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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.

*Summary Sensitivity to ultraviolet-B (UVB) radiation (280–320 nm) varies widely among rice cultivars. We previously indicated that UV-resistant rice cultivars are better able to repair cyclobutane pyrimidine dimers (CPDs) through photorepair than are UV-sensitive cultivars. In this paper, we report that UVB sensitivity in rice, in part, is the result of defective CPD photolyase alleles. Surjamkhi (indica) exhibited greater sensitivity to UVB radiation and was more deficient in CPD photorepair ability compared with UV-resistant Sasanishiki (japonica). The deficiency in CPD photorepair in Surjamkhi resulted from changes in two nucleotides at positions 377 and 888 in the photolyase gene, causing alterations of two deduced amino acids at positions 126 and 296 in the photolyase enzyme. A linkage analysis in populations derived from Surjamkhi and Sasanishiki showed that UVB sensitivity is a quantitative inherited trait and that the CPD photolyase locus is tightly linked with a quantitative trait locus that explains a major portion of the genetic variation for this trait. These results suggest that spontaneously occurring mutations in the CPD photolyase gene cause different degrees of sensitivity to UVB in rice, and that the resistance of rice to UVB radiation could be increased by increasing the photolyase function through conventional breeding or bioengineering.

Growth of a near-isogenic line (NIL) for the purple leaf gene Pl of rice with a genetic background of Taichung 65 (T-65) rice was significantly retarded by supplementary ultraviolet-B radiation (UV-B), despite the fact that the amounts of UV-absorbing compounds and anthocyanins in NIL were significantly higher than those in T-65. In order to understand the role of flavonoids in UV-B induced damage protection in T-65 and the NIL, both the (1) relationships between changes in the steady state of cyclobutane pyrimidine dimer (CPD) levels and changes in accumulation of anthocyanins and UV-absorbing compounds in leaves with leaf age, and (2) the susceptibility to CPD induction by UV-B radiation and the ability to photorepair CPD were examined. Although supplementary UV-B elevated the steady state of CPD levels in leaves in both strains, the level in the leaf of the NIL was higher than that in T-65 at any time. The susceptibility to CPD induction by short-term (challenge) UV-B exposure was lower in the NIL than in T-65. On the other hand, the CPD photorepair was also lower in the leaves of the NIL than in those of T-65. The decrease in CPD-photorepair in the NIL was due to a lowering of the leaf-penetrating blue/UV-A radiation, which is effective for photoreactivation by photolyase, by anthocyanins. Thus, accumulation of anthocyanins and UV-absorbing compounds did not effectively function as screening against damage caused by elevated UV-B radiation in the NIL, and the retardation of growth in the NIL resulted from its lower ability to photorepair CPD by higher amounts of anthocyanins.

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 ...

The aim of this study was to investigate the regulatory effect of ultraviolet-B (UV-B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre-acclimation of plants to UV-B radiation prior to exposure by UV-B during treatment. Results showed that mRNA accumulation was similar during acute short-term UV-B exposure for chalcone synthase (Chs) and short-chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV-B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV-B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV-B-induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV-B levels resulted in significantly higher basal levels of CPDs than in non-acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes.

— 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.

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.

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.

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.

Conidiation in A. cichorii Nattras is reversibly stimulated by near UV radiation (NUV .apprx. 313 nm) and inhibited by blue light (.apprx. 450 nm) and apparently is a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. Both the blue-absorbing component (presumably a flavo-protein) and the PNUV (NUV absorbing moiety) of the mycochrome system are membrane-bound. The transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53.degree. with the transition moment associated with NUV absorption in PNUV.

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).

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 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.