Graduation date: 1994

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Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The aim of this study was to determine (l) the influence of elevated dissolved inorganic carbon (DIC) on the nitrogen use efficiencies (NUE) of tomato seedlings grown with different nitrogen sources, (2) how changes in the regulation and activities of nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPc), carbonic anhydrase (CA) and subsequent changes in metabolites would account for observed changes in NUE, and (3) to what extent elevated DIC contributed to the carbon budget of plants grown with different nitrogen sources. Lycopersicon esculentum cv. Fl44 seedlings were grown in hydroponic culture (pH 5.8) with 2 mM of either N03- or NH4 + and the solutions were aerated with either 0 ppm or 5000 ppm CO2 concentrations. The similar NUEs of NH/-fed plants grown with either root-zone CO2 concentration were largely due to their similar RGRs and N uptake rates. Elevated root-zone DIC had an initial stimulatory effect on N~ + uptake rates, but it seems as if this effect of DIC physiological processes was cancelled out by the toxic effect of unassimilated NH/. The NUE for N03--fed plants supplied with 5000 ppm root-zone CO2 was higher relative to 0 ppm root-zone CO2 and it was possibly due to the higher relative growth rates for similar N uptake rates of 5000 ppm compared to 0 ppm root-zone CO2. Nitrate-fed plants grown with 5000 ppm compared to 0 ppm root-zone CO2 had higher in vivo NR and in vitro NR and PEPc activities. These increases in enzymes activities possibly lead to increases in organic acid synthesis, which could have been used for biomass accumulation. This would account for the increased relative growth rates of N03--fed plants grown with 5000 ppm compared to 0 ppm root-zone CO2. The increasing rootzone CO2 concentrations resulted in the Ó15N values of NH/-plants becoming more positive indicating an absence of enzymatic discrimination. This may have been due to the inhibitory effect of DIC on Nll,+ uptake, causing plants to utilise both internal isotopes equally. The Ól3C studies showed that PEPc contributed equally to both N03-- and NH/-fed plants over the long term. From this it can be concluded that the lower NUE of NH/-compared to N03--fed plants grown with 5000 ppm root-zone C02 was due to increased N uptake and exudation of organic compounds into the nutrient solution. Experiments with 813C also showed that at increasing rootzone CO2 concentrations, PEPc made a bigger contribution to the carbon budget via the anaplerotic reaction. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om (1) die invloed van verhoogde opgeloste anorganiese koolstof dioksied (DIC) op die stikstofverbruiksdoeltreffenheid (NUE) van plante wat op verkillende stikstofbronne gekweek is, te bepaal. (2) Veranderinge in die regulering van nitraat reduktase (NR), fosfo-enolpirovaatkarboksilase (PEPc) en karboonsuuranhidrase (CA) is bestudeer en gekorreleer met waargeneemde verskille in NUE. (3) 'n Beraming van die mate waartoe verhoogde DIC bydra tot die koolstofbegroting van plante, gekweek op verskillende stikstofbronne, word bespreek. Lycopersicon esculentum cv. F144 saailinge is in waterkultuur (pH 5.8) met 2 mM N03- of NH/ gekweek en die oplossings is alternatiewelik met 0 ppm of 5000 ppm CO2 belug. Die NUEs van plante gekweek met NH/ en belug met albei C02 konsentrasies was vergelykbaar grootliks as gevolg van hulooreenkomstige relatiewe groeitempo's en Nopname. DIC het aanvanklik NH/ opname gestimuleer, maar enige latere stimulerende effek van DIC op fisiologiese prosesse was klaarblyklik uitgekanselleer deur N~ + toksiteit veroorsaak deur vertraagde assimilasie. Die NUE van plante gekweek met N03- en 5000 ppm CO2 was hoër as dié van plante gekweek met N03- en 0 ppm CO2. Dit is moontlik gekoppel aan hoër relatiewe groeitempo's teenoor onveranderde N opname tempo's. Plante gekweek met N03- en 5000 ppm CO2 het hoër in vivo NR en in vitro NR en PEPc aktiwiteite getoon as plante gekweek met N03- en 0 ppm CO2. Bogenoemde toenames in ensiem aktiwiteite word verbind met biomassa toename deur verhoogde organiese suur sintese. Dit bied 'n moontlike verklaring vir die hoër relatiewe groeitempo's van plante gekweek met N03- en 5000 ppm CO2 teenoor plante gegroei met N03- en 0 ppm CO2. Die 015N waardes van plante gekweek met NH/ en 5000 ppm CO2 was meer positief as dié van plante gekweek met Nl-l,+ en 0 ppm CO2 wat gedui het op die afwesigheid van ensiematiese diskriminasie. Dit kon as gevolg gewees het van die vertragende effek van DIC op Nl-la + opname wat daartoe sou lei dat die plante beide isotope eweveel inkorporeer. Eksperimente met ol3C het getoon dat PEPc oor 'n lang tydperk eweveel begedra het tot die koolstofbegroting van plante gekweek met beide N03- and N~+. Hiervan kan afgelei word dat die laer NUE van plante gekweek met NH4 + en 5000 ppm C02 in vergelyking met dié van plante gekweek met N03- en 5000 ppm CO2 die gevolg was van verhoogde NH/ opname en uitskeiding van aminosure in die voedingsoplossing. Eksperimente met 0"c het ook getoon dat verhoogde DIe konsentrasies die bydrae van PEPc tot die plant se koolstofbegroting laat toeneem.

