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The wood anatomy, hydraulic properties and leaf water status of five sub-tropical plant species were studied. The specimens studied were growing in a private, irrigated garden. Consequently, any differences in xylem anatomy would be a result of phylogenetic and not environmental factors. Podocarpus latifolius, being a gymnosperm, had only narrow, short tracheids as the conducting conduits. The size of the vessels of the four angiosperms increased in the following order: Tecomaria capensis, followed by Cinnamomum camphora, Trichilia dregeana and finally Barringtonia racemosa had the widest vessels. T. capensis and T. dregeana had the shortest vessel lengths. Those of C. camphora were slightly longer and the vessels of B. racemosa were the longest. Measurements of hydraulic conductance (Kh), twig specific conductivity (TSC) and xylem specific conductivity (XSC) followed similar trends to those of conduit diameters. The measurements of leaf specific conductivity (LSC) , however, did not follow these trends. T. dregeana, which had a far higher Kh than P. latifolius, did not have a significantly different LSC. This is because the twigs of T. dregeana supported a far greater leaf area than did the twigs of P. latifolius. There was also no significant difference in LSC among T. capensis, C. camphora and B. racemosa, although their LSC's were all significantly higher than those of P. latifolius and T. dregeana. The consequence of efficient xylem anatomy thus seems to be, not only a greater supply of water to the leaf but also, and perhaps more importantly, it allows a greater leaf area to be produced. The length of the vessels was also shown to have a large effect on the hydraulic conductivity of the twigs. The Kh values measured on excised twigs were found to range between 40% and 87% of the Kh calculated using the Hagen- Poiseuille equation. Conduit size distributions were also found to be important in calculating the Kh. The more efficent xylem anatomy of B. racemosa resulted in little decrease in plant water potential even with large increases in transpiration. P. latifolius on the other hand showed a considerable decrease in leaf water potential with just a slight increase in transpiration. The other three species showed decreases in leaf water potential inter-mediate to these two extremes. The inferred root-to-leaf condutivity, shown by the inverse of the slopes of the water potential versus transpiration curves, were lower than the LSC measurements taken on excised twigs in the laboratory. The difference between the inferred and the measured LSC's could give an indication of resistances such as those within the root and at the soil-root interface. / Thesis (M.Sc.)-University of Natal, Durban, 1991.

