Effect of Phosphlnothricin (Glufosinate) on Photosynthesis and Chlorophyll Fluorescence Emission by Barley Leaves Illuminated Under Photorespiratory and Non-Photorespiratory Conditions

The effect of phosphinothricin (PPT), an inhibitor of glutaminesynthetase, on several aspects of photosynthesis has been studiedin primary leaves of barley (Hordeum vulgare L.). When photorespirationwas suppressed, either by increasing CO₂ concentration to 0.7%,or by decreasing O₂ concentration to 1%, feeding the illuminatedleaves with 0·5 or 1·0 mM PPT did not affect photosynthesisto a noticeable extent. Conversely, when PPT-fed leaves wereilluminated in air, CO₂ uptake decreased continuously. Modificationof the components of chlorophyll fluorescence quenching indicatedincreased reduction of Q_A, the primary acceptor of photosystemII, and increased chloroplast energization. Feeding of PPT toleaves illuminated in air increased the quantum requirementof photosynthesis and decreased photosynthetic rate of oxygenevolution in saturating [CO₂] and high light intensity. It isconcluded that the effect of PPT on the photochemical processesis indirect, through the inhibition of CO₂ assimilation probablycaused by the depletion of intermediates of the reductive pentosephosphate cycle. Key words: Feeding, Hordeumvulgare L., quenching coefficients     

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild‐type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.     

Multivariate hierarchical analyses of Early Jurassic Ostracoda assemblages

Palaeobiogeographic patterns of Early Jurassic ostracods from the northern and southern hemispheres (96 sections located in Europe, North Africa, Western Australia and North and South America) based on 243 species-level records document global patterns of distribution that can be compared to those previously published on ostracods from the European Epicontinental Sea and Tethyan and South Panthalassa areas. All described records of ostracods from both hemispheres spanning the Hettangian to Early Toarcian have been compiled and verified, and their patterns of origin and distribution have been interpreted. Jaccard coefficient of similarity was used to asses similarities among European, American and Tethyan ostracod shelf faunas. The numerical analysis shows a progressive longitudinal gradient in provincialism through the Early Jurassic, consistent with the northward drift of Tethyan ostracod faunas towards the European Epicontinental Sea and the southward movement of European taxa into Tethys and Panthalassa oceans. The spread of cosmopolitan species and extinction of endemic species, allied to the disappearance of geographical barriers, warmer climate conditions and rising sea levels can explain the reduction in ostracod diversity and the east-west provincialism throughout the Early Jurassic. Interchange between hemispheres, including bipolar distributions, are recognized from the Sinemurian time, pointing out that for most of the studied period, the climate worldwide was warm and tropical.     

Genetic diversity among genotypes of Eryngium viviparum (Apiaceae): a plant threatened throughout its natural range

Eryngium viviparum (Apiaceae) is an endangered aquatic plant, listed as threatened in several European documents. The genotypes are distributed patchily in various wetlands in the north‐west of Spain and one is located in north‐west France. The study of the genetic diversity of a small population of a rare species is important for conservation and studies aimed at recovery programmes. Random amplified polymorphic DNA (RAPD) markers were used to assess the genetic diversity among five Spanish and one French genotype. This technique has contributed to the knowledge of the genetic diversity in E. viviparum, showing a greater genetic distance between the Spanish cluster formed by S1, S4 than the second cluster formed by S2, S3, S5 and the French genotype. Mantel testing did not show a significant correlation between genetic and geographical distances, but a significant correlation was found between altitude, habitat and genetic distance. The French genotype showed the highest level of polymorphism (28.16) and the highest percentage of exclusive markers (32%). One of these was isolated, purified, cloned and sequenced, revealing a high homology to a protein mainly expressed in roots. This could represent, for the F genotype, an adaptation to a specific habitat near the sea compared with the Spanish genotypes which grow inland. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 237–244.     

