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1.
The primary and secondary effects of methabenzthiazuron on plankton were studied in outdoor microcosms (6 m3) for five months.
Macrophytes, phytoplankton, zooplankton and the emergence of insects were examined. The herbicide was added to nine of the
twelve mesocosms in concentrations ranging from 10 to 3371 μg a.i. l−1 in a single application. The other three ponds were
used as untreated controls. Phytoplankton population dynamics fluctuated depending on light intensity, temperature, nutrients,
competition and herbicide concentrations. Primary production was temporarily inhibited at test concentrations from 89 to 3371 μg
l−1. Cryptophyta (Phytoflagellata) showed also a recovery at the higher concentrations during the study period. Other primary
producers did not recover at these concentrations, as expected from the disappearance curve of the active ingredient at these
concentrations. This was also indicated by structural indices such as the diversity, eveness and similarity index. The lower
concentrations evoked no or only short-term, weak responses. Chemical water parameters were strongly influenced by the absence
of macrophytes (Elodea canadensis) at the high application rates, which also caused significant changes in zooplankton communities.
No effects were observed on macro-invertebrates and benthic organisms. In conclusion, noticeable effects were detected only
at concentrations clearly above the effect threshold known from standard laboratory tests with aquatic primary producers.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
In this study, we evaluated how cadmium inhibitory effect on photosystem II and I electron transport may affect light energy
conversion into electron transport by photosystem II. To induce cadmium effect on the photosynthetic apparatus, we exposed
Chlamydomonas reinhardtii 24 h to 0–4.62 μM Cd2+. By evaluating the half time of fluorescence transients O–J–I–P at different temperatures (20–30°C), we were able to determine
the photosystem II apparent activation energies for different reduction steps of photosystem II, indicated by the O–J–I–P
fluorescence transients. The decrease of the apparent activation energies for PSII electron transport was found to be strongly
related to the cadmium-induced inhibition of photosynthetic electron transport. We found a strong correlation between the
photosystem II apparent activation energies and photosystem II oxygen evolution rate and photosystem I activity. Different
levels of cadmium inhibition at photosystem II water-splitting system and photosystem I activity showed that photosystem II
apparent activation energies are strongly dependent to photosystem II donor and acceptor sides. Therefore, the oxido-reduction
state of whole photosystem II and I electron transport chain affects the conversion of light energy from antenna complex to
photosystem II electron transport. 相似文献
3.
When wheat seedlings were grown in the presence of 62.5-500μM 4 chloro-5-dimethylamino-2-phenyl-3(2H) pyridazinone, an inhibitor of photosystem II electron transport, there was a marked
inhibition of in vivo photosystem II electron transport as revealed by the analysis of fast chlorophyll a fluorescence transients
in intact leaves and by the inhibition (95% at 500μM) of net photosynthesis in intact leaves Accompanying this inhibition of photosystem II electron transport, there was a decrease
in the content of photosynthetic pigments. The extent of lipid peroxidation, measured in terms of malondialdehyde content
was not increased; rather it was found decreased. An analysis of in vitro lipid peroxidation of the thylakoid membranes of
control and 4-chloro-5-dimethylamino-2-phenyl-3(2H) pyridazinone treated plants in the presence of a sensitizer dye (toluidine
blue) showed a similar rate both in the control and treated samples suggesting that the availability of unsaturated fatty
acids as a substrate for lipid peroxidation was not limiting even though it decreased in the treated plants. On the other
hand, it appears that the availability of the free radicals for lipid peroxidation was decreased byenhanced activity of the
enzyme systems involved in the metabolism of free radicals. Measurements of the activities of enzymes involved in the metabolism
of free radicals showed an increase in the activities of NADPH-glutathione reductase (6–8 fold) and catalase (15–30%) and
a decrease in the activity of superoxide dismutase (30–45%) in the treated plants. 相似文献
4.
Ranjana Singh Prabhat Kumar Srivastava Vijay Pratap Singh Gunjan Dubey Sheo Mohan Prasad 《Acta Physiologiae Plantarum》2012,34(3):1119-1131
The extent of mercury (Hg) toxicity in the heterocystous cyanobacterium Nostoc muscorum grown for 72 h in three different light intensities was tested for various physiological parameters viz. growth, pigment contents, photosynthesis, respiration, reactive oxygen species (ROS), malondialdehyde formation and antioxidants.
