Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--Johns Hopkins University. / Includes bibliographical references.

Thesis (Ph. D.)--University of California, Riverside, 2010. / Includes abstract. Title from first page of PDF file (viewed May 18, 2010). Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 99-102). Also available on the Internet.

The biosynthesis of ABA from R-[2-¹⁴C]-MVA was demonstrated in Persea americana cv. Fuerte mesocarp and in mature seeds of Hordeum vulgare cv. Dyan and cv. Himalaya. Radioactivity from R-[2-¹⁴-C]-MVA was also incorporated into the 1',4'-trans ABA diol in Persea americana mesocarp and a possible role for this metabolite as a precursor of ABA in plants is discussed. The biosynthesis of ABA from MVA could not be demonstrated in either turgid and waterstressed Hordeum vulgare cv. Dyan, Pisum sativum cv. Black-eyed Susan and Phaseolus vulgaris cv. Top-crop or in immature seeds of Pisum sativum and Phaseolus vulgaris. (R,S,)-[2-¹⁴C]-ABA was catabolised to PA, DPA and aqueous conjugates in leaves and mature seeds of Hordeum vulgare cv. Dyan, seedlings and immature seeds of Pisum sativum and Phaseolus vulgaris and in mesocarp from ripening fruits of Persea americana. PA and DPA were identified by either microchemical methods and/or capillary GC-MS. 7'-Hydroxy ABA was characterised as a novel ABA catabolite in light-grown and etiolated leaves of Hordeum vulgare by capillary GC-MS. Circular dichroism analysis revealed that it was derived predominantly from the (R)-enantiomer of ABA. This catabolite was absent in similar studies using the dicotyledons Pisum sativum and Phaseolus vulgaris. Refeeding studies with [¹⁴C]-PA, [C]-DPA and [¹⁴C]-7'-hydroxy ABA were used to confirm the metabolic interrelationship between ABA and its catabolites in both vegetative and non-vegetative tissues from monocotyledonous and dicotyledonous species. The methyl ester of (R,S,)-ABA was hydrolysed efficiently by light-grown leaves of Hordeum vulgare. Older, vegetative tissues catabolised (R,S,)-ABA more efficiently than their younger counterparts. In contrast, small, immature seeds of Pisum sativum catabolised (R,S,)-ABA more effectively than larger, immature seeds of this species. Light did not appear to influence ABA biosynthesis but markedly enhanced ABA catabolism. Light stimulated the overall rate of ABA catabolism in both vegetative and non-vegetative tissue. Water stress reduced ABA catabolism in Hordeum vulgare leaves but had little effect on this process in Phaseolus vulgaris seedlings. Pretreatment of tissues with (R,S,)-ABA retarded the catabolism of (R,S,)-[2-¹⁴C]-ABA, negating ABA-induced conversion to PA. Cycloheximide inhibited ABA biosynthesis and catabolism but did not affect ABA conjugation. Chloramphenicol and lincomycin had little or no effect on ABA metabolism suggesting that the enzymes involved were labile and cytoplasmic in origin. Ancymidol and cycocel inhibited ABA biosynthesis while AM01618 stimulated this process. The cytokinins, benzyladenine, kinetin, isopentenyl adenine and zeatin also inhibited ABA biosynthesis. These results are discussed in relation to the possible involvement of carotenoids in ABA biosynthesis. AM01618, ancymidol andcycocel did not significantly influence the conversion of ABA to PA and DPA while cytokinins appeared to enhance this process only in vegetative tissue. The information derived from these studies was then used in attempts to develop a cell-free system from higher plants capable of metabolising ABA. A cell-free system prepared from imbibed Hordeum vulgare cv. Dyan embryos biosynthesized and catabolised ABA. This is the first demonstration of a cell-free system from non-vegetative tissue capable of metabolising ABA and could prove useful for elucidating its biosynthetic route. This cell-free system generated the terpenyl pyrophosphates IPP, FPP and GGPP from MVA. ABA was produced from both MVA and IPP in the presence of 0₂ and NADPH. The biosynthesis of ABA was stimulated by the addition of the squalene 2,3-oxide cyclase and kaurene synthetase inhibitor, AM01618 and a "cold-pool trap" of (R,S,)-ABA. Ancymidol, cycocel and cytokinins reduced incorporation of label from MVA into ABA. Similar cell-free preparations, in the absence of AM01618, converted (R,S,)-[2-¹⁴-C]-ABA into PA, 7'-hydroxy ABA and water-soluble conjugates. Although the methyl ester of (R,S,)-ABA was efficiently hydrolysed in this cell-free system no DPA was generated. The possible involvement of mixed function oxidase activity and soluble oxidases is discussed in relation to ABA metabolism. While cell-free preparations from Persea americana cv. Fuerte mesocarp and immature seeds of Pisum sativum and Phaseolus vulgaris were unable to synthesize ABA from MVA, these tissue homogenates converted ABA into more polar acidic products. PA and DPA were identified as products of ABA catabolism in extracts from immature seeds of Phaseolus vulgaris and the l',4'-cis diol of ABA in extracts from Pisum sativum immature seeds

