Inheritance of resistance to lettuce root aphid in the lettuce cultivars 'Avoncrisp' and 'Lakeland"

The inheritance of resistance in two lettuce cultivars to lettuce root aphid, Pemphigus bursarius, was studied in a series of laboratory and field experiments at Wellesbourne between 1989 and 1992. A source of total resistance in the cv. ‘Avoncrisp’ which is linked to the downy mildew resistance gene Dm6, was shown to be governed by a single dominant gene. There were no maternal effects evident in the inheritance of this resistance. The basis of the high level of resistance which exists in the cv. ‘Lakeland’ (formerly known as ‘Jubilee’) was also shown to be controlled by the same dominant gene. The linkage between Dm6 and root aphid resistance was broken in ‘Lakeland’ as this cultivar does not possess the Dm6 gene. The linkage was presumably broken when the original cross between the parents of cv. ‘Lakeland’, ‘Calmar’ and ‘Avoncrisp’ was made. Under laboratory conditions small numbers of aphids commence development on cv. ‘Lakeland’ but colonies fail to develop and under field conditions the resistance provides adequate Protectión against the pest. The resistance in both ‘Avoncrisp’ and ‘Lakeland’ was effective against a population of lettuce root aphid collected from an endive crop in southern France as well as being effective against the Wellesbourne population of this aphid.     

Factors affecting the induction of secondary dormancy in lettuce

The relationship between the temperature at which germination of 50% of the seeds is inhibited in the light (GT₅₀ Light) and secondary dormancy was investigated in three cultivars of Lactuca sativa L. Seeds were incubated for varying periods under non-germinating conditions and subsequent germination in response to red light (R) was determined over a wide range of temperatures. Dark incubation at 32 C reduced the GT₅₀ Light of cv. New York but did not affect germination at temperatures below 24 C. Dark, 32 C incubation had no effect on the GT₅₀ Light of cv. Great Lakes. In cv. Grand Rapids, dark incubation at 15, 24, 32, or 35 C initially reduced the GT₅₀ Light. However, longer incubations induced a secondary dormancy, i.e., the seeds became unable to germinate at all temperatures in response to R given after the high temperature incubation. A single exposure to R at the beginning of a 32 C incubation slowed the induction of secondary dormancy. Repeated exposures to R prevented the induction of secondary dormancy, but did not prevent a decline in the GT₅₀ Light. GA₃ mimicked the effect of repeated R.     

Proteomic identification of CBM37-containing cellulases produced by the rumen cellulolytic bacterium <Emphasis Type="Italic">Ruminococcus albus</Emphasis> 20 and their putative involvement in bacterial adhesion to cellulose

The objective of this study was to identify and characterize other proteins than fimbrial proteins potentially involved in R. albus 20 adhesion to cellulose using an adhesion-related antiserum preparation (i.e. anti-Adh serum). From protein fractions of R. albus 20 grown on cellulose, the serum recognized at least 10 cellulose-binding proteins (CBPs), among which homologs of glycoside hydrolases (family 5, 9 and 48) of R. albus 8 (i.e. Cel5G, Cel9B and Cel48A) were identified by a proteomic approach. In strain 20, Cel9B and Cel48A were identified as two major CBPs and as bacterial cell-associated proteins. The anti-Adh serum was also shown to target the C-terminal family 37 carbohydrate-binding module (CBM37) of Cel9B and Cel48A, indicating that this module, unique to R. albus, may play a significant role in bacterial adhesion to cellulose as suggested previously for R. albus 8. Overall, our results support the hypothesis of an adhesion mechanism involving the CBM37 of Cel9B and Cel48A. This adhesion mechanism may not be restricted to these two enzymes but may also involve other CBM37-containing proteins such as Cel5G and the other uncharacterised proteins recognized by the anti-Adh serum. The EMBL accession numbers for the sequences reported in this paper are FM872295 for Cel9B and FM872296 for Cel48A.     

