AB - Simultaneous measurements of photosynthesis (both oxygenic and amoxygenic) and N2 fixation were conducted to discern the relationships between photosynthesis, N2 fixation, and environmental factors potentially regulating these processes in microbial mats in a tropical hypersaline lagoon (Salt Pond, San Salvador Island, Bahamas). Major photoautotrophs included cyanobacteria, purple phototrophic bacteria, and diatoms. Chemosystematic photopigments were used as indicators of the relative abundance of mat phototrophs. Experimental manipulations consisted of light and dark incubations of intact mat samples exposed to the photosystem II inhibitor DEMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea], a dissolved organic carbon source (D-glucose), and normal seawater (37‰). Photosynthetic rates were measured by both O2 and 14C methods, and nitrogenase activity (NA) was estimated by the acetylene reduction assay. Moderate reductions in salinity (from 74 to 37‰) had no measurable effect on photosynthesis, O2 consumption, or NA. CO2 fixation in DCMU-amended samples was 1/4 5% of that in the control (nonamended) samples and demonstrated photosynthetic activity by anoxygenic phototrophs. NA in DCMU-amended samples, which was consistently higher (by a factor of 2 to 3) than the other (light and dark) treatments, was also attributed to purple phototrophic bacteria. The ecological implication is that N2 fixation by anoxygenic phototrophs (purple phototrophic bacteria and possibly cyanobacteria) may be regulated by the activity of oxygenic phototrophs (cyanobacteria and diatoms). Consortial interactions that enhance the physiological plasticity of the mat community may be a key for optimizing production, N2 fixation, and persistence in these extreme environments.
Because light irradiation suppresses changes of chlorophyll, ascorbic acid, free amino acid and reducing sugar in postharvest komatsuna leaves, effect of light quality on changes of these components was studied. Red light suppressed most effectively, as white light, the changes of these components. Blue and green light somewhat suppressed, but farred light had no effect to suppress these components changes. When komatsuna leaf discs were floated on 2×10-5 M 3- (3, 4-dichlorophenyl) -1, 1-dimethylurea (DCMU) solution in white light (2klx), reducing sugar content remarkably decreased in order to inhibit sugar biosynthesis by photosynthesis. Still, under the condition komatsuna leaf discs maintained chlorophyll content the same as water control in light. When red farred photoreversibility was examined by brief irradiation of low light intensity every 3 hours, chlorophyll content had obvious photoreversibility. But, ascorbic acid content had weak photoreversibility only and the maintenance rate was low under this condition, its content strongly depended on light intensity and duration of irradiation. These results suggest that phytochrome system functions in the maintenance of chlorophyll content and ascorbic acid content is affected by high energy reaction like a photosynthesis than phytochrome system.
3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) …
Using isolated chloroplasts in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an analysis was made of the rise of the fluorescence yield effected by weak light. Depending on the pretreatment, the time-course of the rapid photochemical part of the rise varied between nearly first-order and quadratic kinetics, i.e., reflected either a one-quantum or a two-quantum conversion. We consider the occurrence of two photoreductants per system II unit, which are reoxidized in different dark reactions. The data further showed that the “first-order process” is also inhomogeneous.
N2 - The growth and purification of milligram quantities of a large double-stranded DNA virus, PBCV-1, which replicates in a Chlorella-like alga is described. The virus had an adsorption rate constant of ca. 5 × 10-9 ml/min, a latent period of 150 to 180 min, and a burst size of 200 to 350 PFUs when the host was actively growing in the light. The eclipse period was 30 to 50 min shorter than the latent period. PBCV-1 also replicated in dark grown Chlorella but the burst size was reduced ca. 50%. The photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, had no effect on viral replication. Thus viral replication does not require host photosynthesis. Viral infection rapidly inhibited both growth and CO2 fixation of the host Chlorella.
Anoxygenic photosynthesis and nitrogen fixation by a ..
How Atrazine Kills Plants. This video links the action of the herbicide atrazine to the inhibition of photosynthesis. DCMU 3-3,4-dichlorophenyl-1,1-dimethylurea is an algicide and herbicide of the phenylurea class that inhibits photosynthesis. It was introduced by Bayer in 1954 under the trade name of Diuron. Mechanism of actionedit. DCMU is a very specific and sensitive inhibitor of photosynthesis. found that DCMU not only does not inhibit the cyclic photosynthetic pathway.