THE DISTRIBUTION OF VIRUSES IN DIFFERENT LEAF TISSUES AND ITS INFLUENCE ON VIRUS TRANSMISSION BY APHIDS

Exposing both surfaces of leaves systemically infected with cabbage black ring spot virus (CBRSV) or henbane mosaic virus to ultra-violet radiation decreases the infectivity of expressed sap to about one-fifth. As irradiation probably inactivates virus mainly in the epidermis, which occupies about one-quarter the volume of the leaves, these viruses seem to occur at much higher concentrations in sap from the epidermis than in sap from other cells. By contrast, tobacco mosaic virus seems not to occur predominantly in the epidermis.
CBRSV and henbane mosaic virus are normally transmitted most frequently by previously fasted aphids that feed for only short periods on infected leaves, but aphids treated like this transmit rarely from leaves that have been exposed to ultraviolet radiation. Irradiation has relatively little effect on the proportion of aphids that transmit after long infection feedings. Fasting seems to increase transmission by increasing the probability that aphids will imbibe sap from the epidermis of leaves they newly colonize. With longer periods on infected leaves, the ability of fasted aphids to transmit probably decreases because they then feed from deeper cells and their stylets contain sap with less virus. Only virus contained in the stylets seems to be transmitted, not virus taken into the stomach. About half the transmissions of henbane mosaic virus by aphids that have colonized tobacco leaves for hours may be caused by insects that temporarily cease feeding on the phloem and newly penetrate the epidermis.
Irradiating infected leaves affected the transmission of sugar-beet mosaic virus in the same way as that of henbane mosaic virus, but had little effect on the transmission of beet yellows virus, whose vectors become more likely to transmit the longer they feed on infected plants.     

LIGHT QUALITY AND PHOTOREACTIVATION OF PLANTS AND VIRUSES

Visible light of different spectral regions was tested for its ability to reverse three effects of ultra-violet radiation, namely, injury (glazing) of French bean leaves, increased resistance of French bean leaves to infection by the Rothamsted tobacco necrosis virus, and inactivation of potato virus X. The different spectral regions were obtained with colorimetric filters and the filtered and unfiltered light from fluorescent tubes; all three effects were reversed only by regions of wave-lengths shorter than 4700 Å. Thirty minutes of illumination at 300–380 f.c. gave substantial photo-reactivation, but irradiated potato virus X did not become affected by visible light until 30 min. after tobacco leaves were inoculated.     

RESULTS OF IRRADIATING SACCHAROMYCES WITH MONOCHROMATIC ULTRA-VIOLET LIGHT : I. MORPHOLOGICAL AND RESPIRATORY CHANGES

Effects of measured ultra-violet light on the yeast S. cerevisiae have been studied. Methods of culturing and irradiating the yeast, of estimating the nature and extent of the changes produced, and the means used in producing and measuring the radiation are given. No evidence of a stimulative action was observed. The absorbed energy did not produce an all or none effect; arbitrary criteria must be used for judging the various inhibitory and lethal effects. With increase in the incident energy diverse effects were produced until abnormal cell growth and "death" of the cells resulted. Changes in the rate of oxygen consumption did not occur until after a high proportion of the irradiated cells were so damaged that they produced abnormal cells. The shape of the curves relating effect to energy are similar for various wave-lengths but different energies are required to produce the same effect at each of the wave-lengths studied. The similarity of the curves to that for a first order reaction is noted, but attention is called to the modifying influence of accessory factors such as the age of the cells. A comparison is made of the morphological and metabolic changes on the basis of energy requirements, and their relative value as criteria in judging the effects of ultra-violet light on yeast and physiologically similar microorganisms.     

