The transmission of banana bunchy-top virus in micropropagated bananas

Plants were established in vitro from banana bunchy0top virus (BBTV) infeeted plants. Explants containing either vegetative shoot apices or terminal floral apices were used to initiate cultures. Plants multiplied in culture were indistinguishable from non-infected (control) plants and lacked characteristic symptoms of BBTV infection. After 16 months in culture plants were established in the glasshouse and after 1 month in pots some plants started to show symptoms of the disease. After a further 5 months, 73% of the plants showed characteristic symptoms of the disease while 27% were symptomless and similar in appearance to control plants. These plants have been grown to maturity in the field without showing recognizable symptoms. This study demonstrates that BBTV can be transmitted in an apparently symptomless condition in culture and has important consequences for the dissemination of banana germplasm within Australia and internationally.     

Field evaluation of micropropagated bananas derived from plants containing Banana Bunchy-Top Virus

Micropropagated bananas derived from Banana Bunchy-Top Virus (BBTV) infected plants, but displaying no symptoms of the disease, were established in the field. They were grown for three years and produced a plant crop and ratoon crops. No disease symptoms were observed. There was uncertainty as to whether

Growth of micropropagated bananas colonized by root-organ culture produced arbuscular mycorrhizal fungi entrapped in Ca- alginate beads

The effect of root-organ culture (ROC) produced arbuscular mycorrhizal fungi (AMF), i.e. Glomus proliferum, Glomus versiforme and Glomus intraradices, entrapped in Ca-alginate beads on the first stages development of micropropagated bananas (Musa spp. cv. Grande Naine) was investigated. The experimental design consisted of banana plants inoculated with one of the three AMF and two controls, i.e. Control-AL (with empty alginate beads), and Control (no beads). Forty plants were considered per treatment and cultured under greenhouse conditions in a completely randomized design. Eight plants per treatment were harvested 40, 80, 120, 160 and 200 days after inoculation and analysed for root colonization, growth parameters and nutrient concentration. In addition, spores were enumerated in the substrate at the same intervals. Ca-alginate entrapped ROC-produced AMF spores were able (1) to colonize the root system of a micropropagated banana cultivar under nursery conditions, (2) to increase plant P nutrition and biomass, and (3) to proliferate in the commercial nursery substrate, therefore increasing the fungal inoculum biomass. The entrapment of ROC-propagated spores, adaptable to a wide range of Glomeromycetes, represents thus a forthcoming alternative pathogen-free inoculum.     

叶绿体色素提取、分离及理化性质测定实验的改进

分析了《植物生理学》修订本[1]教材中实验"叶绿体色素提取、分离及理化性质测定"中存在的问题,提出了相应的改进建议。     

Fluorescence polarization and pigment orientation in photosynthetic bacteria

Fluorescence polarization of photosynthetic bacteria with various types of chromatophores suggests an orientation of bacteriochlorophylls, but not of carotenoids. Comparison of the in vitro fluorescence polarization spectra of bacteriochlorophyll at high and low concentration and at 77 °K with those in vivo at various temperatures and in the presence of carbowax indicates that dichroism of shape effects the in vivo spectra. Both orientation and shape effects are highest for bacteria containing lamellar-type chromatophores, and lowest in those containing vesicle-type ones.

The polarization values of the bacteria studied are similar for the various red bands, indicating a nearly parallel orientation of the adjacent bacteriochlorophylls.     

The role of marginal hydathodes in foliar water absorption

Summary

Marginal epithem hydathodes may, in some conditions, absorb water. A toothed leaf margin can be regarded as a water-holding structure. It is suggested that the lack of hydathodes in north-temperate evergreens and in the leaves of rain forest trees is related to the need for such species to reduce foliar water absorption. The high proportion of deciduous species with hydathodes in woodland vegetation is thought to be related to the summer potential soil water deficit in Britain, leaf-absorbed water supplementing water from the soil. The term ‘potomorphic’ is suggested for leaves with water absorbing structures.     

Variations and interrelationships of foliar hydraulic and photosynthetic traits for Larix gmelinii

Aims Variations and potential trade-offs of leaf hydraulic and photosynthetic traits are essential for assessing and predicting the effect of climate change on tree survival, growth and distribution. Our aims were to examine variations and interrelationships of leaf hydraulic and photosynthetic traits in response to changes in site conditions for Dahurian larch (Larix gmelinii)—a dominant tree species in Chinese boreal forests.Methods This study was conducted at the Maoershan Forest Ecosystem Research Station. A transect of 27 year-old Dahurian larch plantation was established that consisted of five plots extending from the valley to the ridge of a slope. The predawn leaf water potential (Ψ_pre), area- and mass-based leaf hydraulic conductance (K_area and K_mass, respectively), resistance to embolism capacity (P₅₀), leaf mass per area (LMA), net photosynthetic rate (A), and leaf nitrogen content (N) were measured in August 2016.Important findings The Ψ_pre, K_area, K_mass, P₅₀, A, LMA, and N all varied significantly among the plots (p < 0.05), indicating significant intra-specific variations in these traits in response to the changes in site conditions. The P₅₀ was significantly (p < 0.05) correlated with Ψ_pre, K_area or K_mass, suggesting that a trade-off between hydraulic efficiency and safety exist within the species to some degree. There were significant (p < 0.05) pairwise correlations between A, LMA, and N. Nevertheless, there was no significant (p < 0.05) correlation between the measured photosynthetic traits and hydraulic traits. We concluded that the intra-specific variations and multiple interrelationships of the leaf hydraulic and photosynthetic traits for the larch reflect the plasticity of its leaf traits and strategies of its survival and growth as a result of its acclimation to diverse site conditions.     

The photosynthetic apparatus of Rhodopseudomonas palustris: structures and organization

The structural analysis of the individual components of the photosynthetic apparatus of Rhodopseudomonas palustris, or those of related species, is almost complete. To shed light on the assembly and organization of this machinery, we have studied native membranes of Rps.palustris grown under different light conditions using atomic force microscopy (AFM). The organization of the complexes in the membranes is different from any previously observed: with areas of crystalline core-complexes, crystalline peripheral antennae, mixed domains, and apparently pure lipid membranes devoid of protein. Examination of antennae structure shows that chromatic adaptation is associated with modifications in absorption and size of the peripheral light harvesting complexes (LH2) as light intensity is reduced. The core-complex is observed to contain a reaction centre (RC) surrounded by an elliptical assembly of 15 LH1 subunits and a "gap" attributed to the W-subunit. The localization of the W-subunit is not restricted to the periapsis of the core-complex but randomly located with respect to the RC imposed axis.     

枫香变红过程中叶片组织结构、光合特性及色素含量变化研究

枫香(Liquidambar formosana)因其叶片入秋后逐渐变红而极具观赏价值,是优良的景观生态树种。为了解枫香叶片结构变化与叶色的关系,该文通过连续监测枫香叶片变红过程中组织结构、光合特性及色素含量的变化,分析叶片结构与其光合特性和色素的关系。结果表明：(1)叶片变色过程中,表皮细胞均为椭圆形,紧密排列,未观察到明显的细胞变异,表面未附着绒毛和蜡质,且上表皮细胞与栅栏组织细胞间排列紧密,未出现较大的气室。(2)随着叶片逐渐变红,叶片结构变化显著,其中叶片、上表皮、栅栏组织和海绵组织厚度及气孔开度均逐渐减小,而气孔器长和宽、单个气孔器面积则逐渐增大。(3)随着叶片结构的变化,其叶绿素含量逐渐减少,致使净光合速率逐渐减小,在出现光破坏时,叶片通过在栅栏组织细胞液泡内合成花色苷来自我保护,而大量的花色苷致使叶片表面呈现红色。综上认为,叶绿素含量降低,花色素苷大量积累是导致枫香叶片变红的直接原因,而枫香叶色变红则是其一系列生理结构特征综合作用的结果。     

DA-6对秋季草莓叶片光合速率和植株生长的影响

以‘法国3号’草莓为材料,研究了秋季叶面喷施10、20和30 mg.L-1的DA-6处理对草莓幼苗叶片光合作用、活性氧代谢和植株生长的影响.结果表明:叶面喷施20和30 mg.L-1的DA-6处理使叶片净光合速率分别提高了17.5%和20.6%,并显著提高了叶绿素a、b含量及SOD、CAT酶活性,同时降低了MDA和活性氧含量.20和30 mg.L-1的DA-6处理显著增加了草莓平均单叶干质量,极显著增加了草莓茎和根系干质量,根冠比分别增加了29.9%和29.3%.表明秋季施用一定浓度的DA-6有利于草莓幼苗植株生长.     