Effect of light and temperature on the germination of lettuce seeds

A short period (15–30 min) at 30° C promotes germination of seeds of Lactuca sativa L. cv. Repolhuda in darkness. Far-red light reverses this stimulation, and the escape curves for phytochrome and high-temperature action are quite similar, indicating that the two factors act at a common point in the chain of events leading to germination. It is suggested that high temperature acts by decreasing the threshold of the active, far-red absorbing, form of phytochrome (Pfr) needed to promote germination.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light     

The genomic architecture of disease resistance in lettuce

Genbank and The Compositae Genome Project database, containing over 42,000 lettuce unigenes from Lactuca sativa cv. Salinas and L. serriola accession UC96US23 were mined to identify 702 candidate genes involved in pathogen recognition (RGCs), resistance signal transduction, defense responses, and disease susceptibility. In addition, to identify sequences representing additional sub-families of nucleotide binding site (NBS)-leucine-rich repeat encoding genes; the major classes of resistance genes (R-genes), NBS-encoding sequences were amplified by PCR using degenerate oligonucleotides designed to NBS sub-families specific to the subclass Asteridae, which includes the Compositae family. These products were cloned and sequenced resulting in 18 novel NBS sequences from cv. Salinas and 15 novel NBS sequences from UC96US23. Using a variety of marker technologies, 294 of the 735 candidate disease resistance genes were mapped in our primary mapping population, which consisted of 119 F₇ recombinant inbred lines derived from an interspecific cross between cv. Salinas and UC96US23. Using markers shared across multiple genetic maps, 36 resistance phenotypic loci, including two new loci for resistance to downy mildew and two quantitative trait loci for resistance to anthracnose were positioned onto the reference map to provide a global view of the genomic architecture of disease resistance in lettuce and to identify candidate genes for resistance phenotypes. The majority but not all of the resistance phenotypes were genetically associated with RGCs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

The effect of pH on host plant 'preference' for strains of Rhizobium trifolii using fluorescent ELIS A for strain identification

The effect of pH on host plant ‘preference’ for strains of R. trifolii was studied using the fluorescent ELISA technique. Four white clover cultivars were compared growing at pH 5, 6 and 7 inoculated with 1:1 mixtures of two strains of R. trifolii, CP3B and R4. The growth of these two bacterial strains was also studied at the same pH levels in pure culture. At pH 5, in pure culture, CP3B grew very well but R4 failed to reach the log phase. CP3B also produced the majority of nodules at this pH (86%). At pH 7, in pure culture, R4 grew better than CP3B and also produced 66% of the nodules in the nodulation experiment. However, there was good evidence of host cultivar ‘preference’ with cv. Milkanova having no nodules inhabited by CP3B at pH 7 but cv. S100 having 32%. The results are discussed from the point of view of the establishment of white clover in acid soils and the usefulness of the fluorescent ELISA technique for Rhizobium strain identification is also emphasised.     

Activity and metabolism of 9-substituted cytokinins during lettuce seed germination

The activities of N⁶-benzyladenine (BA) and its 9-substituted methyl, methoxymethyl, tetrahydropyranyl, cyclopentyl, and cyclohexyl analogs were determined for the promotion of lettuce seed (Lactuca sativa L. cv. Grand Rapids) germination. Cytokinin concentrations used were 10^?4, 10^?5, 10^?6 and 10^?7M. All seeds were incubated under total dark conditions at 28 ± 1°C. After 48 h the percentage of germination was recorded. A comparison of means based on Duncan's Multiple Range Test allowed for a ranking of cytokinin activities for the promotion of lettuce seed germination. The activities were: BA = 9-tetrahydropyranyl BA > 9-methyl BA > 9-methoxymethyl BA > 9-cyclopentyl BA > 9-cyclohexyl BA. The results were significant at the 95% confidence level as determined by analysis of variance. In order to study the metabolism of a cytokinin, lettuce seeds were incubated with 9-methyl-BA-methylene-¹⁴C. The labeled cytokinin was prepared by refluxing benzylamine hydrochloride (methylene-¹⁴C) with an equal molar ratio of 6-chloro-9-methylpurine. Final cytokinin concentration was 10^?5M. Incubation periods were 2, 4, 8, 12, 16 and 20 h at 28 ± 1°C under total dark conditions. At the end of the various time periods the seeds were extracted with 70 percent methanol. The resulting extracts were purified and radioactive metabolites identified by solvent fractionation, Sephadex LH-20 column chromatography, and paper chromatography. Co-chromatography with authentic standards in the appropriate solvent system revealed that the metabolites were 9-methyl BA, N⁶-benzyladenosine-5′-monophosphate, and N⁶-benzyladenosine. The results lend support to the theory that the cytokinin ribonucleotide serves as a storage form which is converted to the active ribonucleoside as needed during lettuce seed germination.     