RESULTS OF IRRADIATING SACCHAROMYCES WITH MONOCHROMATIC ULTRA-VIOLET LIGHT : II. THE INFLUENCE OF MODIFYING FACTORS

Possible variation in the probability that absorbed quanta of ultra-violet energy will produce observable inhibitory and lethal effects in the yeast cell, due to non-uniformity in sensitivity of the different regions of the cell, may be further modified by the reproductive stage of the cell at the time of irradiation. Tests of the survival of yeast cells of 15 day and 24 hour cultures indicate that the older resting cells are more resistant to ultra-violet irradiation effects than cells undergoing rapid cell division. The effects of temperature changes within the range of normal growth are evidently small, as judged from the temperature coefficient (1.10). Possible inhibitory effects due to the action of ultra-violet radiation on the malt agar medium and to toxic substances diffused from cells killed by irradiation were not found under the conditions of the experiments. Tests of the validity of the Bunsen-Roscoe reciprocity law for variation in the intensity of the incident ultra-violet radiation up to 30 per cent indicate that for this range the rate of absorption of quanta by the cell does not produce any marked change in the lethal effects observed.     

Blue-green fluorescence excited by UV laser on leaves of different species originates from cutin and is sensitive to leaf temperature

Under ultra-violet excitation, intact leaves generate a strong blue-green fluorescence emission with several bands. Their integrated energy is 6 to 11 times the energy released by chlorophyll a bands (Chappelle et al. 1984, Applied Optics 23, 134–138). This paper provides evidence that the blue-green fluorescence emission comes mainly from outer epidermal layers of the leaves and can be transferred on a quartz lamina by quickly dipping the leaves in organic solvents with subsequent solvent evaporation. Blue-green fluorescence displays a diffusion-controlled quenching of fluorescence intensity between 4°C (high fluorescence) and 37°C (low fluorescence). The blue-green fluorescence emissivity is not linked to short-term metabolic effects other than leaf temperature, but epidermis adaptations both to drought and to excessive radiation increase emissivity.     

冠层部位对金叶女贞叶片结构的影响

金叶女贞是一种在园林绿化上广泛应用的彩叶植物,上层叶金黄色,下层叶深绿色。本文利用常规植物制片技术,研究了叶绿素缺少的金叶女贞上层金叶和下层绿叶的解剖结构。结果表明:(1)金叶女贞上层金叶和下层绿叶的上表皮无显著差异,但是下层绿叶的下表皮细胞较小,气孔密度较低;(2)下层绿叶的叶肉组织较薄,细胞较大,排列疏松;(3)在下层绿叶中叶绿体类囊体片层排列密集,叶肉组织内单位体积叶绿体数量较少;(4)冠层部位对光合色素的积累有明显影响。叶绿素缺少的金叶女贞叶片结构显著受到冠层部位的影响,光合色素的变化幅度较一般植物更大,不同冠层部位叶片叶色有明显差异,可以作为研究植物冠层部位对叶形态、结构和生理生化影响的好材料。     

STUDIES ON BIOLUMINESCENCE : XVII. FLUORESCENCE AND INHIBITION OF LUMINESCENCE IN CTENOPHORES BY ULTRA-VIOLET LIGHT.

1. Small dumps of the luminous cells of Mnemiopsis cannot readily be stimulated mechanically but will luminesce on treatment with saponin solution. Larger groups of luminous cells (such as are connected with two paddle plates) luminesce on mechanical stimulation. This suggests that mechanical stimulation to luminesce occurs chiefly through a nerve mechanism which has been broken up in the small dumps of luminous tissue. 2. The smallest bits of luminous tissue, even cells freed from the animal by agitation, that will pass through filter paper, lose their power to luminesce in daylight and regain it (at least partially) in the dark. 3. Luminescence of the whole animal and of individual cells is suppressed by near ultra-violet light (without visible light). 4. Inhibition in ultra-violet light is not due to stimulation (by the ultra-violet light) of the animal to luminesce, thereby using up the store of photogenic material. 5. Animals stimulated mechanically several times and placed in ultra-violet light show a luminescence along the meridians in the same positions as the luminescence that appears on stimulation. This luminescence in the ultra-violet or "tonic luminescence," is not obtained with light adapted ctenophores and is interpreted to be a fluorescence of the product of oxidation of the photogenic material. 6. Marked fluorescence of the luminous organ of the glowworm (Photuris) and of the luminous slime of Chatopterus may be observed in ultra-violet but no marked fluorescence of the luminous substances of Cypridina is apparent. 7. Evidence is accumulating to show a close relation between fluorescent and chemiluminescent substances in animals, similar to that described for unsaturated silicon compounds and the Grignard reagents.     

