Upcoming PhD defense – Hiie Ivanova

On 8th of January 2016 at 11.00 in Kreutzwaldi 5-2A1 our long-time senior researcher Hiie Ivanova will finally defence her doctoral thesis „Responses of respiratory and photorespiratory decarboxylations to internel and external factors in C3 plants“. (full text available here)

Supervisors: Ülo Niinemets; Olav Keerberg; Tiit Pärnik (all from EMÜ Plant Physiology)

Opponent: Dr. Miquel Ribas-Carbo (University of the Balearic Islands, Spain)


Hiie´s thesis cover


Simultaneously with CO2 fixation in plant leaves during photosynthesis, respiration processes release part of the fixed CO2 in decarboxylation reactions. There are two different respiration processes – respiration and photorespiration, occuring in photosynthesizing leaves only. In this work the significance of internal and environmental factors in regulatory mechanisms determining integration of photosynthetic and respiratory processes was studied. A radio-gasometric method that enables to determine CO2 fluxes of opposite directions in plant leaf and to distinguish between consumption of primary and stored photosynthates as substrates for respiratory and photorespiratory decarboxylation was used. Plant species of different distribution pattern of photoassimilates and genetically modified plants were studied varying temperature, light, CO2 and O2 concentration. Besides, inhibition of respiration in the light, significance of starch and sucrose as substrates of respiratory and photorespiratory decarboxylations in order to determine their role in regulation were investigated. It was found thet all primary and stored photosynthates serve as decarboxylation substrates, however, differences in utilization of soluble end products (mainly sucrose) and starch were observed. In photosynthesizing leaves starch is not decomposed – it is used only under conditions not enabling photosynthesis (in the dark, at high temperature, in CO2-free atmosphere). In these circumstances, the amount of substrate for respiration determines, at least partly, the rate of respiratory decarboxylation; in other cases, the redox state inside the cell is more significant.

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