Subunit composition of VRAC channels determines substrate specificity and cellular resistance to Pt‐based anti‐cancer drugs

Although platinum‐based drugs are widely used chemotherapeutics for cancer treatment, the determinants of tumor cell responsiveness remain poorly understood. We show that the loss of subunits LRRC8A and LRRC8D of the heteromeric LRRC8 volume‐regulated anion channels (VRACs) increased resistance to clinically relevant cisplatin/carboplatin concentrations. Under isotonic conditions, about 50% of cisplatin uptake depended on LRRC8A and LRRC8D, but neither on LRRC8C nor on LRRC8E. Cell swelling strongly enhanced LRRC8‐dependent cisplatin uptake, bolstering the notion that cisplatin enters cells through VRAC. LRRC8A disruption also suppressed drug‐induced apoptosis independently from drug uptake, possibly by impairing VRAC‐dependent apoptotic cell volume decrease. Hence, by mediating cisplatin uptake and facilitating apoptosis, VRAC plays a dual role in the cellular drug response. Incorporation of the LRRC8D subunit into VRAC substantially increased its permeability for cisplatin and the cellular osmolyte taurine, indicating that LRRC8 proteins form the channel pore. Our work suggests that LRRC8D‐containing VRACs are crucial for cell volume regulation by an important organic osmolyte and may influence cisplatin/carboplatin responsiveness of tumors.     

Inhibition of autophagy enhances the effects of the AKT inhibitor MK‐2206 when combined with paclitaxel and carboplatin in BRAF wild‐type melanoma

This study investigates the mechanism of action behind the long‐term responses (12–16 months) of two BRAF WT melanoma patients to the AKT inhibitor MK‐2206 in combination with paclitaxel and carboplatin. Although single agent MK‐2206 inhibited phospho‐AKT signaling, it did not impact in vitro melanoma growth or survival. The combination of MK‐2206 with paclitaxel and carboplatin was cytotoxic in long‐term colony formation and 3D spheroid assays, and induced autophagy. Autophagy was initially protective with autophagy inhibitors and deletion of ATG5 found to enhance cytotoxicity. Although prolonged autophagy induction (>6 days) led to caspase‐dependent apoptosis, drug resistant clones still emerged. Autophagy inhibition enhanced the cell death response through reactive oxygen species and could be reversed by anti‐oxidants. We demonstrate for the first time that AKT inhibition in combination with chemotherapy may have clinical activity in BRAF WT melanoma and show that an autophagy inhibitor may prevent resistance to these drugs.     

Interaction of porphyrins with human organic anion transporting polypeptide 1B1

The existence of a porphyrin uptake transporter in hepatocytes has been hypothesized in recent years, but to date it has not been identified. While the linear tetrapyrrole bilirubin has been shown to be a substrate for the organic anion transporting polypeptide 1B1 (OATP1B1), similar studies have not been conducted for the cyclic tetrapyrroles (porphyrins). The aim of this study was to determine the structural features of linear and cyclic tetrapyroles necessary for interaction with OATP1B1. The interaction was quantified using HEK cells stably expressing OATP1B1 and measuring the inhibition of OATP1B1-mediated uptake of estradiol 17β-d-glucuronide in the presence or absence of various linear and cyclic tetrapyrroles. Ditaurine-conjugated bilirubin was the most potent inhibitor of uptake, with an IC50 of 5 nM, while the substitution of the taurine side chains with methyl ester eliminated the inhibition of estradiol 17β-d-glucuronide uptake. Hematoporphyrin, a cyclic tetrapyrrole with carboxyalcohol side chains at positions C-3 and C-8 and carboxyethyl side chains at positions 13 and 17 had an IC50 of 60 nM, while porphyrins lacking charged side chains such as etioporphyrin I and phthalocyanine did not inhibit OATP1B1. Chlorin e6 and hematoporphyrin were shown to be competitive inhibitors of OATP1B1-mediated uptake of bromosulfophthalein with Kis of 5.8 ± 0.3 and 1.6 ± 0.3 μM, respectively. While these studies do not provide direct evidence, they do support the assumption that tetrapyrroles are transported by OATP1B1. Additionally, these findings offer a possible explanation for the clinical observation that patients suffering from certain porphyrietic diseases have a reduced ability to excrete organic anions.     