A general reduction in growth and pigments, whole cell O2-evolution, photosynthetic electron transport activities and 14CO2-fixation was observed in a metal concentration–dependent manner, and this effect was more pronounced in high light (130 μmol
photon m−2 s−1)–exposed cells as compared to low (10 μmol photon m−2 s−1) and normal (70 μmol photon m−2 s−1) light intensity–exposed cells; however, carotenoids and respiration showed reverse trend. Among photosynthetic electron
transport activities, whole chain activity was found to be most sensitive in comparison with photosystem II (PS II) and photosystem
I (PS I). Comparing the different photosynthetic processes, 14CO2-fixation was most affected in cyanobacterial cells when exposed to Hg and different light intensities. After application
of various exogenous electron donors, diphenyl carbazide was found to be more effective to restore PS II activity, suggesting
that site of damage lies in between oxygen evolving complex and PS II. Level of oxidative stress (superoxide radical and lipid
peroxidation) was maximum at 3.0 μM of Hg when coupled with high light intensity (except hydrogen peroxide). A dose-dependent
increase in enzymatic antioxidants such as superoxide dismutase, peroxidase and catalase as well as non-enzymatic antioxidants
such as proline, ascorbate, cysteine (except under high light intensity) and non-protein thiols [NP-SH] was observed, which
further increased with the increase in light intensity. It was noticed that Hg intoxicates N. muscorum through ROS production, which is aggravated along with the increase in light intensity. Overall results suggest that the
severity of the metal stress does increase with Hg concentrations but when coupled with light, it was the light intensity
that determines the extent of Hg toxicity. 相似文献
5.
The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol−1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol−1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total
Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol
m−2 s−1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for
all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m−2 s−1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin
in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly
PPFD730) to the photoinactivation of PS2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
When seedlings of lettuce and turnip were grown in nutrientsolutions containing different concentrations of linuron, theconcentration in the shoot at the time when toxicity symptomsappeared was related to the solution concentration. With lettuce,for example, symptoms were recorded after 7 d at 0.15 µg/mland the shoot concentration was 2.7 µg/g fresh wt. At0.06 µg/ml, symptoms appeared after 10 d and the shootconcentration was then 1.1 µg/g fresh wt. If grown fordifferent periods in solutions containing linuron and then transferredto fresh nutrient solutions containing no herbicide, turnipor lettuce seedlings which had accumulated 0.70.8 µglinuron/g fresh wt developed toxicity symptoms 4 to 6 d later.Seedlings were also treated with linuron after they had grownfor different periods in control nutrient solutions. The shootconcentrations attained before toxicity symptoms appeared werehigher in those seedlings which were larger when herbicide treatmentbegan. These results show that the herbicide concentration insolution, time of exposure, and age of seedling are interrelatedin determining linuron phytotoxicity. 相似文献
7.
Pyridazinone herbicides, SANDOZ 9785 (4-chloro-5-dimethylamino2-phenyl-3-(2H) pyridazinone), SANDOZ 9789 (4-chloro-5 (methylamino)-2-(α,
α, α-trifluoro-m-tolyl-3-(2H) pyridazinone) and SANDOZ 6706 (4-chloro-5-(methylamino)-2-(α, α, α-trifluoro-m-tolyl-3-(2H)
pyridazinone) inhibited photosystem II electron transport inChlorella protothecoides, when the herbicides were added to the assay medium. The inhibitory eficiency varied with the algal species and the nature
of substitution of pyridazinones. Using 3 algal systemsviz., Chlorella, Scenedesmus andAnacystis, the I50 value of for the inhibition of photosynthesis of 3 substituted pyridazinones (SANDOZ 9785, SANDOZ 6706 and SANDOZ 9789) were
determined. SANDOZ 9789 was found to be the weakest inhibitor of photosystem II electron transport (H2O→ benzoquinone) as compared to SANDOZ 9785 and SANDOZ 6706. In general, the order of inhibition could be given as SANDOZ
6706 >- SANDOZ 9785 > SANDOZ 9789. The I50 value of photosynthetic particles obtained fromChlorella cells was similar to that of whole cells, suggesting that the cell wall ofChlorella did not act as a barrier for the herbicide action. Studies on the light intensity dependence of SANDOZ 9785 inhibition of
electron transport (H2O→ benzoquinone) showed that the light-dependent portion of the curve was more sensitive than the light independent portion
of the curve. It is suggested that the site of action was on the reducing side of photosystem II. 相似文献
8.
