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A cDNA clone derived from a novel gene (uvi-1) that is inducible by near-UV light was isolated by a differential screening procedure from a cDNA library of the fungus Bipolaris oryzae and characterized further. Sequence analysis of the clone revealed that uvi-1 encodes a protein with a putative molecular mass of 17 kDa; the UVI-1 protein shows significant similarity to a putative protein encoded by a cDNA which is expressed during appressorium formation in the rice blast fungus, Magnaporthe grisea. The corresponding genomic clone was also isolated, and Southern analysis of genomic DNA indicated the presence of a single copy of the uvi-1 gene in B. oryzae. Northern analysis showed that the uvi-1 transcripts are induced by exposure to near-UV light, but not by blue or red light. Furthermore, accumulation of uvi-1 transcripts is observed during differentiation of the appressorium.

The effects of supplementary UV-B radiation (290-320 nm, +UV-B) on the development of wilt disease of spinach (Spinacia oleracea) caused by the fungus Fusarium oxysporum f. sp. spinaciae were investigated under natural light condition in a glasshouse. The disease incidence in these plants greatly increased at low inoculum concentrations in soil inoculation experiments compared with plants without UV-B supplementation (-UV-B). In needle inoculation experiments with F. oxysporum f. sp. spinaciae, wilt occurred in plants under +UV-B as severely as in soil inoculation experiments. F. oxysporum f. sp. spinaciae was isolated from the roots of all wilted plants, as well as some symptomless plants in both soil inoculation and needle inoculation experiments. Re-isolation frequency under +UV-B was ca. 3.5 times higher than that of plants under -UV-B during the first three days of growth under UV-B supplementation. However, the re-isolation frequency in inoculated plants in both experiments irrespective of UV-B supplementation was over 80% by the end of both experiments. The results indicated that supplementary UV-B radiation incited disease development.

The effects of UV-B radiation (290–320 nm) on development of damping-off of spinach (Spinacia oleracea) caused by the fungusFusarium oxysporum were examined in a growth cabinet. The incidence of disease greatly increased when experimental plants were grown in visible radiation with supplementary UV-B radiation. This increase was suppressed by increasing the irradiation of visible radiation.Fusarium oxysporum was isolated from the roots of all damping-off plants and the roots of some unwilted plants, indicating that spinach infected with the pathogen did not necessarily suffer from damping-off in 15d. Supplementary UV-B radiation suppressed the increase in growth components such as the number of leaves, the plant height and the fresh weight of aboveground plant parts, but did not affect the fresh weight of roots. The ratio of the number of plants infected with pathogen to the total number of plants was over 80% irrespective of light conditions. It was suggested that the defense response of spinach to this pathogen was greatly influenced by the physiological state of aboveground plant parts resulting from supplementary UV-B radiation.

Two types of fungi based on the light required for induction of conidiophore formation are known as ‘photo-induced’ and ‘non-photo-induced’ sporulators. Conidial development in a ‘photo-induced’ strain of Bipolaris oryzae (formerly, Helminthosporium oryzae) is controlled by antagonistic action of blue and near-UV radiation mediated through the ‘mycochrome’ system at two developmental stages: conidiophore induction and conidiophore maturation. Otherwise, conidial development in a ‘non-photo-induced’ strain of B. oryzae, unlike that in the ‘photo-induced’ strain, is controlled by antagonistic action of blue and near-UV radiation at the conidiophore maturation stage alone. In this study, we collected fungi, B. oryzae, from brown lesion spots on rice leaves cultivated in paddy fields, and investigated the possible existence of a new ecotype different from known ‘photo-induced’ and ‘non-photo-induced’ sporulators. We also investigated the sensitivity of conidial development of each isolate to blue and near-UV radiation. The isolates were identified as B. oryzae by morphology of hyphae and conidia and the symptomatic brown lesion spots on rice leaves caused by each isolate. There was no distinction between ‘photo-induced’ and ‘non-photo-induced’ strains on rDNA base. Moreover, the existence of a new type of ‘non-photo-induced’ sporulator different from the one presently known was confirmed. In this newly identified sporulator, conidial development was not affected by light irradiation. Among 153 isolates, one isolate belonged to a previously known ‘non-photo-induced’ sporulator, five isolates belonged to a new ‘non-photo-induced’ sporulator ecotype, and over 95% of the isolates were “photo-induced” sporulators. Among ‘photo-induced’ strains, there were several subtypes having different sensitivities to near-UV radiation required for inducing conidiophore formation.