Phytochrome-mediated synthesis of novel growth inhibitors,A-2α and β, and dwarfism in peas

Variations in the content of A-2α and β, novel endogenous growth inhibitors, andcis,trans- andtrans, trans-xanthoxins were determined in 6- or 7-d-old, dark-grown seedlings of peas (Pisum sativum L. cvs. Progress No. 9, dwarf, and Alaska, tall) under various treatments with red light (R), and compared with R-induced growth inhibition. After transfer of the plants to continuous R the contents of the A-2s in cv. Progress increased after a 20-min lag, and reached plateaus after 12 h, whereas they remained almost unchanged in darkness. Both the rates of increase of the A-2s and the plateau levels were proportional to the logarithm of the irradiance applied. After a 10-min R pulse, the contents of both A-2α and β increased with the same rapidity to reach peaks after 6 h, and then gradually decreased to the initial levels after about 24 h. The effect of R was shown to be phytochrome-dependent, being nullified by far-red light. The level of neithercis,trans- nortrans,trans-xanthoxin showed such a close correlation with growth inhibition, although both xanthoxins increased as a result of phytochrome action. It is highly suggestive that the A-2s, rather than the xanthoxins, are responsible for phytochrome-dependent growth inhibition in cv. Progress. In cv. Alaska, in contrast, R-induced increase of the A-2s was rapid but slight, and could not explain the transient growth inhibition, which was found to be as large as that in cv. Progress shortly after the onset of R. The large content of the A-2s in cv. Progress in the steady state under continuous R, compared with that in cv. Alaska, may explain the dwarfism of cv. Progress. Dedicated to Professor Hans Mohr on the occasion of his 60th birthday     

Detection and Identification of ‘Candidatus Phytoplasma prunorum’, ‘Candidatus Phytoplasma mali’ and ‘Candidatus Phytoplasma pyri’ in Stone Fruit Trees in Poland

A survey was made to determine the incidence of phytoplasmas in 39 sweet and sour cherry, peach, nectarine, apricot and plum commercial and experimental orchards in seven growing regions of Poland. Nested polymerase chain reaction (PCR) using the phytoplasma‐universal primer pairs P1/P7 followed by R16F2n/R16R2 showed the presence of phytoplasmas in 29 of 435 tested stone fruit trees. The random fragment length polymorphism (RFLP) patterns obtained after digestion of the nested PCR products separately with RsaI, AluI and SspI endonucleases indicated that selected Prunus spp. trees were infected by phytoplasmas belonging to three different subgroups of the apple proliferation group (16SrX‐A, ‐B, ‐C). Nucleotide sequence analysis of 16S rDNA fragment amplified with primers R16F2n/R16R2 confirmed the PCR/Restriction Fragment Length Polymorphism (RFLP) results and revealed that phytoplasma infecting sweet cherry cv. Regina (Reg), sour cherry cv. Sokowka (Sok), apricots cv. Early Orange (EO) and AI/5, Japanese plum cv. Ozark Premier (OzPr) and peach cv. Redhaven (RedH) was closely related to isolate European stone fruit yellows‐G1 of the ‘Candidatus Phytoplasma prunorum’ (16SrX‐B). Sequence and phylogenetic analyses resulted in the highest similarity of the 16S rDNA fragment of phytoplasma from nectarine cv. Super Queen (SQ) with the parallel sequence of the strain AP15 of the ‘Candidatus Phytoplasma mali’ (16SrX‐A). The phytoplasma infecting sweet cherry cv. Kordia (Kord) was most similar to the PD1 strain of the ‘Candidatus Phytoplasma pyri’ (16SrX‐C). This is the first report of the occurrence of ‘Ca. P. prunorum’, ‘Ca. P. mali’ and ‘Ca. P. pyri’ in naturally infected stone fruit trees in Poland.     

