Call number: LD2668 .T4 1979 A53 / Master of Science

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No description available.

As a direct approach to investigate the molecular basis of embryogenesis in Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), a cDNA library made from poly(A)⁺ RNA of developing seeds was differentially screened for clones representing transcripts abundant in the developing seeds but absent in mature seeds. Of a number of clones isolated, two groups were selected for further sequence and gene expression analysis. A group of four cDNA clones (PM2S1, PM2S2, PM2S3 and PM2S4) shared a significant nucleotide and deduced amino acid sequence similarity with each other and with gymnosperm 2S seed storage protein cDNAs. The deduced amino acid sequences had low similarity with angiosperm 2S storage proteins but contained all conserved cysteine residues in an arrangement suggestive of a structural similarity between the 2S seed storage proteins from gymnosperms and angiosperms. Northern blot analysis revealed PM2S mRNAs were present specifically in seeds and temporally during seed development. However, the relatively low abundance of PM2S3 mRNAs and the decline of PM2S2 mRNAs in megagametophyte which occurred before that of the other mRNAs suggested that their expression was regulated differentially. The accumulation of PM2S transcripts in megagametophyte started during the early embryogenesis and reached a peak before that in zygotic embryos. PM2S mRNAs were present in Douglas-fir somatic embryos at the same developmental stages as those in zygotic embryos, and ABA and osmoticum stress were necessary for the expression of PM2S genes in somatic embryos. Southern blot analysis of genomic DNA suggested that the Douglas-fir 2S seed protein genes consisted of at least two sub-families each including several gene members. A gene designated gPm2Sl was isolated and sequenced. A comparison of the upstream sequence of gPm2Sl with the promoters of known 2S storage protein genes did not reveal significant sequence similarity except the presence of RY-repeated element (GCATGC), and the frequent occurrence of ACGT-containing motifs and E-box motifs (CANNTG). The 1.2-kb gPm2Sl promoter was fused to a P-glucuronidase (uidA) reporter gene and transformed into developing Douglas-fir seeds using particle bombardment and into tobacco via Agrobacterium tumefaciens. Histochemical analysis showed that the promoter was active in both systems and the gene expression was confined to endosperm and embryos of transgenic tobacco, indicating a common seed-specific regulatory mechanism between angiosperms and conifers. Another cDNA clone, PM2.1, hybridized to a 0.5 kb transcript and was predicted to encode a metallothionein (MT)-like protein. Alignment of the PM2.1 predicted amino acid sequence with other plant MT-like gene products revealed a general paucity of Cys and Cys-Xaa-Cys sequences and the presence of serine residues within the conserved Cys-Xaa-Cys motifs in the C-terminal domain. Phylogenetic analysis showed that PM2.1 grouped with class I/type 3 MT-like genes. The PM2.1 was expressed in somatic and zygotic embryos, in megagametophyte, as well as in hormone- and metal-treated seeds and seedlings. The PM2.1 transcripts were detected in the needles of 10-week-old seedlings, but not the root tissue or mature pollen. The expression of the PM2.1 gene in embryos was dependent upon ABA and osmoticum and was differentially modulated by metals, suggesting that the PM2.1 gene product may play a role in the control of microelement availability during Douglas-fir seed development and germination. Southern blot analysis of genomic DNA suggested that the PM2.1 was encoded by a multigene family. Three genomic clones were isolated and one of these clones (gPmMTa) was cloned and sequenced. The sequence analysis of its 5'-flanking region identified a number of putative regulatory elements such as ACGT-containing motifs, metal-responsive element (TGCGCC) and ethylene-responsive elements (ATTTCAAA) which may be responsible for gene transcription. DNase I-footprinting experiments with nuclear extracts isolated from Douglas-fir megagametophyte identified two protein-protected sites, a 31-bp sequence locating in the -176/-146 region that contained two ACGT-core motifs, and a 12-bp sequence, 5'-TGCCACGGAAGG-3', of unknown function. To identify promoter regions responsible for the regulation of gPmMTa gene expression, a series of deletions in the 0.9-kb fragment of the gPmMTa promoter was fused to the uidA reporter gene and the chimeric gene constructs were assayed in Douglas-fir and transgenic tobacco. Transient expression assays in megagametophyte and zygotic embryos indicated that the sequence lying between -190 and +88 of gPmMTa was sufficient to drive the expression of the reporter gene and the 225-bp fragment (-677 to -453) contained sequences necessary for high level expression. The gPmMTa promoter was not active in the seeds of transgenic tobacco. / Graduate

