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Featured researches published by Katia Georgieva.


Journal of Plant Physiology | 1993

Temperature Dependence of Chlorophyll Fluorescence Parameters of Pea Seedlings

Katia Georgieva; Ivan Yordanov

Summary The thermosensitivity of the photosynthetic apparatus of 12 day-old seedlings of Pisum sativum cv. Ran was investigated within the temperature range 2–50°C at intervals of 2°C. The parameters of prompt chlorophyll fluorescence were used as a criteria of photosynthetic capacity, measured after 5 min temperature treatment (simultaneously with dark adaptation) at the respective temperature. It was established that in the temperature interval 2–42°C the ground fluorescence (Fo) did not change significantly, but above 42°C it increased dramatically. This gave us reason to suppose that temperatures higher than 44°C induced irreversible injuring of pea thylakoid membranes. The variable fluorescence (Fv) remained unchanged from 2°C to 20°C, after 22°C started to decrease first monotonously, then sharply and at 50°C it comprised only 6 % of its initial level. It was also shown that in the temperature range 2–30°C the ratio Fv/Fm, considered as a measure of PS2 activity, did not change significantly, but began to decrease at higher temperatures. After 42°C its level strongly decreased and at 50°C it was only about 10 % of the initial value of Fv/Fm. Similar changes were found for the Fv/Fo ratio. It is concluded that the physiological state and capacity of PS2 for electron transport do not changes significantly in a wide temperature range.


Journal of Plant Physiology | 1994

Temperature Dependence of Photochemical and Non-Photochemical Fluorescence Quenching in Intact Pea Leaves

Katia Georgieva; Ivan Yordanov

Summary The thermosensitivity of the photosynthetic apparatus of 12-day-old seedlings of Pisum sativum cv. Ran was investigated within the temperature range of 2–50 °C. Fluorescence quenching was used as a criteria. The photochemical (qP) and non-photochemical (qN) fluorescence quenching were measured after a 5-min treatment at the respective temperature. It was established that low and high-temperatures strongly affect the pattern of the fluorescence induction curve. The results obtained show that qP increases with the temperature rise from 2 to 35 °C and at temperatures higher than 40 °C it decreases sharply. Temperatures enhancing from 2 to 25 °C led to a decrease of qN. The values of this parameter increased strongly at temperatures higher than 45 °C. The results showed that within the temperature range of 15–40 °C the photochemical quenching dominated over the non-photochemical one. The influence of temperature on the quantum efficiency of PS2 photochemistry ϕPS2 was very similar to that of qP. It is concluded that the physiological state and the activity of PS2 are preserved in a wide temperature interval. The unfavourable temperatures provoke the switching on of the protective mechanisms as a qN enhancement and stimulation of cyclic electron transport through PS1, which allows the plants to endure the stress conditions.


Acta Parasitologica | 2006

Ultrastructure of spermiogenesis and mature spermatozoon of Skrjabinoporus merops (Cyclophyllidea, Metadilepididae)

Aneta Yoneva; Katia Georgieva; Yana Mizinska; Boyko B. Georgiev; Stoyanka Stoitsova

The ultrastructure of the mature spermatozoon and the spermiogenesis of a cestode belonging to the family Metadilepididae is described for the first time. The mature spermatozoon of Skrjabinoporus merops is characterized by twisted peripheral microtubules, the presence of a single crested body, periaxonemal sheath and electron-dense rods, and the absence of intracytoplasmic walls and inclusions (glycogen or proteinaceous granules); no peripheral microtubules where nucleus contacts the external plasma membrane. Four morphologically distinct regions of the mature spermatozoon are differentiated. The proximal part (Region I) contains a single crested body, periaxonemal sheath is absent in some (proximal) sections and is present in others situated closer to the nucleus. The central Region II is nucleated, and is followed by Region III that contains a periaxonemal sheath. The distal pole, Region IV, is characterized by disintegration of the axoneme. Spermiogenesis follows the type III pattern (Bâ and Marchand 1995) although in S. merops a slight flagellar rotation is observed. The differentiation zone is characterized by the absence of striated roots and intercentriolar body; two centrioles are present, one of which gives rise to a free flagellum. The latter rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone. Spermiological characters of S. merops are similar to those of the families Taeniidae and Catenotaeniidae. The mature spermatozoon differs from those of the Dilepididae (where the metadilepidid species have previously been classified) by the lack of glycogen.


