MORPHOLOGICAL AND MOLECULAR VARIATION ACROSS A MIGRATORY DIVIDE IN WILLOW WARBLERS,PHYLLOSCOPUS TROCHILUS

A migratory divide is a narrow region in which two populations showing different migratory directions meet arid presumably also mate and hybridize. Banding of willow warblers, Phylloscopus trochilus, in Europe has demonstrated a migratory divide latitudinally across central Scandinavia. In autumn, southern birds migrate southwest to tropical West Africa, whereas northern birds migrate southeast to East and South Africa. The migratory divide is associated with concordant differences in size and plumage coloration. Based on morphology, we estimate the width of the transition zone between northern and southern willow warblers to be less than 350 km. We found indication of linkage disequilibria around the migratory divide, in that measures of body size were correlated with plumage coloration within the contact zone, but uncorrelated within the populations south or north of the contact zone. The presence of linkage disequilibria and the fact that several morphological clines occur together suggest that the hybrid zone is a result of secondary contact between populations that have differentiated in allopatry. This interpretation is in accord with the knowledge of the recolonization pattern of the Scandinavian peninsula after the last glaciation; animals and plants appeared to have colonized either from the south or from the north around the northern bay of the Baltic Sea. If northern and southern willow warblers resided in allopatric populations during late Pleistocene glaciations and the hybrid zone is a result of postglacial range expansions, we would expect some degree of genetic differentiation accumulated during the period in isolation. In contrast, northern and southern willow warblers are near panmictic in the frequencies of alleles of mitochondrial DNA and at two microsatellite loci. The observed pattern, clear morphological and behavioral differentiation without genetic differentiation at neutral loci, suggests either that the differences are maintained by strong selection on the expressed genes in combination with high levels of current gene flow or, in the case of weak gene flow, that the divergence in morphology and behavior is very recent.     

Narrow hybrid zone between two subspecies of big sagebrush (ARTEMISIA TRIDENTATA: Asteraceae). IX. Elemental uptake and niche separation

The concentrations of selected elements and their biological absorption coefficients were determined for leaves from plants in native stands and reciprocal transplant gardens to determine whether niche differentiation occurs among the parental taxa and their hybrids in the big sagebrush hybrid zone in Utah. The bounded hybrid superiority model predicts such niche differentiation, while the ecologically neutral dynamic equilibrium model predicts complete niche overlap, at least in the vicinity of the hybrid zone. The concentrations of elements in the leaves of site-indigenous sagebrush and the biological absorption coefficients differed significantly between the subspecies and between either parental taxon and hybrids. Within reciprocal transplant gardens, both the elemental concentrations and the biological absorption coefficients differed among the gardens and taxa. Significant genotype-by-environment interactions were observed for several essential elements. Niche differentiation was evident as correspondence analyses ordinated the parental taxa and hybrids into separate groups even when raised in the same garden. These findings support the ecologically based bounded hybrid superiority model and suggest that the big sagebrush parental taxa and their hybrids have adapted to their respective unique habitats.     

Electron Microscopic Cytochemical Study of Cyclic Adenosine Monophosphate Phosphodiesterase Activity During Gold Acclimation of Wheat Seedlings

Comparative studies on localization and distribution of cyclic adenosine monophosphate phosphodiesterase (cAMP-PDEase) activity in the young leaf cells of two different cold resistant wheat (Triticum aestivurn L.) varieties during cold acclimation were carried out by means of ultracytochemical method. The results indicated that the reaction products of cAMP- PDEase activity in two varieties of the seedlings grown at optimum temperature (20–25℃) were mainly localized at plasmalemma, nucleoli and chromatin. When the wheat seedlings were subjected to low temperature acclimation, cAM P-PDEase activity in the strong cold resistant variety Yanda 1817 seedlings was markedly decreased; however, little alteration of this enzyme activity was observed in the weak cold resistant variety Zhengzhou 39-1. cAMP-PDEase activity was recovered after deacclimation. The results suggested that changes in cAMP-PDEase activity during cold acclimation were closely related to the development of plant cold hardiness.     

Callus Formation from Somatic Hybridization of Wheat (Triticum aestivum L.) and Ryegrass (Lolium perenne L.) by Electrofusion

Somatic hybrid calli were recovered following electrofusion of protoplasts from a chloroplast-containing cell suspension culture of wheat (Triticum aestivum L.) and a cell suspension culture of ryegrass (Lolium perenne L.). The protoplasts of wheat were inactivated by iodoacetamide; in addition morphology and colour were used as markers to aid selection of putative hybrid calli. For isozyme analysis of putative hybrids, nine isozymes were tested for differences in bands between the parental lines. Of these, three showed differences (ADH, GOT, SDH). Analysis of ADH bands of calli indicated that six lines were hybrids. These lines were analysed with the ,ther isozymes, and at the DNA level by Southern hybridisation with a wheat ribosomal DNA probe. The overall results indicated that one line was an almost complete combination of the genomes of the parental lines, but the other 5 lines were probably partial hybrids. In the latter, some loss of the wheat genome had probably occurred.     

Structure of Embryo Sac Before and After Fertilization and Distribution of Transfer Cells in Ovules of Green Gram

The structure of embryo sac before and after fertilization, embryo and endosperm development and transfer cell distribution in Phaseolus radiatus were investigated using light and transmission electron microscopy. The synergids with distinct filiform apparatus have a chalazal vacuole, numerous mitochondria and ribosomes. A cell wall exists only around the micropylar half of the synergids. The egg cell has a chalazally located nucleus, a large micropylar vacuole and several small vacuoles. Mitochondria and plasrids with starch grains are abundant. No cell wall is present at its chalazal end. There are no plasma membranes between the egg and central cell in several places. The zygote has a complete cell wall, abundant mitochondria and plastids containing starch grains. Both degenerated and persistent synergids migh.t serve as a nutrient supplement to proembryo. The wall ingrowths occur in the central cell, basal cell, inner integumentary cells, suspensor cells and endosperm cells. These transfer cells may contribute to embryo nutrition at different developmental stages of embryo.     

