Aerenchyma and lenticel formation in pine seedlings: A possible avoidance mechanism to anaerobic growth conditions

Seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.], and loblolly pine ( P. taeda L., wet-site and drought-hardy seed sources) were grown in hydroponic solution culture using a non-circulating, continuously flowing design under anaerobic or aerobic conditions to determine whether flooding tolerance was correlated with enhanced internal root aeration. Transport of atmospheric O₂ from the shoot to the root of anaerobically grown loblolly and pond pine seedlings was demonstrated via rhizosphere oxidation, using both reduced indigo-carmine solution and a polarographic, ensheathing Pt-electrode. Stem and root collar lenticels were the major sites of atmospheric O₂ entry for submerged roots in these seedlings. No O₂ leakage was detected from roots of aerobically grown pine seedlings. Longitudinal and radial pathways for gaseous diffusion via intercellular air spaces in the pericycle and between ray parenchyma cells, respectively, were demonstrated histo-logically in anaerobically grown loblolly and pond pines. Rhizosphere oxidation, and lenticel and aerenchyma development in roots of flood-intolerant sand pine seedlings grown in anaerobic solutions were minimal. Only 15 days of anaerobic growth conditions were necessary to increase internal root porosities of loblolly and pond pine seedlings – although not to the extent found in seedlings treated for 30 or 75 days. Histological results indicated that root tissue in the secondary stage of growth was capable of forming intercellular air spaces, demonstrating a degree of internal plasticity – at least in the more flood-tolerant loblolly and pond pine seedlings.     

Comparative studies of pollen and fluorescent dye transport by bumble bees visiting Erythronium grandiflorum

Summary In the Colorado Rocky Mountains the glacier lily Erythronium grandiflorum exhibits a striking dimorphism in pollen color and is commonly pollinated by the bumble bee Bombus occidentalis. We induced bees to visit sequences of flowers in a flight cage, and compared dispersal of distinctively-colored pollen and fluorescent pigment (dye) that the bee had picked up at a single donor flower. Nonparametric and parametric analyses showed that dispersal properties of pollen and dye differed; consistently less pollen was deposited and it was carried consistently shorter distances than dye. Dye thus does not provide an accurate means of assessing exacty where or how far pollen travels in this plant-pollinator system. On the other hand, both pollen and dye responded similarly to several experimental manipulations of donor and recipient flowers. Hence dye may well be of value for a qualitative investigation of how floral traits influence pollen dispersal.     

Cationic probes: Specificity of distribution of metal-binding sites in bovine sperm

Salts of transition elements that alter the rate of sperm cell movement act at or near calcium-binding sites. After living bull sperm cells had been preincubated in VO₄^3?, Ni²⁺, Zn²⁺, Mn²⁺, and also La³⁺, they were then fixed. Crisply defined organelles and the absence of particulate deposits in the morphological controls contrasted sharply with the treated specimens; the latter contained regions of increased electron density, the nature and distribution of which depended on the test substance, reflecting the differential affinities of the specific ions. La³⁺ formed fine dense areas, mainly at the exocytic surface of the plasma membrane. VO₄^3? marks the cell surface but also left particulate densities within the cell. Ni²⁺ caused a nearly uniformly dense deposit at the surface and on the satellite fibers and axonemal microtubules. Zn²⁺ formed less uniform but coarser deposits, while in Mn²⁺ the distribution was similar to that in Zn²⁺ but much denser in the axonemal matrix and on the satellite fibers. Verapamil restricted the size and number of the opacities, while procaine permitted a similar distribution of slightly larger size reaction product. The differences in size and distribution of the enhanced densities were consistent and replicable for the individual assay substances. Vanadate, which specifically inhibits Na, K-ATPase, bound to ouabain-sensitive enzyme loci, however, completely disrupting the axonemal complex. This suggests that an important role of dynein in flagellar motion may relate to intracellular transport of Ca²⁺.     

A Comparison of Internal Standards for Plant Cytophotometry

Plant cell nuclei were compared with chicken erythrocyte nuclei for use as internal standards for microspectrophotometry. The amount of DNA per nucleus and the coefficient of variation for measurement of individual nuclei were determined for cells from dormant embryos of Pinus taeda and Pinus coulteri, from onion root tips and from chicken erythrocytes. The chicken erythrocytes had the least variability and thus were best suited for use as a standard. Onion root tips were least suitable, with a coefficient of variation 2 1/2 times that of erythrocytes. Although onion root tips have been used as an internal standard in other studies, their mitotic activity, in contrast with the nonreplication of DNA of mature erythrocytes, is reflected in a broad distribution of nuclei with values in the 2C-4C range. Coulter pine mature embryos were at the 3C level, whether dry or hydrated, while loblolly pine embryos were in the 2C state. This confirms previous reports. The coefficient of variability for the pine embryo cells was 1 1/2 times that of erythrocytes for nonhydrated seeds and twice the erythrocyte value for hydrated seeds. The larger 2C values for pine (26 pg for P. taeda and 17 pg for P. coulteri) are closer to values expected for many plant species than the 3 pg level of the chicken erythrocytes. Dormant P. taeda embryo cells (2C) are suggested as an alternative where the experimental material has large DNA values and/or chicken erythrocytes are difficult to procure. Large sample size is recommended for the plant materials if they are to be used as internal standards in Feulgen cytophotometry.     

