An Evaluation of EPR Measurements of the Organic Free Radical Content of Individual Seeds in the Non-destructive Testing of Seed Viability

Hepburn, H. A., Goodman, B. A., McPhail, D. B., Matthews, S.and Powell, A. A. 1986. An evaluation of EPR measurements ofthe organic free radical content of individual seeds in thenon-destructive testing of seed viability.—J. exp. Bot.37: 1675–1684. Electron paramagnetic resonance (EPR) spectra of individualintact seeds of a range of legumes and brassicas have been obtainedin order to measure their organic free radical contents. Norelationship was found between free radical content and seedviability or early seedling growth for both legumes and brassicas.The testa had a much greater free radical concentration thaneither the embryo axes or the cotyledons for all cultivars ofseed tested. The general high free radical content of the testasuggests that there is little possibility of EPR being usedto predict the viability of individual seeds. The spectroscopicsplitting factor of g = 2·0045 reported for the intactseeds is consistent with the radicals' arising from melanictype compounds. Key words: Seed viability, free radical content     

Biomass: Is it a useful tool in paleocommunity reconstruction?

In general, more of the biomass of the community is preserved than is its numerical abundance. Thus, the paleontologist, on the average, works with more of the community when biomass is used. Community characteristics such as taxon dominance and habitat proportions are at least as accurately derived from biomass as numerical abundance. The use of biomass is clearly more appropriate in describing energy flow and trophic proportions. Whenever possible, biomass should be used as a complement to numerical abundance in future paleoecologic reconstructions.     

Studies on Foliar Penetration: VIII. EFFECTS OF CHLORINATION ON THE MOVEMENT OF PHENOXYACETIC AND BENZOIC ACIDS THROUGH CUTICLES ISOLATED FROM THE FRUITS OF LYCOPERSICON ESCULENTUM L.

The effects of chlorine substitution on the movement of phenoxyaceticand benzoic acids through enzymatically-isolated cuticles ofLycopersicon fruits were determined by following the transferof each acid containing ¹⁴C from a donor to a receiver solution.This cuticle is characterized by an isotropic cutin matrix,within which patches of birefringent cuticular waxes are foundnear the outer surface. The outer, morphological surface isrelatively smooth while at the junction with the outer wallsof the epidermal cells there is extensive cuticular developmentextending down between the anticlinal walls. The epicuticularwax appears as a soft sheet-like covering of which the surfaceis relatively featureless. Chlorination of phenoxyacetic acid results in an enhanced transferacross the isolated cuticle. The order was 2,4,5- and 2,4,6-trichlorophenoxyacetic> 2,4- and 3,5-dichlorophenoxyacetic > 2-chlorophenoxyacetic> phenoxyacetic acid. Removal of the epicuticular wax resultedin greater permeability for all compounds; transfer of the morepolar acids was favoured. In contrast, chlorination of benzoicacid decreases passage through the cuticle; the rate is highestfor benzoic acid followed in descending order by 2-chlorobenzoic,2,4- and 2,5-dichlorobenzoic and 2,3,6-trichlorobenzoic acid.Chlorination also depresses the passage of both phenoxyaceticand benzoic acid through a dialysis membrane. The effects ofchlorination on the lipid solubility of both series of compoundsare discussed in relation to differences in transfer acrossthe cuticle.     

The Importance of Genetically Determined Seed Coat Characteristics to Seed Quality in Grain Legumes

Comparisons of five pairs of isogenk lines of peas, differingonly in the A gene for seed coat colour showed that white seeds(genotype aa) imbibed more rapidly than coloured seeds (AA),suffered greater imbibition damage revealed by dead tissue onthe cotyledons, and higher solute leakage. Seed-coat pigmentationwas closely associated with slow water uptake, since when expressionof the A gene was suppressed by the recessive pollens gene,the resulting white seeds {palpal AA) imbibed rapidly. The slowwater uptake by coloured seeds was not due to the restrictionof water entry by the seed coat since the differences in imbibitionrate were maintained when a portion of the seed coat was removedand seeds were imbibed with the exposed cotyledon in contactwith moist filter paper. Imbibition of similarly treated seedsby immersion in polyethylene glycol solutions (1–4%) whichincreased the seed/solution wettability, had little effect onthe water uptake of coloured seeds compared to imbibition inwater whereas that of white seeds increased in the first 10mins imbibition. Poor wettability of the inner surface of colouredseed coats did not therefore explain the slow imbibition ofthese seeds. The white seed coats loosened rapidly during imbibitionwhilst the coloured seed coats remained closely associated withthe cotyledons suggesting that the adherence of the seed coatto the cotyledons and therefore the ease of access of waterbetween the testa and cotyledons determines the rate of imbibition.The rapid water uptake by white-coated seeds and the subsequentimbibition damage may explain the high incidence of infectionof these seeds by the soil-bome fungus Pythhan after 2 d insoil. Improved seed quality and emergence may therefore be achievedby breeding for seed coat characteristics leading to reducedrates of imbibition Pisum sativum, isogenic lines, A gene, seed coat colour, imbibition, imbibition damage, wettability, pollens gene, seed quality, grain legumes     