Induced responses to grazing by an insect herbivore (Acentria ephemerella) in an immature macrophyte (Myriophyllum spicatum): an isotopic study

While the mechanisms by which adult terrestrial plants deploy constitutive and induced responses to grazing pressure are well known, the means by which young aquatic plants defend themselves from herbivory are little studied. This study addresses nitrogen transport in the aquatic angiosperm Myriophyllum spicatum in response to herbivore exposure. Nitrogen tracers were used to monitor nitrogen uptake and reallocation in young plants in response to grazing by the generalist insect herbivore Acentria ephemerella. Total nitrogen content (N%) and patterns of nitrogen uptake and allocation (δ¹⁵N) were assessed in various plant tissues after 24 and 48 h. Following 24 h exposure to herbivore damage (Experiment 1), nitrogen content of plant apices was significantly elevated. This rapid early reaction may be an adaptation allowing the grazer to be sated as fast as possible, or indicate the accumulation of nitrogenous defense chemicals. After 48 h (Experiment 2), plants' tips showed depletion in nitrogen levels of ca. 60‰ in stem sections vulnerable to grazing. In addition, nitrogen uptake by grazed and grazing‐prone upper plant parts was reduced and nutrient allocation into the relatively secure lower parts increased. The results point to three conclusions: (1) exposure to an insect herbivore induces a similar response in immature M. spicatum as previously observed in mature terrestrial species, namely a rapid (within 48 h) reduction in the nutritional value (N%) of vulnerable tissues, (2) high grazing intensity (100% of growing tips affected) did not limit the ability of young plants to induce resistance; and (3) young plants exposed to herbivory exhibit different patterns of nutrient allocation in vulnerable and secure tissues. These results provide evidence of induced defense and resource reallocation in immature aquatic macrophytes which is in line with the responses shown for mature aquatic macrophytes and terrestrial plants.     

Contribution of organic anion transporting polypeptide OATP2B1 to amiodarone accumulation in lung epithelial cells

The accumulation mechanisms of amiodarone (AMD) involving transporters in lung alveolar epithelial type II cells were studied. The uptake of AMD was examined using human alveolar epithelial-derived cell line A549 as a model. AMD was transported by the carrier-mediated system, and the apparent K_m and V_max values were 66.8 ± 30.3 μM and 49.7 ± 9.7 nmol/mg protein/5 min, respectively. The uptake of AMD by A549 cells was Na⁺-independent and was inhibited by substrates of human organic anion transporting polypeptide (OATP). The inhibition profiles were similar to the inhibitory effects of several compounds on OATP2B1-mediated E-3-S transport, and RT-PCR analysis showed mRNA expression of OATP2B1 and 1B3 in A549 cells. SiRNAs targeted to the OATP2B1 gene decreased the OATP2B1 mRNA expression level in A549 cells up to about 50% and reduced the uptake of AMD up to about 40%. These results indicate that AMD uptake mediated by carriers, including OATP2B1, might lead to accumulation of AMD in the lung and AMD-induced pulmonary toxicity (AIPT).     

Telomere length determined by the fluorescence in situ hybridisation distinguishes malignant and benign cells in cytological specimens

Background

Telomeres are tandem repeats of TTAGGG at the end of eukaryotic chromosomes that play a key role in preventing chromosomal instability. The aim of the present study is to determine telomere length using fluorescence in situ hybridisation (FISH) on cytological specimens.

Methods

Aspiration samples (n = 41) were smeared on glass slides and used for FISH.

Results

Telomere signal intensity was significantly lower in positive cases (cases with malignancy, n = 25) as compared to negative cases (cases without malignancy, n = 16), and the same was observed for centromere intensity. The difference in DAPI intensity was not statistically significant. The ratio of telomere to centromere intensity did not show a significant difference between positive and negative cases. There was no statistical difference in the signal intensities of aspiration samples from ascites or pleural effusion (n = 23) and endoscopic ultrasound‐guided FNA samples from the pancreas (n = 18).

Conclusions

The present study revealed that telomere length can be used as an indicator to distinguish malignant and benign cells in cytological specimens. This novel approach may help improve diagnosis for cancer patients.     

