The role of copper in photosynthetic organisms depends greatly on its concentration. Copper, as cupric ion, in trace amounts is an essential micronutrient for algae and higher plants (17,20) and is an essential constituent of several enzymes such as polyphenol oxidase (3) and plastocyanin (8), a component of photosynthetic electron transport. Concentrations higher than 1 /tm are increasingly toxic to algal and higher plant tissues (4, 13). Cupric sulfate has been extensively used as an algaecide since the beginning of the century (12). The cupric ion has been shown to be an inhibitor of photosynthesis in algal cells (4,11,16) and to inhibit photosynthetic electron transport in isolated chloroplasts (5, 10).The mechanism by which the Cu'+ inhibits the photosynthetic apparatus has been only partially elucidated thus far. The data on inhibition of photosynthesis in isolated chloroplasts gives an incomplete picture of the specific sites of inhibition in the electron transport chain. Macdowall (10) He studied the effect of light intensity on inhibition and concluded that the light reactions were directly affected by Cu21. In addition, Haberman (5) using chloroplasts from Phytolacca americanca showed that both the Hill and Mehler reactions were inhibited by Cu2+ but that the Mehler reaction was inhibited by lower concentrations of the ion.In contrast to Macdowall, Haberman concluded that Cu2+ was inhibiting a dark reaction and did not alter the reactions associated with the photoacts. She observed that Mn2+ added at a concentration of 0.5 mm reduced the inhibition of chloroplasts by Cu2+ and postulated that the Cu2+ was affecting the site of manganese function in 02 evolution. Recently exogenous Mn2+ has been shown to donate electrons after the water oxidation site of photosystem II of isolated chloroplasts (2), suggesting that, at high concentrations, manganese functions in a way other than its primary role in the water oxidation act.This work was conducted with the purpose of resolving the sites of Cu2+ inhibition in photosynthetic electron transport. Since previous work and our preliminary experiments pointed to the fact that photosystem II is preferentially inhibited by Cu2+ emphasis was given to finding the specific sites of inhibition within this photosystem. MATERIALS AND METHODSChloroplasts were prepared from market-grown spinach (Spinacia olercacea L.) as described by Robinson and Stocking (14). MnCl2 was excluded from the grinding and resuspending media in the preparations where Mn2+ was used as an electron donor. Chlorophyll was determined by the method of Arnon (1). Ferredoxin was isolated by the method of San Pietro (15) as modified by Swader and Jacobson (18). The 02 evolving capacity of the chloroplasts was destroyed by a mild heat treatment as described by Hinkson and Vernon (6). The chloroplasts were uncoupled by adding ammonium ions following the principle discovered by Krogman et al. (9).The normal reaction media for studying 02 evolution had the following composition in a total volume of 2...
Light and electron microscopic studies of Wolffiu arrl~izu L. frond development during vegetative reproduction showed that the fronds were composed entirely of chlorenchymous cells. Chloroplasts in the epidermal cells other than the guard cells were uni ue in that they contained no starch. Cell division occurred only at the proximal end of daughter fronjs early in their development. Meristematic cells contained chloroplasts with clearly defined grana. P roplastids, commonly observed in meristematic cells of apical regions of other plants, were absent in the cells of these plants. ANDERSON, J. L., W. W. THOMSON et J. A. SWADER. 1973. Fine structure of Wolfla urrlriza. Can. J. Bot. 51: 1619-1622. Des etudes en microscopie photonique et electroniq~~e du dCveloppeme11t de la fronde de W o l ' a r r l~i z aL. au cours de la reproduction vegetative rnontrent que les frondes sont entikrement composEes de cellules chlorencl~ymate~~ses. Les chloroplastes des cel1~1lesCpidermiques autres que les cellules stomatiques ont un caractkre unique: elles ne contiennent pas d'amidon. La div~sion cellulaire se produit seulement B llextrCmitC proximale des frondes-filles t6t au cours de leur dkveloppement. Les cellules mCristematiques contiennent des chloroplastes avec des grana bien dCfinis. Dans les cellules de ces plantes on ne rencontre pas de protoplastes, lesquels sont couramment observe's dans les cellules meristCmatiques des rigions apicales d'autres plantes.[Traduit par le journal]
Autotrophic growth, photosynthesis, and respiration ofChlorella sorokinianaShihira and Krauss were inhibited by the cupric ion, but photosynthesis was more sensitive than respiration. The percent inhibition was determined by the ratio of cells to cupric ions present. Photosynthesis and respiration were inhibited within 2 and 5 min, respectively, after adding 1.0 mM cupric ions.Chlorellacells which had been incubated for a short time in concentrations of the cupric ion that completely inhibited photosynthesis were not able to grow when cultured in a fresh medium without cupric ions, indicating high concentrations of the ion may have destroyed the photosynthetic apparatus and deprived the cells of their ability for autotrophic growth. Dark preincubation of the cells, as well as high bicarbonate concentrations in the assay medium, decreased inhibition. Treatment with cupric ions reduced the cellular chlorophyll and sulfhydryl content, but anaerobiosis, a condition that increased toxicity, had little effect on the sulfhydryl content. Electron transport in photosystems I and II in intactChlorellacells was inhibited, but the specific sites of inhibition in the photosynthetic electron transport chain could not be determined using intact cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.