Philosophiae Doctor - PhD / Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summerblooming,deciduous and bulbous geophytes that grow naturally in the semi-arid succulent Karoo biome of South Africa. Both species grow under full sun conditions and have four distinctive growth phases: a winter (cold and wet) growing phase, leaf senescence phase towards spring, flowering phase during the hot and dry summer months, and fruit and leaf formation phase in autumn. The medicinal uses of this genus (including G. multifolia “Kukumakranka” and G.villosa “hairy kukumakranka”) range from cures for colic, digestive disturbances,teething problems, fatigue, boils, bruises and insect bites, to being used as an aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in the ‘Vulnerable’ category of the ‘Red Data List of Southern African Plants’ and the ‘IUCN-World Conservation Union List of Plants’. The literature indicate that the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not known to which extent these factors may pose a threat to the existence of both species. The first objective of this investigation was to determine the costs of vegetative and reproductive growth during the seasonal life cycle of the plant, using carbon(C) and nitrogen (N) as a physiological currency. The second objective was to elucidate a functional basis to explain the difference in the conservation status of both species in their natural habitat. Both species were subjected to drought and shading as environmental stresses and the plant physiological performance was investigated via photosynthetic gas exchange. The third objective of the study was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and flavanone content) and antioxidant capacity [ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3-ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of natural populations and plant samples that were exposed to photo-and-drought environmental stresses. This study was done to elucidate the antioxidant profile of plant parts of natural populations as well as providing farmers, traditional healers and pharmaceutical companies with cultivation environmental conditions to enhance the antioxidant properties of the species. This investigation also attempted to isolate and characterize, by means of thin-layer chromatography (TLC) and column chromatography (CC), natural compounds from both species to lend support to the purported antioxidant benefit of both species and to further lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in vivo studies or human trials to support published literature of the medicinal benefits of the genus.

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EEffffeecctt ooff ddrroouugghhtt oonn tthhee mmeettaabboolliissmm ooff ttaabbaaccccoo ppllaannttss (Nicotiana tabacum L.) Diploma thesis - abstract Lucia Miedzińska, Bc. Work Supervisor: Doc. RNDr. Helena Ryšlavá, CSc. Consultant: RNDr. Veronika Doubnerová, PhD. Drought stress is one of the most frequent form of plant stress, which occurs not only under condition of limited water availability, but also under reduced ability to accept water by roots, for example in salted or cold soils. In this thesis the changes in enzyme activities of: NADP-malic enzyme (EC 1.1.1.40; NADP-ME), phosphoenolpyruvate carboxylase (EC 4.1.1.31; PEPC) and pyruvate, phosphate dikinase (EC 2.7.9.1; PPDK) in tobacco plants (Nicotiana tabacum L., cv. W38) after drought were investigated. Enzyme activities in tobacco leaves were significantly increased during 11 days of stress, PEPC 2-fold, PPDK 3,3- fold and NADP-ME 4-fold compared to control plants. The regulation of NADP-ME and PEPC activities were studied on transcriptional level - by the real-time PCR method and on translational level - immunochemically. The expression of NADP-ME protein and transcription of mRNA for chloroplast NADP-ME isoform were increased, but mRNA for cytosolic isoform was not affected. The protein expression of PEPC was slightly increased, transcription of...