The 24 hour recovery kinetics from n starvation in Phaeodactylum tricornutum and Emiliania huxleyi

The response of N (nitrate) starved cells of the diatom Phaeodactylum tricornutum and the coccolithophore Emiliania huxleyi to a pulse of new N were measured to investigate rapid cellular and photosynthetic recovery kinetics. The changes of multiple parameters were followed over 24 h. In P. tricornutum, the recovery of F_v/F_m (the maximum quantum yield of PS II) and σ_PSII (the functional absorption cross‐section for PSII) started within the first hour, much earlier than other parameters. Cellular pigments did not recover during the 24 h but the chlorophyll (chl) a/carotenoid ratios increased to levels measured in the controls. Cell division was independent of the recovery of chl a. In E. huxleyi, the recovery of F_v/F_m and σ_PSII started after an hour, synchronous with the increase in cellular organic N and chl a with pigments fully recovered within 14 h. P. tricornutum prioritized the recovery of its photosynthetic functions and cell divisions while E. huxleyi did not follow this pattern. We hypothesize that the different recovery strategies between the two species allow P. tricornutum to be more competitive when N pulses are introduced into N‐limited water while E. huxleyi is adapted to N scarce waters where such pulses are infrequent. These findings are consistent with successional patterns observed in coastal environments. This is one of only a few studies exploring recovery kinetics of cellular functions and photosynthesis after nitrogen stress in phytoplankton. Our results can be used to enhance ecological models linking phytoplankton traits to species diversity and community structure.     

Hydrosols evaluation in pest control: insecticidal and settling inhibition potential against Myzus persicae (Sulzer)

The hydrosols are by‐products derived during the extraction of essential oils. Although essential oils have been widely evaluated for their insecticidal activities, the possible use of hydrosols in pest control has been almost unknown. The effects of the hydrosols of Origanum majorana (marjoram), Mentha pulegium (pennyroyal), and Melissa officinalis (lemon balm) on the survival and settling behaviour of the aphid pest Myzus persicae were investigated. The hydrosols were isolated using Clevenger hydrodistillation (i) with conventional heating (HD) and (ii) assisted by microwaves (MWHD). GC‐MS analysis showed that the volatiles occurring in the hydrosols were similar between the two techniques. Hydrosols were assayed for possible settling inhibitory effects on M. persicae in Petri dishes (15 cm diameter). In each dish, a sprayed together with an unsprayed eggplant leaf piece was placed. An adult aphid <24 h old was released on the treated leaf and its path length was recorded during the initial 10 min. Then, its position (on the treated or untreated leaf) was recorded 10, 20, 30, 60 min and 24 h after spraying. M. officinalis HD hydrosol resulted in fourfold increase of the path length compared with the control (deionized water). The last observation (24 h) revealed that M. officinalis and M. pulegium HD hydrosols had the strongest inhibitory effect. Additionally, O. majorana hydrosols caused 10–15% aphid mortality after 24 h. In this study, the wider use of the MWHD technique is further supported as in addition to its well‐known advantages (i.e. shorter distillation time, less energy consumption), the effects of the hydrosols produced are comparable to those obtained by HD. Most importantly, the results clearly showed that the potential of hydrosols in pest control ought not to be ignored and should attract the interest of future studies.     

Activation of Systemic Resistance to Magnaporthe oryzae in Rice by Substances Produced by Fusarium solani Isolated from Soil

Of 70 micro‐organisms (fungi, bacteria and actinomycetes) isolated from soil using vegetable tissue baits, 16 produced substances in culture fluids capable of preventing the development of blast caused by Magnaporthe oryzae on rice leaves with little or no inhibitory effect on the conidial germination of the pathogen. Isolate KS‐F14, which secreted substances capable of activating resistance in untreated leaves, was selected and identified as Fusarium solani. The resistance‐inducing substances were effective at pH values ranging from 5 to 10 and were stable under high temperatures, maintaining approximately the same level of activity even after autoclaving for 20 min. After application, the activated resistance in rice leaves persisted for 14 days. The polar solvent extracts of freeze‐dried KS‐F14 secretions were effective in activating resistance against M. oryzae in rice plants. The non‐polar solvent extracts were also effective, albeit not as effective as the polar solvent extracts, indicating that although the majority of the secreted resistance‐inducing compounds are hydrophilic, some of the compounds are hydrophobic. Treating secretions with cation or anion exchange resins only partially reduced their resistance‐inducing ability, suggesting that the resistance‐inducing components include both charged and non‐charged compounds. The resistance‐inducing compounds produced by F. solani have the potential to be developed into a commercial product for the control of rice blast and possibly other plant diseases.     

