Učinak svjetlosnog stresa na fotosintezu

undergraduate thesis

• Title (english): Effect of light stress on photosynthesis
• Author: Ivana Pavičić
• Mentor: Željka Vidaković-Cifrek (mentor)
• Granter: University of Zagreb; Faculty of Science; (Department of Biology); Zagreb
• Defense date and country: 2015, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Biology

Abstract

Biljke proizvode svoju vlastitu energiju i organske spojeve procesom fotosinteze pretvarajući svjetlosnu energiju u kemijsku. Iako fotosinteza zahtijeva sunčevu svjetlost, ona u prirodnim uvjetima može imati negativan učinak na fotosintetske reakcije zbog stalne promjene intenziteta svjetlosti. Zbog toga su biljke razvile različite mehanizme odgovora na promijenjene svjetlosne uvjete u okolišu, od gibanja listova i kloroplasta do prilagodba na molekularnoj razini u kojima sudjeluju proteini fotosintetskog aparata. Ovisno o količini i kvaliteti svjetlosne energije, dolazi do razvoja kloroplasta specifičnih za visoki intenzitet svjetlosti ili kloroplasta specifičnih za niski intenzitet svjetlosti. S druge strane, ako je reduciran veliki udio molekula plastokinona, nije moguć prijenos elektrona između fotosistema II i I pa elektroni mogu „pobjeći“ i reagirati s kisikom pri čemu nastaje singletni kisik koji uzrokuje oksidacijski stres i oštećuje fotosintetski aparat. Zbog toga se u biljaka povećava količina karotenoida koji djeluju kao antioksidansi i mogu zaštititi klorofil od fotooksidacije do koje dolazi zbog povećane količine reaktivnih oblika kisika. Osim toga dolazi i do indukcije ksantofilatskog ciklusa te sinteze fenolnih spojeva, tanina, flavonoida i antocijana. Reaktivni oblici kisika imaju i ulogu signalnih molekula kada je biljka izložena svjetlosnom stresu. Polipeptid D1 u PSII je glavna meta oštećenja induciranih svjetlošću. D1 polipeptid se brzo degradira i zamjenjuje novosintetiziranom kopijom kako bi se omogućilo normalno funkcioniranje PSII. Možemo zaključiti da biljka kako bi se uspješno prilagodila uvjetima u okolišu mora uspješno odgovoriti na veliki broj različitih signala iz okoliša. U taj je proces uključeno nekoliko različitih mehanizama kao i koordinirana ekspresiju gena iz jezgrinog i plastidnog genoma.

Abstract (english)

Plants produce their own energy and organic compounds through photosynthesis, converting light energy into chemical energy. Although photosynthesis requires sunlight, the changes of light intensity in nature - from low to high light, may have a negative effect on photosynthesis reactions. As a result, plants have developed different response mechanisms to changing light conditions - from leaves and chloroplasts movements to adjustments at the molecular level. Depending on the intensity and quality of light, plants develop chloroplasts specific for high light intensity or chloroplasts specific for low light conditions. Moreover, if the high portion of plastocyanin molecules are in reduced form, the transfer of electrons between photosystems II and I is disturbed, so the electrons can "escape" and react with oxygen to form singlet oxygen which can cause oxidative stress and damage photosynthetic apparatus. In such conditions, the increased amounts of carotenoid molecules act as antioxidants and protect the chlorophyll from photo-oxidation that occurs due to the increase of reactive forms of oxygen. In addition, the induction of xanthophyll cycle and synthesis of phenolic compounds, tannins, flavonoids and anthocyanins occurs. Reactive oxygen species may have the role of signalling molecules during the exposure of plants to light stress. Polypeptide D1 in PSII is the main target of photo-induced damage. It is rapidly degraded and replaced by a newly synthesized copy to allow the normal functioning of the PSII. It could be concluded that the plant, in order to successfully adapt to the environmental light conditions, must respond to a number of different signals from the environment. In this process a number of different mechanisms such as coordinated expression of the plastid genome and the nuclear genome are included.

• Keywords: fotosinteza; svjetlosna energija
• Keywords (english): photosynthesis; light energy
• Language: croatian
• URN:NBN: urn:nbn:hr:217:021585
• Study programme: Title: Molecular Biology; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/prvostupnica (baccalaureus/baccalaurea) molekularne biologije (sveučilišni/a prvostupnik/prvostupnica (baccalaureus/baccalaurea) molekularne biologije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-12-15 13:13:17