The light-dependent pH changes in the suspending medium of guard cell protoplasts (GCP) from Vicia faba were studied. Upon illumination, the medium was initially slightly alkalinized and then acidified. The extent of alkalinization was lower in CO(2)-free air than in normal air. This initial alkalinization was inhibited by DCMU. Acidification in CO(2)-free air became observable in shorter durat...

A Chlamydomonas reinhardtii chloroplast transformant, designated MU7, carrying a chimeric (rbcL promoter: beta-glucuronidase [GUS]: psaB 3' end) gene whose transcripts have been found previously to be unstable in light (half-life of 20 min in light as opposed to a half-life of 5 h in the dark), was used to study the role of electron transport and of the redox state in the degradation of chlorop...

In this research, we demonstrated that the plastoquinone-related electron-transport kinetics in photosynthesis could be sufficiently described with as few as three state variables, Q(A)(-), Q(B)(-), and Q(B)(2-). A third-order kinetic model structure was developed with delayed fluorescence as the measurable output. Delayed fluorescence emissions from drought-stressed, DCMU [3-(3,4-dichloropheny...

We have investigated the possible role of silicomolybdate and silicotungstate as acceptors of electrons in chloroplasts directly from Q, the primary electron acceptor of Photosystem II. Our data show: 1. Either of these compounds can accept electrons directly from Q in a 3-(3', 4'-dichlorophenyl)-1, 1-dimethylurea (DCMU)-insensitive electron transport; however, the DCMU insensitivity is only s...

Chlorophyll (Chl) b is non-fluorescent in utio as it transfers excitation energy with 100% efficiency to Chl a [l-3]. There is no record of Chl b fluorescence in viva. We show here, for the first time, that Chi b is slightly fluorescent in vivo (at 660-665 nm) when the cells are exposed to bright light, or treated with DCMU (see footnote*); this emission was uncovered when we compared the ratio...

Oxygen evolution by photosystem II membranes was inhibited by Cu(II) when 2,6-dichlorobenzoquinone or ferricyanide, but not silicomolybdate, was used as electron acceptor. This indicated that Cu(II) affected the reducing side of the photosystem II. The inhibition curves of Cu(II), o-phenanthroline and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), were compared; the inhibitory patterns of Cu(I...

In this study, we investigated the combined effects of UV-B irradiation and herbicides (glyphosate, GPS; 2-Methyl-4-chlorophenoxyacetic acid, MCPA-Na; 3-(3,4-dichlorophenyl)-1,1-dimethylurea, DCMU) and the antioxidant (ascorbic acid, ASC) on photosynthesis, antioxidant enzymes and DNA damage in two bloom-forming cyanobacteria, Anabaena sp. and Microcystis viridis. UV-B irradiance increased reac...

Isolated etioplasts from 8-day-old dark-grown pea seedlings incorporated [1-(14)C]acetate into lipid at a relatively low rate. Plastids from seedlings that had been illuminated for at least 2 hr showed an enhanced incorporation provided the plastids were illuminated during incubation with the labeled acetate. Dark incubation or the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) decr...

The possibility that photosynthetic competence is gratuitous for light-induced chloroplast development in Euglena gracilis var. bacillaris was examined by incubating dark-grown resting cells in the light with DCMU, an inhibitor of photosynthesis. Under these conditions photosynthetic carbon dioxide fixation was inhibited essentially completely at all times during chloroplast development, but ab...

This study examines the capacity of intact spinach (Spinacia oleracea L.) chloroplasts to fix (14)CO(2) when supplied with Benson-Calvin cycle intermediates in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Under these conditions, substantial (14)CO(2) fixation occurred in the light but not in the dark when either dihydroxyacetone phosphate, ribulose 5-phosphate, fructose 6-pho...