拟南芥QUA1基因在光信号途径中的表达与功能分析

光信号在植物生长发育过程中具有非常重要的作用。不同的光信号通过调节植物下游基因的表达,进而影响细胞分化、结构和功能的改变,以及组织和器官的形成,参与植物光形态建成。QUA1 (QUASIMODO1)是拟南芥糖基转移酶家族中的一个成员,参与植物细胞壁中果胶的合成。本文以拟南芥qua1-1/cry1以及qua1-1/phyB双突变体为材料,对QUA1基因在光信号途径中的功能进行了分析。结果显示,qua1-1突变体在暗、蓝光、红光以及远红外光培养条件下下胚轴的伸长均受到抑制,QUA1基因的表达同样受到光信号的调节,而且突变体中多种光信号调节基因的表达也受到了影响。通过对qua1-1突变体下胚轴的观察发现,突变体下胚轴表皮细胞长度明显变短。与cry1以及phyB突变体相比,qua1-1/cry1和qua1-1/phyB双突变体下胚轴长度明显变短,而且双突变体中光信号调节基因的表达也有明显变化,表明QUA1可能参与了CRY1以及PHYB介导的蓝光及红光信号传导。以上结果表明QUA1影响了下胚轴细胞的伸长以及光信号调节基因的表达,并参与调控多种光信号传导途径。     

Sensing of UV-B radiation by plants

Daylight UV-B (UV-B) radiation (280–315 nm) is, because of its photochemical effects and potential destructive impact, an important environmental factor for plants. After decades of fruitless attempts, a receptor molecule, UVR8, for sensing of ambient UV-B radiation by plants has been characterized, and the initial steps in signal transduction have been identified. There are, however, other signaling pathways, and there are apparent contradictions in the literature. There is still much to find out about the complex signaling network in plants for processing of information about the daylight surrounding them.     

Photomorphogenetic responses to UV radiation and short-term red light in lettuce seedlings

Effects of red light (R), far-red light (FR) and UV radiation on growth and greening of lettuce seedlings (Latuca sativa L., cv. Berlinskii) have been investigated. UV-B and UV-C inhibited hypocotyl elongation and stimulated cotyledonary growth. R in combination with UV-B and UV-C partly eliminated these effects, but FR increased those and reversed the R effect. Chlorophyll accumulation was inhibited by UV-B and UV-C. In comparison with cotyledonary growth, R strengthened the UV inhibitory effect, and FR reversed this effect of R. Thus, UV and phytochrome system modify the effects of each other on hypocotyl and leaf growth in lettuce seedlings depending on the level of active phytochrome formed.     

Cytological evidence for DNA chain elongation after UV irradiation in the S phase

Human cells irradiated with UV light synthesize lower molecular weight DNA than unirradiated cells. This reduction in molecular weight is greater in xeroderma pigmentosum (XP) cells than in normal cells. The molecular weight of DNA is further reduced by the addition of caffeine to XP cells. By several hours after irradiation, DNA fragments are barely detectable. Cells from excision-proficient and excision-deficient XP patients were studied autoradiographically to produce cytological evidence of DNA chain elongation. Replicate cultures with and without caffeine were synchronized and irradiated with UV light during the S phase. Caffeine was removed in G₂, and the cells were labeled with ³H-thymidine. Results showed significantly increased labeling during G₂ of excision-deficient XP cells. Labeling was dependent on both time of irradiation and presence of caffeine. The XP variant cells had no increase in labeling for any irradiation time.Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper No. 1608. Supported by N.I.C. Grant TO1CA05170-10.     

The influence of season on adenine nucleotide concentrations and energy charge in four marsh plant species

Unilateral pulse ultraviolet irradiation caused positively phototropic coiling (> 180°) and curvature (≤ 180°) in the growth zone of dark-grown broom sorghum ( Sorghum bicolor Moench, cv. Acme Broomcorn and Sekishokuzairai Fukuyama) first internodes. Coiling was induced by irradiation at 257 to 302 nm, and proceeded to develop almost linearly during 72 h or more involving new tissue produced after irradiation. Curvature, caused at 308 to 413 nm and by red light, developed rapidly during the first several hours then slowly to cease by about 24 h, and did not surpass 120° even at the optimum photon fluences. Action spectra were higher towards shorter wavelengths, having a shoulder at about 287 nm, and could not separate the two photoresponses. The curvature was partially but markedly suppressed by far-red following the ultraviolet irradiation, whereas the coiling was not affected. Possible involvement of a specific UV-B photoreceptor and phytochrome in curvature and of a UV-C photoreceptor in coiling is discussed.     

Hypocotyl growth in Sinapis alba L: the roles of light quality and quantity

Abstract. A comparison is made of the relative effectiveness of light quality and light quantity on the elongation growth of Sinapis alba hypocotyls. The results show that hypocotyl extension rate in plants which have not previously been exposed to light is controlled primarily by the prevailing photon fluence rate when the phytochrome photostationary state lies between ∼0.033 and ∼0.81. Below ∼0.033, changes in photostationary state also have a marked effect on extension rate. Elongation growth in light-adapted plants is controlled by both photon fluence rate and the spectral quality of the incident radiation at all photoequilibria. Photosynthesis can modify these responses but is not essential as a prior condition for a green plant to respond to changes in light quality and quantity.     

