Observations on the maintenance and measurement of soil water in simple pot experiments and its effects on seed-borne Fusarium culmorum seedling blight of winter wheat

A simple method for maintaining and measuring soil water and the relationship between soil water and seed-borne Fusarium culmorum seedling blight of wheat was investigated under controlled environmental conditions to develop reproducible assay conditions for epidemiological studies and the testing of fungicide seed treatments. For reproducibility, soil matric potential (ψ_m) was used to define soil water, and a range of watering regimes were tested. Treatments were watered to either a maximum ψ_m or to maintain a mean ψ_m in order to establish which parameter best described the effect that soil water had on the incidence of disease symptoms. The severity of disease symptoms was closely related to the mean soil water status and not the maximum ψ_m value. Watering intervals, ranging from three times a day to once every three days, did not affect this relationship. The percentage of seedlings showing symptoms after emergence (i.e. localised or extensive necrotic lesions) was inversely related to the mean ψ_m. With increasing soil dryness (mean ψ_m from -0.14 MPa to -0.17 MPa) the percentage of seedlings with post-emergence symptoms decreased from 50% to 20%. However, as the mean ψ_m changed from -0.14 MPa to -0.17 MPa the percentage of seedlings dying before emergence increased from 25% to 55% in direct proportion to ψ_m. Overall the incidence of infection as indicated by the total number of seedlings showing symptoms either before or after emergence remained relatively constant, and was not significantly related to mean ψ_m.     

The Ultrastructure and Analytical Microscopy of Silicon Deposition in the Aleurone Layer of the Caryopsis of Setaria italica (L.) Beauv.

Silicon deposition in the caryopsis of foxtail millet (Setariaitalica (L.) Beauv.) from Lin Xian, Northern China was investigatedusing transmission electron microscopy and energy dispersiveX-ray analysis. The highest silicon count rates were obtained from the pericarpand outer aleurone cell walls, and particularly from a granularelectron-opaque layer external to the outer aleurone cell wall.Silicon was not detected in tissues interior to the aleurone. A possible mechanism for silicon deposition in the caryopsisis suggested, and the results are discussed with respect tothe high incidence of oesophageal cancer in Lin Xian, NorthernChina. Setaria italica (L.) Beauv., foxtail millet, silicon deposition, alcurone layer, caryopsis, ultrastructure, X-ray analysis     

Some Implications of Climatic Change for Agriculture in Europe

Initial results are reported of a study to evaluate the broad-scalesensitivity of agriculture in Europe to climatic change. Thestudy relates an agroclimatic index, effective temperature sum(ETS), to the cultivable limits of grain maize. A computer mappingsystem for the European region is adopted to map ETS on thebasis both of present-day and of possible future mean temperatures.In this way, changes in climate can be depicted as geographicalshifts of the limit of potential grain maize cultivation. The results indicate that a mean annual temperature increaseof only 1 °C (within the present-day range of inter-annualvariability) would open up large areas in southern England,the Low Countries, eastern Denmark, northern Germany, and northernPoland to potential grain maize cultivation. An increase of4°C would move the limit into central Fennoscandia and northernRussia. The latter changes are similar to those projected bygeneral circulation models (GCMs) for an equivalent doublingof atmospheric carbon dioxide, and represent rates of northwardshift of approximately 200–350 km/°C in western Europeand 250–400 km/°C in eastern Europe. Results using information from GCM transient-response experimentsindicate that such shifts could occur as soon as the 2050s ifthe current exponential growth in emission rates of greenhousegases were to continue unabated. The rate of shift of the grainmaize limit implied for this high (and improbable) emissionsscenario is in the order of 150–200 km per decade overthe next 70 years, slower than this during the next few decades,but faster thereafter. It is probable that the actual rate willbe lower than this, but even values of half those calculated,if sustained, would still represent rates of shift in agroclimaticpotential that are unprecedented in the historical record.     

Chimaeras of the Rubisco Large Subunit from Wheat and Anacystis do not Assemble into Active Enzyme in E. coli

A new restriction site was engineered in the cloned gene codingfor the large subunit polypeptide of ribulose 1, 5-bisphosphatecarboxylase (Rubisco) of the cyanobacterium Anacystis nidulans.This change resulted in the mutation of a phenylalanine residueto an isoleucine residue in the encoded polypeptide but hadno effect on the assembly or biochemical properties of Rubiscocontaining the polypeptide. The mutation was in a loop regionlinking highly structured domains at the N and C termini ofthe complete large subunit. Using the new restriction site, and a corresponding EcoRl restrictionsite in the cloned gene for the native large subunit polypeptideof wheat Rubisco, chimaeric genes were made encoding the polypeptidewith either the 140 residues of the N-terminal part of the wheatlarge subunit fused to the 336 residues forming the C-terminalregion of the A. nidulans large subunit, or the alternativeof 136 residues comprising of the N-terminal chains of A. nidulanssubunit and the 338 residue chain at the C-terminus of the wheatlarge subunit polypeptide. The chimaeric proteins expressedin E. coli, together with the small subunit of the A. nidulansRubisco, formed an insoluble inactive aggregate mainly in inclusionbodies. The possible reasons for the failure to obtain activeholoenzyme are discussed. Key words: Rubisco, protein engineering, site-directed mutagenesis     

Loss of decreased-rubisco phenotype between generations of wheat transformed with antisense and sense rbcS