Structure and Development of Stigmatic Branches and Style and Their Relation to Pollen Tube Growth in Wheat

The style of wheat divides into 2 branches, separated from its base and covered with a large number of slender stigmatic branches. The stigma is of dry type. The style is solid. There is no transmitting tissue differentiated in the style. Young stylar cells appear polygonal in transverse sections and elongated in longitudinal sections with an increase in length of the cells from periphery towards center. In transverse sections, mature stylar cells look extremely irregular. They are contorted and mosaicked with one another. During their development, stylar cells elongated vigorously with intrusive growth. The wall of stylar cells is thin, except at the corners where cells connect, that slight thickening of the cell wall occurs. Stylar cells start vacuolation at the earlier stages and gradually become highly vacuolated, but still remain rich in organelles, such as mitochondria, endoplasmic reticulum, dictyosomes and chloroplasts, the amount of which varied with the development stages of the style. Stigmatic branches are differentiated from the stylar epidermal cells, composed of 4 files of cells which link end to end with one another. Not long before anthesis, wall material in the intercellular corners becomes loose and porous. After pollination, pollen tubes grow along the intercellular spaces among the 4 files of cells in the stigmatic branches and then enter the style. Pollen tubes may pass through any intercellular corner throughout the 2 branches of the style, except for the lateral-outer portion which is composed of larger stylar cells. Eventually, pollen tubes enter the ovary.     

Characteristics and Distributions of Isozymes of Superoxide Dismutase in Leaf Cella of Peanut and wheat

The isozymes of superoxide dismutase (SOD) in leaves of wheat and peanut were investigated and identified by isoelectric focusing gel electrophoresis. The total four bands were found in wheat leaves, among them the band with the highest mobility was proved to be the chloroplastic SOD, the others with intermediate mobilities were probably cytoplasmic SODs. It was observed that there was apparent difference between patterns of SOD isozymes from leaves of wild and cultivated peanut. Leaves of wild peanut contain three different types of SOD isozyme (band A, band B and band C). Band A and B were cyanide-sensitive, hence they should be Cu-Zn-SOD. Band C was cyanide- insensitive and might be Mn-SOD located in mitochondria. The major part of SOD activity in cultivated peanut leaves was concentrated in chloroplasts, and it was cyanide-sensitive. The experiments of SOD activity inhibition by KCN showed that leaves of cultivated peanut contained more Cu-Zn-SOD. On the contrary, the percentage of non-Cu-Zn-SOD was highter in wild species than in cultivated. The PI values of distinct bands were determined and the significance of this study for the further evaluation of resistance of peanut plant is discussed.     

An Approach to a Function of Photorespiration in C3 Plants

Intact attached leaves of wheat were illuminated at 2000 μmol m-2·s-1 in CO2-free gas for 3 hours, inhibition percentage of photosynthesis in these leaves by illumination was related lo oxygen concentration in the gas. (1) The damage to the leaves became less gradually when oxygen concentration rose from 0 to 10%. (2) Almost no damage occurred between 10%–50% O2. (3) The damage appeared again when oxygen concentration exceeded 50%. The duration of CO2 outburst of wheat leaves in CO2-free gas containing 8%–11% O2 was 0nly about 15–30 min. However, no photoinhibition could be observed under this condition. Oxygen also could prevent isolated chloroplasts from the damage by strong light. No matter what concentration of oxygen in CO2-free gas was during photoinhibition treatment, the photodamaged site was always in PSⅡ. It is concluded from the results that the way in which photoinhibition was alleviated by oxygen seems not only to be photorespiration, but also the other unknown mechanisms waich may play more important part in it.     

The Effects of Water Stress on Photosystem Ⅱ in Wheat

The fluorescence yield at room temperature, the capacity of excitation energy distribution between photosystem Ⅰ and Ⅱ by Mg2+, variable fluorescence yield, variable fluorescence quenching rate and fluorescence complementary area were decreased under water stress. These indicated that photosystem Il was impaired. The inhibited variable fluorescence yield could be partly recovered by the addition of artificial electron donor DPC. Therefore, water stress inhibited not only the oxidizing site of photosystem Ⅱ but also impaired partly the reaction center of photosystem Ⅱ.     

Self-Fertile Transgenic Wheat Plants Expressing Herbicide Bromoxynil Resistance

Genetic manipulation of wheat (Triticum aestivum L. ) by biotechnological approaches is currently limited by a lack of efficient and reliable transformation method. The authors report a reproducible protocol for rapid production of transgenic wheat via microprojectile bombardment. The experiment was carried out by using the immature embryo excised from caryopsis 14 to 18 days postanthesis and the plant expression plasmid carrying a CaMV 35S-controlled bxn gene, for resistance to herbicide bromoxynil and a selectahle marker gene NPT I. After bombarding the precultured immature embryos isolated from 13 wheat varieties with plasmid DNA-coated tungsten particle, these embryos were transferred on MS medium containing 10 mg/L geneticin G418 sulphate to select and regenerate transformants step by step. As a result, 16 transformed plants were obtained from a total of 849 bombarded embryos. The characterization of these plants by inoculation with herbicide bromoxynil and Southern analysis with bxn gene as a probe showed that 4 of the self-fertile transformed plants contained the target gene and presented herbicide resistance. In several independent transformation experiments, the fastest one took only 6 months from embryo excision to characterization of regenerated plants. Therefore, this procedure is a rapid and efficient technique for delivering foreign DNA into wheat.