Gymnosperms, unlike angiosperms, are able to synthesize chlorophyll and form photosystems in complete darkness. Photosystem I (PSI) formed under such conditions is fully active, but photosystem II (PSII) is present in its latent form with inactive oxygen evolving complex (OEC). In this work we have studied light-induced gradual changes in PSII function in dark-grown cotyledons of Norway spruce (Picea abies) via the measurement of chlorophyll a fluorescence rise, absorption changes at 830 nm, thermoluminescence glow curves (TL) and protein analysis. The results indicate that in dark-grown cotyledons, alternative reductants were able to act as electron donors to PSII with inactive OEC. Illumination of cotyledons for 5 min led to partial activation of PSII, which was accompanied by detectable oxygen evolution, but still a substantial number of PSII centers remained in the so called PSII-Q(B)-non-reducing form. Interestingly, even 24 h long illumination was not sufficient for the full activation of PSII centers. This was evidenced by a weak attachment of PsbP protein and the absence of PsbQ protein in PSII particles, the absence of PSII supercomplexes, the suboptimal maximum yield of PSII photochemistry, the presence of C band in TL curve and also the presence of up-shifted Q band in TL in DCMU-treated cotyledons. This slow light-induced activation of PSII in dark-grown cotyledons could contribute to the prevention of PSII overexcitation before the light-induced increase in PSI/PSII ratio allows effective operation of linear electron flow.

• MeSH
• chlorofyl chemie   metabolismus   MeSH
• fotosyntéza účinky záření   MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• kotyledon růst a vývoj   metabolismus   účinky záření   MeSH
• kyslík metabolismus   MeSH
• luminiscenční měření metody   MeSH
• rostlinné proteiny metabolismus   MeSH
• semenáček růst a vývoj   metabolismus   účinky záření   MeSH
• smrk růst a vývoj   metabolismus   účinky záření   MeSH
• světlo * MeSH
• teplota MeSH
• tma * MeSH
• transport elektronů účinky záření   MeSH
• tylakoidy metabolismus   účinky záření   MeSH
• western blotting MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH