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Аннотация:Excess light excitation of thylakoid membranes may result in the
degradation of the Photosystem II (PSII) complex. This phenomena
is known as photoinhibition (Aro et al 1993). Plants have evolved
several mechanisms to protect PSII from photoinhibition. One of
them is electron transport to O2 or Mehler reaction (Mehler 1951),
which dissipates excessively absorbed excitation energy and might be
associated with acclimation to environmental stresses. (Asada 1999,
Niyogi 2000, Ort & Baker 2002).
The main site of the Mehler reaction is usually related to the
Photosystem I (Asada 1999), however, since 1976 a number of data
confirmed oxygen photoreduction in PSII (Bekina et al 1976, Bekina
& Lebedeva 1977). In the last decade, O2 generation by primary
quinine acceptor QA (Ananyev et al 1994), and oxygen reduction
to H2O2 by pheophytyn or QB (Zastrizhnaya et al 1997) also was
proposed. Nevertheless, today there is no common opinion
concerning the role and significance of the O2 photoreduction via
Mehler reaction in PSII locality under stress conditions, such as high
intensity illumination. It has been shown that O2 and H2O2 generation
in locality of the PSII could induce PSII acceptor side photoinhibition
and D1 protein degradation (Bradley et al 1991, Miyao et al 1995). On the other hand, no electron transport inactivation under artificially generated O2 was revealed, and it was proposed that O2 photoproduction are not related to PSII (Hideg et al 1995).
To clarify the role and significance of the Mehler reaction in PSII
locality we studied oxygen photoreduction in PSII preparations of
BBY-type under excessive illumination.