ISSN 1021-4437, Russian Journal of Plant Physiology, 2017, Vol. 64, No. 4, pp. 543–552. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © A.A. Aver’yanov, T.D. Pasechnik, V.P. Lapikova, T.S. Romanova, C.J. Baker, 2017, published in Fiziologiya Rastenii, 2017, Vol. 64, No. 4, pp. 285–294.
Systemic Reduction of Rice Blast by Means of Photosensitizers
A. A. Aver’yanov
*, T. D. Pasechnik
, V. P. Lapikova
, T. S. Romanova
, and C. J. Baker
All-Russia Research Institute of Phytopathology, Bolshie Vyazemy, Moscow oblast, 143050 Russia
Molecular Plant Pathology Laboratory, Agricultural Research Service, USDA, Beltsville, Maryland, 20705 United States
Received June 10, 2016
Abstract⎯Systemic disease resistance of plants may be induced by exogenous reactive oxygen species or their
sources. Certain compounds (photosensitizers) produce ROS at the expense of light energy. Of them, this
study used photodynamic dyes bengal rose and methylene blue, which yield singlet oxygen, and mercaptopy-
ridine-N-oxide, which yields hydroxyl radical. The goals were to find out whether they can systemically pro-
tect rice (Oryza sativa L.) from blast caused by the fungus Magnaporthe oryzae Conouch et Kohn and whether
ROS is involved in defense mechanisms. The tested compounds were placed on the fourth (uppermost) leaf.
When the fifth leaf developed (in approximately 7 days), it was inoculated with virulent fungal strain. We
found that almost all the chemical treatments altered the fourth leaf and all of them reduced disease symp-
toms on the fifth leaf. Antioxidants combined with the tested substances compromised the disease control.
Photosensitizers applied to the fourth leaf increased superoxide production in drop diffusates of healthy and,
to larger extent, infected fifth leaf. In these diffusates, fungitoxicity also increased, which was diminished by
antioxidants added to the diffusates. Besides, treatment with mercaptopyridine-N-oxide systemically weak-
ened the endogenous antioxidative (H
-decomposing) activity of a diffusate. It is suggested that the oxida-
tive burst in the treated leaves induced the systemic disease resistance, whose accomplishment might include
the secondary oxidative burst in systemic leaves suppressing the pathogen’s development.
Keywords: Oryza sativa, Magnaporthe oryzae, reactive oxygen species, antioxidative activity, rice blast, sys-
temic disease resistance, photosensitizers
Many biotic and abiotic factors, while causing local-
ized damage to plants, can also initiate systemic resis-
tance to diseases in distal plant parts, where it becomes
evident upon subsequent inoculation of these parts .
Damages inducing such resistance are often associated
with local oxidative bursts, namely, the overproduction
of reactive oxygen species. It occurs, for example,
during the hypersensitive plant cell death caused by
avirulent bacteria . The oxidative burst in the treated
tissues precedes systemic resistance induced by Para-
quat , K
, benzothiadiazole (BTH) , or
β-aminobutyric acid (BABA)  and is apparently
involved in the induction mechanisms.
Among exogenous sources and stimulators of
endogenous sources of ROS, the resistance inducers
are probably more numerous than is conventionally
thought. In this regard, light is an important environ-
mental factor. Due to its energy, certain compounds
(photosensitizers) produce ROS . Of them, furano-
coumarins, polyacetylenes, and thiophens support the
natural resistance of plants to pathogens and pests .
Exogenous flavin compounds systemically protect
plants from fungal pathogens: tobacco from Alternaria
alternata  and rice from Magnaporthe oryzae .
Phthalocyanine metal complexes also systemically
control rice blast  and potato late blight . Pho-
todynamic dyes methylene blue (MB) and bengal rose
(BR) systemically reduce cucumber scab ; BR also
controls tobacco mosaic . Such dyes are known to
be directly cytotoxic under light , but the mecha-
nism of their systemic control of diseases is obscure.
Irrespective of the inducer nature, susceptible
plants treated with it react to infections similarly to
resistant ones. In particular, their systemically pro-
tected parts may respond to inoculation by production
of a secondary oxidative burst . The resulting ROS
are involved in diverse anti-infective responses,
including direct suppression of pathogenic microbes.
The secondary oxidative burst occurs not only inside
but also outside cells—in the apoplast and infection
droplet. Thus, rice blast resistance caused by soil
amendment with tricyclazole, probenazole , or
cobalt phenanthroline complex  is accompanied
by the intense superoxide production in diffusates of
Abbreviations: BABA—β-aminobutyric acid; BR—bengal rose;
INA—isonicotinic acid; —MPNO—mercaptopyridine-N-oxide;
—superoxide radical; SOD—superoxide dismutase.