Chlorophyll and light gradients in sun and shade leaves of Spinacia oleracea

Abstract. Light gradients were measured and correlated with chlorophyll concentration and anatomy of leaves in spinach (Spinacia oleracea L.). Light gradients were measured at 450, 550 and 680 nm within thin (455 μm) and thick (630 μm) leaves of spinach grown under sun and shade conditions. The light gradients were relatively steep in both types of leaves and 90% of the light at 450 and 680 nm was absorbed by the initial 140 μm of the palisade. In general, blue light was depleted faster than red light which, in turn was depleted faster than green light. Light penetrated further into the thicker palisade of sun leaves in comparison to the shade leaves. The distance that blue light at 450 nm travelled before it became 90% depleted was 120 μm in sun leaves versus 76 μm in shade leaves. Red light at 680 nm and green light at 550 nm travelled further but the trends were similar to that measured at 450nm. The steeper light gradients within the palisade-of shade leaves were caused by increased scattering of light within the intercellular air spaces and/or cells which were less compact than those in sun leaves. The decline in the amount of light within the leaf appeared to be balanced by a gradient in chlorophyll concentration measured in paradermal sections. Progressing from the adaxial epidermis, chlorophyll content increased through the palisade and then declined through the spongy mesophyll. Chlorophyll content was similar in the palisade of both sun and shade leaves. Chloroplast distribution within both sun and shade leaves was relatively uniform so that the chlorophyll gradient appeared to be caused by greater amounts of chlorophyll within chloroplasts located deeper within the leaf. These results indicate that the anatomy of the palisade may be of special importance for controlling the penetration of photo-synthetically active radiation into the leaf. Changing the structural characteristics of individual palisade cells or their arrangement may be an adaptation that maximizes the absorption of light in leaves with varying mesophyll thickness due to different ambient light regimes.     

Light-guiding function of foliar sclereids in the evergreen sclerophyll Phillyrea latifolia: a quantitative approach

The anatomy and orientation of the foliar sclereids of the evergreen sclerophyll Phillyrea latifolia suggest a light-guiding function. Light microscope observations of enzymatically isolated sclereids showed that they possessed very thick cell walls, lobes and branches which occurred mainly at the end of the idioblasts reaching the abaxial epidermis. Leaf cross-sections showed that sclereids occurred diffusely within the mesophyll and were oriented vertically with respect to the lamina. In paradermal sections, the cut cell walls of the sclereids appeared as bright light spots among the dark-green background of the mesophyll cells. The heterogeneity of the radiation field transmitted through the same paradermal section was quantified by image analysis and two- or three-dimensional representations. The amount of light transmitted through the sclereids was found to be up to 30-fold higher compared to that transmitted through the neighbouring mesophyll cells. The light guiding capacity of the sclereids at the spongy mesophyll level was estimated to be 40-80%. In leaves illuminated from the adaxial surface, light passing through the ends of the sclereids seemed to be reflected from the internal surface of the abaxial epidermis. In sunny conditions when leaf thickness tends to increase, the number of sclereids per unit leaf area was increased significantly compared to the shaded ones. It is proposed that the anatomy and orientation of the foliar osteosclereids of P. latifolia, are suitable for a light-guiding function. Thus foliar sclereids, besides other roles, may contribute both qualitatively and quantitatively, to the enhancement of the light microenvironment within the mesophyll of these sclerophyllous leaves.Keywords: Phillyrea latifolia L. (incl. P. media L.), foliar sclereids, light guiding, image analysis.      