Differentiation of freezing tolerance and vernalization responses in Cruciferae exposed to a low temperature

High levels of freezing tolerance were induced in leaves of different Cruciferae species including Brassica napus, Arabidopsis thaliana, Barbarea vulgaris, Thlaspi arvenses and Descurainia sophia by low-temperature acclimation. Concomitantly, the amount of total RNA doubled in these three species. Analyses of methylation patterns and dosage of rRNA genes were carried out to determine whether or not alterations occur in this DNA during development of freezing tolerance. Hybridizations of Southern transfers with an rDNA probe revealed two additional EcoRI sites in purified DNA isolated from freezing-tolerant leaves of winter B. napus cv Jet Neuf and D. sophia (both of which require low temperatures for vernalization), but not in isolates of A. thaliana or spring B. napus cv Topas. An increase of rDNA cistrons was also observed in both B. napus cv Jet Neuf and D. sophia but not in A. thaliana or B. napus cv Topas upon cold acclimation. These results suggest that low temperature induced amplification of rDNA and the differential methylation of EcoRI sites may possibly be related to the vernalization process but may not be related to the development of freezing tolerance. However, the higher activity of RNA polymerase (2.5 times more) observed upon cold acclimation may explain the concomitant increase in total RNA and may be related to the development of freezing tolerance in the Cruciferae.     

Functional xylem anatomy in root-shoot junctions of six cereal species

In cereals, the formation of safety zones in the root-shoot junction could protect the vessels of roots from embolism originating in the shoot. The root-shoot junction was examined both anatomically, with a light microscope, and experimentally, using a pressurized-air method, in the base of seminal and adventitious roots of maize (Zea mays L. cv. Seneca 60-II), a corngrass mutation of maize (Cg mutant), sorghum (Sorghum bicolor L. cv. Ho-Pak), winter oats (Avena sativa L. cv. Ogle), spring wheat (Triticum aestivum L. cv. Glenlea), winter wheat (T. aestivum cv. Monopol), winter barley (Hordeum vulgare L. cv. Wysor), spring rye (Secale cereale L. cv. JO-02 Finland), and winter rye (S. cereale cv. Musketeer). Two types of hydraulic architecture were found in the cereal roots: (i) a very safe root vessel system, as in winter rye, in which the vessels of the roots are separated from those of the shoots by tracheids, versus (ii) a completely unsafe system, as in corngrass, where the vessels in the root are continuous with the vessels in the shoot. The xylem anatomy of the seminal roots is generally correlated with the species-specific overall root morphology. Rye, wheat and barley, which develop four to six seminal roots, show a high degree of vascular segmentation resulting in, the formation of safe root vessels; maize, sorghum and oats, which typically develop a primary seminal root, contain unsafe vessels that are continuous through the mesocotyl and through the first node. In adventitious roots, vascular segmentation is not related to overall root morphology. Differences in the proportion of safe adventitious roots in which all the vessels end in the root-shoot junction range from 9 to 98% in the cereals studied. In the unsafe roots of these cereals, the number of vessels per root that are continuous through the junction range from 1 to 14. As significant differences in vascular segmentation of the root-shoot junction occur not only between species, but also between cultivars, we suggest that selection based on the occurrence of safety zones might be used in breeding programs designed to improve adaptation of cereals to drought and cold temperatures.This research project was supported by the Natural Sciences and Engineering Research Council of Canada through an International Scientific Exchange Award to R.A. and Dr. C.A. Peterson, and through an Operating Grant to M.G. We thank Dr. G. McLeod (Agriculture Canada, Swift Current, Sask., Canada), Dr. N.P.A. Huner (University of Western Ontario, London, Ont., Canada) and Dr. W.F. Tracy (University of Wisconsin, Madison, USA) for providing seeds; Dr. C.A. Peterson and Dr. W.B. McKendrick (University of Waterloo) for use of the Zeiss photomicroscopes; Dr. M.A. Dixon (University of Guelph, Guelph, Ont.) for use of the Moore pressure gauge; and Dr. R.J. O'Hara-Hines (University of Waterloo) for statistical advice.     

