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Controlled Drug Delivery in Photodynamic Therapy and Fluorescence-Based Diagnosis of Cancer
Published in Mary-Ann Mycek, Brian W. Pogue, Handbook of Biomedical Fluorescence, 2003
The most important approach in the PDT and PD of cancer using specific deficiencies of the metabolism of neoplastic cells is based on the systemic or topical administration of 5-aminolevulinic acid (ALA). ALA is not a photoactive substance by itself, but forms part of a substrate in the biosynthetic pathway of heme, the iron(II) complex of protoporphyrin IX (PpIX) (see Fig. 8). In contrast to heme, PpIX is a fluorescent molecule with a 1O2 quantum yield of approximately 0.5 [148], which makes it suitable for PDT and PD. Almost all nucleated cells in mammals exhibit the ability to produce PpIX. The route by which cells produce PpIX endogenously forms part of the overall scheme for the production of chemical energy. Nowadays the biosynthetic pathway of heme is relatively well understood and has been reviewed recently by Peng and coworkers [149]. In brief, the initial step in heme biosynthesis is the enzymatically catalyzed formation of ALA from glycine and succinyl-CoA inside the inner mitochondrial membrane. Following the entry of ALA into the cytosolic space, ALA dehydrase induces the condensation of two ALA molecules to form porphobilinogen (PBG). Subsequently, PBG deaminase (PBG-D) and uroporphyrinogen III cosynthase catalyze the cyclization of four PBG molecules to form the tetrapyrrolic skeleton. Finally, a series of decarboxylations and oxidations inside the cytoplasm as well as in the mitochondria have to take place before PpIX is formed, by the removal of six hydrogens from the protoporphyrinogen IX, catalyzed by protoporphyrinogen oxidase, which is embedded in the inner mitochondrial membrane. Ferrochelatase, also located in the inner mitochondrial membrane, catalyzes the incorporation of iron into the PpIX cycle to form nonfluorescent heme. Heme biosynthesis is regulated by numerous control mechanisms, among which is the negative feedback control on the ALA synthase (ALA-S) activity as well as on the transcription, translocation, and transport of the enzyme into the mitochondria.
Nitrogen Cycle Bacteria in Agricultural Soils
Published in Vivek Kumar, Rhizomicrobiome Dynamics in Bioremediation, 2021
Guillermo Bravo, Paulina Vega-Celedón, Constanza Macaya, Ingrid-Nicole Vasconez, Michael Seeger
The application of herbicides is widely used in the management practices of crop production in modern agriculture (Singh and Jauhari 2017). Globally, more than eight thousand species of weeds injure crops, causing losses of 13% (Zhang et al. 2011, 2018). There are 9 main herbicide categories: phenoxies, triazines, amides, carbamates, dinitroanilines, urea derivates, sulfonyl ureas, bipiridils and uracils (Zhang 2018). Diverse mechanisms of action have been reported: acetyl-CoA carboxylase inhibitors, acetolactate synthase or acetohydroxy acid synthase (AHAS) inhibitors, photosystem ΙΙ inhibitors, photosystem Ι inhibitors, protoporphyrinogen oxidase (PPG oxidase or protox) inhibitors, carotenoid biosynthesis inhibitors, enolpyruvylshikimate-3-phosphate (EPSP) synthase inhibitors, glutamine synthetase inhibitors, dihydropteroate synthetase inhibitors, mitosis inhibitors, cellulose inhibitors, oxidative phosphorylation uncouplers, fatty acid and lipid biosynthesis inhibitors, synthetic auxins and auxin transport inhibitors (Forouzesh et al. 2015). The modes of action of many herbicides are well defined and the targeted enzyme in weeds is known. Interestingly, some of these targets are also present in a range of non-target organisms, including soil microorganisms (Thiour-Mauprivez et al. 2019). Glyphosate and atrazine herbicides affect also non-target organisms. Bacteria play a crucial role in nitrogen cycling in the soil ecosystem, including nitrification and denitrification processes. Herbicides’ application affect nitrification and denitrification bacteria (Hernández et al. 2011, Mertens et al. 2018, Tyler and Locke 2018). The countries with the highest herbicide consumption are USA, Brazil and Argentina, exceeding 203, 153 and 116 thousand tonnes on average from 1990 to 2017, respectively (http://www.fao.org/faostat/en/#data). Three of the most commonly used agricultural herbicides by USA are glyphosate, atrazine and 2,4-dichlorophenoxyacetic acid (2,4-D) (Meyer and Scribner 2009, Fernández-Cornejo et al. 2014), which belong to a not classified, triazine and phenoxy categories of herbicides (Sherwani et al. 2015, Zhang 2018). These types of herbicides will be further discussed.
Growth and physiological responses of three poplar clones grown on soils artificially contaminated with heavy metals, diesel fuel, and herbicides
Published in International Journal of Phytoremediation, 2020
Andrej Pilipović, Ronald S. Zalesny, Saša Orlović, Milan Drekić, Saša Pekeč, Marina Katanić, Leopold Poljaković-Pajnik
Although herbicides such as Oxyfluorfen and Pendimethalin have not shown impacts on juvenile growth and performance of some ornamental trees and shrubs (Derr and Salihu 1996; Woeste et al.2005) nor ‘Pannonia’ grown for nursery production (Vasic et al.2015), the herbicide treatments in this study decreased net photosynthesis in all three clones (‘Bora’, ‘PE 19/66’, and ‘Pannonia’), with the greatest impact occurring during the first growing season. These early impacts were not unexpected, given that the primary action of more than half of currently-used herbicides is to block photosynthetic functions (Pfister and Antzen 1979). Depending on dose, herbicides can act on crucial physiological pathways or processes in both inhibitory and stimulatory ways. This can have detrimental impacts to such mechanisms in non-target plants (e.g., the poplars in this study), with affected processes ranging from photosynthesis, pigment content, WUE parameters (e.g., turgor pressure, stomatal conductance, relative water content, water potential, etc.), and some enzymes such as nitrate reductases and amylases (Wasfi and Samia 2016). For instance, photobleaching diphenyl ether (DPE) herbicides such as Oxyfluorfen used in this study are known to inhibit protoporphyrinogen oxidase, which is the last common enzyme in heme and chlorophyll biosynthesis (Yanagida et al.1999). While less is known about the physiological effects of herbicides on poplars (Pilipović et al.2016), their phytoremediation-relevant impacts in other plants include disturbance of: (1) photosystem II and quantum efficiency (Iftikhar Hussain et al.2010), (2) photosynthetic yield (Haynes et al.2000), (3) chlorophyll content and fluorescence (Shabana et al.2001; Wasfi and Samia 2016), and (4) antioxidant content (Yanagida et al.1999).