Zea mays plants kept at ambient (ca 375ppm) and elevated CO₂ (ca 650 to 700ppm) were used to examine the possibility of a symplasmic loading, unloading and transport pathway in dark-adapted and illuminated (200μmolm⁻²sec⁻¹ ) sink and source leaves. 5,6-carboxyfluorescein diacetate was introduced into the mesophyll cells and symplasmic transfer observed 3h after application. In sink and source leaves exposed to ambient CO₂ and illuminated at 200 molm-2sec-1, the fluorescence front was observed approximately 3cm from the point of application, while in dark-adapted plants, the fluorescence front was observed approximately 1cm from the point of application. Under elevated CO₂ conditions the fluorescence front in illuminated plants appeared to transport faster moving approximately 5cm from the point of application, and in dark-adapted plants, only 3cm from the point of application. Based on the increase in 5,6-CF accumulation under elevated CO₂ conditions, the present study suggests that there was an increase in capacity for assimilate loading and transport under elevated CO₂ conditions. In source leaves, 5,6-CFDA was taken up into the mesophyll cells, loaded symplasmically and transported basipetally. In sink leaves 5,6- CFDA was taken up from basal mesophyll and after symplasmic loading, was transported acropetally where it was offloaded into the younger immature sink region. Transport in the sieve tubes was confirmed by using aniline blue, which was applied 3h after 5,6-CF transport. Aniline blue coupled with 5,6-CF transport studies showed that the sieve tubes of both cross and longitudinal veins are involved in symplasmic unloading, loading and transport processes in sink and source leaves. Apoplasmic uptake of 5,6-CFDA by cut leaves showed that after apoplasmic transport via the transpiration stream, 5,6-CFDA was offioaded to the xylem parenchyma where it was metabolically cleaved , releasing fluorescent 5,6-CF into the xylem parenchyma. Transverse sections cut after 3h of uptake were observed after 120 and 180 min suggesting that a retrieval of solutes occurs from the xylem to the xylem parenchyma, bundle sheath, phloem parenchyma and to the th in-walled sieve tubes. It was not possible to determine if the thick-walled sieve tubes were involved or if they took up 5,6-CF. Given the available data on loading and offioading of assimilates in sink and source leaves respectively, this study demonstrated that a slow symplasmic pathway exists from the mesophyll to the phloem, and that offloading from the phloem in sink leaves can occur via a symplasmic route.

No description available.

Protoplasts were isolated from tobacco and barley leaves in sucrose or mannitol using commercially available cellulases and macerozymes. Barley growth and protoplast isolation and purification conditions were optimized so that protoplasts were obtained in high yields free of unwanted debris and organelles. A technique for processing barley and tobacco protoplasts for examination by scanning electron microscopy was developed in which protoplasts seem to have maintained their structural integrity. Barley and tobacco protoplasts took up 3H-B. subtilis DNA, 125I-B. subtilis DNA or 125I-M. luteus DNA as a linear function of time (0-6 hr) and DNA concentration (0-200 μg/ml). Up to 16 pg of exogenous DNA was taken up per protoplast of which approximately one half became nuclear associated. Protoplasts were viable after the uptake as shown by standard staining and culturing techniques. Approximately 20% of the DNA taken up after typical 4 hr uptake reactions was of average gene size (5-10 x 105 daltons), and therefore of potential significance to host gene expression.

Landolphia kirkii is scrambling shrub forming an integral part of the flora along the coastal areas of north-eastern South Africa. The non-sustainable harvesting of fruit as food source, by monkeys and rural communities and the highly recalcitrant nature of their seeds threatens the continuation of the species. In addition, the ability of the plants to produce high quality rubber makes its long-term conservation highly desirable. Previously, attempts have been made to cryopreserve germplasm of L. kirkii, but no survival had been recorded at cryogenic temperatures of below -140ºC. The present study reports on the effects of rapid dehydration, chemical cryoprotectants and various cooling rates, thawing and imbibition treatments on survival of embryonic axes excised with cotyledons completely removed, as well as with 3 mm portion of each cotyledon attached, from fresh, mature, recalcitrant seeds of L. kirkii. Survival was assessed by the ability for both root and shoot development in in vitro culture, the tetrazolium test and electrolyte leakage readings. At seed shedding, embryonic axes were at the high mean water content of 2.24 g gˉ¹ (dry mass basis). All axes (with and without attached cotyledonary segments) withstood rapid (flash) drying to a water content of c. 0.28 g gˉ¹; however, the use of chemical cryoprotectants, singly or in combination, before flash-drying was lethal. Rapid cooling rates were detrimental to axes flash-dried to 0.28 g gˉ¹, with no explants showing shoot production after exposure to -196ºC and -210ºC. Ultrastructural examination revealed that decompartmentation and loss of cellular integrity were associated with viability loss after rapid cooling to cryogenic temperatures, although lipid bodies retained their morphology regardless of the thawing temperature employed. Furthermore, analysis of the lipid composition within embryos of L. kirkii revealed negligible amounts of capric and lauric acids, suggested to be the medium-chained saturated fatty acids responsible for triacylglycerol crystallisation when lipid-rich seeds are subjected to cryogenic temperatures. Hence, lipid crystallisation was not implicated in cell death following dehydration, exposure to cryogenic temperatures and subsequent thawing and rehydration. Rapid rehydration of embryonic axes of L. kirkii by direct immersion in a calcium-magnesium solution at 25ºC for 30 min (as apposed to slow rehydration on moistened filter paper or with rehydration in water) was associated with highest survival post-dehydration. Cooling at 1ºC minˉ¹ and 2ºC minˉ¹ facilitated survival of 70 and 75% respectively of axes with attached cotyledonary segments at 0.28 g gˉ¹ after exposure to - 70ºC. Viability retention of 40 and 45% were recorded when embryonic axes with attached cotyledonary segments were cooled at 14 and 15ºC minˉ¹ to temperatures below -180ºC. However, no axes excised without attached cotyledonary segments produced shoots after cryogenic exposure. The use of slow cooling rates is promising for cryopreservation of mature axes of L. kirkii, but only when excised with a portion of each cotyledon left attached. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.