Leaf carbon management in slow-growing plants exposed to elevated CO2

Two slow‐growing plant species (Chamaerops humilis, L. and Cycas revoluta Thunb.) were exposed to elevated CO₂ conditions over a 20‐month period in order to study the CO₂ effect on growth, photosynthetic capacity and leaf carbon (C) management. The ambient isotopic ¹³C/¹²C composition (δ¹³C) of the greenhouse module corresponding to elevated CO₂ (800 μmol mol^?1 CO₂) conditions was changed from δ¹³C ca. ?12.8±0.3‰ to ca. ?19.2±0.2‰. Exposure of these plants to elevated CO₂ enhanced dry mass (DM) by 82% and 152% in Chamerops and Cycas, respectively, mainly as a consequence of increases in plant level photosynthetic rates. However, analyses of A–C_i curve parameters revealed that elevated CO₂ diminished leaf photosynthetic rates of Chamaerops whereas in Cycas, no photosynthetic acclimation was detected. The fact that Chamaerops plants had a lower DM increase, together with a longer leaf C residence time and a diminished capacity to respire recently fixed C, suggests that this species was unable to increase C sink strength. Furthermore, the consequent C source/sink imbalance in Chamaerops might have induced the downregulation of Rubisco. Cycas plants were capable of avoiding photosynthetic downregulation due to a greater ability to increase C sink strength, as was confirmed by DM values, and ¹²C‐enriched CO₂ labeling data. Cycas developed the ability to respire a larger proportion of recently fixed C and to reallocate the recently fixed C away from leaves to other plant tissues. These findings suggest that leaf C management is a key factor in the responsiveness of slow‐growing plants to future CO₂ scenarios.     

Tomato yellow leaf curl viruses: ménage à trois between the virus complex,the plant and the whitefly vector

Tomato yellow leaf curl disease (TYLCD) is one of the most devastating viral diseases affecting tomato crops in tropical, subtropical and temperate regions of the world. Here, we focus on the interactions through recombination between the different begomovirus species causing TYLCD, provide an overview of the interactions with the cellular genes involved in viral replication, and highlight recent progress on the relationships between these viruses and their vector, the whitefly Bemisia tabaci. Taxonomy: The tomato yellow leaf curl virus‐like viruses (TYLCVs) are a complex of begomoviruses (family Geminiviridae, genus Begomovirus) including 10 accepted species: Tomato yellow leaf curl Axarquia virus (TYLCAxV), Tomato yellow leaf curl China virus (TYLCCNV), Tomato yellow leaf curl Guangdong virus (TYLCGuV), Tomato yellow leaf curl Indonesia virus (TYLCIDV), Tomato yellow leaf curl Kanchanaburi virus (TYLVKaV), Tomato yellow leaf curl Malaga virus (TYLCMalV), Tomato yellow leaf curl Mali virus (TYLCMLV), Tomato yellow leaf curl Sardinia virus (TYLCSV), Tomato yellow leaf curl Thailand virus (TYLCTHV), Tomato yellow leaf curl Vietnam virus (TYLCVNV) and Tomato yellow leaf curl virus(TYLCV). We follow the species demarcation criteria of the International Committee on Taxonomy of Viruses (ICTV), the most important of which is an 89% nucleotide identity threshold between full‐length DNA‐A component nucleotide sequences for begomovirus species. Strains of a species are defined by a 93% nucleotide identity threshold. Host range: The primary host of TYLCVs is tomato (Solanum lycopersicum), but they can also naturally infect other crops [common bean (Phaseolus vulgaris), sweet pepper (Capsicum annuum), chilli pepper (C. chinense) and tobacco (Nicotiana tabacum)], a number of ornamentals [petunia (Petunia×hybrida) and lisianthus (Eustoma grandiflora)], as well as common weeds (Solanum nigrum and Datura stramonium). TYLCVs also infect the experimental host Nicotiana benthamiana. Disease symptoms: Infected tomato plants are stunted or dwarfed, with leaflets rolled upwards and inwards; young leaves are slightly chlorotic; in recently infected plants, fruits might not be produced or, if produced, are small and unmarketable. In common bean, some TYLCVs produce the bean leaf crumple disease, with thickening, epinasty, crumpling, blade reduction and upward curling of leaves, as well as abnormal shoot proliferation and internode reduction; the very small leaves result in a bushy appearance.