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Rice cultivars vary widely in their sensitivity to ultraviolet B (UVB) and this has been correlated with cyclobutane pyrimidine dimer (CPD) photolyase mutations that alter the structure/function of this photorepair enzyme. Here, we tested whether CPD photolyase function determines the UVB sensitivity of rice (Oryza sativa) by generating transgenic rice plants bearing the CPD photolyase gene of the UV-resistant rice cultivar Sasanishiki in the sense orientation (S-B and S-C lines) or the antisense orientation (AS-D line). The S-B and S-C plants had 5.1- and 45.7-fold higher CPD photolyase activities than the wild-type, respectively, were significantly more resistant to UVB-induced growth damage, and maintained significantly lower CPD levels in their leaves during growth under elevated UVB radiation. Conversely, the AS-D plant had little photolyase activity, was severely damaged by elevated UVB radiation, and maintained higher CPD levels in its leaves during growth under UVB radiation. Notably, the S-C plant was not more resistant to UVB-induced growth inhibition than the S-B plant, even though it had much higher CPD photolyase activity. These results strongly indicate that UVB-induced CPDs are one of principal causes of UVB-induced growth inhibition in rice plants grown under supplementary UVB radiation, and that increasing CPD photolyase activity can significantly alleviate UVB-caused growth inhibition in rice. However, further protection from UVB-induced damage may require the genetic enhancement of other systems as well.

The effects of supplementary ultraviolet-B (UV-B) radiation on the changes in synthesis and degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and light-harvesting chlorophyll ...

We produced near isogenic lines (NILs) for three purple leaf genes, Pl, Plw and Pli of rice with a genetic back-ground of T-65 to characterize each allele. Three NILs each had characteristic tissue-specific anthocyanin pigmentation. T-65 Plw was newly found to make the root purple when the root was exposed to light. To explore the inducible characteristics of the three genes, we examined the responses of the three NILs to UV-B irradiation. Although the accumulation of anthocyanin increased in all NILs with the increase in the intensity of UV-B irradiation, we observed differential responses for the accumulation of anthocyanin in the NILs: T-65 Pli accumulated the largest amounts of anthocyanin under weak and intermediate intensity of UV-B, though this NIL reduced anthocyanin accumulation under a high intensity of UV-B. T-65 Pl or Plw increased anthocyanin accumulation with increasing intensity of UV-B. Anthocyanin accumulation of the Pl NIL was higher than that of the Plw NIL under each intensity of UV-B. In addition, the total biomass of all the irradiated NILs decreased with the increasing dose of UV-B irradiation and the decrease was negatively correlated with the increase in anthocyanin accumulation in the dose range of UV-B irradiation.

An investigation was made of the variations in growth and grain yield in response to increased exposure to UV-B radiation of Japanese lowland rice ( Oryza sativa L.) in a cool rice-growing region. Two cultivars, UV-resistant cv. ‘Sasanishiki’ and UV-sensitive cv. ‘Norin 1’, were examined in a lowland field at Kashimadai (37°28′E, 141°06′E) in Miyagi Prefecture, Japan, for four cropping seasons from 1994 to 1997. The two cultivars were grown in a lowland field with or without supplemental UV-B radiation, which was provided by UV-B-emitting fluorescent lamps, with a 0.1-mm-thick cellulose diacetate film as a filter. In both cultivars, significant decreases in tiller number as the result of supplemental UV-B radiation were observed during the tillering stage in 1994, 1995 and 1997. Furthermore, decreases in grain size from supplemental UV-B radiation were recorded in all seasons. The trend towards small grain size was pronounced in 1996. In that year, the mean daily middle temperatures were lower throughout most of the cropping season and the mean daily hours of sunshine during the tillering stage and between the end of the panicle differentiation stage and the beginning of the ripening stage were shorter. In 1993 when the temperature and the amount of sunshine were both lower, the tiller number, the dry mass of aboveground parts and the panicle number were significantly reduced by supplemental unfiltered UV-B radiation. There was a cultivar difference in the inhibitory effects of supplemental UV-B radiation on growth between the sensitive cultivar Norin 1 and the resistant cultivar Sasanishiki. These results indicate that supplemental UV-B radiation has a positive effect on the growth and grain development of rice, which may be enhanced by unusual climatic conditions such as lower temperature and less sunshine, in cool rice-growing regions.