Evolution of the control of pigment and plastid development in photosynthetic organisms

How do bioenergetic organelles relate to the cells they are in and how was this relationship established over the course of evolution? Plastids and mitochondria are viewed as prokaryotic residents in eukaryotic cells. These organelles are semiautonomous: they perpetuate themselves by division but regulate and are subject to regulation by the cell in which they are residents. Although these organelles are usually constitutive, their development is arrested in certain organisms when an inducing substrate is absent (light, for example, in the case of the chloroplast) with the formation of precursor organelles such as proplastids. Various trends in the evolution of photocontrol systems are discussed including those concerned with photoperception and photomorphogenesis. The photocontrol of chloroplast development by blue and red light is discussed in relation to its possible evolutionary origins in a system for finding the right light for photosynthesis. Models for various types of cellular regulation by light during chloroplast development are discussed. Also considered is the evolution of plastid pigments in response to available light. A parallel evolution of accessory pigments and chlorophylls is suggested which led to chlorophyll reaction centers serving as energy sinks for light absorbed by accessory pigments and, therefore, having their absorptions pushed to the longest possible wavelengths as accessory pigments evolved to fill the middle of the spectrum in response to ecological selection. An endosymbiotic origin of bioenergetic organelles is suggested based on polyphyletic origins of chloroplasts from a number of oxygenic procaryotic precursors. The similarity between proplastids and these oxygenic procaryotes suggests that the original invading organelle may have resembled a modern proplastid rather than a mature chloroplast.     

相同环境下3种藓类植物光合色素含量的比较

光合色素是客观反映植物利用光照能力的一类重要指标,往往可以作为判断植物光合生理能力、反映环境胁迫状况的重要指标[1~3].不同植物具有不同的光合色素含量特征,研究表明,植物光合色素因环境变化和生长发育阶段的不同而变化[1,4~8].     

Hyperhydricity in micropropagated carnation shoots: the role of oxidative stress

The physiology of hyperhydricity in relation to oxidative stress, mineral nutrients, antioxidant enzymes and ethylene has been studied in three micropropagated carnation cultivars under experimentally induced hyperhydricity. A marked increase in Fe content in comparison with normal tissues was observed in the hyperhydric tissues from the three cultivars. The levels of ethylene, solute leakage and malondialdehyde content were also significantly higher in the hyperhydric tissues. In relation to the time course of H₂O₂ production measured by fluorescence quenching, a similar trend could be observed for the three cultivars, with a clear increase in the generation of hydrogen peroxide in hyperhydric tissues. The activities of all the antioxidative enzymes studied, except lipoxygenase, were higher in the hyperhydric shoots. Phenylalanine ammonia-lyase (PAL) showed a significant decrease in activity in the hyperhydric tissues in comparison with the controls for the three cultivars. Soluble guaiacol peroxidase had a strong increase in activity in hyperhydric shoots of the three cultivars. These results provide, for the first time, direct evidence of H₂O₂ generation in hyperhydric tissues, characterize the response of the antioxidant system to an oxidative stress during hyperhydricity in carnation leaves and point to the accumulation of toxic forms of oxygen as the inducer of some of the abnormalities observed.     

The role of manganese in photosynthetic water oxidation

Summary The process of photosynthetic water oxidation to dioxygen under proton release takes place via a sequence of four univalent redox steps in a manganese-containing unit. In this mini-review the current state of knowledge is briefly described with special emphasis on the following topics: (a) the nature of the catalytic site, (b) the structure of the redox chemistry of the manganese-containing active site, (c) the ligand structure and the entry of substrate water into the redox cycle, and (d) problems of the stoichiometry of proton release coupled with individual redox steps and the possible role of other cofactors (Cl^–, Ca²⁺).