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STUDY ON BIOPHOTON EMISSION FROM PLANT-MICROBE INTERACTION, FOCUSING ON SUSTAINABLE AGRICULTURE AND FORESTRY
Takahiro Makino, Kimihiko Kato and Hiroyuki Iyozumi
Shizuoka Agricultural Experiment Station, 678-1 Tomigaoka Iwata Shizuoka 438-0806 Japan
E-mail:makino@agri-exp.pref.shizuoka.jp
The increasing interest in using microorganisms will contribute to achieving the dream of low input sustainable agriculture and forestry. Plant-microbe interactions have been investigated, mainly focusing on plant growth promoting rhizobacteria, nitrogen fixating bacteria and biological control of root diseases. Many beneficial microorganisms selected in a laboratory do not work in a natural soil environment. Our limited understanding of the plant-microbe interaction is undoubtedly an important cause for the lack of success in improving plant growth. We seek answers to how to select beneficial microorganisms and to optimize the plant response to them.
We found that biophoton emission greatly increased when plants expressed defense responses against the pathogens. It appears that the biophoton results in substantial reactions of plants. By studies on the biophoton, we may estimate the ability both of systemic disease resistance and of growth promotion, induced in plants by microorganisms. In addition, measurement of the biophoton is expected as a strong method for analyzing a mechanism of signal transduction.
Much microbial ability may be estimated by measurement of biophoton emission from plants, such as productivity of microbial plant growth regulatory substances, pathogenicity of microorganisms, substances from microbial origin or not inducing systemic resistance.
Biophoton emission was tested from pathogenic and non-pathogenic microorganisms showing various effects on plants.
Resistant varieties of plants such as tobacco, melon and sweet potato were distinguished from sensitive ones by the patterns of biophoton emission against their specific pathogens.
Remarkable photon emission was also observed on storage roots of a few plants treated with various kinds of plant growth regulatory substances (PGRs) originating in microbe. In some PGRs, intensity of biophoton emission depended on their concentration. Plant growth promoting rhizobacteria (PGPR) and deriterious rhizobacteria (DRB) we are able to be distinguished by the patterns of biophoton emission. We obtain a possibility of an evaluating system for PGPRs and DRBs.
Chenopodium quinoa inoculated with a virus, used as a test plant for identifying a virus infection, developed necrotic spots on its leaves. The necrotic spots resulted from activation of defense response. Biophoton emission was observed before necrotic spot formation in case of cucumber mosaic virus.
Nematode transmitted by insects causing a serious disease on pine trees was inoculated on sweet potato. The pattern of biophoton emission was similar to those from defense response against bacterial and fungal infection. We hope to develop a screening method for resistant pine trees and resistant genes measuring biophoton emission.
We can discuss a phenomenon of biophoton emission on the basis of biochemical reactions in relation to plant defense responses. Oxidative bursts are observed specifically in cells in contact with a pathogen only a few minutes after inoculation of a pathogen. Most likely, this active oxygen is catalyzed by a NADPH oxidase. It is feasible that the resistance gene-mediated recognition of pathogen proteins activates a preexisting Ca2+ channel to cause an influx of Ca2+ ions. The elevated cytosolic Ca2+ would activate a latent NADPH oxidase to generate active oxygen species. Chemiluminescence chemicals such as DBPH (Dojin chemicals) specifically reacting with active oxygen species reacted strongly a few minutes after inoculation of a pathogen. At that time, strong biophoton emission was observed. Thus, biophoton emission is in sync with oxidative burst. However, this observation was not found in later increase of biophoton emission. This reaction was greatly suppressed by a NADPH oxidase inhibitor and by suppressing the respiration. Why did not DBPH react in later increase of biophoton emission? It is necessary to analyze the phenomenon.
Sustainable agriculture and forestry need disease control technology instead of environmentally deleterious agricultural chemicals. Biological control of diseases will be one of answers. Biophoton studies will give us useful informations on optimizing biological control such as the selection of microbe and plant variety for determining the best match between them.
