Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
Chloroplast protein CYP38 is a cyclophilin-like peptidyl-prolyl cis-trans isomerase involved in photosystem II (PSII) assembly. It also serves as a regulator of thylakoid protein phosphatase. In this work the efficiency of PSII in CYP38 deficient Arabidopsis thaliana M13 plants has been analyzed by measuring in vivo chlorophyll a (Chl a) fluorescence transient (OJIP test). Significant differences in overall photosynthetic performance (PIABS), absorption (ABS/RC), trapping (TRo/RC), electron transport (ETo/RC), and dissipation (DIo/RC) were observed between A. thaliana M13 and the wild type (WT) plants. Increased Chl a and Chl b levels, as well as decreased Chl a/Chl b ratio were measured in M13 plants, indicating the adjustment of PSII antenna for increasing light absorption capability. Based on the obtained results, it can be concluded that the deficiency in CYP38 protein leads to impaired function of PSII due to the conversion of a certain fraction of active reaction centres to dissipative ones. This leads to a decrease in overall photosynthetic performance (PIABS) in M13 plants. Such effect was due to lowering of TRo/DIo parameter, which was influenced mostly by significant increases in energy dissipation (DIo/RC) and in trapping of electrons (TRo/RC) per active reaction centre.Kloroplastni je protein CYP38 peptidil-prolil cis-trans izomeraza slična ciklofilinima, a sudjeluje u izgradnji fotosustava II (PSII). Istodobno ovaj protein služi kao regulator tilakoidne proteinske fosfataze. U ovom je radu analizirana učinkovitost PSII u CYP38 delecijskom mutantu biljke Arabidopsis thaliana korištenjem in vivo mjerenja kratkotrajne promjene fluorescencije klorofila (Chl) (OJIP test). Značajno smanjenje fotosintetske učinkovitosti (PIABS), apsorpcije (ABS/RC), hvatanja elektrona (TRo/RC), prijenosa elektrona (ETo/RC) i disipacije (DIo/RC) uočeno je u skupini biljaka M13 u usporedbi s divljim tipom (WT) A. thaliana. U skupini M13 biljaka izmjeren je povećani udjel Chl a i Chl b i smanjeni omjer Chl a/Chl b, što upućuje na prilagodbe antena PSII za povećanim kapacitetom apsorpcije svjetla. S obzirom na dobivene rezultate može se zaključiti da pomanjkanje proteina CYP38 uzrokuje slabljenje funkcije PSII zbog konverzije nekog broja aktivnih reakcijskih centara u disipativne centre, što dovodi do smanjenja ukupne fotosintetske učinkovitosti (PIABS) u skupini biljaka M13. Ovaj se učinak može objasniti snizivanjem parametra TRo/DIo, što je uglavnom uzrokovano značajnim povećanjem rasipanja energije (DIo/RC) i hvatanja elektrona (TRo/RC) po aktivnom reakcijskom centru
