metra ux, J-P.;Kessmann, H.; Ryals, J. (1996) A benzothiadiazole derivative

induces systemic acquired resistance in tobacco. Plant Journal10, 6170.

Kanoh, H.; Haga, M.; Iwata, M.; Sekizawa, Y. (1993) Transmem-brane signaling operated at rice blade cells stimulated by blastfungus elicitor I. Operation of the phospholipase C system.Journal of Pesticide Science18, 299308.

Kiribuchi, K.; D unlap, D . Y.; Ma tsumura, F.; Yamaguchi, I. (1998)Protein kinase C as a biomarker for assessing the effect of envi-ronmental stress and fungal invasion on plant d efencemechanism. Journal of Pesticide Science23, 123128.

Iw at a, M .; Suzuki, Y.; Wat anabe, T.; M ase, S.; Sekizaw a, Y. (1980)Effect of probenazole on the activities of enzymes related to theresistant reaction in the rice plant. Annals of t he Phytopatholog-ical Society of Japan46, 297306.

Midoh, N.; Iwata, M. (1996) Cloning and characterization of a

probenazole-inducible gene for an intracellular pathogenesis-related protein in rice. Plant Cell Physiol ogy37, 918.

Nojiri, H.; Sugimori, M.; Yamane, H.; Nishimura, Y.; Yamada, A.;Shibuya, N .; Koda ma, O .; M urofushi, N.; Omori, T. (1996)Involvement of jasmonic acid in elicitor-induced phytoalexinproduction in suspension-cultured rice cells. Plant Physiol ogy110, 387392.

Sakamoto , K.; Tada , Y.; Yokozeki, Y.; Akagi, H.; Ha yashi, N.;Fujimura , T., Ichikaw a, N . (1999) C hemical induction of d iseaseresistance in rice is correlated with the expression of a geneencoding a nucleotide binding site a nd leucine-rich repeat s.Plant Molecular Biol ogy40, 847855.

Schaff rath, U.; Z abba i, F.; D udler, R. (2000) Chara cterization ofRCI-1, a chloroplastic rice lipoxygenase whose synthesis isinduced by chemical plant resistance activators. European

Journal of Biochemistry267, 5935-5942.Sekizaw a, Y.; Aoyama , H .; Kimura, M .; Yamaguchi, I. (1995)

G TPase activity in rice plasma membrane prepara tion enhanced

Figure 3. Hypothetical actionsite of probenazole in diseasedefence system of rice plant.PBZ1,RPR1, probenazole-induced gene products; PLA2,phospholipase A2; LOX,lipoxygenase; PAL, phenylala-nine ammonia-lyase; TAL,tyrosine ammonia-lyase;POX, peroxidase; CH2=CH2,ethylene; G, GTP bindingprotein; PIP2,phosphatidyli-nositol 4,5-bisphosphate; IP3,inositol 1,4,5-triphosphate;DAG, diacylglycerol; ER,endoplasmic reticulum.

Figure 4. Structure of acibenzolar-S-methyl.

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by a priming effector for plant d efence reactions. Journal ofPesti cide Science20, 165168.

himono, M.; Yazaki, J.; Nakamura, K.; Kishimoto, N.; Kikuchi,S.; Kubo, N.; Kadowaki, K.; Mochizuki, A.; Yamamoto, K.;Sasaki, T.; Nishiguchi, M . (2000) Ana lysis of gene expression inrice plants treated with an inducer of disease resistance,probenazole using D NA microarray. . Annals of thePhytopathological Society of Japan66, 115116 (Ja paneseabstract).

himura, M .; M ase, S.; Iw ata , M .; Suzuki, A.; Wata nabe, T.;Sekizaw a, Y.; Sasaki, T.; Furihata, K.; Seto, H. ; O take, N.(1983) Anti-conidial germinat ion f acto rs induces in the presenceof probenazole in infected host leaves. III. Structural elucidationof substances A and C. Agri cultural and Biological Chemistry47, 19831989.

Taka hashi, A.; Kaw asaki, T.; H enmi, K.; Shii, K.; Koda ma, O .;Satoh, H .; Shimamoto, K. (1999) Lesion mimic mutants o f ricewith alterations in early signaling events of defence. PlantJournal17, 535545.

Pesticide O utlook Fe b r u a ry 2001 3 1

RICE BLAST CONTROL

Michiaki Iwatais a plant pathologist at the Pharmaceutical Research

Center of Meiji Seiki Kaishi Ltd. He has been involved in research

into the control of plant diseases for 30 years, and in particular has

extensive experience in the elucidation of plant self-defence systems.

JAPAN PLANT PROTECTION ASSOCIATION

The Japan Plant Protection Association (JPPA) was established in 1953 for the promotion of scientific and technicalaspects of crop protection, particularly with pesticides, as an incorporated body under the supervision of theMinistry of Agriculture, Forestry and Fisheries.

MembershipThe membership consists of private individuals, supporting members and affiliated prefectural plant protectionsociety members (Japan is divided into 47 prefectures)

OrganisationThe JPPA is composed of 4 divisions (General Affairs, Promotion, Test and Study and Publication Divisions) and aresearch institute. The latter operates a research and test farm at Ushiku, Ibaraki Prefecture, and two test farms at

Noichi, Kochi Prefecture and at Sadowara, Miyazaki Prefecture.

ActivitiesConferences and symposia

The JPPA holds annual district plant protection conferences in 6 districts, and annual symposia and field observationtours.

Research and testing

Here work is done, firstly on research to develop and improve testing procedures to evaluate the efficacy ofcandidate products in controlling target pests and diseases, to study effects on non-target organisms and carry outenvironmental fate studies.

Publications

Plant Protection(Shokubutsu Roueki) monthly journal in JapaneseAgrochemicals Japan biennial journal in Englishand a number of books

International activites

The JPPA hosted the 6th International Congress of Entomology in 1980, the 5th International Congress of PesticideChemistry in 1982 and the 5th International Congress of Plant Pathology on 1988 (all in Kyoto).

Further informationJapan Plant Protection Association (JPPA), 43-11, 1-chome, Komagome, Toshima-ku, Tokyo 170, Japan.

Tel.: +81 (0)3 3944 1561; FAX: +81 (0)3 3944 2103

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