We have examined the changes in the steady-state levels of cyclobutyl pyrimidine dimer (CPD) in rice plants (Oryza sativa L.) growing indoors and outdoors with or without supplemental UV-B radiation. The CPD levels remain between 3 and 6 CPD Mb−1 throughout the day in plants grown under sunlight although the levels fluctuate. The CPD levels are slightly elevated with UV-B (1 W m−2) supplementation, but remain constant (between 5 and 8 CPD Mb−1) throughout the day. In plants grown under visible radiation in a growth chamber, the CPD levels remain constant but are lower compared with those in outdoor-grown plants; they are slightly elevated by supplementation with UV-B radiation. Under exposure to UV-B radiation without visible radiation, the CPD levels gradually increase with lengthening of the irradiation time and reach a level of approximately 35 CPD Mb−1 at dusk. However, this level decreases during the night and then increases again the next day. It is thus evident that the CPD levels are strictly maintained within constant limits throughout the day in plants growing indoors and outdoors with or without supplemental UV-B radiation. It is also found that excision repair occurs during the night in plants having higher CPD levels.

— We examined the effects of a light environment during culture of rice plants (Oryza sativa) on the steady-state cyclobutyl pyrimidine dimer (CPD) level, CPD induction by challenge UVB exposure and the ability to photorepair CPD. The steady-state CPD level in plants grown under visible radiation with supplemental UVB radiation in a growth chamber was several times higher than in plants grown without supplemental UVB radiation, whereas in outdoor-grown plants, it was not enhanced by supplemental UVB radiation. The susceptibility to CPD induction by challenge UVB exposure was highest in dark-grown plants and decreased with increasing irradiance of visible radiation at low and high levels and outdoors. Chronic UVB radiation reduced the susceptibility to UV-induced CPD in plants grown both indoors and outdoors. There was a significant negative correlation between CPD levels induced by challenge UVB exposure and the content of UV-absorbing compounds. The UV-induced CPD could be reduced by subsequent blue radiation in all samples except in dark-grown seedlings. The higher the irradiance of visible radiation in the culture, the greater the ability to photorepair CPD. Chronic UVB radiation did not increase the ability to photorepair CPD.

We have examined the susceptibility to cyclobutyl pyrimidine dimer (CPD) induction by UVB radiation, the ability to photorepair cyclobutyl pyrimidine dimers (CPDs), and the levels of ultraviolet (UV)-absorbing compounds in various developing stages of leaves in UVB-resistant (Sasanishiki) and -sensitive (Norin 1) rices (Oryza sativa L.). UVB produces more CPDs in the second, third and fourth fully expanded leaves than in the fifth and sixth fully expanded leaves. In leaves in which the levels of UV-absorbing compounds are lower, more CPDs are produced. The ability to photorepair CPDs in fully expanded leaves of different stages of each cultivar remains approximately constant, although the photorepair capacity in the fourth leaf rapidly increases from leaf emergence until full expansion. The photorepair capacity is lower in Norin 1 than that in Sasanishiki in all the leaf stages or different aged leaves. These results therefore suggest that rice plants could be more susceptible to CPD induction at the stage when the second, third or fourth leaves are developing, and UVB sensitivity correlates with low CPD photorepair.

Parental cultivars (Oryza sativa L. Japanese lowland cultivars Sasanishiki and Norin 1), F2 plants, and F3 Iines were grown under visible light with or without supplemental UV-B radiation in a phytotron, to determine whether the accumulation of UV-absorbing compounds plays a role in the difference in UV-B resistance between these rice cultivars. The level of UV-absorbance per unit leaf area increased with the UV-B treatuent in all the leaves of these two rice cultivars, but was higher in Sasanishiki than in Norin 1 irrespective of UV-B treatment. An analysis by thin-layer chromatography and the UV-absorption spectra of the extracts did not show any qualitative difference in UV-absorbing compounds in leaf tissues between these two cultivars. There was a significant positive correlation between the level of UV-absorbance per unit leaf area and the fresh weight of aerial parts in the F2 plants exposed to UV-B radiation. Furthermore, the level of UV-absorbance per unit leaf area tended to be higher in the F3 Iines resistant to UV-B radiation than in those sensitive to such radiation regardless of whether these F3 lines were exposed to supplemental UV-B radiation. These results suggest that the differences in UV-B resistance between Sasanishiki and Norin 1 are associated with genetic differences in the level of accumulation of UV-B absorbing compounds in leaf tissues. Based on these results we suggest that the accumulation of UV-B absorbing compounds is an important factor contributing to UV-B resistance in rice cultivars. Since the accumulation of UV-absorbing compounds in leaves appears to minimize the latent negative impact of UV-B radiation on rice production, it may be a useful character to select in ordinary breeding.