Penetration of UV-A, UV-B and blue light through the leaf trichome layers of two xeromorphic plants, olive and oak, measured by optical fibre microprobes

Quartz fibre-optic microprobes were used to monitor the light microenvironment beneath trichome layers of the xeromorphic leaves of two Mediterranean evergreen sclerophylls, Olea europaea and Quercus ilex . Young developing leaves of both plants were densely pubescent on both surfaces of the lamina, whereas the mature leaves were pubescent only on the abaxial side. Trichome layers of young as well as of mature leaves of both plants attenuated almost all incident ultraviolet (UV)-B (310 nm) and UV-A (360 nm) radiation and a considerable portion of blue light (430 nm). Abaxial trichome layers of young leaves were more effective in screening out the incident radiation compared to the adaxial ones of the same leaves and also compared to the abaxial layer of the mature leaves. The abaxial epidermis of dehaired mature leaves of O. europaea was ineffective in absorbing most of the incident UV-B and UV-A radiation. UV and visible spectra beneath trichome layers of O. europaea in mature leaves confirmed that the light microenvironment on the epidermis was deprived in the UV-B, UV-A and partly in the blue spectral regions. It is proposed that the occurrence of a dense trichome layer, especially in young leaves, may play a protective role against not only UV-B radiation damage, but also against high visible irradiance. This function is performed irrespective of the differing anatomy of individual hairs of both plants. The protection provided by the trichomes could afford advantages under stress conditions, especially during leaf development.     

The effect of exposure to enhanced UV-B radiation on the penetration of monochromatic and polychromatic UV-B radiation in leaves of Brassica napus

Using quartz optical fibres, penetration of both monochromatic (310 nm) and polychromatic UV-B (280–320 nm) radiation in leaves of Brassica napus L. (cv. Ceres) was measured. Plants were grown under either visible light (750 μmol m⁻² s⁻¹ photosynthetically active radiation) or with the addition of 8. 9 KJ m⁻² day⁻¹ biologically effective UV-B (UV-B_BE) radiation. Results showed that of the 310 nm radiation that penetreated the leaf, 90% was within the intial one third of the leaf with high attenuation in the leaf epidermis, especially in UV-treated plants. Polychromatic UV-B radiation, relative to incident radiation, showed a relatively uniform spectral distribution within the leaf, except for collimated radiation. Over 30% of the UV-screening pigments in the leaf, including flavonoids, were found in the adaxial epidermal layer, making this layer less transparent to UV-B radiation than the abaxial epidermis, which contained less than 12% of the UV-screening pigments. UV-screening pigments increased by 20% in UV-treated leaves relative to control leaves. Densely arranged epicuticular wax on the adaxial leaf surface of UV-treated plants may have further decreased penetration of UV-B radiation by reflectance. An increased leaf thickness, and decreases in leaf area and leaf dry weight were also found for UV-treated plants.     

SOME EFFECTS OF VIRUS INFECTION ON LEAF WATER CONTENTS OF NICOTIANA SPECIES

Infection with tobacco mosaic virus decreases the water content which detached tobacco leaves attain when kept for 20 hr. in conditions of minimum water stress, and does so more when the plants are kept in light before inoculation than when they are kept in darkness. No such effects of infection during the first day after inoculation were obtained with tobacco leaves infected with either tobacco etch virus or potato virus X , or with Nicotiana glutinosa leaves infected with tobacco mosaic virus. These results, like those showing early effects of TMV on respiration and photosynthesis of tobacco leaves, suggest that inoculation with TMV affects deeper leaf tissues than the epidermis earlier in tobacco leaves than in other leaves, and earlier than other viruses in tobacco leaves.     

Accumulation of malate in guard cells of Vicia faba during stomatal opening

Summary The level of malate in the epidermis from illuminated leaves of Vicia faba was greater than in that from dark-treated leaves. A difference in the malate level was still detected after the epidermis had been treated by rolling so that only the guard cells remained alive. The results suggest that malate may accumulate in guard cells on illumination. In subsequent experiments, stomatal apertures were measured, and potassium as well as malate was analysed in extracts of epidermis. In illuminated leaves, the potassium content of rolled epidermis increased from about 90 to about 335 picoequivalents mm^-2 of epidermis whele malate increased from about zero to about 71 pmoles mm^-2 and the stomata opened; in dark-treated leaves, the potassium content of rolled epidermis decreased slightly, the malate level remained about zero, and the stomata showed very slight further closure. The measured increase in potassium is likely to represent an increase in potassium concentration in the guard cells of about 0.4 Eq l^-1 with stomatal opening; the increase in malate could correspond to 0.23 Eq l^-1 (with respect to potassium) in the guard cells. Thus, malate accumulating in guard cells could balance about half of the potassium taken up by guard cells when stomata open in the light.     