The phytohormones auxin and cytokinin control plant development through a complex network of interactions which include synergistic, additive, and opposite effects whose mechanisms are unknown. The auxin-insensitive diageotropica (dgt) mutant provided a tool to dissect the relationship between auxin- and cytokinin-induced responses in tomato. Morphological, physiological, and molecular data support the proposal that auxin and cytokinins control a common set of developmental processes through separate signal transduction pathways which interact downstream from the DGT gene product. Morphological traits of dgt plants, such as reduced root and shoot growth, reduced leaf complexity, and reduced apical dominance were phenocopied by exogenous cytokinin application to wild-type plants, demonstrating that cytokinins and the DGT-mediated auxin response control a common set of phenotypic characteristics. Because the dgt mutation had no detectable effects on the levels of endogenous cytokinins or on the cytokinin sensitivity of whole plants, cytokinins were hypothesized to cause dgt-like effects on plant development through inhibiting auxin-induced responses. This hypothesis was supported by physiological experiments showing that auxin-induced elongation and ethylene synthesis were inhibited in cytokinin-treated wild-type and in untreated dgt hypocotyls. Differences between the effects of cytokinins and the dgt mutation on auxin responses became apparent at the molecular level. Experiments on the auxin-induced accumulation of transcripts for two ACC-synthase genes and one SAUR gene demonstrated that cytokinin treatment selectively reduced the auxin-induced expression of only one ACC-synthase gene, while the dgt mutation inhibited the auxin-inducibility of all three genes. The effects of the dgt mutation were thus more pleiotropic than the cytokinin effects, suggesting that cytokinins inhibit auxin-responses downstream from the DGT gene product. In vitro culture of dgt hypocotyl explants and calli demonstrated shared or interacting signal transduction pathways for auxin and cytokinin in the stimulation of cell division, and independent pathways for the control of organ regeneration and vascular differentiation. / Graduation date: 1997

Thesis (DTech (Environmental Health))--Cape Peninsula University of Technology, 2016. / Trihalomethanes are disinfection byproducts of chlorinated waters, and there is a growing interest to understand plant responses to organohalogens. This study investigates the effects of increasing trihalomethane dose on the physiology of tomato (Solanum lycopersicum) and determines whether the extent of physiological impacts of trihalomethane exposure on seedling radicle length, biomass accumulation, concentration levels of 12 key nutrients, oxidative stress, fatty acids and α-tocopherol content in membrane lipids of tomato correlated with either the number of bromine or chlorine atoms in the trihalomethane molecules. The 2 x 4 x 5 factorial experiment was laid out in CRD with four replications. Two cultivars of tomato were exposed to 4 levels of trihalomethanes (bromodichloromethane, bromoform, chloroform and dibromochloromethane) and 5 levels of concentration (0.0, 2.5, 5.0, 7.5, and 10.0 mg.L-1) in a green house. The decrease in seedling biomass and the inhibition of radicle growth increased with increasing trihalomethane concentrations in a dose dependent manner. Also, both these parameters decreased in response to an increase in the number of bromine atoms in the trihalomethane molecule. However, in growing plants the decrease in concentration levels of seven essential nutrients namely nitrogen (N), phosphorus (P), potassium (K), sulphur (S), copper (Cu), zinc (Zn) & boron (B) correlated to an increase in the number of chlorine atoms. Increase in trihalomethane dose also induced a decrease in all the above mentioned nutrients with the addition of manganese (Mn), although the decrease in P and S were not significant at P ≤ 0.05. The increase in trihalomethane dose induced an increase in oxidative stress parameters such as the total phenolic content, ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and lipid peroxidation. The increase in the above parameters correlated to an increase in the number of chlorine atoms, however, no such correlations were observed in superoxide dismutase (SOD) activity, general lipid peroxidation, α-tocopherol content and totalsoluble proteins. In plant membrane lipids, increase in the saturated fat hexadecanoic acid was observed in both tomato cultivars that correlated to the degree of chlorination in the trihalomethane molecule. The increase in α-linolenic acid stress signaling correlated with an increase in the degree of chlorination in only one tomato cultivar suggesting variable tolerance between cultivars to chemical action. Membrane lipids adjustments in tomato plants exposed to increasing trihalomethane dose were based on two factors; first the adjustments of membrane fluidity with the increase in plant sterols and fatty acids content and secondly, the increase in lipophyllic antioxidants such as phenols, quinones and α-tocopherol content. The phenolic lipophyllic antioxidant was tentatively identified to be 2,2’-methylenebis [6-(1,1-dimethylethyl)-4-methyl] phenol. In conclusion, the magnitude of plant responses to trihalomethanes is more dependent on the halogenation number of the molecule and less on its concentration.