M. 1991. Flowering responses to light-breaks in photomorphogenic mutants of Arabidopsis thaliana, a long-day plant. Flowering response and plant form of photomorphogenic mutants (hyl, hy2, hy3, hy4 and hy5) oi Arabidopsis thaliana (L.), a long-day plant, were examined in loog and short days. There were only slight differences among genotypes including Landsberg wild type with respect to the flowering time tjnder long days. The effect of 1 h light-(night)-breaks of far-red, red, bloe 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 ntimber 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 ligbt 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 ntimber 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 phytoehrome to the P[, form, (c) Mutant hyl, which behaves anomalously with respect to relatiotis between flowering time and number ol rosette leaves; late flowering with reduced number of rosette leaves. Red. blue and far-red light are effective, but white light is ineffective for reducitig the ntimber 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.

SummaryRice 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.

Muco-obstructive lung diseases (MOLDs), like cystic fibrosis and chronic obstructive pulmonary disease, affect a spectrum of subjects globally. In MOLDs, the airway mucus becomes hyperconcentrated, increasing osmotic and viscoelastic moduli and impairing mucus clearance. MOLD research requires relevant sources of healthy airway mucus for experimental manipulation and analysis. Mucus collected from endotracheal tubes (ETT) may represent such a source with benefits, e.g., in vivo production, over canonical sample types such as sputum or human bronchial epithelial (HBE) mucus. Ionic and biochemical compositions of ETT mucus from healthy human subjects were characterized and a stock of pooled ETT samples generated. Pooled ETT mucus exhibited concentration-dependent rheologic properties that agreed across spatial scales with reported individual ETT samples and HBE mucus. We suggest that the practical benefits compared with other sample types make ETT mucus potentially useful for MOLD research.

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.

Norin 1, a progenitor of many economically important Japanese rice strains, is highly sensitive to the damaging effects of UVB radiation (wavelengths 290 to 320 nm). Norin 1 seedlings are deficient in photorepair of cyclobutane pyrimidine dimers. However, the molecular origin of this deficiency was not known and, because rice photolyase genes have not been cloned and sequenced, could not be determined by examining photolyase structural genes or upstream regulatory elements for mutations. We therefore used a photoflash approach, which showed that the deficiency in photorepair in vivo resulted from a functionally altered photolyase. These results were confirmed by studies with extracts, which showed that the Norin 1 photolyase-dimer complex was highly thermolabile relative to the wild-type Sasanishiki photolyase. This deficiency results from a structure/function alteration of photolyase rather than of nonspecific repair, photolytic, or regulatory elements. Thus, the molecular origin of this plant DNA repair deficiency, resulting from a spontaneously occurring mutation to UV radiation sensitivity, is defective photolyase. INTRODUCTIONUV radiation can damage plants, decreasing growth and productivity (Teramura, 1983). UV radiation-augmentation studies have identified many UV radiation-sensitive cultivars of higher plants that are of economic importance, including rice (Kumagai and Sato, 1992;Bornman and Teramura, 1993;Hidema et al., 1996;Correia et al., 1998), and UV radiationexclusion studies indicate that prevention of such damage can increase plant growth (Krizek et al., 1997(Krizek et al., , 1998. UV radiation also induces photodamage in DNA, including damage to the cyclobutane pyrimidine dimer (CPD) and the (6-4)-pyrimidine-pyrimidone photodimer. Such damage can be lethal or mutagenic to simple and complex organisms; it can also impede replication and transcription, a possible mechanism for the adverse effects observed in higher plants.Photoreactivation is the major pathway in plants for repairing UV radiation-induced DNA damage (reviewed in Britt, 1996Britt, , 1999. This one-enzyme repair path is mediated by an enzyme, photolyase, which binds to a dimer to form a complex that is stable in the absence of light. When a photon in the wavelength range of 300 to 600 nm is absorbed (Saito and Werbin, 1969;Pang and Hays, 1991;Takeuchi et al., 1998), the dimer is reversed to two monomer pyrimidines and the enzyme is released. Photorepair of CPDs has been reported in several plant species, including gingko (Trosko and Mansour, 1969), Arabidopsis (Pang and Hays, 1991;Britt et al., 1993), alfalfa (Quaite et al., 1994b), soybean (Sutherland et al., 1996), cucumber (Takeuchi et al., 1996), rice (Hidema et al., 1997), maize (Stapleton and Walbot, 1994;, and wheat (Taylor, 1996).Increased sensitivity to UV radiation may result from failure to repair photodamage in DNA. The UV radiation-sensitive uvr1 mutant of Arabidopsis cannot photorepair (6-4)-pyrimidine-pyrimidone photodimers (Britt et al., 1993). Landry et al. (1997) s...