Flowering response and plant form of photomorphogenic mutants (hy1, hy2, hy3, hy4 and hy5) of Arabidopsis thaliana (L.), a long-day plant, were examined in long and short days. There were only slight differences among genotypes including Landsberg wild type with respect to the flowering time under long days. The effect of 1 h light-(night)-breaks of far-red, red, blue and white light given in the middle of the dark period of plants grown under short days, was studied. Effects of far-red light applied at the end or the beginning of the main photoperiod on flowering and plant form were also examined. The light-breaks with all the above mentioned light qualities promoted floral initiation of all the genotypes including the wild type in terms of both the flowering time and the number of rosette leaves. In general, far-red light was most effective. It is possible to classify the hy-mutants into 3 groups by their responses to light-breaks under short day conditions: (a) Mutants hy2 and hy3, which have a reduced number of rosette leaves, and flower early. Red light is as effective as far-red light. The wavelength of light-breaks is relatively unimportant for flowering response. (b) Mutants hy4, hy5 and Landsberg wild type, which have a greater number of rosette leaves, and flower relatively late. The effectiveness of light-breaks is in the following order, far-red, blue, and red light, which is in reverse order to the transformation of phytochrome to the Pfr form. (c) Mutant hy1, which behaves anomalously with respect to relations between flowering time and number of rosette leaves; late flowering with reduced number of rosette leaves. Red, blue and far-red light are effective, but white light is ineffective for reducing the number of rosette leaves. When far-red light was given in the middle of the night or at the end of the main photoperiod, it markedly reduced the number of rosette leaves compared to those grown under short days for all the genotypes, while when applied at the beginning of the main photoperiod far-red light did not affect the number of rosette leaves. Different effects on the plant form dependent on the time of treatment with far-red light-breaks are also discussed.

The inheritance of light dependence for conidial development inBipolaris oryzae was analyzed using single-ascospore isolates. When a photo-induced strain was crossed with another photo-induced strain, only photo-induced progeny were produced. When a photo-induced strain was crossed with a non-photo-induced (I) strain, photo-induced and nonphoto-induced (I) progeny were produced in a ratio of 1∶1. However, when a photo-induced strain was crossed with a non-photo-induced (II) strain, a non-photo-induced (I) progeny were formed in addition to parental types. It was suggested that genes for photo-control of conidiophore induction and genes for photo-control of conidiophore maturation are located on the same chromosome.

There is a cultivar difference in the response to ultraviolet-B (UVB: 280-320 nm) in rice (Oryza sativa L.). Among Japanese lowland rice cultivars, Sasanishiki, a leading Japanese rice cultivar, is resistant to the damaging effects of UVB while Norin 1, a close relative, is less resistant. We found previously that Norin 1 was deficient in cyclobutane pyrimidine dimer (CPD) photorepair ability and suggested that the UVB sensitivity in rice depends largely on CPD photorepair ability. In order to verify that suggestion, we examined the correlation between UVB sensitivity and CPD photolyase activity in 17 rice cultivars of progenitors and relatives in breeding of UV-resistant Sasanishiki and UV-sensitive Norin 1. The amino acid at position 126 of the deduced amino acid sequence of CPD photolyase in cultivars including such as Norin 1 was found to be arginine, the CPD photolyase activities of which were lower. The amino acid at that position in cultivars including such as Sasanishiki was glutamine. Furthermore, cultivars more resistant to UVB were found to exhibit higher photolyase activities than less resistant cultivars. These results emphasize that single amino acid alteration from glutamine to arginine leads to a deficit of CPD photolyase activity and that CPD photolyase activity is one of the main factors determining UVB sensitivity in rice.