Comparing constitutive and induced costs of symbiont‐conferred resistance to parasitoids in aphids

Host defenses against parasites do not come for free. The evolution of increased resistance can be constrained by constitutive costs associated with possessing defense mechanisms, and by induced costs of deploying them. These two types of costs are typically considered with respect to resistance as a genetically determined trait, but they may also apply to resistance provided by ‘helpers’ such as bacterial endosymbionts. We investigated the costs of symbiont‐conferred resistance in the black bean aphid, Aphis fabae (Scopoli), which receives strong protection against the parasitoid Lysiphlebus fabarum from the defensive endosymbiont Hamiltonella defensa. Aphids infected with H. defensa were almost ten times more resistant to L. fabarum than genetically identical aphids without this symbiont, but in the absence of parasitoids, they had strongly reduced lifespans, resulting in lower lifetime reproduction. This is evidence for a substantial constitutive cost of harboring H. defensa. We did not observe any induced cost of symbiont‐conferred resistance. On the contrary, symbiont‐protected aphids that resisted a parasitoid attack enjoyed increased longevity and lifetime reproduction compared with unattacked controls, whereas unprotected aphids suffered a reduction of longevity and reproduction after resisting an attack. This surprising result suggests that by focusing exclusively on the protection, we might underestimate the selective advantage of infection with H. defensa in the presence of parasitoids.     

Grapevine VpPR10.1 functions in resistance to Plasmopara viticola through triggering a cell death‐like defence response by interacting with VpVDAC3

As one of the most serious diseases in grape, downy mildew caused by Plasmopara viticola is a worldwide grape disease. Much effort has been focused on improving susceptible grapevine resistance, and wild resistant grapevine species are important for germplasm improvement of commercial cultivars. Using yeast two‐hybrid screen followed by a series of immunoprecipitation experiments, we identified voltage‐dependent anion channel 3 (VDAC3) protein from Vitis piasezkii ‘Liuba‐8’ as an interacting partner of VpPR10.1 cloned from Vitis pseudoreticulata ‘Baihe‐35‐1’, which is an important germplasm for its resistance to a range of pathogens. Co‐expression of VpPR10.1/VpVDAC3 induced cell death in Nicotiana benthamiana, which accompanied by ROS accumulation. VpPR10.1 transgenic grapevine line showed resistance to P. viticola. We conclude that the VpPR10.1/VpVDAC3 complex is responsible for cell death‐mediated defence response to P. viticola in grapevine.     

Effect of UV‐C Radiation on Resistance of Romaine Lettuce (Lactuca sativa L.) Against Botrytis cinerea and Sclerotinia minor

The aim of this research was to examine the effect of UV‐C on resistance of lettuce to Botrytis cinerea and Sclerotinia minor. Analysis of the lesion surfaces showed that plants exposed to UV‐C were less susceptible to the two pathogens, especially on the fourth day after inoculation. Chlorophyll, carotenoid contents and malondialdehyde and hydrogen peroxide were assayed after 1 day and 4 days. Lettuces treated with UV‐C and inoculated showed an increase in chlorophyll and carotenoid content, especially 24 h after inoculation, and low values of the two indicators of oxidative stress as compared with lettuces which were inoculated but did not receive UV‐C treatment.     

Variation in abundance of predicted resistance genes in the Brassica oleracea pangenome

Brassica oleracea is an important agricultural species encompassing many vegetable crops including cabbage, cauliflower, broccoli and kale; however, it can be susceptible to a variety of fungal diseases such as clubroot, blackleg, leaf spot and downy mildew. Resistance to these diseases is meditated by specific disease resistance genes analogs (RGAs) which are differently distributed across B. oleracea lines. The sequenced reference cultivar does not contain all B. oleracea genes due to gene presence/absence variation between individuals, which makes it necessary to search for RGA candidates in the B. oleracea pangenome. Here we present a comparative analysis of RGA candidates in the pangenome of B. oleracea. We show that the presence of RGA candidates differs between lines and suggests that in B. oleracea, SNPs and presence/absence variation drive RGA diversity using separate mechanisms. We identified 59 RGA candidates linked to Sclerotinia, clubroot, and Fusarium wilt resistance QTL, and these findings have implications for crop breeding in B. oleracea, which may also be applicable in other crops species.     

