Influence of mitochondrial genome rearrangement on cucumber leaf carbon and nitrogen metabolism

The MSC16 cucumber (Cucumis sativus L.) mitochondrial mutant was used to study the effect of mitochondrial dysfunction and disturbed subcellular redox state on leaf day/night carbon and nitrogen metabolism. We have shown that the mitochondrial dysfunction in MSC16 plants had no effect on photosynthetic CO2 assimilation, but the concentration of soluble carbohydrates and starch was higher in leaves of MSC16 plants. Impaired mitochondrial respiratory chain activity was associated with the perturbation of mitochondrial TCA cycle manifested, e.g., by lowered decarboxylation rate. Mitochondrial dysfunction in MSC16 plants had different influence on leaf cell metabolism under dark or light conditions. In the dark, when the main mitochondrial function is the energy production, the altered activity of TCA cycle in mutated plants was connected with the accumulation of pyruvate and TCA cycle intermediates (citrate and 2-OG). In the light, when TCA activity is needed for synthesis of carbon skeletons required as the acceptors for NH4+ assimilation, the concentration of pyruvate and TCA intermediates was tightly coupled with nitrate metabolism. Enhanced incorporation of ammonium group into amino acids structures in mutated plants has resulted in decreased concentration of organic acids and accumulation of Glu

Fenoolkarboksüülhapete metabolismist ja esinemisvormidest õunapuu lehtedes

https://www.ester.ee/record=b3595397*es

Respiratoorse ja fotorespiratoorse dekarboksüülimise vastused sisemiste ja väliste faktorite toimele C3 taimedes

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.Samaaegselt CO2 fikseerimisega fotosünteesil toimuvad taimelehes hingamisprotsessid, milles osa seotud süsihappegaasist eraldub dekarboksüülimisreaktsioonides. Taimedes on kaks erinevat hingamisprotsessi – hingamine ja fotohingamine, mis on ainult taimedele omane fotosünteesiga kaasnev protsess. Töös uuriti, milline on sisemiste ja väliskeskkonna faktorite osa fotosünteesi ja hingamisprotsesside integratsiooni tagavates regulatsiooni- mehhanismides. Selleks kasutati radiogasomeetrilist meetodit, mis võimaldab mõõta erisuunalisi CO2 voogusid taimelehes ja eristada fotosünteesi esmas- ja lõpp-produktide kasutamist respiratoorse ja fotorespiratoorse dekarboksüülimise substraadina. Uuriti fotoassimilaatide erineva jaotumismustriga taimeliike ja geneetiliselt modifitseeritud taimi, varieerides temperatuuri, valgust, CO2 ja O2 kontsentratsiooni. Samuti võrreldi hingamise inhibeerimist valguses, tärklise ja sahharoosi osatähtsust respiratoorse ja fotorespiratoorse dekarboksüülimise substraatidena ning muutusi hingamises ja fotohingamises selleks, et selgitada välja nende osatähtsus regulatsioonis. Selgus, et kõik fotosünteesi esmas- ja lõpp-produktid võivad olla dekarboksüülimiste substraadiks, kuid on erinevused lahustuvate lõpp-produktide (põhiliselt sahharoos) ja tärklise kasutamises. Fotosünteesivas lehes tärklist ei lagundata – seda kasutatakse ainult tingimustes, kus fotosünteesi ei toimu (pimedas, kõrgel temperatuuril, CO2-vabas keskkonnas) ja sellistes tingimustes määrab hingamissubstraadite kogus vähemalt osaliselt respiratoorse dekarboksüülimise kiiruse; teistel juhtudel on olulisem rakusisene redoks-seisund.Publication of this thesis is supported by Estonian University of Life Sciences. This research was supported by the EU through the European Regional Development Fund (Center of Excellence ENVIRON)