Der bereits stattfindende Klimawandel mit ansteigenden Temperaturen, einer Zunahme von Trockenperioden und Hitzewellen während der Vegetationsperiode wird das Risiko von Trockenstress für Bäume und Sträucher erheblich erhöhen. Eine der Herausforderungen ist daher die erfolgreiche Etablierung von gesunden, langlebigen und an die spezifischen urbanen Standorte adaptierten Bäume, um die ökologischen und ökonomischen Wohlfahrtswirkungen städtischen Grüns auch in Zukunft zu gewährleisten. Das Ziel dieser Arbeit war es deshalb, sowohl die Eignung einiger häufig verwendeter Straßenbaumarten für stark versiegelte Straßenbaumstandorte als auch deren Toleranz gegenüber Trockenstress am Beispiel von Dresden zu identifizieren. Die Arbeit verfolgt einen dendrochronologischen und einen physiologischen Ansatz. Im dendrochronologischen Teil der Arbeit wurden die Jahrringzeitreihen von 16 Straßenbaum-Chronologien, 3 Einzelbaum-Chronologien im Stadtgebiet von Dresden und 4 Chronologien eines trockenen Waldstandortes in einem Naturschutzgebiet sowie 2 Chronologien frischer Waldstandorte analysiert. Auf Basis der trendbereinigten Zuwachszeitreihen wurden Klima-Zuwachs-Relationen, moving correlations, Weiserjahranalysen und superposed epoch analyses (SEA) durchgeführt. Im physiologischen Teil der Arbeit wurde in den Sommermonaten der Jahre 2009 und 2010 auf vier urbanen Straßenbaumstandorten der lichtgesättigte Gasaustausch von sechs Baumarten und das Blattwasserpotential von vier Baumarten ermittelt. Für die Messperioden und in ausgewählten Trockenperioden wurde die Wassernutzungseffizienz der Baumarten verglichen. Auf urbanen Straßenbaumstandorten reagieren die Arten Acer platanoides, Acer pseudoplatanus und Fagus sylvatica stark sensitiv auf Trockenheit. Im Gegensatz dazu können die Arten Platanus x hispanica, Quercus robur subsp. sessiliflora und Quercus rubra als weniger trockenheitsempfindlich betrachtet werden. Die dendrochronologischen und physiologischen Ergebnisse erlauben für Tilia cordata Mill., Tilia platyphyllos und Pyrus communis eine Einordnung in eine mittlere Eignung für versiegelte Flächen. Aus den dendrochronologischen und physiologischen Ergebnissen dieser Untersuchung lässt sich schließen, dass sich die höheren Temperaturen und die zunehmenden Trockenperioden für alle untersuchten Arten negativ auswirken können. Dennoch zeigen die Baumarten Platanus x hispanica, Quercus robur subsp. sessiliflora und Quercus rubra, dass sie den sich verändernden Klimabedingungen auf stark versiegelten urbanen Standorten gut widerstehen können und auch in Zukunft eine hohe Vitalität beibehalten werden.

Climate warming in recent decades has resulted in more frequent and severe drought events in the western United States. These changes are projected to continue, making it exceedingly important to understand how forests respond to severe drought stress, and how we can manage these forests to reduce mortality during future events. The 2012-2015 California drought is a recent example of a severe, multi-year drought that was coupled with an epidemic-scale outbreak of western pine beetle, killing nearly 90% of ponderosa pines in the central and southern Sierra Nevadas. In the first portion of this study, we compared pairs of surviving and dead ponderosa pines following this drought event to determine how the surviving trees were able to survive. We were also interested in how closely ponderosa pine tree-rings were recording ecosystem responses to this drought event. In the second portion of this study, we compared tree-ring growth rates and stable isotopes to data from an on-site flux tower to determine whether tree-rings were recording important information regarding ecosystem carbon and water fluxes during this severe drought event. Overall, we sought to better understand how the 2012- 2015 California drought event affected ponderosa pines to inform future management practices in forests of the western United States.

>Magister Scientiae - MSc / Agricultural practices are significantly affected by drought. Drought is one of the most important plant stresses, causing several physiological, morphological, biochemical, and molecular changes in plants. Drought stress is of great challenge for crop growth, development and yield. Zea mays (maize) is one of the important crops worldwide due to the nutritional profile and other uses such as human consumption, manufacturing and animal feed. Under unfavorable conditions, plants produce high amounts of reactive oxygen species (ROS). Excessive formation of ROS is harmful for plant survival and can induce cell death. Defense mechanisms activated in response to drought in plants include antioxidant enzyme activity and proline accumulation. There is evidence of the use of nitric oxide (NO) donors and hydrogen peroxide (H2O2) at low concentrations to enhance the activity of antioxidant enzymes in stressed plants. Hence, the aim of the study is to examine the role of NO and H2O2 in regulation of antioxidant enzyme activity in maize subjected to water deficit. / 2023

