Cross compatibility between diploid and tetraploid perennial ryegrass (Lolium perenne L.)

Summary A number of crosses were made between diploid and tetraploid Lolium perenne plants in order to determine the degree of cross compatibility between the two different ploidy levels. The range of hybridization undertaken involved diploidxdiploid, and tetraploid x tetraploid control crossings, diploid x tetraploid crosses, tetraploid x diploid crosses and mixed pollinations. The seed set, the germination capacity of resultant hybrid seeds, and the chromosome constitution of derived seedlings was determined. In addition attempts were made to culture 12 day-old hybrid embryos from the diploid x tetraploid and reciprocal crosses.The crossing results obtained indicated no barrier to fertilization between diploids and tetraploids, but the irregular and poor development of the seed accompanied by much reduced germination, indicated unsatisfactory endosperm establishment of large numbers of triploids, as confirmed by the result of culturing embryos dissected from 12-day old seeds.In preliminary studies undertaken to determine the extent to which diploid and tetraploid ryegrass varieties intercross when grown in close proximity for seed production, Griffiths and Pegler (1966) observed a very low incidence of triploids amongst the progenies of diploid plants exposed to the pollen of tetraploid plants and also amongst the progenies of tetraploid material exposed to the pollen of diploid plants.In these and subsequent studies it was noted that only a very small proportion of the so-called fully formed seeds derived from diploid x tetraploid crosses did actually germinate. When, in 1964, propagules of clones of S.24 perennial ryegrass, well separated from one another, were placed in drills of the tetraploid perennial ryegrass variety Reveille, the proportion of florets which formed caryopses, and of caryopses which germinated was as follows (Table 1).The data (Table 1) clearly indicate that a considerable proportion of the S.24 florets had been fertilized by 2n pollen and had formed caryopses, but most of these had proved to be defective. As noted in the previous studies, the frequency of triploid seedlings was low, thus suggesting incompatibility between the n and 2n gametes for the production of viable zygotes.Of the total progenies classed as tetraploids in the early seedling stage, 80% proved to be ryegrass x tall fescue F₁ hybrids. These arose as a result of free crossing with     

Relationships between water-use traits and photosynthesis in Brassica oleracea resolved by quantitative genetic analysis

The genetic control of water‐use and photosynthetic traits in Brassica oleracea is resolved by genetic analysis of quantitative trait loci (QTL). Variations in leaf conductance, photosynthetic assimilation rate, leaf thickness and leaf nitrogen content were assessed in a segregating population of F₁‐derived doubled haploid (DH) B. oleracea lines. In addition, stable carbon isotope ratios in leaf organic material were used as a surrogate measure of plant water‐use efficiency. Analysis of an existing linkage map for the population revealed significant QTL on seven linkage groups. Single significant QTL explained between 3.4% and 36.6% of the phenotypic variance in each of the traits measured. The locations of QTL for several traits were found to coincide in a physiologically meaningful way; stable carbon isotope discrimination had QTL co‐locating with leaf level water‐use efficiency, photosynthetic capacity with leaf thickness and nitrogen content and stomatal density with leaf thickness. Taken together, these results suggest that single genes or clusters of genes at these loci may have an influence on the expression of physiologically related traits controlling water‐use and photosynthesis.     

Kinetics of single-layer graphite oxidation: evaluation by electron microscopy

Etch-decoration reveals that the rate of removal of carbon atoms exposed at monolayer steps on graphite surfaces is very different from the rate of removal, under identical conditions, at multilayer steps. At 1113 degrees K and a pressure of 1.33 newtons per square meter of oxygen, the rate of oxidation (along the layer planes) is less by a factor of nearly 100 than that at multilayer steps.     

Lysosomal enzyme inhibition by trypan blue: a theory of teratogenesis

A mechanism of mammalian teratogenesis involving inhibition of embryotrophic nutrition is suggested and exemplified by the action of trypan blue on pregnant rats. There is evidence for the localization of trypan blue in heterolysosomes of the epithelium of the visceral yolk sac, and our experiments indicate that the dye is an inhibitor of a selection of hydrolytic enzymes present in lysosomal fractions from homogenates of rat visceral yolk sac. It seems likely that trypan blue inhibits the intracellular digestion of embryotroph by the visceral yolk-sac epithelium; the conceptus may therefore be deprived of essential nutrients at critical stages of development.     

Blockade of N-methyl-D-aspartate receptors may protect against ischemic damage in the brain

In rats ischemia of the forebrain induced by a 30-minute occlusion of the carotid artery, followed by 120 minutes of arterial reperfusion, produced ischemic lesions of selectively vulnerable pyramidal cells in both hippocampi. Focal microinfusion into the dorsal hippocampus of 2-amino-7-phosphonoheptanoic acid, an antagonist of excitation at the N-methyl-D-aspartate-preferring receptor, before ischemia was induced protected against the development of ischemic damage. It is proposed that excitatory neurotransmission plays an important role in selective neuronal loss due to cerebral ischemia.     

Peptidoglycan in the cell wall of the primary intracellular symbiote of the pea aphid

Primary intracellular symbiotes of the pea aphid, Acyrthosiphon pisum (Harris), when fixed with potassium permanganate, revealed a distinctly staining area between the cytoplasmic membrane and the outer cell-wall envelope. This area is thought to be analogous to the peptidoglycan complex of the Eubacteriales. In addition, the diagnostic bacterial peptidoglycan amino compounds, muramic acid and diaminopimelic acid, were detected in a hydrochloric acid hydrolyzate of isolated symbiotes.     

Linking albinism and immunity: the secrets of secretory lysosomes

Lysosomes are membrane-bound organelles that are found in all mammalian cells and contain hydrolases and lipases required for protein and membrane degradation. In many cells of the immune system, lysosomes also contain secretory proteins that can be released by regulated exocytosis in response to an external stimulus, providing different cell types with a wide range of effector functions. Melanosomes also use a lysosome-related organelle to secrete melanin for pigmentation. Links between albinism and immunity in patients have uncovered a number of key proteins required for lysosomal secretion and have revealed a versatile secretory mechanism that can be fine-tuned by distinct interactions in different cell types.