Influence of root diameter on the penetration of seminal roots into a compacted subsoil

A field experiment was conducted to evaluate the influence of root diameter on the ability of roots of eight plant species to penetrate a compacted subsoil below a tilled layer. The soil was a fine sandy loam red-brown earth with a soil strength of about 3.0 MPa (at water content of 0.13 kg kg^-1, corresponding to 0.81 plastic limit) at the base of a tilled layer. Relative root diameter (RRD), which was calculated as the ratio of the mean diameters of roots of plants grown in compacted soil to the mean diameters of those from uncompacted soil, was used to compare the sensitivity of roots to thicken under mechanical stress.Diameters of root tips of plants grown in soil with a compacted layer were consistently larger than those from uncompacted soil. Tap-rooted species generally had bigger diameters and RRDs than fibrous-rooted species. A higher proportion of thicker roots penetrated the strong layer at the interface than thinner roots. There were differences between plant species in the extent to which root diameter increased in response to the compaction. The roots which had larger RRD also tended to have higher penetration percentage.The results suggest that the size of a root has a significant influence on its ability to penetrate strong soil layers. It is suggested that this could be related to the effects which root diameter may have on root growth pressure and on the mode of soil deformation during penetration.     

Fecundity,reproductive effort,and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 g egg^–1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.     

Effect of crab effluent and scent of damaged conspecifics on feeding,growth, and shell morphology of the Atlantic dogwhelk Nucella lapillus (L.)

Juvenile Nucella lapillus of two different shell phenotypes, exposed shore and protected shore, were maintained in running seawater under each of three experimental conditions for 94 d: a) laboratory control, b) exposed to the effluent of crabs (Cancer pagurus) fed frozen fish (fish-crab), and c) exposed to the effluent of crabs fed live conspecific snails (snail-crab). Rates of barnacle consumption and rates of body weight change varied significantly between phenotypes and among experimental conditions. Individuals from the protected-shore consumed consistently fewer barnacles and grew consistently less than those from the exposed shore. Body weight increases in the fish-crab treatments were from 25 to 50% less than those in the controls and body weights in the snail-crab treatment either did not change or actually decreased. The perceived risk of predation thus appears to have a dramatic effect on the rates of feeding and growth of N. lapillus.At the end of the experiment, size-adjusted final shell weights for both phenotypes were consistently higher than controls (no crab) in both the fish-crab and snail-crab treatments. In addition, apertural tooth height, thickness of the lip, and retractability (i.e. the extent to which a snail could withdraw into its shell), with few exceptions all varied in an adaptive manner in response to the various risk treatments. Similar changes in the shell form of starved snails exposed to the same stimuli suggest very strongly that the morphological responses of both phenotypes were not just due to differences in rates of growth. These differences, at least in part, represented a direct cueing of the shell form of Nucella lapillus to differences in the perceived risk of predation. Somewhat surprisingly, the extent of phenotypic plasticity appeared to differ between the populations examined. Both field and laboratory evidence suggest that the exposed-shore population was much more labile morphologically than the protected-shore population.In many instances, particularly among starved snails, the development of antipredatory shell traits was greater in the fish-crab treatment than in the snail-crab treatment. Because the scent of crabs was present in both treatments, these results suggest a) that, at the frequency/concentration used in the experiments, the scent of damaged conspecifics may have been a supernormal stimulus and b) that the morphological response in these treatments might have been greater if the stimulus had been provided at a lower level.     

Isolation of a cloned DNA segment containing a ribosomal protein gene of Drosophila melanogaster

A Drosophila genomic DNA library in the vector Charon 4 was screened using cDNA derived from the small (6S-12S) poly(A)+ mRNA of 2-6-h-old Drosophila embryos. This fraction of mRNA is enriched for ribosomal protein-coding sequences. The selected recombinants were hybridized to total mRNA under conditions which allowed for isolation of homologous mRNAs. The mRNA from these RNA/DNA hybrids was eluted and translated in vitro. The translation products were analyzed by one- and two-dimensional electrophoresis with authentic ribosomal proteins as standards. One cloned DNA segment was found to contain a ribosomal protein gene, and a sequence which hybridizes strongly to at least 5 other ribosomal protein mRNAs.     

Synthesis of phosphatidylglycerol by chloroplasts from leaves of Spinacia oleracea L. (spinach)

Purified chloroplasts from leaves of Spinacia oleracea L. (spinach) incorporated glycerol 3-phosphate into diacylglycerol, monoacylglycerol, phosphatidylglycerol, phosphatidic acid, and lysophosphatidic acid. The omission of ATP or CTP, CoA or illumination decreased the incorporation markedly. The fraction of incorporated glycerol 3-phosphate found in phosphatidylglycerol was greatly reduced by the omission of bicarbonate, acetate, and ATP, or in darkness, low-osmolarity medium, or high magnesium ion concentration (10 mM). Incorporation of glycerol 3-phosphate into lipid and specifically into phosphatidylglycerol was optimal at a $\text{Mg}{}^{\mathrm{2+}}\text{CTP}$ ratio of 1, whereas the optimal ratio for $\text{Mg}{}^{\mathrm{2+}}\text{ATP}$ was closer to 2. The $\text{Mg}{}^{\mathrm{2+}}\text{CTP}$ gave lower total incorporation but a higher fraction of incorporation in phosphatidylglycerol. Triton X-100 inhibited incorporation of glycerol 3-phosphate into lipid, especially into phosphatidylglycerol.     

Evolution of skull shape in carnivores 1. Representative modern carnivores

Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.     

Biotransformation of endorphins by a synaptosomal plasma membrane preparation of rat brain and by human serum.

β-Endorphin (β-LPH 61–91), γ-endorphin (61–77), des-tyrosine-γ-endorphin (62–77), α-endorphin (61–76), and β-LPH 61–69 either labeled with [¹²⁵I] at the N-terminal 61-tyrosine residue or unlabeled were incubated with a crude synaptosomal plasma membrane fraction of rat brain or in human serum. At different time intervals the release of [¹²⁵I]-tyrosine or the change in immunoreactivity of the endorphins was determined. The cSPM preparation displayed both high aminopeptidase and endopeptidase activities. In contrast, human serum mainly contained aminopeptidase activity. The data suggest that functional endorphin metabolism may occur at the synaptosomal plasma membrane. These membranes may potentially be involved in the formation of behaviorally active endorphin fragments.