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 ...

Three seedling lethal mutants of Zea mays with impaired photosynthesis are described. These recessive mutants were selected on the basis of high chlorophyll fluorescence. They have normal chlorophyll pigmentation but are unable to fiX C02 fully. Evidence is presented from fluorescence characteristics of isolated chloroplasts that both photosystem I and II mutants were isolated. Using conventional measures of photosynthetic electron transport, we suggest that the photosystem I mutant has limited ability to reduce NADP. The other two mutants are clearly blocked in photosystem II, one possibly lacking the primary electron acceptor.The use of genetic mutants is an indispensable tool in the study of complex biochemical reactions. This approach for gaining insight into the mechanism of the photosynthetic process has been successfully employed, most notably by Levine (13) with Chlamydomonas and by Bishop (6) with Scenedesmus. However, very little work has been done using genetic mutants of higher plants (14). Most of the work with higher plants has involved mutants selected on the basis of pigment abnormality. A mutant of Vicia faba which appears to be inhibited in the ferredoxin-NADP oxidoreductase has been described (11). Homann and Schmid (12) have reported a mutant of Nicotiana which lacks Hill activity and a series of mutant Oenothera were reported (8) which resulted in blocks of either photosystem I or II. These-were the major photosynthetic mutants reported in higher plants and all showed some degree of pigment and structure abnormalities.Following the development of an acceptable screening technique for selection of mutants in higher plants (20), we have isolated a number of full green photosynthetic mutants of maize and here report on the characterization of three such mutants. MATERIALS AND METHODSPlant Material. Maize seedlings were grown to the three leaf stage (about 10 days) in a controlled environment chamber. They were subject to 14 hr of light at 30 C and 10 hr of darkness at 25 C. Light was provided by fluorescent (coolwhite type) and incandescent lamps at an intensity of 5 X 104 ergs cm-2 sec'1. Kernels were germinated and grown in vermiculite contained in 7-X 38-cm plastic trays. Plants were provided with a nutrient solution (Ortho 12-6-6) weekly. The maize stocks used were from lines treated with the mutagen EMS2, and most were previously selected as necrotic or seedling lethal. The method of mutant induction and the genetic handlings of the material have been described by Neuffer (22). Briefly, it consists of treating pollen with mutagen, pollinating, selfing all the progeny of treated plants to make any mutation homozygous, and examining the resulting plants.Mutant Selection. Suspected mutant plants from the above maize stocks were screened for inactivation of photosynthesis by a technique described elsewhere (20). The procedure is a modification of that used for green algae (4, 9), and selects for plants with abnormally high Chl fluorescence.Chloroplast Isolation. Twice-washed leaves o...

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