Prolonged aerated hydration for improvement of seed quality in Brassica oleracea L.

Seeds of cauliflower cv. Hipop and Brussels sprouts cv. Asmer Aries were aged at 20% moisture content for 24 h; all seeds retained a germination of over 70% after ageing although the mean germination time increased. Prolonged aerated hydration for up to 32 h at 20°C followed drying resulted in improved performance of both unaged and aged cauliflower seeds and aged Brussels sprouts. Thus, all seed showed reductions in the mean germination time to the extent that after 32 h hydration the aged cauliflower seeds performed as well as high quality unaged seed. The improvement of aged seeds was also revealed an increase in germination after the controlled deterioration test following up to 24 h (cauliflower) or 32 h (Brussels sprouts) aerated hydration. This increase was indicative of a decrease in the extent of deterioration present after aerated hydration. Deleterious effects of prolonged hydration were observed in Brussels sprouts after 32 h although these may be explained desiccation injury after treatment since radicle emergence had occurred during hydration. The improvements in seed performance may be explained the activation of metabolic repair occurring during the early part of the hydration period therereducing the extent of deterioration that has been sustained during ageing, with further improvements due to the advancement of the germination process.     

Scaling relationships within the maxillary tooth row of the Felidae, and the absence of the second upper premolar in Lynx

Suggestions that short-faced members of the Felidae tend to lack the second upper premolar (P2) imply a possible shift in scaling associated with the palate and maxillary tooth row in Lynx , which lacks P2, as compared to felids that retain it. This hypothesis is tested using a scaling model that relates the lengths of the palate, and the upper tooth row and its components, to post-palatal skull length in the small to moderately large felids Felis catus (domestic cat), L. canadensis (Canada lynx), F. pardalis (ocelot), and F. concolor (cougar). Scaling relationships of both palate and tooth row length to post-palatal skull length do not differ significantly from isometry in all four species. However, ocelots have a significantly shorter palate and tooth row than lynxes over their overlapping ranges of post-palatal skull length, suggesting that the absence of P2 is not correlated with the length of the face in these species. CI, P3 and P4 tend to be relatively longer in larger felids; none the less, ocelots have a relatively small P3 and lynxes have a proportionately large P4. Because both lynxes and ocelots have a relatively small gap between CI and P3, the absence of P2 is not correlated with available space within the tooth row in adults. However, lynxes also appear to have a relatively long dP3 that almost obliterates the diastema within the deciduous tooth row. The absence of P2 in Lynx may be an engineering artefact that is associated with a shift in proportions within the deciduous toothrow, resulting in inhibition of the development of P2 and dP2 early in ontogeny. Despite the variable occurrence and polymorphism associated with P2 in the Felidae, this character has systematic value within this clade and is a synapomorphy for Lynx.     

The Strategy of Carbon Utilization in Uniculm Barley: II. THE EFFECT OF CONTINUOUS LIGHT AND CONTINUOUS DARK TREATMENTS

