National Vegetable Research Station

Warwick, United States

National Vegetable Research Station

Warwick, United States

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The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik | Year: 2013

Previously undetected race-specific resistance to Bremia lactucae (downy mildew) was located in many lettuce cultivars hitherto considered to be universally susceptible to this disease. This resistance factor(s) may also be widely distributed in other cultivars known to carry combinations of already recognised factors R1 to R11. Specific virulence to match this resistance is almost invariably present in pathogen collections. This situation may be either a relic of the evolutionary history of the B. lactucae - L. sativa asssociation or may reflect a rare mutation in B. lactucae for avirulence on all but a few specialised L. sativa genotypes.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik | Year: 2013

The effects of hexane, high humidity, flower age and temperature in overcoming the self-incompatibility of Brassica oleracea were studied using three plants, each of which was homozygous for a different dominant S-allele. Hexane had a significant effect in all cases, but the size of the effect varied considerably. In one plant there was a marked interaction between the effect of hexane, humidity and flower age, but temperature had relatively little effect. In another plant high humidity alone gave a very much greater response than hexane alone. This plant gave as many self-seeds from the high humidity treatment as from bud selfing, indicating that the incompatibility reaction was almost completely overcome by the high humidity. The results are discussed in the light of current views of the mechanism of incompatibility in Brassica.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik | Year: 2013

Seven onion cultivars of Japanese and European origin were evaluated in autumn-sown trials, at six sites over two seasons. Within each season genotypic differences were detected for winter-kill, bolting, maturity time and yield. In general the Japanese cultivars showed consistently lower levels of bolting and winter-kill and earlier maturity relative to the European cultivars. Environmental effects were important with differences between seasons, sites and sowings recorded for most characters. It was concluded that the use of early and late August sowings would provide suitable screening environments for bolting and winter-kill respectively. There were also differences between genotypes in their linear response to environments as shown by joint regression analyses. Express Yellow O-X (hybrid) showed least response to environments for bolting and winter-kill and Senshyu semi-globe Yellow gave the most consistent time to maturity over environments.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik | Year: 2013

The relative ability of cross- and self-pollen to achieve fertilisation in Brassica was studied by making double pollinations using cross-pollen carrying a dominant seedling marker gene. With simultaneous self- and crosspollination 12-40% self-seed was set, but when cross-pollen was applied to the stigma four hours before self-pollen, only 2-4% self-seed was obtained. In two plants to which cross-pollen was applied at various time intervals after self-pollen there was a tendency for the percentage of self-seed to increase as the time interval increased. In a third plant this trend was not apparent, probably because of a greater degree of self-incompatibility. The competitive advantage of the first pollen to arrive on the stigma is discussed in relation to the strength of the self-incompatibility and the sib problem in F1 hybrid brassicas.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: Planta | Year: 2013

The integrity of ribosomal RNA (the percentage of complete, un-nicked molecules) in seeds was studied by electrophoresis under denaturing conditions. Two batches of carrot seed, harvested at different stages of maturity, and four batches ofNicotiana seed stored for various times were used. Within each species, there was a correlation between the integrity of the rRNA of the dry seed and the rate of germination of that seed. In carrot seed, there was extensive degradation of existing rRNA in both the embryo and endosperm during the first two days of imbibition.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik | Year: 2013

182 plants representing 7 cultivars of Cape broccoli were tested for their S-alleles using the standard Brassica S-allele collection. In all but 12 plants both S-alleles were identified. A total of 20 different S-alleles were found, 9 of which occurred in the autumn types but not in the spring, 5 of which occurred in the spring types and not the autumn, and 6 of which were common to both. Most of the S-alleles detected in Cape broccoli were also found in Brussels sprouts or kales, but of the three which were not, two were confined to Cape broccoli while the third occurred only in Cape broccoli and Savoy cabbage. By far the commonest S-allele in Cape broccoli was S2, with an overall frequency of 35%. Three S-alleles were found (S14, S25 & S45) which were completely recessive in the stigma in certain combinations. The general pattern of distribution of S-alleles in Cape broccoli, with highly unequal frequencies, was similar to that in Brussels sprouts. The results indicate a high level of outcrossing in Cape broccoli which has implications for the breeding of this crop.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: Planta | Year: 2013

The solubilised ethylene-binding site (EBS) of Phaseolus vulgaris L. cotyledons is an asymmetrical protein with a sedimentation coefficient of 2 S and a Stokes radius of 6.1 nm (determined by ultracentrifugation on isokinetic gradients and gel-permeation chromatography, respectively). The molecular weight and frictional ratio were calculated as 52 000-60 000 and 2.37-2.48, respectively. The EBS has an isoelectric point at between pH 3-5, determined by isoelectric focussing and exhibits a negative charge at pH 8 during non-denaturing electrophoresis. The electrical charge on the EBS is shielded; the EBS does not bind to anion-exchange media under the experimental conditions reported here, is not precipitated by ammonium sulphate and does not precipitate at its isoelectric pH. The EBS preferentially partitions into detergent phases. The results indicate that the EBS is a hydrophobic protein complexed with detergent in aqueous solution. The techniques used to characterise the EBS also resulted in varying degress of purification.


The performances of four gas chromatographic detectors (nitrogen-phosphorus, flamephotometric, electron-capture and flame-ionisation) were compared for the analysis of permethylated cytokinins. The nitrogen-phosphorus and flame-photometric detectors (selective for nitrogen and sulphur-containing compounds respectively) gave greatly enhanced sensitivity and-or specificity compared with the flame-ionisation detector for a wide range of cytokinin types. The response of the electron-capture and flame-ionisation detectors was quantitatively similar. The improved performance of the nitrogen-phosphorus and flame-photometric detectors was used to develop rapid and simple purification techniques for the assay of zeatin and zeatin riboside in coconut milk; dihydrozeatin and dihydrozeatin riboside in bean leaves and cytokinin nucleosides in wheat-germ transfer RNA.


PubMed | National Vegetable Research Station
Type: Journal Article | Journal: Planta | Year: 2013

The ethylene-binding site (EBS) from Phaseolus vulgaris cv. Canadian Wonder cotyledons can be solubilised from 96,000 g pelleted material by Triton X-100 or sodium cholate. Extraction of 96,000 g pellets with acetone, butanol or butanol and ether results in a total loss of ethylene-binding activity. Like the membrane-bound form, the solubilised EBS has an apparent KD(liquid) of 10(-10) M at a concentration of 32 pmol EBS per gram tissue fresh weight. Propylene and acetylene act as competitive inhibitors, carbon dioxide appears to promote ethylene binding and ethane has no significant effect. The solubilised EBS is completely denatured affect. The solubilised EBS is completely denatured after 10 min at 70C, by 1 mM mercaptoethanol and 0.1 mM dithiothreitol, but not by trypsin or chymotrypsin. However, solubilisation decreases the rate constant of association from 10(3) M(-1) s(-1) to 10(1)-10(2) M(-1) s(-1) and hence does not permit experimental determination of the rate constant of dissociation. The pH optimum for ethylene binding is altered from the range pH 7-10 in the membrane-bound form to the pH range 4-7 in the solubilised form. The EBS appears to be a hydrophobic, intergral membrane protein, which requires a hydrophobic environment to retain its activity. Partitioning of the EBS into polymer phases is determined by the detergent used for solubilisation indicating that when solubilised, the EBS forms a complex with detergent molecules.

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