In conclusion, the sequence of the tpk5-UTR needs to be properly annotated using its full-length cDNA. The tpk5-e mutant plants that were light-adapted proved to be unaffected in their ETR-activity and O2-evolution was statistically significantly lower in the tpk5-e mutant in comparison with the wild-type during high light exposure. The decreased O2-evolution in light-adapted tpk5-e mutants indicate that the photosystem II (PSII) activity in the chloroplast is affected by the AtTPK5 deficiency.