After a photoperiod of 8.25 h during which the youngest fullyexpanded leaf of uniculm barley plants was allowed to assimilate¹⁴CO₂ for 30 min, groups of plants were transfered either tocontinuous light or to continuous dark. Plants were harvestedover a 72 h period to examine the effect of the treatments (comparedwith control plants growing in normal light/dark cycles) onthe transport of ¹⁴C from the exposed leaf, the distributionof ¹⁴C assimilates to the rest of the plant, and the chemicalfate of assimilated ¹⁴C. In continuous light a substantial quantity (22% at 72 h) ofthe ¹⁴C assimilated by the leaf remained in that leaf in theform of starch and neutral sugars compared with only 4% in thecontrol fed leaf. Also the total amount of ¹⁴C respired fromplants maintained in continuous light was significantly less(c. 18% of the total originally fixed by 24 h) than that respiredfrom control plants (c. 36%). The result was that approximatelyequal amounts of ¹⁴C were accumulated in the growing leavesand roots of plants given continuous light or normal light/darkcycles. In continuous dark the fate of ¹⁴C was similar to that of controlplants. This is probably because the two treatments shared acommon light/dark environment for the first 22 h, during whichtime almost complete distribution and utilization of ¹⁴C occurred.     

The use of DNA markers to estimate the extent and nature of genetic variability in Solatium tuberosum cultivars

High levels of DNA polymorphism were detected in 27 Solanum tuberosum cultivars examined. Combinations of at least two c-DNA clones have been identified which in conjunction with EcoRI allow important UK potato cultivars to be characterised by their molecular profiles. The widely grown North American cultivar Russett Burbank was also successfully fingerprinted. Estimates of genetic diversity based on restriction fragment length polymorphism (RFLP) data indicate the important role that wild potato species and exotic germplasm have played in the development of the cultivars studied. A graphical method for simultaneously highlighting similarities and differences between genotypes for individual hybridising fragments is presented. This approach is particularly useful in identifying and recording fragments which are unique to certain genotypes. Two potato cultivars: Fiona and Morag produce unique RFLP profiles when digested with EcoRI and EcoRV and probed with a flax ribosomal DNA sequence. Both Fiona and Morag possess incomplete or partial (quantitative) type resistance to G. pallida which was transferred from S. vernei. The preferential transmission of the r-DN A fragments from S. vernei may indicate that this locus is associated with genetic factors controlling resistance to G. pallida.     

A quantitative description of the forest vegetation on an altitudinal gradient in the Mount Field National Park,Tasmania, and a discussion of its history and dynamics

The aim of this study was to describe the forest vegetation along an altitudinal transect running from 158 m to 1220 m (treeline) in the Mount Field National Park, Tasmania. Eighteen 1 ha plots were sampled along this transect, using a modified point-centred quarter method for species composition and density. Size frequency distributions were used to calculate basal areas. Estimates of relative density, frequency and basal area for each species were combined in to an importance value. The altitudinal ranges of all woody species were determined. The altitudinal temperature lapse rate was measured, and data on soil pH obtained. The initial ‘direct gradient’ analysis revealed relatively well marked discontinuities in the vegetation which were further examined by ordination and classification techniques. The latter provided a simple threefold classification into altitudinal zones. The lower zone reaches from the Park entrance (158 m) to between 600 and 670 m, and comprises tall open forest dominated by Eucalyptus regnans and/or E. obliqua and with a ‘wet sclerophyll’ understorey characterized by Olearia argophylla. The middle zone stretches from c. 670 to 940 m and comprises closed rainforest or ‘mixed’ forest (i.e. with senescent emergent eucalypts) dominated by Nothofagus cunning hamii and Atherosperma moschatum. This zone is characterized by the absence of O. argophylla and the presence of Phyllocladus aspleniifolius. The upper part of this zone constitutes an interdigitating transition to the subalpine forests, usually dominated by E. coccifera and occurring on suitable sites between c. 880 m and the timberline. The transition to subalpine forests is associated with a marked decline in basal area. Species richness (of woody plants) increases with altitude to reach a peak in the sub-alpine zone. This trend is the reverse of that normally encountered elsewhere in the world, and is mainly due to relatively high α and β diversities in the shrub stratum of this zone. The significance of fires, aspect and substrate is discussed in relation to the variations in composition within each zone. The low diversity of Nothofagus-dominated rainforest is thought to be due, in part, to the intense competitive thinning in the eucalypt re-growth phase following burning, and the subsequent ‘capture’ of the Eucalyptus niche by Nothofagus. It is speculated that, in Tasmania, the downhill migrations during the cooling phases of the Pleistocene were associated with extinctions of lowland forest taxa, while uphill migrations during warming phases were associated with speciation on the plateaux of the present subalpine zone. This hypothesis implies that the relative proportions of land area available at different altitudes, now and in the past, have determined the relative rates of speciation and extinction, and hence the altitudinal gradients of species richness.