"Derivative isolates" with 4- to 8-fold and 8- to 16-fold increases in MICs of vancomycin and teicoplanin, respectively, were selected from 2 susceptible clinical isolates of Staphylococcus aureus by serial incubation in low-level vancomycin. A protein of approximately 39 kDa was demonstrable in the cytoplasmic fraction and occasionally in the membrane fraction by SDS-PAGE of both derivatives. This protein was purified by DEAE chromatography, preparative SDS-PAGE, and electroelution. Derivative bacteria were larger on transmission electron microscopy, had thicker cell walls, and had changes in colony morphology on solid media. Further evidence for cell wall reorganization included loss of phage and capsular typing, decreased susceptibility to lysostaphin/lysozyme killing, and changes in condition for detection of optimal coagulase activity. The mechanism of decreased susceptibility to glycopeptide antibiotics among S. aureus derivative isolates is uncertain. The production of the approximately 39-kDa cytoplasmic protein and cell wall reorganization may mediate changed affinity of glycopeptide-peptidoglycan binding or impairment of glycopeptide access to its cell wall target.

Persistence and leaching of thiamethoxam in soil were studied under laboratory conditions. The persistence studies carried out at two fortification levels and under three moisture regimes revealed that thiamethoxam persisted beyond 90 days in all the treatments with half-life varying from 46.3 to 301.0 days. Under dry conditions, the dissipation was faster at 10 mg kg(-1) level as compared to 1 mg kg(-1), whereas the reverse trend was observed under field capacity moisture and submerged conditions. The effect of moisture was prominent and longer persistence was observed under dry conditions (t1/2 200.7-301.0 days) followed by field capacity moisture (t1/2 91.2-94.1 days) and submerged condition (t1/2 46.3-75.3 days). The leaching experiment carried out under laboratory conditions showed that on leaching the soil column with water equivalent to 65 cm rainfall, 66-79% of the applied thiamethoxam was recovered from leachate and no residues were detected in soil. Results showed that thiamethoxam has a potential to leach down under heavy rainfall conditions.

No abstract

T h e duration of the mitotic cycle with its colnponent phases in Nicotinnn plzt~1zbngi7zifolio (pbg, 277= 20) and a hybrid derivatile of N . tnbnczuiz (tbc, 27t = 48 and N . phr7rzbngi7zifolin was determined from the root tips. A 30 minute pulse label of H'-thymidine was employed for the autoradiographic detection of the labeled prophases.T h e time intervals, for the total generation time ( T ) , postsynthetic phase ( G , ) , prophase, synthetic phase (S), and the combined prcsynthetic phase, metaphase, anaphase, telophase ( G , + M + A + T ) in N . phr7i1bngi7zifoli~ were estimated as 11.0, 3.4, 1.3, 5.7 and 0 6 hours, respectively. In the hybrid derivative the corresponding estimates were 9.0, 1.4, 0.8, 3.8 and 3.0 hours.T h e G,, S and G , periods of N . plz~7nbnginifolin were found significantly different from those of the hybrid derivative, but the duration of the mitotic cycle did not show a significant difference. O n the basis of the distribution of heterochromatin and its late replication in N. phr?izbngiliifoliir chromosomes, possible causes of instability of alien pbg cl~romosomes in N . tilboczl7n nuclei are discussed. , J phases of thle cell cvcle, distribution of hetdochromatin in the turo s~e c i e s and , , its significance in relation to c h r o n~o s o n~e duplication are discussed. I 'Present address:

Persistence of two neonicotinoids viz thiacloprid and acetamiprid in soil as affected by UV and sunlight exposure was studied. Treated soil was placed in petri-plates, brought to field capacity moisture and then exposed to UV and sunlight. Dissipation for both the pesticides followed monophasic first order kinetics under sunlight, however under UV-light biphasic dissipation was recorded. Residues of acetamiprid and thiacloprid in soil dissipated with half-lives of 11.1 and 12.8 days under UV light and 25.1 and 19.1 days under sunlight, respectively. Residues of both the neonicotinoids dissipated quickly under UV light as compared to sunlight. Exposure of thin film of acetamiprid and thiacloprid to UV and sunlight revealed that acetamiprid is more photo labile than thiacloprid. More than 95% acetamiprid dissipated within 24 h as compared to approximately 70% dissipation observed for thiacloprid.