Xylem is an inherent feature of all vascular plants and functions in water transport and mechanical support. In order to efficiently transport water, xylem cells are reinforced by secondary walls before they undergo programmed cell death and their cell contents are removed by autolysis to create a hollow tube. During their differentiation, xylem cells express various hydrolytic enzymes, such as proteases, nucleases and lipases, but only in a few examples has their role in xylem cell death been characterized. This thesis focuses on the regulatory aspects of xylem cell death and the autolytic cell clearance in vessel elements and fibers of hybrid aspen (Populus tremula L. x tremuloides Michx.) and in vessel elements of Arabidopsis thaliana. Using comparative transcriptomic analysis, candidate genes for fiber-specific cell death processes were identified. Further, a hypothesis is presented on the regulation of thermospermine levels in the vasculature by a negative feedback-loop involving auxin and the class III Homeodomain-Leucine Zipper (HD-ZIP III) transcription factor HOMEOBOX8 (PtHB8). The role of the Arabidopsis METACASPASE9 (AtMC9) in xylem cell death was characterized using molecular tools, such as reporter lines and fluorescent fusion proteins, and electron microscopy (TEM). This showed that cell death initiation is not controlled by AtMC9. Instead, evidence is presented for the involvement of AtMC9 in the post mortem autolysis of vessel elements that follows tonoplast rupture and leads to the formation of the hollow conduit. Cell death-associated genes were further observed to be expressed during the emergence of lateral roots in Arabidopsis thaliana. This led to the discovery that cells overlying a lateral root primordium undergo cell death, which was demonstrated by detection of DNA degradation and TEM analysis. It is concluded that cell death facilitates emergence of lateral roots through the overlying tissues in a concerted manner with cell wall remodelling. Together, these findings show that although individual hydrolytic enzymes may be dispensable for plant growth and development, their common regulators are the tool for understanding their function and importance. / Xylem är en karakteristisk vävnad i alla kärlväxter som leder vatten och mineraler samt har mekanisk stödfunktion. För att effektivt kunna transportera vatten förstärks xylemceller med sekundära cellväggar innan de dör genom programmerad celldöd. Deras cellinnehåll bryts ner genom autolys för att skapa ett ihåligt rör. Xylemceller uttrycker under sin differentiering olika hydrolytiska enzymer, såsom proteaser, lipaser och nukleaser, men bara för ett fåtal av dessa har funktionen under xylemcelldöd kartlagts. Denna avhandling fokuserar på reglering av xylemcelldöden och den autolytiska nedbrytningen av cellen, i såväl kärlelement och fibrer av hybridasp (Populus tremula L. x tremuloides Michx.) som i kärlelement av backtrav (Arabidopsis thaliana). Med hjälp av jämförande transkriptomanalys identifierades kandidatgener för fiber-specifika celldödsprocesser i hybridasp. Vidare utvecklades en hypotes om reglering av termosperminnivåer i vaskulaturen genom en negativ feedback-loop, som omfattar auxin reglering och klass III homeodomän-leucinzipper (HD-ZIP III) transkriptionsfaktorn HOMEOBOX8 (PtHB8). Funktionen av Arabidopsis METACASPASE9 (AtMC9) under xylemcelldöd karakteriserades med molekylära verktyg, såsom reporterlinjer och fluorescerande fusionsproteiner och elektronmikroskopi (TEM). Dessa analyser visade att celldödens initiering inte styrs av AtMC9. Istället presenteras bevis för en roll av AtMC9 i autolysen av kärlelement som sker post mortem efter att vakuolen har gått sönder och som slutför bildandet av det tomma kärlet. Genuttryck som associeras med celldöd observerades också under utvecklingen av laterala rötter i Arabidopsis thaliana. Detta ledde till upptäckten att celler som ligger ovanför ett lateralrotprimordium dör en programmerad celldöd och visar tecken på DNA-nedbrytning och autolys i TEM-analyser. Slutsatsen av denna studie är att celldöd i samspel med cellväggsmodifiering underlättar utväxten av laterala rötter genom de överliggande cellagren. Sammantaget tyder dessa upptäckter på att även om enstaka hydrolyserande enzymer inte är nödvändiga för växternas tillväxt och utveckling, så kan deras gemensamma reglering nyttjas för att förstå deras funktion och betydelse.

A review of the literature established that there were areas of cytokinin transport which needed further investigation, in order to determine the function and/or mode of action of cytokinins during certain stages of plant development. Radioactive zeatin was applied to plant systems suitable for determining more about specific problems of cytokinin transport. The metabolism of the radioactive zeatin was monitored in relation to transport. The metabolism in, and possible export of, radioactive zeatin out of immature, mature and senescing Ginkgo biloba leaves was monitored using explants. The results showed that approximately the same percentage radioactivity was exported from the leaves at all three stages of their development. This indicates that these deciduous leaves could potentially export cytokinins, but the results were not regarded as being significant. Cytokinins would not have been expected to be transported out of expanding leaves, which rapidly utilize cytokinins, and in comparison greater cytokinin export would have been expected to occur from senescing leaves, but this did not occur. The resuIts could indicate that cytokinin glucosides in deciduous leaves are primarily inactivation products rather than storage compounds. The metabolism and transport of radioactive zeatin, applied to the leaves of Citrus sinesis trees, was monitored during the flush of new growth following a dormant period. Some of the radioactive zeatin applied to these leaves appeared to be utilized in the new shoot growth. This could imply that accumulated cytokinin glucosides in these evergreen leaves are exported out of the leaves and reutilized, and thus fulfil a storage function; although the extent to which export occurred as opposed to interconversion and/or catabolic metabolism in the leaves could not be determined. The distribution of radioactive zeatin applied to the xylem and phloem of Phaseolus vulgaris plants at three stages of development was also monitored. There appeared to be preferential transport of cytokinins in the transpiration stream, that is, applied to the xylem. The vegetative apices, buds and flowers appeared to be the major sinks for radioactive compounds in the vegetative and flowering plants, and the leaves were the most important sink in the fruiting plants. Radioactive zeatin in the phloem appeared to move passively with the assimilate stream. The transport of radioactive zeatin applied to the primary leaves appeared to confirm that cytokinins in the phloem were transported along with the assimilate stream. The results also indicated that the accumulated cytokinin glucosides in these annual leaves were primarily inactivation products, involved in regulating leaf metabolism, although some re-utilization of these cytokinins could potentially take place. could have reflected normal cytokinin transport occurring in the tissues. The main metabolic pathway, oxidation, did not, however, appear to be the main metabolic pathway in the plant tissues and may have been the result of the exogenous application of zeatin. The fact that metabolism did not appear to be the normal metabolism of the tissues, could potentially have affected transport. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