Among Indica rice cultivars (Oryza sativa L. cvs.) that belong to the aus ecotype from the tropical Bengal region, where the amount of ultraviolet-B (UV-B) radiation in the solar radiation is relatively great, Marich-bati cultivar has exhibited resistance to UV-B radiation, while Surjamkhi cultivar appeared to be less resistant. We have examined the susceptibility to cyclobutane pyrimidine dimer (CPD) induction by UV-B radiation and the ability to photorepair CPDs using these two cultivars. UV-B radiation produced similar dimer levels in the leaves of the two cultivars. In contrast, the ability to photorepair CPDs in the UV-sensitive Surjamkhi cultivar was lower than that in the UV-resistant Marich-bati cultivar. These results were similar to our previous data, namely, that a UV-sensitive Japanese rice cultivar (Oryza sativa L. cv. Norin 1) cultivated in the moderate climate of Japan is deficient in its ability to photorepair CPDs. Thus, these results suggest that a strong correlation exists between the sensitivity to UV-B and the photorepair deficiency, and that a low ability in CPD photorepair may be a principal factor in determining the UV-B sensitivity in rice plants.

Verticillium agaricinum (Link) Corda, grown in a yeast extract-sucrose medium, conidiated abundantly in darkness after irradiation with near ultraviolet (290–400 nm) for 15 min or blue light (400–550 nm) for 60 min. Few conidia were formed in total darkness. Exposure to 30 min of near ultraviolet light suppressed conidiation. Conidiation was also suppressed by phosphate in excess of 10−4M irrespective of light condition. After irradiation with near ultraviolet light for more than 30 min, there was a cessation of growth and a change in colony color from yellow to reddish. The color does not appear to be due to a carotenoid because the colonies turned from red to yellow when covered with acid. At pH lower than 6.0 the pigment has an absorption maximum around 390 nm, whereas at higher pH it is around 540 nm. Thus, it appears that irradiation of V. agaricinum with near ultraviolet may cause an increase in pH, which in turn produces the change of colony color from yellow to reddish.

Coniditation the fungus, Alternaria cichorii Nattras (IMI 225641), was repeatedly induced and inhibited by alternating doses of near ultraviolet and blue radiation. The final response largely depended on the last kind of radiation administered. When the final radiation was near ultraviolet, conidiophore formation was induced, and conidia were then produced in the subsequent dark period; when it was blue, the induction of conidiation was suppressed. The inductive effect of near ultraviolet was promoted by anaerobiosis, but the reversing effect by blue radiation was not influenced by molecular oxygen. Thus, the “mycochrome” system apprears to control induction of conidiation in Alternaria cichorii, and oxidation-reduction processes may be involved in its function.

Photosporulation of Alternaria tomato was very little influenced by polyoxin at concentrations below 10 μg/ml, although hyphae and conidia were morphologically affected. The hyphae grown in the presence of polyoxin were easily disrupted.

Lemna paucicostata Hegelm. T-101, a short-day plant, flowers when plants preirradiated with red light (R) for 24 h are subjected to inductive darkness for 72 h followed by two short-day cycles (6 h R+ 18 h dark). However, flowering is inhibited by blue-or far-red-light pulses applied at the beginning of the inductive dark period. These inhibitory light effects are fully reversible by a R pulse. The action spectra for the inhibitory light effect and for its reversal show that the light pulses act exclusively through phytochrome. It is concluded that a low level of Pfr at the beginning of the inductive dark period prevents flowering.

