Incorporation of [³⁵S]methionine in higher plants reveals that stimulation of the D1 reaction centre II protein turnover accompanies tolerance to heavy metal stress

Abstract

were studied in vivo and in vitro. Treatments of pea (Pisum sativum) and broad bean (Vicia faba) plants with 0·05-5 mM cadmium (CdCl 2 ) modified PSII activity with a resulting increase in electron transfer followed by an inhibition and damage to the oxygen-evolving complex. Pulsechase experiments with [35 S]methionine in vivo followed by the separation of the radiolabelled thylakoids into grana and stroma exposed regions indicated that the synthesis, degradation and assembly of the D1 protein were greatly affected by cadmium. Initially D1 synthesis increased, later slowing down when the stress became advanced; at the same time the D1 degradation was increased. Binding studies with radiolabelled [ 14 C]herbicide revealed that the Q B pocket activity was also altered. However, the primary consequence of cadmium stress was the disassembly of the stacked regions. The measurements indicated differential tolerance to cadmium stress between the two plant species, which was not caused by either differential metal uptake or binding to the PSII complex. This suggests that the resulting changes in D1 turnover are a consequence of an unknown primary effect of cadmium on the PSII apparatus. However, we show that the higher tolerance to heavy metal stress found in broad bean plants relative to pea is accompanied by stimulation of D1 turnover. These experiments supported by previous data suggest that modulation of D1 turnover under stress is a commonly occurring process.Key-words: cadmium stress; D1 protein turnover; photosystem II; tolerance. INTRODUCTIONPhotosynthesis represents a central anabolic pathway in plants that results in the production of energy-rich organic compounds necessary for growth. The interaction between the production and consumption of assimilates requires a strict regulation of light energy conversion and of photosynthetic electron transport to satisfy the demand for energy and reduction equivalents used in the Calvin cycle. Photosystem II (PSII) is essential to the regulation of photosynthesis because it catalyses the oxidation of water into oxygen and supports electron transport. PSII consists of a core, a light-harvesting antenna and an oxygen-evolving system. The core is comprised of the reaction centre proteins, D1 and D2, cytochrome b 559 , the internal antennae chlorophyll proteins CP43 and CP47, the 33 kDa manganese stabilizing protein and several minor proteins PsbI, PsbW, PsbT . All pigments and prosthetic groups necessary for charge separation and stabilization are bound to the D1 and D2 proteins (Nanba & Satoh 1987). Under optimal physiological conditions, the D1 protein exhibits a light-dependent turnover several times higher than that of other chloroplast proteins (Mattoo, Marder & Edelman 1989). Its synthesis occurs at the stroma exposed membranes and D1 is probably immediately incorporated into the PSII complex because only minor amounts of free protein have been detected so far (Mattoo et al. 1989;Elich, Edelman & Mattoo 1992). PSII is inactivated by a variety of stresses -high irradia...

Community-Level Analysis of psbA Gene Sequences and Irgarol Tolerance in Marine Periphyton

“…Some studies have also described increased D1 turnover as a physiological stress-compensating mechanism. Increased D1 turnover occurs in response to fumigation with ozone (36) or with mixtures of air pollutants (O 3 , NO 2 , and SO 2 ) (58), as well as during potassium deficiency (58), cadmium exposure (30,34), and drought (35). It has been proposed that D1 turnover acts as a general adaptive response to environmental extremes (35), which gives further support to our hypothesis of increased D1 turnover as an Irgarol tolerance mechanism.…”

Combined effects of cadmium and fluoranthene on germination, growth and photosynthesis of soybean seedlings

“…In the present study, F 0 was greater when soybeans were exposed to Cd or FLT. It has been reported that Cd can inhibit the flow of photosynthetic electrons, destroy the antennae pigments, inhibit the water-splitting complex of the oxidizing site of PSII, down-regulate PSII proteins, as well as competitively bind to the essential Ca 2+ site in PSII (Geiken et al, 1998;Mallick and Mohn, 2003;Faller et al, 2005). While mechanisms responsible for greater F 0 caused by FLT are not known, there are several possible hypotheses.…”

Toxicity of Cu (II) to the green alga Chlorella vulgaris: a perspective of photosynthesis and oxidant stress

“…During photosynthesis, photosystem II (PSII) is essential to the regulation because it catalyzes the oxidation of water into oxygen (oxygen-evolving complex-Hill reaction) and supports electron transport (Geiken et al 1998). Chlorophyll fluorescence parameters can be used as indicators of stress affecting photochemical pathway of utilization of absorbed light energy based on chlorophyll fluorescence techniques (Branquinho et al 1997, Krause andWeis, 1991).…”