Interaction of Anthonomus grandis and cotton genotypes: biological and behavioral responses

The boll weevil, Anthonomus grandisBoheman (Coleoptera: Curculionidae), is a key pest of cotton, Gossypium hirsutumL. (Malvaceae). Knowledge about boll weevil feeding and oviposition behavior and its response to plant volatiles can underpin our understanding of host plant resistance, and contribute to improved monitoring and mass capture of this pest. Boll weevil oviposition preference and immature development in four cotton genotypes (CNPA TB90, TB85, TB15, and BRS Rubi) were investigated in the laboratory and greenhouse. Volatile organic compounds (VOCs) produced by TB90 and Rubi genotypes were obtained from herbivore‐damaged and undamaged control plants at two phenological stages – vegetative (prior to squaring) and reproductive (during squaring) – and four collection times – 24, 48, 72, and 96 h following herbivore damage. The boll weevil exhibited similar feeding and oviposition behavior across the four tested cotton genotypes. The chemical profiles of herbivore‐damaged plants of both genotypes across the two phenological stages were qualitatively similar, but differed in the amount of volatiles produced. Boll weevil response to VOC extracts was studied using a Y‐tube olfactometer. The boll weevil exhibited similar feeding and oviposition behavior at the four tested cotton genotypes, although delayed development and production of smaller adults was found when fed TB85. The chemical profile of herbivore‐damaged plants of both genotypes at the two phenological stages and time periods (24–96 h) was similar qualitatively, with 30 identified compounds, but differed in the amount of volatiles produced. Additionally, boll weevil olfactory response was positive to herbivory‐induced volatiles. The results help to understand the interaction between A. grandis and cotton plants, and why it is difficult to obtain cotton genotypes possessing constitutive resistance to this pest.     

Role of ethylene and related gene expression in the interaction between strawberry plants and the plant growth‐promoting bacterium Azospirillum brasilense

• Induced systemic resistance (ISR) is one of the indirect mechanisms of growth promotion exerted by plant growth‐promoting bacteria, and can be mediated by ethylene (ET). We assessed ET production and the expression of related genes in the Azospirillum–strawberry plant interaction.
• Ethylene production was evaluated by gas chromatography in plants inoculated or not with A. brasilense REC3. Also, plants were treated with AgNO₃, an inhibitor of ET biosynthesis; with 1‐aminocyclopropane‐1‐carboxylic acid (ACC), a precursor of ET biosynthesis; and with indole acetic acid (IAA). Plant dry biomass and the growth index were determined to assess the growth‐promoting effect of A. brasilense REC3 in strawberry plants. Quantitative real time PCR (qRT‐PCR) was performed to analyse relative expression of the genes Faetr1, Faers1 and Faein4, which encode ET receptors; Factr1 and Faein2, involved in the ET signalling pathway; Faacs1 encoding ACC synthase; Faaco1 encoding ACC oxidase; and Faaux1 and Faami1 for IAA synthesis enzymes.
• Results showed that ET acts as a rapid and transient signal in the first 12 h post‐treatment. A. brasilense REC3‐inoculated plants had a significantly higher growth index compared to control plants. Modulation of the genes Faetr1, Faers1, Faein4, Factr1, Faein2 and Faaco1 indicated activation of ET synthesis and signalling pathways. The up‐regulation of Faaux1 and Faami1 involved in IAA synthesis suggested that inoculation with A. brasilense REC3 induces production of this auxin, modulating ET signalling.
• Ethylene production and up‐regulation of genes associated with ET signalling in strawberry plants inoculated with A. brasilense REC3 support the priming activation characteristic of ISR. This type of resistance and the activation of systemic acquired resistance previously observed in this interaction indicate that both are present in strawberry plants, could act synergistically and increase protection against pathogens.

     

HIF prolyl hydroxylase inhibition prior to transient focal cerebral ischaemia is neuroprotective in mice

This study investigated the effects of 2‐(1‐chloro‐4‐hydroxyisoquinoline‐3‐carboxamido) acetic acid (IOX3), a selective small molecule inhibitor of hypoxia‐inducible factor (HIF) prolyl hydroxylases, on mouse brains subject to transient focal cerebral ischaemia. Male, 8‐ to 12‐week‐old C57/B6 mice were subjected to 45 min of middle cerebral artery occlusion (MCAO) either immediately or 24 h after receiving IOX3. Mice receiving IOX3 at 20 mg/kg 24 h prior to the MCAO had better neuroscores and smaller blood–brain barrier (BBB) disruption and infarct volumes than mice receiving the vehicle, whereas those having IOX3 at 60 mg/kg showed no significant changes. IOX3 treatment immediately before MCAO was not neuroprotective. IOX3 up‐regulated HIF‐1α, and increased EPO expression in mouse brains. In an in vitro BBB model (RBE4 cell line), IOX3 up‐regulated HIF‐1α and delocalized ZO‐1. Pre‐treating IOX3 on RBE4 cells 24 h before oxygen–glucose deprivation had a protective effect on endothelial barrier preservation with ZO‐1 being better localized, while immediate IOX3 treatment did not. Our study suggests that HIF stabilization with IOX3 before cerebral ischaemia is neuroprotective partially because of BBB protection, while immediate application could be detrimental. These results provide information for studies aimed at the therapeutic activation of HIF pathway for neurovascular protection from cerebral ischaemia.

