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Start Over Coverage 209-216

3. Sensitivity of the algal biotest ISO 10253 to the photosystem 2 herbicides in seawater

Creator:
Soukupová, J., Lukavská, A., Lukavský, J., and Nedbal, L.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
bioassay, chlorophyll fluorescence, DCMU, 3-[3,4-dichlorophenyl]-1,1-dimethylurea, diuron, Phaeodactylum tricurnutum, and quinone acceptors
Language:
Multiple languages
Description:
The sensitivity of marine algal biotest ISO 10253 to the photosystem 2 (PS2) herbicide diuron (DCMU) was determined. Using the diatom Phaeodactylum tricornutum, we found that the algal growth rate was reduced to 50 % of the control value (EC50) for ca. 200 nM DCMU. This value is too high to allow a practical application of the biotest for concentrations of the PS2 herbicides found in natural waters. The mechanisms causing the low sensitivity of the biotest to the PS2 herbicide were investigated by measuring parameters of photosynthetic apparatus in the diatom prior and during the biotest. The apparent dissociation constant for DCMU in P. tricornutum found by measurements of inhibition of oxygen evolution and of variable fluorescence was in the range 60-90 nM. This should lead to a much higher sensitivity of the biotest than found in our experiments. The low biotest sensitivity is caused by an acclimation to sub-lethal DCMU concentrations. The acclimation is manifested by the chlorophyll content per cell that is increasing with the DCMU concentration. During a prolonged exposure to sub-lethal herbicide concentrations, we observed also a selection of DCMU resistant organisms indicating that also an adaptation may decrease the test sensitivity. The biotest sensitivity may increase when the acclimation and adaptation are limited by shortening of the experiment duration. and J. Soukupová ... [et al.].
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

4. The local kinematics of young objects

Creator:
Palouš, Jan
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
statistics, kinematics, and general velocity
Language:
Czech
Description:
The radial velocities of star forming regions and young open star clusters from our galaxy are investigated statistically. We use the cubic, plane approximation of a general veloclty fleld and conclude that with all objects from our sample, which reside withln 10 kpc from the Sun, the veloclty field is close to clrcular. However, the young objects from the local spiral arm deviate. This deviatlon is dlfferent from that caused by the llnear denslty wave or by the collislonless expansion from a small region. We propose that the velocities of young local objects may be Interpreted as a consequence of a large scale multl-supernova remnant.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

5. Ultrastructure of spermiogenesis and spermatozoa of Discocotyle sagittata (Monogenea: Polyopisthocotylea: Discocotylinea)

Creator:
Cable, Joanne and Tinsley, Richard C.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
Platyhelminthes, TEM, fluorescent nuclear labelling, spermatogenesis, and spermatozoon
Language:
English
Description:
Ultrastructural analysis revealed that the spermatozoon of Discocotyle sagittata (Leuckart, 1842) is composed of two parallel axonemes, mitochondrion, nucleus and cortical microtubules. The nucleus, which occupies a central/distal position and has an unusual crescent-shaped profile, is slightly shorter than the mitochondrial rod. The two axonemes, which are of unequal length, and the cortical microtubules (up to 68 forming a continuous ring in the principal region) extend almost the entire length of the spermatozoon. A fold of the plasma membrane creates a unilateral flange or undulating membrane. Epifluorescence microscopy indicated that spermatogenesis gives rise to clusters of 64 spermatids connected to a common cytophore. Spermiogenesis and the structure of the filiform sperm of D. sagittata conform to the typical polyopisthocotylean pattern.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public