The effects of UVB radiation on the growth of two cultivars of Japanese lowland rice {Oryza sativa L.), Sasanishiki and Norin 1, were examined in a phytotron. Supplementation of visible radiation with UVB radiation reduced plant length, tiller number, the fresh and dry weights of the aboveground parts of plants, and the amounts of total leaf nitrogen, chlorophyll, soluble protein and ribulose-l,S-bisphosphate carboxylase/oxygenase (Rubisco) in the eighth leaf, the youngest fully expanded leaf. By contrast, UVB radiation significantly increased the accumulation of UV-absorbing compounds. There was a difference between the two cultivars in the resistance to the effects of UVB radiation. The reduction in the amounts of Rubisco was smaller in Sasanishiki, while the increase in the accumulation of UV-absorbing compounds was greater in Sasanishiki. Parameters of plant growth, with the exception of the amount of Rubisco, decreased in direct proportion to decreases in total leaf nitrogen in plants grown under lower or higher doses of UVB radiation. However, the decrease in the Rubisco content of Norin 1 grown under a high dose of UVB radiation was exceptionally marked, and was not observed similarly in Sasanishiki. These results suggest that the remarkable reduction in Rubisco content in Norin 1 might have been due to the specific effects of UVB radiation. It is also suggested that the difference between cultivars in the resistance to UVB radiation might be due to the differences in the levels of Rubisco and in UV-absorbing compounds that are induced by UVB radiation.

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.

Genetic analysis of resistance to the inhibitory effects of UV radiation on growth of rice (Oryza sativa L.) cultivars was carried out. Some experimental plants were grown in visible radiation supplemented with UV radiation containing a large amount of UV-B and a small amount of UV-C in a phytotron, while others were grown without UV radiation. The degree of resistance to UV radiation was estimated in terms of the degree of reduction caused by supplemental UV radiation in the fresh weight of the aboveground plant parts and the chlorophyll content per unit fresh weight. Fresh weight and chlorophyll content in F2 plants generated by reciprocally crossing cv. Sasanishiki, a cultivar more resistant to UV radiation, and Norin 1, a cultivar less resistant to such radiation exhibited a normal frequency distribution. The heritabilities of these two properties in F2 plants were low under conditions of non-supplemental UV radiation. Under elevated UV radiation, the F2 population shifted to the lower range of fresh weight and chlorophyll content, and the means were close to those of Norin 1. The heritabilities of these two properties were the same in the reciprocal crosses, indicating that maternal inheritance was not involved. Inheritance of chlorophyll content per unit fresh weight was further determined in F3 lines generated by self-fertilizing F2 plants of Sasanishiki and Norin 1. The results showed that the F3 population was segregated into three genotypes, namely, resistant homozygotes, segregated heterozygotes and sensitive homozygotes, with a ratio of 1:65:16. It was thus evident that the resistance to the inhibitory effect of elevated UV radiation in these rice plants was controlled by recessive polygenes.

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.

Application of an inhibitor of gibberellin biosynthesis alleviated the UV-B injury in rice seedlings when tested for chlorophyll content per unit fresh and dry weight. A genetic study was conducted by crossing Tan-ginbozu, a gibberellin-deficient mutant, against two floating rice cultivars that presumably contain large amounts of endogenous gibberellins. The heritabilities of plant height, and chlorophyll content per unit fresh and dry weight were high in the F2 plants in non UV-B irradiated control populations. When those plants were treated with UV-B irradiation, the F2 population tended to shift to the lower range in the chlorophyll content per unit weight, and the value of heritability fluctuated depending on the cross and characters measured. Selection of plants that are highly resistant to UV-B irradiation can be made possible by finding the range of UV-B energy that increases the difference between sensitive and resistant, while also increasing the value of the heritability.

• Background Depletion of the stratospheric ozone layer leads to an increase in ultraviolet-B (UVB: 280–320 nm) radiation reaching the earth's surface, and the enhanced solar UVB radiation predicted by atmospheric models will result in reduction of growth and yield of crops in the future. Over the last two decades, extensive studies of the physiological, biochemical and morphological effects of UVB in plants, as well as the mechanisms of UVB resistance, have been carried out. • Scope In this review, we describe recent research into the mechanisms of UVB resistance in higher plants, with an emphasis on rice (Oryza sativa), one of the world's most important staple food crops. Recent studies have brought to light the following remarkable findings. UV-absorbing compounds accumulating in the epidermal cell layers have traditionally been considered to function as UV filters, and to play an important role in countering the damaging effects of UVB radiation. Although these compounds are effective in reducing cyclobutane pyrimidine dimer (CPD) induction in plants exposed to a challenge exposure to UVB, certain levels of CPD are maintained constitutively in light conditions containing UVB, regardless of the quantity or presence of visible light. These findings imply that the systems for repairing DNA damage and scavenging reactive oxygen species (ROS) are essential for plants to grow in light conditions containing UVB. • Conclusion CPD photolyase activity is a crucial factor determining the differences in UVB sensitivity between rice cultivars. The substitution of one or two bases in the CPD photolyase gene can alter the activity of the enzyme, and the associated resistance of the plant to UVB radiation. These findings open up the possibility, in the near future, of increasing the resistance of rice to UVB radiation, by selective breeding or bioengineering of the genes encoding CPD photolyase.

