Inhibition of Photosystem II in Isolated Chloroplasts by Lead

Abstract

Inhibition of photosynthetic electron transport in isolated chloroplasts by lead salts has been demonstrated. Photosystem I activity, as measured by electron transfer from dichlorophenol indophenol to methylviologen, was not reduced by such treatment. However, photosystem II was inhibited by lead salts when electron flow was measured from water to methylviologen and Hill reaction or by chlorophyll fluorescence. Fluorescence induction curves indicated the primary site of inhibition was on the oxidizing side of photosystem II. That this site was between the primary electron donor of photosystem II and the site of water oxidation could be demonstrated by hydroxylamine restoration of normal fluorescence following lead inhibition.A great deal of interest has been generated recently by the effect of lead on plants and animals (7). The large concentration of airborne lead accumulates in soils (9, 33). Lead pollutants are incorporated into animal tissues (4,8) and have been shown to inhibit various enzyme systems (12,29,31,34).Despite these effects on animal systems, little is known about the effect of lead on plant enzymes. We know that lead is taken up and transported in plants (3. 4, 24, 32, 33) and can decrease cell division at very low concentration (13,14). Koeppe and Miller (23) examined the effect of lead salts on corn mitochondria and found an inhibition of electron transport, especially in the absence of phosphate.Because of the increasing concentration of lead in our environment, the toxigenic effects of lead on animal enzyme systems, the increasing reliance we have upon photosynthesis to sustain our environment, and the similarity of the electron transport chain of mitochondria to that of photosynthetic electron transport, we feel a preliminary investigation of the effects of lead upon the light reactions of photosynthesis seems to be warranted. Isolation of Chloroplasts. The procedure used was a modification of the technique of Jagendorf and Avron (19). Fresh leaves (20 g) were deveined and washed twice with distilled water. They were cut into small pieces and macerated in a cold blender (Eberbach No. 8475) operated at full speed for 10 sec with 60 ml of cold grinding medium which consisted of 0.8 M sucrose, 20 mm Tricine, and 10 mm NaCl adjusted to a final pH of 7.8. Defatted bovine serum albumin (50 mg) was included in the grinding medium during each extraction. The resulting homogenate was strained through Miracloth (Chicopee Mills, Inc., N.Y.) into chilled centrifuge tubes which were then placed into a refrigerated centrifuge and accelerated to 1,500g and immediately turned off. The supernatant obtained was centrifuged at 1,500g for 8 min to sediment chloroplasts which were resuspended in fresh grinding medium and diluted to a concentration of 1 mg of chlorophyll per ml as determined by the method of Arnon (2). MATERIALS AND METHODSHypotonic chloroplast fragments were prepared as described by Jagendorf and Uribe (22) by resuspension of chloroplasts in 25 ml of cold 10 mm NaCl for 20 min and ...

Inhibition of photosynthetic electron transport in Nostoc muscorum by Ni2+ and Ag+.

“…1B) could be due to a blocking of the electron flow at the reducing side of PS II causing increased fluorescence. Similar results were also reported for Pb2+ (11) and Hg2+ (7) in spinach chloroplasts. Since phycobilisomes (PBsomes) are the main light-harvesting antenna pigments of PS II and the likely targets for metal cations, the effect of Ni2+ and Ag+ on their emission characteristics was studied.…”

Effects of lead on seedling growth of spesia populnea

“…Dense traffic releases detrimental exhaust gases and toxic pollutants like unburnt and partially burnt hydrocarbons and other elements that are contained in petrol polluting the city environment (Iqbal et al 2001). These air pollutants may interfere with the biological processes relating to general metabolism, photosynthetic activities, mitochondrial respiration and stomatal clogging of plants (Miles et al 1972, Ahmed and Qadir 1975, Abdullah and Iqbal 1991.…”

The Inhibition of Soybean Metabolism by Cadmium and Lead

“…Lead is known to inhibit plant growth (14). Pb and Cd also inhibit photosynthesis by isolated chloroplasts (9), and activities of isolated corn mitochondria (5,6).…”