A photoreceptor system, “mycochrome”, is involved in a blue and near UV reversible photo-reaction which in turn plays an important role in the photocontrol of conidial development in Alternaria tomato, Botrytis cinerea and Helminthosporium oryzae. Conidial development was controlled by alternating exposures to blue and near UV light with the final response being determined by the final light received. When the final light was near UV a conidium developed; when it was blue, conidiation was inhibited and a “sterile” conidiophore was formed. The effects of the two lights were alternatively reversible. Blue and near UV reversible photoreaction was also found in a light-minus-dark difference spectrum of an intracellular particulate fraction isolated from dark-grown mycelia of A. tomato, and two pigments, PB (blue absorbing type) and PNUV (near UV absorbing type), were contained in that photoreaction. PB was tightly bound to the particulate fraction and PNUV was either soluble in the cytoplasm or very loosely bound to the particulate fraction. Blue and near UV reversible photoreaction occurred only under the coexistence of PB and PNUV. That is, a dip in the near UV region and peak absorbance in the blue region was induced by irradiation with near UV light; however, both conditions were partially dissipated with a subsequent irradiation of blue light. These absorbance changes were revers-ibly repeated by alternating doses of blue and near UV light. When molecular oxygen was introduced after exposure to near UV light, peak absorbance in the blue region rapidly disappeared, and these absorbance changes were repeatedly reversible. Similar results were obtained by treatment with sodium hydrosulfite and molecular oxygen. Thus, it was concluded that the mycochrome system suggested in photo-conidiation was consistent with certain active substances showing blue and near UV reversible absorbance changes and caused by photooxidation reduction reaction.

In the sporulation of Alternaria tomato, conidiophores are induced by near ultraviolet irradiation but not by darkness, and the conidia develop only when the irradiation is followed by a period of darkness. Conidial development is suppressed by a short exposure to blue light at a definite time during the dark period following the inductive irradiation. The suppression of conidial development by blue light can be reversed by exposure to near ultraviolet light immediately following the blue light irradiation. This reversion is reversibly suppressed by a further exposure to blue light immediately following near ultraviolet irradiation. Thus, at least two stages are involved in the sporulation of A. tomato, the first being a photochemical stage necessary for the induction of conidiophores, and the second essential for the conidial development which proceeds only in the absence of exposure to the blue region of the spectrum. Moreover, conidial development can be controlled by alternating doses of blue and near ultraviolet light, and the subsequent response depends upon the last kind of radiation given. It is concluded that a new pigment system, which we have named “Mycochrome”, is involved in the blue and near ultraviolet reversible photoreaction, and that this compound plays an important role in the photocontrol of conidial development in this fungus.

The effect of light on conidial development of a nonphotoinduced isolate of Helminthosporium oryzae was investigated. Near-ultraviolet light was not required for conidiophore induction, but conidial development was suppressed by blue light applied at a definite stage of conidiophore development, and the conidiophores were dedifferentiated into longer, slender aerial hyphae. Furthermore, the effect of blue light could be reversed by immediate exposure to near-ultraviolet light and the effects of these two spectral regions were alternatively reversible.Thus, it is concluded that a photosensitive system, called mycochrome, is involved in the conidial development of this fungus.

SUMMARY: The effect of the blue and near ultraviolet reversible photoreaction on conidial development in Botrytis cinerea was studied by observing microscopically selected conidiophores. Conidiophore development was divided into six stages: when the developing conidiophores from stage 2 (i.e. a mature conidiophore) to stage 5 (i.e. a conidiophore with conidium initial) were exposed to blue light for a short time, conidiation was suppressed; the conidiophores already formed de-differentiated to ‘sterile’ conidiophores with sharply pointed tips. The suppression of conidial development by blue light could be reversed by subsequent exposure to near ultraviolet light, and conidia then developed normally. This mycochrome system functioned reciprocally within the range of identified conidiophore developmental stages and near ultraviolet light acted only at the same developmental stage as was inhibited by blue light.

Induction of flowering of etiolated Lemna paucicostata Hegelm. T-101, a short-day plant, was inhibited by far-red (FR) or blue light (BL) applied at the beginning of a 72-h inductive dark period which was followed by two short days. In either case the inhibition was reversed by a subsequent exposure of the plants to near-ultraviolet radiation (NUV), with a peak of effectiveness near 380 nm. Inhibition by BL or FR and its reversion by NUV are repeatable, i.e., NUV is acting in these photoresponses like red light although with much lower effectiveness. Thus, it is considered that NUV acts through phytochrome and no specific BL and NUV photoreceptor is involved in photocontrol of floral induction on this plant.