This investigation considered the differentiation tendencies of specific anterior-posterior regions of the neural plate in an attempt to establish the regional differentiation capacity for Ambystoma gracile neuroepithelium. Presumptive neural tissues (hindbrain and trunk spinal-cord) were isolated from the embryo at the time of primary induction (stage 11) to post-neurulation (stage 19) and cultured in vitro alone or with combinations of axial mesoderm (notochord and somite). Prior to primary induction (stage 11), the isolated presumptive neuroepithelium formed only atypical epidermis. Immediately subsequent to this induction (stage 11) both regions (hindbrain and trunk cord) demonstrated unorganized neural histogenesis, while the formation of organized neural tissue appeared later (stage 12-14 isolates). By stage 15-16, the histogenesis of the isolated hindbrain resembled that of the control, whereas the isolated trunk cord only formed a neural tube. The presence of somite tissue enhanced hindbrain differentiation considerably; notochord was effective to a limited extent. The combined effect of both tissues on neurogenesis was greater than with somite alone. The addition of notochord to trunk spinal-cord enhanced histogenesis to a greater extent than either somite alone or the combination of notochord and somite. The trunk neural tissue, whether alone or in combination with mesoderm, never demonstrated normal spinal-cord morphology and seemed to develop independently of the tissue environment during the late neurula stages (16-19). The presence of inherent differentiation tendencies within the hindbrain and the trunk spinal-cord, as well as the possible role of the mesodermal tissue in conditioning the neural tissue microenvironment with metabolic precursors, is discussed. / Science, Faculty of / Zoology, Department of / Graduate

Investigations were made of the association among megagametogenesis, pollen morphology, and seed production in two irradiated apple varieties, Golden Delicious and McIntosh, and in two years, 1964 and 1965. In each year eight to ten clones of each variety were selected on the basis of low, medium, and high pollen abortion. Untreated and treated Golden Delicious and McIntosh clones with normal pollen production, approximately 90% and 50% respectively, had the highest proportion of embryo sacs at the differentiated 8-nucleate stage, and the smallest proportion of embryo sacs at the 2- and 4-nucleate stages. Irradiated clones with the least normal pollen had the highest proportion of immature 2- and 4-nucleate embryo sacs. With both varieties and in both years reduced pollen fertility was positively correlated with retarded embryo sac development. Check clones with high pollen fertility had the highest number of developed seeds per fruit and irradiated clones with reduced pollen fertility had the smallest number of developed seeds per fruit. The number of developed seeds per fruit was positively correlated with the proportion of mature 8-nucleate embryo sacs. The reduction in seed numbers in irradiated apple clones with reduced pollen fertility may be explained, in part, by retarded embryo sac development. / Land and Food Systems, Faculty of / Graduate

Several recent experiments on developing chick spinal cord have established a time window when the developing spinal cord changes from a permissive to a restrictive environment for regeneration. This time window occurs during embryonic days 13-14 (E13-E14) of chick development. Recent experiments in adult rat, have found two proteins that actively inhibit axonal regeneration. This study has sought possible inhibitory proteins, in chicks, correlating to this temporal change. Proteins continuously present after this change (E14-E20) but not before (E11) were identified. Two-dimensional gel electrophoresis was used for separatation of the proteins. Seven protein spots of interest demonstrated this correlative late-expressing neural protein (LNP) profile. Although the functions of these proteins could not be ascertained in this study, further investigation is warranted. / Science, Faculty of / Zoology, Department of / Graduate

Two genera, Pachyceles and Petrolisthes, and five species of the Porcellaniae occur on the California coast north of San Francisco. Of the five species only one has had its larval development described (Pachycheleas rudis). The purpose of the present study is to describe the remaining four species and to provide a key to the species level for the larvae of northern California Porcellanidae.

No description available.

No description available.