Drought and salt stress are the main global factors that reduce the average yield of most major crops. In order to meet global demands, we will need to double food production by 2050 (Tilman, Balzer, Hill, & Befort, 2011). Plant growth-promoting bacteria (PGPB) are a group of bacteria that alleviate the harmful effects of abiotic stresses such as salt, heat and drought stress on plants and decrease the global dependence on hazardous agricultural chemicals. We identified that beneficial microbes isolated from desert plants (indigfera argentea) from Jizan region, in 2012 enhance the tolerance of a variety of crop plants to drought and salt stresses under laboratory conditions and in field trials. We analyzed the interaction of these bacteria with the plants by genetic, biochemical and imaging techniques. The goal of this dissertation is to ultimately improve our understanding of the mechanisms of drought and salt stress tolerance conferred by beneficial microbes that can be used as a sustainable solution for plants and crops in degrading lands (deserts) and land affected by abiotic stresses. Outlines how each of chapter of this dissertation will contribute to the discovery of novel drought and salt stress tolerance strategies using a desert-specific bacterial endophyte.

San Joaquin wooly-threads (Monolopia congdonii; Asteraceae) is a federally-listed, endangered annual plant species from the desert areas of the San Joaquin Valley. Its limited range puts it at risk of extinction if the climate changes in such a way as to hinder its growth and reproduction. The primary aims of the study were to 1) determine how long-lived the seeds of the M. congdonii are, a key determinant of survival of desert annual plant populations through long droughts and 2) determine how severely hotter, drier conditions impact the ability of emerged plants to grow and reproduce. Secondarily, I aimed to test two hypotheses 1) is seed longevity within the genus Monolopia correlated with habitat aridity? 2) do species’ geographic range limits represent their climatic tolerances? In testing the viability of seeds of Monolopia species collected from herbarium specimens and old field collections, I did not find evidence for the predicted pattern of seed longevity. Though, idiosyncrasies in the data suggest possible issues with the longevity of M. congdonii seeds that are collected prematurely and warrant further investigation to develop best practices for seed collections of this species. To test the climatic tolerance of M. congdonii and the relationship between geographic range and climatic tolerance, I grew several desert annual species under three manipulated water treatments. And while, M. congdonii failed to germinate, the other species showed variable tolerance for the drought treatments but this variability was seemingly unrelated to the species’ geographic range. Importantly, Monolopia lanceolata, a close relative of M. congdonii did not show exceptional vulnerability to the drought-stress conditions relative to other co-occuring species. Taken together, the results of this study enable better informed population viability analyses with the end goal of allowing recovery efforts to succeed.

Drought stress was studied in rice (Oryza sativa) and maize (Zea mays) to identify drought-responsive genes and associated biological processes. One experiment with rice examined drought responses in vegetative and reproductive tissues and identified drought-responsive genes in each tissue type. The results showed that brief periods of acute drought stress at or near anthesis reduced photosynthetic efficiency and ultimately lowered grain yield. Yield was reduced as a result both of fewer spikelets developed and of lower spikelet fertility. Affymetrix arrays were used to analyze global gene expression in the transcriptomes of rice vegetative and reproductive tissue. Comparative analysis of the expressed genes indicated that the vegetative and reproductive tissues responded differently to drought stress. An experiment was conducted with maize, using GS-FLX pyrosequencing to identify differentially expressed genes in vegetative and reproductive tissues; and these results were compared with those from the just-described rice transcriptome. Some of the drought-responsive genes in the maize reproductive tissue were validated by quantitative real time polymerase chain reaction (qRT-PCR). The differentially expressed genes common to both maize and rice were further analyzed by gene ontology analysis to reveal core biological processes involved in drought responses. In both species, drought caused a transition from protein synthesis to degradation, and photosynthesis was one of the most severely affected metabolic pathways. In a validating experiment, a drought-responsive transcription factor found in rice and dubbed HIGHER YIELD RICE (HYR) was constitutively expressed in rice, and the transgenic HYR plants were studied. Under well-watered conditions, the HYR plants developed higher rates of photosynthesis, greater levels of soluble sugars (glucose, fructose, and sucrose), more biomass, and higher yield. They also exhibited a drought-resistant phenotype, with higher water use efficiency, photosynthesis, and relative leaf water content under drought stress. Taken together, these studies demonstrate the potential value of newer technologies for identifying genes that might impart drought resistance and for using such genes to make crops more productive either in the presence or in the absence of drought stress. / Ph. D.