UV-B辐射对烟草光合色素和几种酶的影响

对UV-B胁迫条件下烟草叶片相关生理生化指标的变化进行研究.结果表明,UV-B辐照后,烟草叶片内光合色素(叶绿素a、叶绿素b、类胡萝卜素)的含量均呈上升趋势,3种色素比对照分别上升了21%、10%、27%;可溶性蛋白含量呈先上升后下降趋势;过氧化物酶活性明显上升,同工酶图谱分析证实,有一种新的过氧化物酶同工酶表达;利用重组噬夏孢欧文氏菌(Erwinia uredovora)GGPP合成酶免疫家兔,制备了兔抗GGPP合成酶的抗血清.Western blot检测显示,UV-B辐照可使烟草叶片GGPP合成酶(GGPS)的表达量显著提高.     

cis-urocanic acid suppression of contact hypersensitivity induction is mediated via tumor necrosis factor-alpha.

Ultraviolet B (UVB) light impairs the induction of contact hypersensitivity to epicutaneously applied haptens in certain strains of mice by a genetically determined mechanism that depends upon the participation of TNF-alpha. Because the superficial epidermis contains large amounts of trans-urocanic acid (trans-UCA), because exposure to UVB radiation converts this compound to cis-UCA, and because cis-UCA has been reported to be immunosuppressive, we have examined the possibility that the TNF-alpha-dependent effects of UVB on contact hypersensitivity induction in mice are mediated via conversion of trans- to cis-UCA. By injecting cis-UCA intradermally before application of dinitrofluorobenzene, by treating cis-UCA-injected mice systemically with neutralizing anti-TNF-alpha antibodies, and by comparing the consequences of these maneuvers in UVB-susceptible and UVB-resistant strains of mice, we have determined a) that cis-UCA can impair the induction of contact hypersensitivity in a manner similar to UVB radiation, and that the impairment is dependent upon TNF-alpha; b) that cis-UCA altered the morphology of epidermal Langerhans cells in a manner similar to UVB radiation, and that the alteration was dependent, in part, upon TNF-alpha; and c) that the inhibitory effects of cis-UCA on induction of contact hypersensitivity and the histologic effects of this compound on epidermal Langerhans cells appear to be influenced by alleles at the Tnf alpha and Lps loci. Based on these findings we propose that UVB radiation impairs the induction of contact hypersensitivity in mice by converting trans-urocanic acid to cis-UCA within the epidermis; cis-UCA in turn causes the local release of TNF-alpha, which thwarts sensitization by its ability to trap epidermal Langerhans cells transiently within the epidermis, and thereby prevents the immunogenic signal from reaching the draining lymph node where activation of unprimed, Ag-specific T cells must occur.     

Photosynthetic energy storage in aquatic leaves measured by photothermal deflection

In a study of photosynthetic energy storage efficiency (ES), the adaxial surface of the leaves of Vallisneria americana exhibited the highest ES values (22%) of the four aquatic plants examined. V. americana leaves have a dispersed structure and it was possible to measure the energy storage properties of the epidermal cells independently of the rest of the leaf. The abaxial epidermis had a higher value of ES at zero light fluence than the adaxial epidermis but ES in the abaxial epidermis declined much more rapidly with light fluence. Thus the abaxial epidermis is more suited to lower light fluences than the adaxial epidermis. ES declined as the pH rose from 4.0 to 8.0 at a constant dissolved inorganic carbon concentration. This paralleled the change from carbon dioxide to bicarbonate and suggests that these leaves utilise CO₂ more efficiently than bicarbonate. ES increased by about 50% at pH 8.0 as leaf sections further from the leaf tip were examined which demonstrates that the older epidermal cells are less well able to use bicarbonate. Exposure to 30 min of a saturating light fluence caused the epidermal chloroplasts to move from the periclinal walls to the anticlinal walls. This decreased the photothermal signal by increasing the thermal diffusion distance and lowering the light fluence due to greater chloroplast shading. The latter effect increased ES. It appears that chloroplast movement could assist the epidermis to survive harmful light fluences.Abbreviations APW artificial pond water; atrazine- (2-chloro-4-ethylamino-6-(isopropylamine)-s-triazine) - DCMU (3-(3,4 dichlorophenyl)-1,1-dimethyl urea) - DIC dissolved inorganic carbon - DMSO dimethyl sulfoxide - ES energy storage efficiency - HEPES N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] - MOPS 3-[N-Morpholino]propanesulfonic acid - PD photothermal deflection     