The effect of nectar guides on pollinator preference: experimental studies with a montane herb

Summary Rare albino morphs of the montane larkspur Delphinium nelsonii differ from common blue-flowered morphs in overall flower color, and in the strength of a contrasting color pattern at the center of the flower that presumably guides pollinators to concealed nectar. Previous studies showed that bumblebees and hummingbirds discriminate against albinos when presented with mixtures of the 2 morphs, and that it takes these pollinators longer to fly between successive flowers on albino than on blue-flowered inflorescences. To explore the link between these observations, we measured pollinator preferences and flower-to-flower flight times (handling times) before and after painting flowers in 2 alternative ways that enhanced albino nectar guides. In all of 16 experimental replicates discrimination against albinos was reduced or eliminated after painting, and albino handling times declined toward values for blue-flowered inflorescences. This consistent result indicates that an inferior nectar guide increases the energetic cost of foraging at albinos. Increased cost in turn explains discrimination, under the reasonable assumption that hummingbirds and bumblebees are sensitive to foraging economics.     

Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism

Branched-chain amino acid metabolism in skeletal muscte promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation.     

Leghemoglobin-like sequences in the DNA of four actinorhizal plants

Summary A cloned cDNA partial copy of a soybean leghemoglobin mRNA was used to probe genomic DNA of four species of actinorhizal plants. Southern blot hybridization revealed the presence of sequences with homology to the leghemoglobin probe in DNA from Alnus glutinosa, Casuarina glauca, Ceanothus americanus and Elaeagnus pungens. The hybridization patterns of the restriction fragments revealed some fragment size conservation between the DNA of soybean and the DNA of four actinorhizal plants which are taxonomically unrelated to soybean or to each other. The results presented here indicate that globin gene sequences are much more widely distributed in the plant kingdom than has previously been thought. Furthermore, if sequence conservation is actually as high as the restriction fragment patterns suggest, the evolution of the DNA surrounding the globin sequences has been highly constrained.     

Restriction fragment polymorphisms as probes for plant diversity and their development as tools for applied plant breeding

Summary Maize and tomato cDNA clones have been hybridized in Southern blotting experiments to plant genomic DNA prepared from different lines to detect restriction fragment polymorphisms (RFPs). In maize we have found that a high degree of genetic variability is present, even among domestic inbred lines. Most randomly chosen maize cDNA clones can be used to detect elements of this variability. Similar levels of polymorphism are observed when genomic DNA is digested with any of a number of different restriction enzymes and probed with individual clones. When a clone is hybridized to genomic DNAs prepared from several different maize lines, a number of different alleles are often detected at a single locus. At the same time one clone can often detect more than one independently segregating locus by cross hybridization to related sequences at other loci. As expected these markers are inherited as simple codominant Mendelian alleles from one generation to the next and colinkage of these markers can be demonstrated in the progeny from a heterozygous parent. In similar studies with tomato, remarkably different results were found. Few RFPs were demonstrable among domestic Lycopersicon esculentum lines although a higher level of variability could be detected when comparing esculentum with its wild Lycopersicon relatives. These results are discussed in relation to the applied uses of RFPs in plant breeding as well as the inherent variability of different plant genomes.This work was supported in part by funds from Sandoz Ltd. (Basel, Switzerland) and its subsidiary company, Northrup King Co. (Minneapolis, Minn., U.S.A.) as well as by NSF SBIR grant #BSR-8360870.     

Interactions betweenAcyrthosiphon kondoi [Homoptera: Aphidoidea] andAphelinus asychis [Hymenoptera: Chalcidoidea] and other parasites and hosts

In laboratory trials to investigate the parasite/host spectra of certain aphid pests and hymenopterous parasites, the aphidAcyrthosiphon kondoi Shinji encapsulated the egg of the aphelinid parasiteAphelinus asychis Walker. The resultant brown, sclerotic capsule was formed within 24 h of exposure of the aphid to parasitization and as far as is known prevented the development of the parasite to the larval stage. The capsule remained throughout the life of the aphid, whose longevity and fecundity were apparently not seriously impaired. A small number ofAphelinus escaped encapsulation, especially in aphids already containing capsule(s), and developed into normal, reproductive adults.A. kondoi did not encapsulate, andA. asychis was not encapsulated by any other species. However, thoughA. asychis readily parasitizedAphis citricola van der Goot,A. nerii Boyer de Fonscolombe andToxoptera citricidus (Kirkaldy), most of its progeny ceased development in these aphids before reaching the mummification stage, and died within the dead or dying, non-mummified aphid host.