Evidence for Repair Processes in Onion Seeds during Storage at High Seed Moisture Contents

Survival curves of four seed lots of onion held at 15%, 20%and 25% seed moisture content (me) and 45 ° C for 24 h showeda fall in seed germination at all moisture contents. The rateof loss of viability was less for seeds held at 20% and 25%me than that of seeds held at 15% me, with low vigour seedsshowing the greatest reduction in the rate of deteriorationat the high moisture contents. This is interpreted as evidencefor the activation of repair processes in seeds during periodsof partial seed hydration and discussed in relation to seedinvigoration treatments. Key words: Seed moisture content; Storage, Repair, Priming, Invigoration     

Changing Assumptions in Primate Ecology

Ecological research on nonhuman primates developed separately from the discipline of ecology as a whole, and has in the past been characterized by a distinctive set of goals and assumptions. This paper examines some of the problems surrounding these assumptions. Recently, primate ecologists have begun to adopt the conceptual framework of other ecologists; it is argued here that this trend does not in fact solve all the old problems. Finally, the future of primate ecology is considered briefly . [Primates, ecology, adaptation, strategies, optimization]     

The Influence of Testa Condition on the Imbibition and Vigour of Pea Seeds

Seed lots of peas with high rates of water uptake which containeda large proportion of seeds with at least one crack in the testaand were low in vigour, as indicated by electrolyte leakageand poor field emergence. Comparisons of the tetrazolium chloridestaining of the cotyledons after imbibition in water and polyethyleneglycol of two seed lots both with and without scarificationshowed that cracks in the testa could cause cell death by increasingthe rate of water uptake. Although the major cause of poor seedvigour appeared to be the incidence of cracks in the testa whichresulted in rapid water uptake, cell death, and solute leakage,the condition of the embryo also influenced the response towater uptake. The practical significance of these observationsto the problems of field emergence and seed production in peasis discussed.     

Agouti Protein Inhibits the Production of Eumelanin and Phaeomelanin in the Presence and Absence of α-Melanocyte Stimulating Hormone

Melanocytes synthesise two types of melanin: the brown-black eumelanin and the red-yellow phaeomelanin. In mice, the relative proportions of these two melanins are regulated by α-MSH, which preferentially increases the synthesis of eumelanin and by the Agouti protein (AP), the expression of which correlates with the growth of yellow phaeomelanin-containing hair. It has been proposed that AP acts by antagonizing the action of α-MSH at the MCI receptor, although it has been suggested that it may also act independently of α-MSH. In the present study we show that AP inhibits melanogenesis in B16F1 melanoma cells in the presence and absence of α-MSH and also causes dose-related decreases in the synthesis of both eumelanin and phaeomelanin. In the presence of α-MSH AP had a greater effect on eumelanin production and this is consistent with an antagonistic action at the MCI receptor. In the absence of α-MSH however, AP produced similar reductions in the synthesis of both melanins. These changes were not seen in B16G4F cells which lack the MCI receptor, suggesting that even in the absence of α-MSH AP acts at the MCI receptor. How this action is mediated at the intracellular level is not yet clear, although it appears to be associated with a decrease in tyrosinase activity.     

Oral deformities in tadpoles (Ranacatesbeiana) associated with coal ash deposition: effects on grazing ability and growth

1. Tadpoles of the bullfrog ( Rana catesbeiana ) collected in a coal ash deposition basin (contaminated with As, Cd, Cr, Cu, Se and other elements) and a downstream drainage swamp had a reduced number of labial teeth and deformations of labial papillae when compared with tadpoles from reference areas. Tadpoles from the coal ash-affected areas had 90% fewer teeth in anterior tooth row number 2 and 40% fewer teeth in posterior row number 1 than reference animals. In the deposition basins, drainage swamp and reference ponds, respectively, 96.2, 85.1 and 2.9% of tadpoles had oral deformities.
2. Tadpoles with deformities were less able to graze periphyton than were normal tadpoles, when tested in the laboratory. When presented with periphyton as a sole food source, tadpoles with deformed teeth had lower (negative) growth rates than those with normal teeth, which had slightly positive growth rates. When particulate food was also available, tadpoles grew well regardless of deformities.
3. It appears that the morphological deformities associated with this coal ash-polluted environment can have ecological ramifications for the affected organisms by limiting the type of food that can be consumed and the ability to grow when multiple food types are unavailable.     

METHODS FOR THE STUDY OF BLOWFLY POPULATIONS

The variance of groups of traps sampling the blowfly populations of areas of different degrees of complexity is examined from data for three representative types of pasture—semi-arable, reclaimed peat bog, and upland sheepwalk.
For mean catches of under twenty flies the coefficient of variation was less for limited areas of homogeneous vegetational cover than for larger areas and greater diversity of vegetation; at intermediate mean levels the difference was negligible, hut it reappeared at mean levels of 40 and upwards.
Throughout the range of catches examined the variance was much greater than the mean. For very low catches even the standard deviation exceeded the mean, and at no level of mean was it less than 40%.
Even for uniform areas such as association fragments the high variance made results with less than six traps difficult to interpret, and ten or more traps are advised.
Two methods of comparative sampling of populations are discussed—stratification of the area to be sampled into subunits of relatively uniform vegetational or edaphic facies, and random distribution of the traps over the whole area. For the mean catches by these methods standard regression lines are suggested, from which variance estimates may be made when comparing observed means. Both regressions consist of two straight lines, the lower in each case having a steeper slope. The lines are:
Sections S.D. =+ 1 and 0·5+7.
Subsection blocks S.D. = 0·8+ 1 and 0·4+9     

Axillary Bud Development in White Clover in Relation to Defoliation and Shading Treatments

A period of growth under shade netting in the glasshouse allowedthe cultivation of white clover stolons with an accumulationof undeveloped axillary buds similar to that often found onstolons from grass/clover swards. The subsequent capacity ofthese nodes to develop branches under different circumstanceswas investigated in three experiments. Removal of the laminaeand petioles subtending sets of four buds along a stolon reducedthe rate at which branches were initiated from the buds. Treatmentsin which petioles, or petioles plus laminae, were retained initiatedbranches more quickly. Shading the stolons reduced both therate of initiation and the percentage of buds which developed,unless both petioles and laminae were retained. There was someevidence that conditions applied to individual buds may actin the same way as the same conditions applied to sets of fourbuds and that illuminated nodes may depress the performanceof neighbouring shaded notes. Fewer buds developed at older nodes than at younger nodes duringthe summer, but during the autumn younger buds initially developedmore slowly than older buds. This suggests that buds can developat a younger nodal age in summer than in winter. When leafless stolons were cut up into component internodesbuds developed faster than on intact stolons, provided the budwas located at the end of the internode nearest the main stolongrowing point. If the bud was at the other end, branch developmentwas slower than on intact stolons. The results are discussedin relation to clover growth in sward conditions. White clover, Trifolium repens, axillary bud development, branching, growing points, defoliation, shading     

A method for measuring hydraulic conductivity and embolism in xylem

Abstract Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time-dependent reductions in flow rate, and because of variable degrees of embolism. Using Acer saccharum Marsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m^?3 oxalic) prevent long-term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow-impeding air emboli have been removed by repeated high-pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long-term (> 4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short-term (< 4h) measurements may be caused by movements of air emboli in vessels and/or participate matter.