Riethmuller-Haage I Bastiaans L Harbinson J Kempenaar C Kropff MJ 《Photosynthesis research》2006,88(3):331-341
The influence of the acetolactate synthase inhibitor metsulfuron-methyl on the operation of the photosynthetic apparatus was examined on 4-weeks-old climate chamber-grown Solanum nigrum plant. To have an indication on the relative performance of the photosynthetic apparatus of ALS-treated plants, the level of carbon dioxide (CO2) fixation, the relative quantum efficiency of photosystem I (ΦPSI) or photosystem II (ΦPSII) electron transport and leaf chlorophyll content were assessed for both control and treated plants at 2, 4 and 7 days after application of the herbicide. Results indicated a progressive inhibition of the level of CO2 fixation, the relative quantum efficiency of photosystem I (ФPSI) and II (ФPSII) electron transport and the leaf chlorophyll content already 2 days after application of the herbicide. The linear relationship between the photosystem I and II was unaltered by herbicidal treatment and was sustained under conditions where large changes in pigment composition of the leaves occurred. It appears that the stress-induced loss of leaf chlorophyll is not a catastrophic process but rather is the consequence of a well-organised breakdown of components. Under photorespiratory and non-photorespiratory conditions, the relationship between the index of electron transport flow through photosystem I and II and the rate of CO2 fixation is altered so that electron transport becomes less efficient at driving CO2 fixation. 相似文献
9.
Jordi Urmeneta Óscar Alcoba Efrén Razquín Elena Tarroja Antoni Navarrete Ricardo Guerrero 《Current microbiology》1998,37(3):151-155
Photosynthetic and respiratory activities at low light intensities (300 μE m−2 s−1) in the microbial mats of the Ebro Delta were measured by the oxygen exchange method in the laboratory. The response to H2S concentration, a significant factor in the dynamics of that ecosystem, was assessed. Total photosynthesis reached 23.78–28.17
μg O2 cm−2 h−1. Photosynthetic activity was not significantly different at the two temperatures tested. Respiratory activity reached a consumption
of 6.95–8.56 μg O2 cm−2 h−1 at 25°C and 11.42–11.70 μg O2 cm−2 h−1 at 35°C. The Q10 value for respiration was 1.37–1.64. Oxygen production in Microcoleus chthonoplastes, the most abundant cyanobacterium in those microbial mats, was highly resistant to sulfide inhibition. Concentrations less
than 0.02 mM sulfide did not affect the rate of photosynthesis. Concentrations up to 0.1 mM sulfide caused different degrees
of partially reversible inhibition, with a maximum of 67% at 0.78 mM sulfide. Primary production (g C assimilated/m2/year) in those microbial mats was also assessed and compared with data from other ecosystems.
Received: 24 October 1997 / Accepted: 18 December 1997 相似文献
10.
Macrophyte presence is an indicator of enhanced denitrification and nitrification in sediments of a temperate restored agricultural stream 总被引:1,自引:0,他引:1
Stream macrophytes are often removed with their sediments to deepen stream channels, stabilize channel banks, or provide habitat
for target species. These sediments may support enhanced nitrogen processing. To evaluate sediment nitrogen processing, identify
seasonal patterns, and assess sediment processes relative to stream load, we measured denitrification and nitrification rates
in a restored third- to fourth-order agricultural stream, Black Earth Creek, Wisconsin, and estimated processing over a 10 km
reach. Our results show that sediments with submerged and emergent macrophytes (e.g., Potomageton spp. and Phalaris arudinacea) support greater denitrification rates than bare sediments (1.12 μmol N g−1 h−1 vs. 0.29). Sediments with macrophytes were not carbon limited and organic matter fraction was weakly correlated to denitrification.
The highest denitrification potential occurred in macrophyte beds (5.19 μmol N g−1 h−1). Nitrification rates were greater in emergent beds than bare sediments (1.07 μg N ml−1day−1 vs. 0.35) with the greatest nitrification rates during the summer. Total denitrification removal in sediments with macrophytes
was equivalent to 43% of the nitrate stream load (463.7 kg N day−1) during spring and nitrification in sediments with macrophytes was equivalent to 247% of summer ammonium load (3.5 kg N day−1). Although the in-channel connectivity to nitrogen rich water was limited, actual stream nitrogen loads could increase with
removal of macrophytes. Macrophyte beds and supporting fringing wetted areas are important if nitrogen management is a concern
for riparian stream restoration efforts. 相似文献