Intramolecular uncoupling of chromophore photoconversion from structural signaling determinants drive mutant phytochrome B photoreceptor to far-red light perception

The phytochrome (phy) photoreceptor family regulates almost all aspects of plant development in a broad range of light environments including seed germination, onset of the photomorphogenic program in seedling stage, the shade avoidance syndrome in competing plant communities, flowering induction and senescence of adult plants. During evolution two clearly distinct classes of phy-s emerged covering these very different physiological tasks.¹ PhyA is rapidly degraded in its activated state. PhyA functions in controlling seed germination at very low light intensities (very low fluence response, VLFR) and seedling establishment under photosynthetic shade conditions (high irradiance response, HIR) where the far-red portion of the transmitted light to understorey habitats is substantially enhanced. Arabidopsis phyB together with phyC, D and E belongs to the relatively stable sensor class in comparison to the light labile phyA. PhyB functions at all stages of development including seed germination and seedling establishment, mediates classical red/far-red reversible low fluence responses (LFR) as well as red light high irradiance responses, and it is considered to be the dominating phytochrome sensor of its class.     

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

An interaction is demonstrated between the effects of phytochrome and cryptochrome (the specific blue-light photoreceptor) in the inhibition of hypocotyl elongation of light-grown cucumber (Cucumis sativus L.) cv. Ridge Greenline seedlings. At certain fluence rates of blue light the total inhibition response is greater than the sum of the separate responses to each photoreceptor. The threshold for response to blue light is reduced at least 30-fold by additional red-light irradiation. The synergistic effect is demonstrated for two different fluence rates of red light. Synergism is mediated by phytochrome in both the cotyledons and the hypocotyl.Abbreviations and symbols BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - photostationary state of phytochrome - _c calculated      

CELL SURVIVAL CHARACTERISTICS AND MOLECULAR RESPONSES OF ANTARCTIC PHYTOPLANKTON TO ULTRAVIOLET-B RADIATION1

Twelve species of Antarctic diatoms were studied to assess UV sensitivity in relation to cellular and molecular aspects of DNA damage and repair. Responses of cell survival, induction of DNA damage, and DNA repair capacity were determined. There was a wide range of interspecific UV-sensitivity among diatoms. D₃₇ values (average fluence to kill one cell) ranged from 681 J · m^?2 (most sensitive) to 25,338 J · m^?2 (most resistant). Molecular analysis (by radioimmunoassay) of UV-induced DNA damage [induction of cys-syn cyclobutane dimers and pyrimidine (6-4) pyrimidone photoproducts] also revealed considerable variability among species [0.98–84 lesions · (10⁸ daltons DNA)^?1 induced by exposure to 2500 J · m^?2]. Repair of DNA damage ranged from 0.18 to 2.72 lesions removed · (10⁸ daltons DNA)^?1 in 6 h; removal represented 0.72–73.5% of initial damage. Comparison of cellular responses associated with photoenhanced repair and nucleotide excision (“dark”) repair indicated that light-mediated correction of UV damage was an important factor in cell survival. There was a relationship between the number of photoproducts induced and cell survival, but not between repair efficiency and survival. The data also indicate a general dependence of photoproduct induction and D₃₇ values on cell size and shape (expressed as the surface area: volume ratio which ranged from 0.07 to 0.66 between species) and suggest that these factors are indicators of UV sensitivity. Smaller cells with greater surface area: volume ratios sustained more damage per unit of DNA, had lower D₃₇ values, and were more sensitive to UV exposure. The wide species variations observed in molecular and cellular responses to UV exposure emphasize the ecological implications of changes in natural UV regimes. These changes can act as determinants of cell size and taxonomic structure within phytoplankton communities and have as yet unknown effects on trophic interactions within the Antarctic ecosystem.     

A brief history of the DNA repair field

The history of the repair of damaged DNA can be traced to the mid-1930s. Since then multiple DNA repair mechanisms, as well as other biological responses to DNA damage, have been discovered and their regulation has been studied. This article briefly recounts the early history of this field.     

Multifunctionality of the LEC1 transcription factor during plant development

LEC1 acts as a key regulator of embryogenesis in Arabidopsis thaliana, but is involved in a wide range of functions, all the way from embryo morphogenesis to seed maturation. New data show that LEC1, partially in conjunction with abscisic acid, affects auxin synthesis, and both brassinosteroid and light signaling. The phenotype of LEC1 overexpressors confirms LEC1's known participation in the regulation of somatic embryogenesis, but also indicates additional roles in embryonic and extra-embryonic cell elongation. Here we present an integrated model of LEC1 function and suggest potential directions to be taken in future research in this important area of plant science.