Hundreds of proteins have been detected in phloem and xylem sap, even though the cells involved in long distance phloem and xylem transport are incapable of protein synthesis at maturity. We are now beginning to learn the identity and function of these proteins, but this knowledge is generally limited to annual plants. The first objective of this study was to identify phloem and xylem sap proteins in the perennial, poplar. Using LC-MS/MS, 48 proteins were identified in poplar phloem exudate and 98 proteins were identified in xylem sap. A large number of phloem exudate proteins are insect defense proteins that include protease inhibitors and polyphenol oxidase and also members of the pop3/SPI gene family, whereas a number of xylem sap proteins were pathogenesis-related proteins such as thaumatin-like proteins (TLPs) and chitinases that function in pathogen defense. The importance of xylem sap proteins in pathogen defense has been previously demonstrated, however, the role of phloem proteins in insect defense is currently unknown. A major question to be addressed in order to understand the function of phloem proteins is if they are differentially regulated in response to insect herbivory. The second objective of this study was to identify poplar phloem proteins differentially regulated in response to simulated insect feeding. Using two-dimensional gel electrophoresis, two proteins, PtTLP1 and pop3.1, were consistently upregulated 24 hours post-wounding. The third objective of this study was to produce antibodies against these proteins to use to further characterize their expression and localization patterns. Antibodies were also produced against another phloem exudate protein, pop3.4, which is 40% similar to pop3.1. The origin of all three proteins inside sieve elements was confirmed with immunolocalization. PtTLP 1, pop3.1 and pop3.4 antisera labelled organelle-like structures in sieve elements and also phloem parenchyma cells. For PtTLP1, these structures were identified as starch and starch containing plastids. All three antisera also labelled cell wall proteins in different cell types. Overall, this study represents the first large-scale analysis of phloem and xylem sap proteomes from a perennial and describes the first observation of wound-inducible phloem sap proteins.

Development in multicellular organisms requires a strict balance between cell division and differentiation. The simple architecture of the Arabidopsis thaliana root makes it an ideal model for studying molecular mechanisms controlling both the transition from cell division to cell differentiation and cell fate determination. The class III Homeodomain-Leucine Zipper (HD-ZIP III) transcription factors (TFs) are well known developmental regulators, controlling important aspects of embryogenesis, shoot meristem activity, leaf polarity and vascular patterning. The HD-ZIP III TFs are under post-transcriptional control of microRNA165 (miR165) and miR166. In this thesis, I present a cell-to-cell signalling pathway underlying root vascular patterning and describe signaling pathways downstream of the HD-ZIP III TFs in their control of root development. The TF SHORTROOT (SHR), moves from the vascular stele cells to the surrounding endodermal cell layer. We show that SHR acts here to transcriptionally activate MIR165A and MIR166B, and the miR165/6 produced in the endodermis act non-cell autonomously to post-transcriptionally restrict HD-ZIP III mRNA levels in the peripheral stele. The resulting graded HD-ZIP III activity domain in the radial stele dose-dependently determines vascular cell type; high levels of HD-ZIP III in the central stele result in metaxylem formation while lower levels in the peripheral stele result in protoxylem. We provide evidence that the HD-ZIP III factors act as de novo xylem specifiers, because the quintuple mutant lacking all five HD-ZIP III genes forms no xylem. Furthermore, reducing the plasmodesmatal aperture through callose accumulation inhibits the bi-directional mobility of both signalling molecules, providing evidence that both SHR and miR165/6 move cell-to-cell via plasmodesmata to control root development. I present downstream components of the miR165/HD-ZIP III TFs in the root meristem, identified through a time-course induction of miR165 coupled to transcriptome analyses. This experiment revealed novel roles for HD-ZIP III TFs in vascular patterning and meristem size control. I show that HD-ZIP III directed repression of auxin hormone signalling in the xylem axis is essential for proper xylem differentiation. Furthermore, I provide data to show that they also control the balance of reactive oxygen species in the root meristem, thereby directing meristem size and ultimately controlling root growth.

This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

Thesis (M.S.)--Oregon State University, 2005. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Ohio University, March, 2010. / Title from PDF t.p. Includes bibliographical references.