Acta Parasitologica | 2006

Ultrastructure of spermiogenesis and mature spermatozoon of Angularella beema (Clerc, 1906) (Cestoda, Cyclophyllidea, Dilepididae)

Aneta Yoneva; Jordi Miquel; Zdzisław Świderski; Katia Georgieva; Yana Mizinska; Boyko B. Georgiev

The ultrastructure of the spermiogenesis of a dilepidid cestode species is described for the first time. The spermiogenesis of Angularella beema is characterised by absence of both flagellar rotation and proximodistal fusion. The differentiation zone is surrounded by cortical microtubules and is delimited by a ring of arching membranes. It contains two centrioles, one of which develops the axoneme that grows directly into the elongating cytoplasmic protrusion. This pattern of spermiogenesis was described as the Type IV spermiogenesis of cestodes. Among cestodes, similar pattern of spermiogenesis is known in the family Hymenolepididae and in some representatives of the family Anoplocephalidae. The mature spermatozoon of A. beema consists of five regions differing in their ultrastructural characteristics. It is characterised by the presence of cortical microtubules (spirally arranged at angle of 30–40° to the spermatozoon axis) and a single crested body. There is a periaxonemal sheath in certain parts of the spermatozoon as well as glycogen-like granules between the periaxonemal sheath and the cortical microtubules. The comparisons of the mature spermatozoon of A. beema with those of other two dilepidid species (Dilepis undula and Molluscotaenia crassiscolex) demonstrate some variation within the family: presence of periaxonemal sheath in A. beema and D. undula and its absence in M. crassiscolex; presence of electron-dense rods in D. undula and their absence in A. beema.


Parasitology Research | 2008

Spermiogenesis and sperm ultrastructure of Valipora mutabilis Linton, 1927 (Cestoda, Cyclophyllidea, Gryporhynchidae)

Aneta Yoneva; Zdzisław Świderski; Katia Georgieva; Pavel N. Nikolov; Yana Mizinska; Boyko B. Georgiev

This is the first ultrastructural study of the spermiogenesis and the mature spermatozoon of a cyclophyllidean cestode of the family Gryporhynchidae. The spermiogenesis of Valipora mutabilis begins with the formation of a differentiation zone delimited by arching membranes and containing two centrioles. One of the centrioles develops an axoneme that grows directly into the cytoplasmic protrusion. The other centriole remains situated in a cytoplasmic bud and is subsequently aborted (type IV of cestode spermiogenesis). The mature spermatozoon of V. mutabilis is a filiform cell, tapered at both extremities and lacks mitochondria. The anterior extremity is characterised by the presence of an apical cone and a single helicoidal crested body. The axoneme is of 9 + ‘1’ trepaxonematan pattern, with a periaxonemal sheath. The cortical microtubules are twisted at an angle of about 45° to the spermatozoon axis. The nucleus is electron dense and spirally coiled around the axoneme. The cytoplasm is electron lucent and contains numerous granules of electron-dense material. In contrast to a recent opinion for close phylogenetic relationships, these ultrastructural data demonstrate the distant position between gryporhynchids and the family Taeniidae. The most similar pattern in the ultrastructure of the spermiogenesis and the mature spermatozoon has been described for dilepidids, some hymenolepidids and some anoplocephalids.


Acta Zoologica | 2010

Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda, Cyclophyllidea, Paruterinidae)

Aneta Yoneva; Katia Georgieva; Yana Mizinska; Pavel N. Nikolov; Boyko B. Georgiev; Stoyanka Stoitsova


Folia Parasitologica | 2009

Ultrastructure of spermiogenesis and mature spermatozoon of Triaenorhina rectangula (Cestoda: Cyclophyllidea: Paruterinidae).

Aneta Yoneva; Katia Georgieva; Pavel N. Nikolov; Yana Mizinska; Boyko B. Georgiev; Stoyanka Stoitsova


Dokladi na B lgarskata akademiâ na naukite | 2007

Lectin binding characteristics of Fasciola hepatica rediae

Katia Georgieva; Aneta Yoneva; Y. Mizinska-Boevska


Dokladi na B lgarskata akademiâ na naukite | 2005

Lectin-binding properties of the surface of Fasciola hepatica sporocysts

Katia Georgieva; Aneta Yoneva; I. Popov; Y. Mizinska-Boevska; S. Stoitsova


Acta Biologica Hungarica | 2005

Ultrastructure of the contact surfaces of Passalurus ambiguus (Rudolphi, 1819) (Nematoda)

Katia Georgieva; Aneta Yoneva; Y. Mizinska-Boevska; I. Todev

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Aneta Yoneva

Bulgarian Academy of Sciences

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Boyko B. Georgiev

Bulgarian Academy of Sciences

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Yana Mizinska

Bulgarian Academy of Sciences

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Pavel N. Nikolov

Bulgarian Academy of Sciences

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Stoyanka Stoitsova

Bulgarian Academy of Sciences

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Ivan Yordanov

Bulgarian Academy of Sciences

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Jordi Miquel

University of Barcelona

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