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Summary Studies were conducted in 22 non-calcareous soils (India) to evaluate various extractants,viz. (6N HCl, 0.1N HCl, EDTA (NH4)2CO3, EDTA NH4OAc, DTPA+CaCl2 and 1M MgCl2) to find critical levels of soil and plant Zn for green gram (Phaseolus aureus Roxb.). The order of extractability by the different extractants was 6N HCl>0.1N HCl>EDTA (NH4)2CO3<EDTA NH4OAc DTPA+CaCl2>1M MgCl2.
Critical levels of 0.48 ppm DTPA × CaCl2 extractable Zn, 0.80 ppm EDTA NH4OAc extractable Zn, 0.70 ppm EDTA (NH4)2CO3 extractable Zn, and 2.2 ppm 0.1N HCl extractable Zn were estimated for the soils tested. The critical Zn concentration in 6 weeks old plants was found to
be 19 ppm. The 0.1N HCl method gave the best correlation (r=0.588**) between extractable Zn and Bray's per cent yield, while with DTPA+CaCl2, it was slightly low (r=0.542**). The DTPA + CaCl2 method gave significant (r=0.73**) correlation with plant Zn concentration. The 0.1N HCl gave the higher correlation with Zn uptake (r=0.661**) than DTPA (r=0.634**) 6N HCl and 1M MgCl2 method gave nonsignificant positive relationship with Bray's per cent yield. For noncalcareous soils apart from the common
use of DTPA+CaCl2, 0.1N HCl can also be used for predicting soil available Zn. The use of 0.1N HCl would be much cheaper than DTPA and other extractants used in the study. 相似文献
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Clifford M. Renk Rishab K. Gupta Donald L. Morton 《Cancer immunology, immunotherapy : CII》1980,9(1-2):55-62
Summary Supernatants from two human breast carcinoma cell lines, 734B and 231, have been shown to inhibit lymphocyte activation by mitogens and antigens. This inhibition appears to be specific for lymphocytes or recently stimulated cells, while having no effect on the growth of established cell lines. Studies of the mechanism of inhibition revealed that the factors inhibit lymphocyte activation and that the factors must be present at the initiation of lymphocyte stimulation for inhibition to occur. The supernatants do not inhibit lymphocyte activation by blocking binding of PHA to lymphocytes. Preliminary purification steps have shown that the inhibitory factors present in the tissue culture supernatants are precipitated at 50% ammonium sulfate saturation and their molecular weights are greater than 100 000. The inhibitory capacity of the 734B supernatants was destroyed by heating at 70° C, while the factors present in the 231 supernatants were only partially destroyed by heating to 90° C. The possible mechanism of action of the inhibitory substances released by tumors and their relevance to tumor growth are important to understanding of immune responses to neoplasia. 相似文献
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The regulation of nucleotide excision repair and base excision repair by normal and repair deficient human cells was determined. Synchronous cultures of WI-38 normal diploid fibroblasts and Xeroderma pigmentosum fibroblasts (complementation group D) (XP-D) were used to investigate whether DNA repair pathways were modulated during the cell cycle. Two criteria were used: (1) unscheduled DNA synthesis (UDS) in the presence of hydroxyurea (HU) after exposure to UV light or after exposure to N-acetoxy-acetylaminofluorene (N-AcO-AAF) to quantitate nucleotide excision repair or UDS after exposure to methylmethane sulfonate (MMS) to measure base excision repair; (2) repair replication into parental DNA in the absence of HU after exposure to UV light. Nucleotide excision repair after UV irradiation was induced in WI-38 fibroblasts during the cell cycle reaching a maximum in cultures exposed 14–15 h after cell stimulation. Similar results were observed after exposure to N-AcO-AAF. DNA repair was increased 2–4-fold after UV exposure and was increased 3-fold after N-AcO-AAF exposure. In either instance nucleotide excision repair was sequentially stimulated prior to the enhancement of base excision repair which was stimulated prior to the induction of DNA replication. In contrast XP-D failed to induce nucleotide excision repair after UV irradiation at any interval in the cell cycle. However, base excision repair and DNA replication were stimulated comparable to that enhancement observed in WI-38 cells. The distinctive induction of nucleotide excision repair and base excision repair prior to the onset of DNA replication suggests that separate DNA repair complexes may be formed during the eucaryotic cell cycle. 相似文献
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Goutam Gupta Manju Bansal V. Sasisekharan 《Biochemical and biophysical research communications》1980,95(2):728-733
A novel zig-zag (Z) structure is proposed for poly d(GC).poly d(GC). The proposed model closely resembles the crystal structure of d(CG)3. 相似文献