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This investigation was undertaken to determine whether elevated concentrations of dissolved inorganic carbon (DIC) supplied to plant roots could improve plant growth and alleviate the effects of salinity stress on tomato plants infected with arbuscular mycorrhizae. Lycopersicon esculentum cv. FI44 seedlings were grown in hydroponic culture (pH 5.8) with 0 and 75 mM NaCI and with or without infection with the fungus Glomus mosseae. The root solution was aerated with ambient CO2 (360 ppm) or elevated CO2 ( 5 000 ppm) concentrations. The arbuscular and hypha I components of mycorrhizal infection as well as the percentages total infection were decreased or increased according to the variation in seasons. The plant dry weight of mycorrhizal plants was increased by 30% compared to non-mycorrhizal plants at elevated concentrations of CO2, while the dry weight was decreased by 68% at ambient CO2 concentrations. Elevated CO2 also stimulated the growth of the mycorrhizal fungus. Elevated CO2 increased the plant dry weight and stimulated fungal growth of mycorrhizal plants possibly by the provision of carbon due to the incorporation of HCO)- by PEPc. Plant roots supplied with elevated concentrations of CO2 had a decreased CO2 release rate compared to roots at ambient CO2. This decrease in CO2 release rate at elevated CO2 was due to the increased incorporation of HC03- by PEPc activity. Under conditions of salinity stress plants had a higher ratio of N03-: reduced N in the xylem sap compared to plants supplied with 0 mM NaCI. Under salinity stress conditions, more N03- was transported in the xylem stream possibly because of the production of more organic acids instead of amino acids due to low P conditions under which the plants were grown. The N03· uptake rate of plants increased at elevated concentrations of CO2 in the absence of salinity because the HCO)- could be used for the production of amino acids. In the presence of salinity, carbon was possibly used for the production of organic acids that diverted carbon away from the synthesis of amino acids. It was concluded that mycorrhizas were beneficial for plant growth under conditions of salinity stress provided that there was an additional source of carbon. Arbuscular mycorrhizal infection did not improve the nutrient uptake of hydroponically grown plants. / AFRIKAANSE OPSOMMING: In hierdie studie was die effek van verhoogde konsentrasies opgeloste anorganiese koolstof wat aan plant wortels verskaf is, getoets om te bepaal of dit die groei van plante kan verbeter asook of sout stres verlig kon word in tamatie plante wat met arbuskulêre mikorrhizas geïnfekteer was. Lycorpersicon esculentum cv. FJ44 saailinge was in water kultuur gegroei (pH 5.8) met 0 en 75 mM NaCI asook met of sonder infeksie met die fungus Glomus mosseae. Die plant wortels was bespuit met normale CO2 (360 dele per miljoen (dpm)) sowel as verhoogde CO2 (5 000 dpm) konsentrasies. Die arbuskulere en hife komponente, sowel as die persentasie infeksie was vermeerder of verminder na gelang van die verandering in seisoen. Die plant droë massa van mikorrhiza geïnfekteerde plante by verhoogde CO2 konsentrasies was verhoog met 30% in vergelyking met plante wat nie geïnfekteer was nie, terwyl die droë massa met 68% afgeneem het by gewone CO2 konsentrasies. Verhoogde CO2 konsentrasies het moontlik die plant droë massa en die groei van die fungus verbeter deur koolstof te verskaf as gevolg van die vaslegging van HCO)- deur die werking van PEP karboksilase. Plant wortels wat met verhoogde CO2 konsentrasies bespuit was, het 'n verlaagde CO2 vrystelling getoon in vergelyking met die wortels by normale CO2 vlakke. Die vermindering in CO2 vrystelling van wortels by verhoogde CO2 was die gevolg van die vaslegging van HC03- deur PEPk aktiwiteit. Onder toestande van sout stres, het plante 'n groter hoeveelheid N03- gereduseerde N in die xileemsap bevat in vergelyking met plante wat onder geen sout stres was nie, asook meer NO)- was in die xileemsap vervoer moontlik omdat meer organiese sure geproduseer was ten koste van amino sure. Dit was die moontlike gevolg omdat die plante onder lae P toestande gegroei het. Die tempo van NO.; opname was verhoog onder verhoogde CO2 konsentrasies en in die afwesigheid van sout stres omdat die HCO)- vir die produksie van amino sure gebruik was. In die teenwoordigheid van sout was koolstof moontlik gebruik om organiese sure te vervaardig wat koolstof weggeneem het van die vervaardiging van amino sure. Daar is tot die slotsom gekom dat mikorrhizas voordelig is vir die groei van plante onder toestande van sout stres mits daar 'n addisionele bron van koolstof teenwoordig is. Arbuskulere mikorrhiza infeksie het 'n geringe invloed gehad op die opname van voedingstowwe van plante wat in waterkultuur gegroei was.

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