Chloroplast movements in leaves of two evergreen sclerophyllous plants (Ilex aquifolium and Prunus laurocerasus)

ABSTRACT

Chloroplast movements provide a means for fine-tuning the absorption of radiation in leaves. Since evergreen sclerophylls may experience very different light levels during the seasons and at different locations either at the periphery or in the interior of a forest, such a mechanism must theoretically be of great importance for them. Detailed field and laboratory studies on sclerophylls are however lacking. We provide first evidence that chloroplasts in the leaf mesophyll of both Ilex aquifolium (holly) and Prunus laurocerasus (cherry laurel) may be stimulated by low light intensities. Even at winter temperatures close to freezing, chloroplasts move to a position where light absorption is increased. Effects of temperature, light pretreatment and light quality for the induction of movement are described.     

High ultraviolet C resistance of marine Planctomycetes

Planctomycetes are bacteria with particular characteristics such as internal membrane systems encompassing intracellular compartments, proteinaceous cell walls, cell division by yeast-like budding and large genomes. These bacteria inhabit a wide range of habitats, including marine ecosystems, in which ultra-violet radiation has a potential harmful impact in living organisms. To evaluate the effect of ultra-violet C on the genome of several marine strains of Planctomycetes, we developed an easy and fast DNA diffusion assay in which the cell wall was degraded with papain, the wall-free cells were embedded in an agarose microgel and lysed. The presence of double strand breaks and unwinding by single strand breaks allow DNA diffusion, which is visible as a halo upon DNA staining. The number of cells presenting DNA diffusion correlated with the dose of ultra-violet C or hydrogen peroxide. From DNA damage and viability experiments, we found evidence indicating that some strains of Planctomycetes are significantly resistant to ultra-violet C radiation, showing lower sensitivity than the known resistant Arthrobacter sp. The more resistant strains were those phylogenetically closer to Rhodopirellula baltica, suggesting that these species are adapted to habitats under the influence of ultra-violet radiation. Our results provide evidence indicating that the mechanism of resistance involves DNA damage repair and/or other DNA ultra-violet C-protective mechanism.     

盐胁迫下CO2加倍对春小麦一些光合功能的影响

 研究了在盐胁迫下CO2浓度加倍对春小麦(Triticum aestivum)青323光合色素含量和一些光合功能的影响。结果表明,盐胁迫降低春小麦叶片单位鲜重叶绿素(Chl)和类胡萝卜素(Car)的含量、叶绿体对光能的吸收能力,Mg2+对两个光系统(PSⅡ和PSⅠ)之间激发能分配的调节能力,以及荧光猝灭速率(△FV/T)。然而,CO2加倍有提高上述各参数的作用,表明高CO2浓度能减轻盐胁迫对光合功能的不利效应。     

增强UV-B辐射对麻花艽叶片的抗氧化酶的影响

以青藏高原的特有植物麻花艽为材料,研究麻花艽叶片抗氧化酶系统对增强UV-B辐射的响应。结果表明：在UV-B处理初期,麻花艽叶片SOD、POD的酶活性都能增加,但随着处理时间的延长,SOD、POD的活性呈现下降趋势。麻花艽叶片CAT的酶活性在UVB处理后下降明显,但作为清除叶绿体中H2O2的关键酶AP的酶活性表现为明显地增加趋势,说明在对麻花艽叶片增强UV-B辐射反应中AP起有着重要作用。MDA的含量随UV-B处理时间延长而增加,表明UV-B降低了细胞内活性氧自由基的清除能力,膜脂过氧化作用加剧,导致了对麻花艽叶片的伤害效应。