Two mechanisms of recovery from photoinhibition in vivo: Reactivation of photosystem II related and unrelated to D1-protein turnover
✍ Scribed by Joachim Leitsch; Barbara Schnettger; Christa Critchley; G. Heinrich Krause
- Publisher
- Springer-Verlag
- Year
- 1994
- Tongue
- English
- Weight
- 814 KB
- Volume
- 194
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Recovery (at 20 ~ C) of spinach (Spinacia oleracea L.) leaf sections from photoinhibition of photosynthesis was monitored by means of the fluorescence parameter Fv/FM of intact leaf tissue and of PSII-driven electron-transport activity of isolated thylakoids. Different degrees of photoinactivation of PSII were obtained by preillumination in ambient air (at 4 or 20 ~ C), CO2free air or at low and high 0 2 levels (2 or 41%) in N 2. The kinetics of recovery exhibited two distinct phases. The first phase usually was completed within about 20-60 min and was most pronounced after preillumination in low O 2. The slow phase proceeded for several hours leading to almost complete reactivation of PSII. Preincubation of the leaves with streptomycin (SM), which inhibits chloroplast-encoded protein synthesis, inhibited the slow recovery phase only, indicating the dependence of this phase on resynthesis of the reaction-centre protein, D1. The fast recovery phase remained largely unaffected by SM. Both phases were strongly but not totally dependent on irradiation of the leaf with low light. When SM was absent, net degradation of the D1 protein could neither be detected upon photoinhibitory irradiation nor during following incubation of the leaf sections in low light or darkness. In the presence of SM, net D1 degradation was seen and tended to increase with 0 2 concentration during photoinhibition treatment. Based on these data, we suggest that photoinactivation of PSII in vivo occurs in at least two steps. From the first step, reactivation appears possible in low light without D1 turnover (fast recovery phase). Action of oxygen then may lead to a second step, in which the D1 protein is affected and reactivation requires its removal and replacement (slow phase).