Embryo induction and regeneration from root explants of Medicago truncatula after osmotic pre-treatment

Embryo induction and regeneration from suspension culture of two Medicago truncatula cvs. (cv. R 108 1 and cv. Jemalong) have been studied. The influence of osmotic pre-treatment (1 M solution of sucrose for 48 h and 72 h) of roots as an initial explant, on embryogenic efficiency of the suspension culture was assessed. In comparison to the control, the level of abscisic acid (ABA) increased significantly after osmotic stress. The increased ABA level did not correlate with the induction of embryogenesis neither with the improved embryogenic potential of cv. R 108 1. The shortest regeneration period and the highest percent of conversion to plants were found in cv. R 108 1 after 72-h pre-treatment of roots. The efficiency of somatic embryo conversion was less after 48-h pre-treatment and much less for the untreated control. Osmotic stress did not positively affect the process of embryogenesis from root explants of cv. Jemalong, confirming its cultivar dependence. A single cell suspension fraction was produced in both Medicago trunacatula cvs. during the somatic embryo maturation stage. A higher embryogenic potential than the initial suspension culture was established only for the cell suspension originating from 72-h pre-treated roots of cv. R 108 1. The data confirms that the process of somatic embryo induction and embryo conversion from root explants of cv. R 108 1 could be promoted by osmotic stress pre-treatment.     

Light effects upon dry lettuce seeds

Germination of certain dry seeds (achenes) of Lactuca sativa L. cv. Grand Rapids was increased to ca. 75% after irradiation with 665 nm red light (R; 1x10³ J m^-2); this response was eliminated by far-red light (FR) following the R. The response of dry seeds required an order of magnitude more light than that of wetted seeds, and was not maximal until 48 h after irradiation. Other seeds, which could not be stimulated by R in dry state, showed a partial response after 10 min hydration. Irradiation of dry seeds (or seeds wetted 1 h) with FR (1x10³ J m^-2) reduced dark germination from 26% to 2%. Seeds dehydrated in an oven (60°C, 90 min) showed a decrease in germination if irradiated with R (1x10⁵ J m^-2) before wetting. The results show that phytochrome is present in dry lettuce seeds (and functional in some seed lots) prior to wetting; and that in other seed lots the molecule becomes functional within minutes after wetting the seeds. Transformation of the FR absorbing from of phytochrome (P_FR) to the inactive from (P_R) occurs at lower seed moisture content than the reverse reaction. It appears that dormancy in seeds ripened in sunlight might be assured during seed drying and maturation by the more effective transformation of P_FR to P_R than vice versa as phytochrome is dehydrated.Abbreviations FR far-red - R red - CAL seeds from California - NC seeds from North Carolina (see text)     

Regulation of the nitrate reductase inPisum sativum andtriticum aestivum by irradiation

Nitrate reductase (NR) activity of bothPisum sativum L. cv. Bonneville andTriticum aestivum L. cv. Sonalika seedlings was influenced by the phytochrome system. Short durations of “red” irradiation (R) increased extractable levels of NR whereas subsequent short “far-red” irradiation (FR) partially inhibited the R modulated increases. Qualitatively, a negative correlation existed between thein vitro NR activities andin vivo phytochrome levels inPisum. “Blue” irradiation (B) also increased extractable levels of NR inTriticum. A partial action spectrum study made by exposing excised etiolated leaves ofTriticum and shoot apices ofPisum revealed a maximum increase in extractable NR activities and tissue nitrate level (inTriticum) at 656 nm. A partial action spectrum for the extracted enzyme ofTriticum indicated that at 700 nm the level of activity was increased (as compared to dark controls) more than by R (656 nm), FR (725 nm) or B (425 or 450 nm) irradiation, although all wavelengths used increased NR activity.     

Genetic analysis of tetraploid and hexaploid wheat by utilization of monopentaploid hybrids

Summary This report deals with a method of analysis which uses existing hexaploid wheat monosomics to establish gene-chromosome associations in a tetraploid variety. Monosomics of Triticum aestivum cv. Chinese Spring belonging to the 14 lines of A and B genomes were crossed as female parents with Triticum durum cv. Capeiti, a spring type at present widely grown in Italy. For each line, two F ₁ populations were obtained, normal pentaploids (2 n = 35) and monopentaploid (2 n = 34), in which, in turn, the monosomic A or B chromosome present was supplied by the tetraploid wheat. The morphological and physiological differences observed in the monopentaploid lines are attributed to differential expression of the genetic information concerning the character investigated, carried by the chromosome present in hemizygous condition. Then, only recessive or partially dominant alleles of the variety to be tested can be identified and attributed to a specific chromosome in the F ₁ generation.Eight parameters were analyzed: culm and spike length, length and width of 1st (flag) and 2nd uppermost leaves, days from germination to heading and awn development.As far as culm length is concerned, although heterotic effect is present, seven chromosomes seem to be responsible for the modification of this character (1A, 2A, 2B, 3B, 4B, 5B, and 6 A); chromosomes 2A and 2B in particular, carry major factor (s) for plant height. A similar picture is presented by spike length which seems to be controlled by factors located in several chromosomes belonging to homoeologous groups 1, 2, 3 and 5, as well as the chromosome 4B.Leaf length, also, shows a complex pattern of inheritance. Monosomic conditions for chromosomes 1A and 1B increased, while monosomy for 5A and 5B significantly decreased, leaf length. A highly significant correlation was found between the mean lengths of the 1st and 2 nd leaves (= 0.74). Some monosomic lines (4A, 4B, 5A; 5B; 6A; 7A and 7B) had leaves significantly narrower than in the control and only monosomic 2A had broader leaves. The period from germination to heading seems to be influenced by at least 6 chromosomes. Three monosomic lines are significantly earlier (mono 1A, 7A and 5B) and three (mono 5A, 2B and 7B) are significantly later than the hybrid control.Finally, 8 monosomic lines were found to interfere significantly with awn development. Three lines (mono 2A, 2B and 7A) show a decrease and 5 (mono 1B; 3A, 3B; 4B and 6B) show an increase in awn development. On the basis of evidence in the literature and our own results, it appears that this analysis fits previous results perfectly and actually adds to the picture two further awn-promoting factors, A9 and A10, located on the 7A and 1B chromosomes respectively.Contribution n. 220 from the Laboratorio per le Applicazioni in Agricultura del C. N. E. N., Centro Studi Nucleari della Casaccia, S. Maria di Galeria, Roma, Italy.With the technical assistance for cytological and statistical analyses of P. Mannino.     

Effect of salt on malondialdehyde and antioxidant enzymes in seedling roots of Jerusalem artichoke (<Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L.)

Two cultivars of Jerusalem artichoke (Helianthus tuberosus L.) differing in genotype, Red skin (cv. R., salt-tolerant but low-yield) and White skin (cv. W., salt-sensitive but high-yield), were used to investigate malondialdehyde (MDA) content and antioxidant enzyme activity changes in their roots under a hydroponic culture system with 250 mM NaCl. The results showed that MDA contents in roots of the two genotypes increased, but MDA content of cv. R. was higher than that of cv. W. Changes in all antioxidant enzymes in roots of both varieties exhibited a similar trend, namely increased initially and then decreased. However, there were still some differences existing between the two cultivars. In other words, activities of the other two antioxidant enzymes except catalase (CAT) and peroxidase (POD) in roots of cv. R. were less than controls at 48 h, while all others except ascorbate peroxidase (APX) in roots of cv. W. were greater than controls. The peak of superoxide dismutase (SOD) activity of cv. W. was observed to appear earlier than that of cv. R. CAT activity of cv. W. was significantly greater than the value of cv. R. and the latter showed a moderate trend. POD activity of cv. R. obtained the maximum at 6 h, whereas the peak of cv. W. displayed at 24 h. APX activity of cv. R. declined more than that of cv. W. These results suggested that there was a lower efficiency of scavenging reactive oxygen species (ROS) in cv. R. roots. Concomitantly, salt stress caused more severe damage to roots of cv. R. Antioxidant enzymes in roots were inadequate to elucidate salt-tolerance mechanisms of the whole plant.     

