Die Wirkung von UV-Strahlen auf die Lipochinon-Pigment-Zusammensetzung isolierter Spinatchloroplasten / Effect of uv-light on the lipoquinone and pigment composition of isolated spinach chloroplasts
The changes in quinone and pigment composition of isolated spinach chloroplasts were investigated after treatment with UV-light of 254 mμ, which is known to decrease the Hill- reaction activity. The plastidquinones are more UV-sensitive than carotenoids (except neoxanthin) and chlorophylls. Neoxanthin, reduced plastoquinone 45 and α-tocopherol function consecutively as lipid antioxidants and are first destroyed. The latter are oxidized to the corresponding quinones plastoquinone 45 and α-tocoquinone, which thus seem to be less UV-sensitive. The decrease of the Hillreaction activity runs parallel with the decomposition of plastoquinol (= Plastohydrochinon) and not with that of plastoquinone as has been assumed so far. This indicates that plastoquinol is needed for performance of the Hill - reaction. The naphthoquinone vitamin K1, bound to the pigment system I of photosynthesis, is less UV-sensitive than the plastidquinones of the benzoquinone type which are associated mainly with the pigment system II. The possible function of vitamin K1 as one natural cofactor of cyclic photophosphorylation is discussed.