On the Mechanism of Photosystem Ii Deterioration by Uv‐b Irradiation

Abstract

The influence of UV‐B irradiation on photosystem II activities has been investigated using isolated photosystem II membrane fragments from spinach. It was found: (a) The average amount of DCIP reduced per flash declined drastically with increasing irradiation time in the absence of DPC but remained almost unaffected in its presence, (b) After UV‐B irradiation, the maximum amplitude of laser flash induced 830 nm absorption changes decreases only slightly; whereas the relaxation kinetics exhibit marked effects: the (JLS components dominate the decay at the expense of ns components. The γ.s kinetics already arise after illumination with a single flash of dark adapted samples, (c) The manganese content decreases only partly at irradiation times where the oxygen evolution capacity is almost completely lost, (d) The polypeptide pattern is hardly affected; the number of atrazine binding sites markedly decreases. Based on the results of this study, UV‐B irradiation is inferred to deteriorate primarily the function of water oxidation. The action spectrum of the UV‐B effect does not reveal a specific target molecule. It is assumed that structural changes of the D‐l/D‐2 polypeptide matrix are responsible for the modification by UV‐B irradiation of the capacity of water oxidation and atrazine binding.

Effects of solar ultraviolet radiation on photosynthesis of the marine red tide alga Heterosigma akashiwo (Raphidophyceae)

“…Photoprotection, based on the xanthophyll cycle, was also found in higher plants [12,14] and refers to dissipation of excitation energy in the antennae [10]. In contrast to this, photoinactivation, due to damage to the D1 protein of PS II, cause a decrease in the electron transport rate [11,12]. In long-term scales (> day, weeks), however, the cells can show different degrees of acclimation after exposure to high radiation through the synthesis of UV-absorbing compounds (e.g.…”

“…Photoinactivation, as the definitions proposed in a recent review of Franklin et al [10], usually occurs when the D1 protein in PSII is damaged, causing a decrease in the electron transport [11,12]. It was found, however, that a fast synthesis of the D1 protein was enough to cope with photodamage, at least in Synchocystis sp.…”

UV-B effects on leaves—Oxidative stress and acclimation in controlled environments

“…Damage to photosystem II is mostly attributed to ROS produced as by-product of electron transport malfunctioning, caused by UV-B absorption in the oxygen evolving complex [9] or other quinone redox components [10]. A sequential, integrative model assuming specific redox states of the donor side and involving several redox components has also been proposed [11].…”

Analysis of limitations to CO2 assimilation on exposure of leaves of two Brassica napus cultivars to UV‐B

“…Numerous investigations have demonstrated that photosystem II (PSII) is the most sensitive component of the thylakoid membrane photosynthetic apparatus to increased exposure to UV-B (Noorudeen & Kulandaivelu 1982;Iwanzik et al 1983;Renger et al 1989;Kulandaivelu, Nedunchezhian & Annamalainathan 1991;Melis, Nemson & Harrison 1992). Consequently, PSII damage has often been implicated as the major potential limitation to photosynthesis in UV-B-treated leaves (Bomman 1989;Caldwell, Teramura & Tevini 1989;Stapleton 1992;Teramura & Sullivan 1994;Fiscus & Booker 1995), as is the case in the photoinhibition of photosynthesis by excess photosynthetically active radiation (380-700 nm) (Baker & Bowyer 1994), although it has been suggested that the mechanism of UV-B-induced damage may be different (Friso et al 1994;Jansen et al 1996).…”