Identification of a maize linkage group related to apomixis in Brachiaria

 A bulked segregant analysis using RFLPs and RAPDs was carried out to identify molecular markers co-segregating with apomixis in a Brachiaria F₁ population. The test population used was a cross between sexual B. ruziziensis R44 and the aposporous apomictic Brachiaria brizantha cv Marandu. The Brachiaria genome was systematically scanned using 61 cDNA and genomic maize clones detecting 65 loci located at 40 cM, on average, one from each other in the maize genome. The finding of a clone that presented a polymorphic band co-segregating with apomixis (umc147) led to the identification of another marker within the same area (umc72). The clones belong to a duplicated linkage group that maps to the distal part of maize chromosome-1 long arm and chromosome-5 short arm. RAPD analysis using 184 primers from Operon sets yielded one more marker (OPC4) significantly linked to the trait mapping the same locus. OPC4 had been previously reported as a potential marker for apospory in Pennisetum. A map of the region was constructed using additional clones that belong to the same maize linkage group. Since that was the only genomic region that presented an apomixis-linked polymorphism our observations support the existence of a single locus directing apospory in Brachiaria. Received: 9 September 1996 / Accepted: 20 September 1996     

Design of human granzyme B variants resistant to serpin B9

Human granzyme B (hGB) is a serine protease involved in immune‐mediated apoptosis. Its cytotoxicity makes it potentially applicable in cancer therapy. However, the effectiveness of hGB can be hampered by the cytosolic expression of a natural protein inhibitor, human Serpin B9 (hSB9). Here, we used computational approaches to identify hGB mutations that can affect its binding to hSB9 without significantly decreasing its catalytic efficiency. Alanine‐scanning calculations allowed us to identify residues of hGB important for the interaction with hSB9. Some variants were selected, and molecular dynamic simulations on the mutated hGB in complex with hSB9 in aqueous solution were carried out to investigate the effect of these variants on the stability of the complex. The R28K, R201A, and R201K mutants significantly destabilized the interaction of the protein with hSB9. Consistently, all of these variants also retained their activity in the presence of the Serpin B9 inhibitor in subsequent in vitro assays of wild‐type and mutated hGB. In particular, the activity of R201K hGB with and without Serpin B9 is very similar to that of the wild‐type protein. Hence, R201K hGB emerges as a promising species for antitumoral therapy applications. Proteins 2012. © 2012 Wiley Periodicals, Inc.     

Characterization of New Highly Virulent German Isolates of Bremia lactucae and Efficiency of Resistance in Wild Lactuca spp. Germplasm

Four German isolates (FS1, SR2, SAW1 and DEG2) of Bremia lactucae originating from lettuce cultivars with R‐factors R18 and Dm6 + R36 were used for detailed characterization of virulence factors (v‐factors) and for the study of the resistance efficiency in wild Lactuca spp. germplasm. The highest complexity of v‐phenotype was recognized in isolate DEG2, which overcomes resistance in cv. Mariska (R18) and line CS‐RL (L. serriola × L. sativa, R18 + ?), until now known as resistant to all known races of B. lactucae in Europe. However, some sparse sporulation also occurred on cv. Titan (Dm6 + R36). The isolates SR2 and SAW1 overcome the resistance based on the gene R36, but are avirulent to R18. The v‐phenotype of SR2 is highly complex with the most important v‐factors being present except for v14 and v18. The isolate FS1 is the first in Germany originating from a cultivar with R18 (cv. Samourai). The search for efficient sources of resistance in 64 accessions of 11 wild Lactuca spp. and primitive forms of L. sativa showed broad variation in accession–isolate interactions. Expression of race‐specific resistance in wild Lactuca spp. (L. serriola, L. viminea, L. virosa) was recorded frequently. Lactuca indica and L. saligna could be considered as the most efficient sources of resistance against isolates FS1, SR2 and SAW1. The isolate DEG2 showed the highest level of virulence. On seedlings of L. saligna, which is considered as a most important source of resistance against B. lactucae, there was frequently recorded limited sporulation, however this response cannot be considered as a susceptible. Except for some L. saligna accessions (CGN 05310 and CGN 05315), the resistance to all studied isolates was only observed in one accession of L. serriola (PI 253467).     

Characterization of Sym plasmids of Rhizobium leguminosarum strains able to nodulate Pisum sativum cv Afghanistan

Rhizobium leguminosarum strains that can form nodules on Pisum sativum cv. Afghanistan have been reported as uncommon in Europe, North America and Africa [11, 12]. The organization of the nodulation regions of the symbiotic plasmids of five strains of R. leguminosarum originating from Denmark [9], which can nodulate P. sativum cv. Afghanistan, was compared with that of a Turkish strain (TOM [18]) by DNA hybridizations. Four of the five Danish strains were found to be very similar to the Turkish strain with respect to the overall organizations of their respective nodulation regions.