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.

— When dark-grown colonies were exposed to near-UV light, conidiophore formation was induced, and conidia developed during a subsequent dark period. Simultaneous exposure to near-UV and blue light inhibited induction of conidiation. The inductive effect of near-UV light irradiation was greatly enhanced by treating colonies with low temperatures for 4 h during the 2nd-6th hour of incubation in the dark following inductive irradiation: the enhancement was greatest at 21°C. The extent of inhibition by blue light increased with the temperature between 10 and 28°C. This diminution by low temperature was greatest when colonies previously kept at a low temperature were exposed to inductive irradiation: the longer the duration between inductive irradiation and temperature treatment, the lower the diminution. Higher fluences of blue light were required to suppress conidial induction at lower temperature. Thus, it is evident that the inductive effect of near-UV light irradiation on conidiation and the suppressive effect of blue light irradiation are each responsive to different temperatures applied at different times.

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.

Conidiophore formation in Helminthosporium oryzae V. Breda de Haan (ATCC 38851) was induced by near-ultraviolet radiation, and the conidia developed in subsequent darkness. With regard to repetitive near-ultraviolet light pulses, more fluence was needed to induce the same level of conidiation as that induced by continuous near-ultraviolet radiation. With a lengthening of the duration of the dark-intervals (50 ms to 10 s) between 50-ms light pulses, much more fluence was required. On the other hand, blue radiation applied just before near-ultraviolet radiation suppressed the induction of conidiation. When preirradiated with repetitive blue light pulses, the fluence needed to suppress induction of conidiation to the same level as that of continuous blue radiation was somewhat less than that for continuous blue radiation. The longer the dark-interval duration (50 ms to 10 s) between light pulses, the less the fluence of blue radiation required. These results indicate that not only the photoreaction but also the dark reaction was very important for the accumulation of photo stimuli for both the blue and the near-ultraviolet light responses; however, they were kinetically quite different from each other.

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.

Induction of conidiation in Alternaria tomato (Cke.) Weber and Helminthosporium oryzae V. Breda de Haan was repeatedly controlled by ulternating doses of near ultraviolet light and blue light. These fungi did not form conidia in total darkness. However, when dark-grown colonies were exposed to near altraviolet light, conidiophore formation was induced, and conidia were then produced upon return to darkness. Conidiation was inhibited by blue light applied immediately after near ultraviolet light. Furthermore, the final response depended on the last kind of light received. The action spectrum for induction of conidiation showed a peak near 300 nm with a shoulder between 310 nm and 330 nm, as is common in photoconidiation of various fungi. The action spectrum for the reversion of induction of conidiation showed a peak near 447 nm with a shoulder between 400 nm and 440 nm, one minor peak around 478 nm and another one near 385 nm. This is very similar to the spectrum for the ubiquitous blue light receptor (cryptochrome).

Conidiophore formation in Alternaria tomato (Cke.) Weber (ATCC 38852) was induced by irradiation with near ultraviolet light, and conidia formed in subsequent darkness. However, blue light applied before the inductive near ultraviolet radiation suppressed the induction. Preirradiation with blue light just before the inductive near ultraviolet radiation was most suppressive. An action spectrum for this suppression showed a peak around 447 nm, with a shoulder between 400 and 440 nm, a minor peak around 478 nm in the blue region, and another near 385 nm in the near ultraviolet region. This action spectrum is very similar to the ubiquitous blue light response (cryptochrome).

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.

— The effects of blue light and near UV light on the induction of conidiation in the fungus, Aliernuriu tomato, were investigated. Induction of conidiation was repeatedly controlled by alternating doses of near UV light and blue light. When the final light was near UV, conidiation was induced and conidia developed in the following darkness; when it was blue, the induction of conidiation was suppressed. When conidiation was induced by irradiation with a light mixed with near UV and blue, not only the time lag for inducing conidiation but also the amount of conidia formed were regulated by the fluence rates of both those lights. Thus, ‘mycochrome’ is considered to function as a photoreceptor system in the induction of conidiation 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.