     

Repair of ochratoxin A-induced DNA damage and modulation of OTA-related genotoxicity by co-incubation with bile acids and methotrexatein vitro

The mycotoxin ochratoxin A (OTA) induced DNA strand breaks in porcine urinary bladder epithelial cells (PUBEC) and in Madin Darby canine kidney (MDCK) cells. A co-incubation with bile acids or methotrexate reduced or even prevented this adverse effect of OTAin vitro. The protective effect is possibly attributable to a decreased OTA uptake in cells, since bile acids and methotrexate are known to share common transport systems such as organic anion transporters (OAT) and/or organic anion transporting polypeptides (OATP) with the mycotoxin. OTA uptake in cells and its modulation can be one factor which determines the extent of adverse effects in different cell types. Another aspect of interest in this regard relates to repair of DNA damage: PUBEC cells are sensitive to OTA-induced damage which is more pronounced when DNA repair is blocked (by cytosine β-D-arabino-furanosid/hydroxyurea). On the other hand, when cells are kept in fresh (toxin-free) medium for 3 h, OTA-induced DNA damage decreased to control levels. Presented at the 26^th Mykotoxin-Workshop in Herrsching, Germany, May 17–19, 2004     

Hepatic uptake of bilirubin and its conjugates by the human organic anion transporter SLC21A6

Bilirubin, the end product of heme catabolism, is taken up from the blood circulation into the liver. This work identifies a high-affinity transport protein mediating the uptake of bilirubin and its conjugates into human hepatocytes. Human embryonic kidney cells (HEK293) permanently expressing the recombinant organic anion-transporting polypeptide 2 (human OATP2, also known as LST-1 or OATP-C; symbol SLC21A6) showed uptake of [(3)H]monoglucuronosyl bilirubin, [(3)H]bisglucuronosyl bilirubin, and [(3)H]sulfobromophthalein with K(m) values of 0.10, 0.28, and 0.14 microm, respectively. High-affinity uptake of unconjugated [(3)H]bilirubin by OATP2 occurred in the presence of albumin and was not mediated by another basolateral hepatic uptake transporter, human OATP8 (symbol SLC21A8). OATP2 and OATP8 differed by their capacity to extract substrates from albumin before transport. In comparison to the high-affinity transport by OATP2, OATP8 transported [(3)H]sulfobromophthalein and [(3)H]monoglucuronosyl bilirubin with lower affinity, with K(m) values of 3.3 and 0.5 microm, respectively. The organic anion indocyanine green potently inhibited transport mediated by OATP2, with a K(i) value of 112 nm, but did not inhibit transport mediated by OATP8. Human OATP2 may play a key role in the prevention of hyperbilirubinemia by facilitating the selective entry of unconjugated bilirubin and its glucuronate conjugates into human hepatocytes.     

Red‐Light‐Induced Resistance to Brown Spot Disease Caused by Bipolaris oryzae in Rice

In this study, the protective effect of red light against the brown spot disease caused by the fungus Bipolaris oryzae in rice was investigated. Lesion formation was significantly inhibited on detached leaves that were inoculated with B. oryzae and kept under red for 48 h, but it was not inhibited when the leaves were kept under natural light or in the dark. The protective effect was also observed in intact rice plants inoculated with B. oryzae; the plants survived under red light, but most of them were killed by infection under natural light or dark condition. Red light did not affect fungal infection in onion epidermis cells or heat‐shocked leaves of rice, and it did not affect cellulose digestion ability; this suggested that the protective effect is due to red‐light‐induced resistance. In addition, the degree of protection increased as the red light dosage increased, regardless of the order of the red light and natural light period, indicating that red‐light‐induced resistance is time dependent. Feeding of detached leaves with a tryptophan decarboxylase inhibitor, s‐α‐fluoromethyltryptophan (0.1 mm ), for 24 h inhibited the development of resistance in response to red light irradiation. Suppression of resistance was also observed in leaves treated with a phenylalanine ammonia‐lyase inhibitor, α‐aminooxy acetic acid (0.5 mm ). These results suggest that the tryptophan and phenylpropanoid pathways are involved in the red‐light‐induced resistance of rice to B. oryzae.