The elite UK winter wheat cv. Riband was transformed with constructs containing rbcS in sense and antisense orientations driven by the maize ubiquitin promoter with a transformation efficiency of 1.2%. Of 77 primary transformants 31% of the sense-rbcS transformed lines and 78% of the antisense-rbcS transformed lines had decreased rubisco content compared to wild-type and marker-only controls, with decreases of up to 60%. However, in the T1 progeny which inherited the transgene, only 5% showed significantly decreased rubisco content and these effects were on the margins of significance. Five potential T2 homozygous lines from T1 parents which had transgene segregation consistent with a single locus were identified. There was no significant decrease in rubisco content relative to wild-type in any of these lines (LSD of 8% for P= 0.05). Expression of antisense rbcS transgenes in two of these T2 lines was low but was increased following exposure of the plants to 37°C for 48 h. However this did not induce a significant decrease in rubisco protein content relative to controls. Southern analysis of two antisense lines showed that they had low copy number and 1–2 insertion events. In one of the two lines there was increased methylation of the ubiquitin intron in T2 samples compared to the TO primary transformant. Further work is required to establish whether methylation occurred in all the lines which lost the phenotype, and therefore the likelihood of this being the cause. The disappearance of the decreased rubisco-content phenotype between generations may therefore be attributable to (1) greater activity of the ubiquitin promoter due to greater stress in the T0 generation plants and/or (2) increased methylation of the transgene promoter region between generations.     

The assessment of enriched apoplastic extracts using proteomic approaches

In plant tissues the extracellular environment or apoplast, incorporating the cell wall, is a highly dynamic compartment with a role in many important plant processes including defence, development, signalling and assimilate partitioning. Soluble apoplast proteins from Arabidopsis thaliana, Triticum aestivum and Oryza sativa were separated by two‐dimensional electrophoresis. The molecular weights and isoelectric points for the dominant proteins were established prior to excision, sequencing and identification by matrix‐assisted laser‐desorption ionisation time of flight mass spectrometry (MALDI ‐ TOF MS). From the selected spots, 23 proteins from O. sativa and 25 proteins from A. thaliana were sequenced, of which nine identifications were made in O. sativa (39%) and 14 in A. thaliana (56%). This analysis revealed that: (i) patterns of proteins revealed by two‐dimensional electrophoresis were different for each species indicating that speciation could occur at the level of the apoplast, (ii) of the proteins characterised many belonged to diverse families reflecting the multiple functions of the apoplast and (iii), a large number of the apoplast proteins could not be identified indicating that the majority of extracellular proteins are yet to be assigned. The principal proteins identified in the aqueous matrix of the apoplast were involved in defence, i.e. germin‐like proteins or glucanases, and cell expansion, i.e. β‐D‐glucan glucohydrolases. This study has demonstrated that proteomic analysis can be used to resolve the apoplastic protein complement and to identify adaptive changes induced by environmental effectors.     

Techniques for Studying Opaline Silica in Grass Leaves

In making surface preparations and sections of grass leaves,special precautions are necessary to recognize and locate silicasecreted as opal in epidermal cells. Treatment with ammonia,oxidation with hydrogen peroxide (and, for surface preparations,with chromic acid), and mounting in media of Refractive IndexI.51–1.54 are recommended. Since grass leaves de-silicifiedby hydrofluoric acid yield consistently good sections, the difficultyof obtaining undamaged opal-bearing sections must be due tothe blade encountering opals. Study of sizes and dispositionsof opals in surface preparations indicates optimum microtomesettings for reducing the frequency of such encounters. In mediachosen to make the opals conspicuous it is difficult to discernthe surrounding structures, but in most cases phase-contrastor polarization methods overcome this difficulty.     

Modelling the predicted geographic and economic response of UK cropping systems to climate change scenarios: the case of potatoes

Geographical changes in suitability in England and Wales for the cultivation of potatoes under a climate change scenario were predicted for the years 2023 and 2065 by integrating a climate database (1951-80) with climate-driven crop growth models. Initially, model outputs were produced as point values (meteorological site locations) of predicted potential yields for current crop production. The model outputs were validated statistically using actual crop yield figures collated from bibliographic analysis. The most suitable model was run again incorporating projected temperature and precipitation changes for 2023 and 2065. These outputs were then used to predict possible economic changes to farm profitability and general market trends. Results indicated that, although yields may rise, gross margins for maincrop and especially early potatoes may also rise due to shifts in production, to a fall in overall potato output and to price increases.     

Variation in Net Photosynthesis, Rubisco Activity and Chloroplast Ultrastructure among Somatic Hybrids of Solanum tuberosum and S. brevidens

The effect of ploidy, parental chloroplast type and parentalnuclear genome dosage on net photosynthesis, Rubisco activityand chloroplast ultrastructure was studied among somatic hybridsof diploid S. brevidens and dihaploid S. tuberosum. An increasein nuclear ploidy resulted in an increase in net photosynthesisand specific leaf weight. There were no significant differencesin net photosynthesis or Rubisco activity between the hybridshaving different parental chloroplast type. Examination of thehexaploid hybrids indicated that Rubisco activity was affectedby nuclear-organelle genome incompatibility, the most affectedcombination being tuberosum chloroplast type with brevidensnuclear genome. Examination of chloroplast ultrastructure revealedwide variation in the size of chloroplasts, starch granules,plastoglobuli and in grana stacking among the hybrids and betweenfusion parents. Key words: Somatic hybrids, Solanum, net photosynthesis, Rubisco, chloroplast ultrastructure