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51.
Plants have developed a range of strategies for resisting environmental stresses. One of the most common is the synthesis
and deposition of callose, which functions as a barrier against stress factor penetration. The aim of our study was to examine
whether callose forms an efficient barrier against Pb penetration in the roots of Lemna minor L. exposed to this metal. The obtained results showed that Pb induced callose synthesis in L. minor roots, but it was not deposited regularly in all tissues and cells. Callose occurred mainly in the protoderm and in the centre
of the root tip (procambial central cylinder). Moreover, continuous callose bands, which could form an efficient barrier for
Pb penetration, were formed only in the newly formed and anticlinal cell walls (CWs); while in other CWs, callose formed only
small clusters or incomplete bands. Such an arrangement of callose within root CWs inefficiently protected the protoplast
from Pb penetration. As a result, Pb was commonly present inside the root cells. In the light of the results, the barrier
role of callose against metal ion penetration appears to be less obvious than previously believed. It was indicated that induction
of callose synthesis is not enough for a successful blockade of the stress factor penetration. Furthermore, it would appear
that the pattern of callose distribution has an important role in this defence strategy. 相似文献
52.
Crisponi G Nurchi VM Pivetta T Gałezowska J Gumienna-Kontecka E Bailly T Burgada R Kozłowski H 《Journal of inorganic biochemistry》2008,102(7):1486-1494
Coordination properties toward Fe(III) and Al(III) of a mixed bisphosphonate-hydroxypyridinonate ligand are presented. Potentiometric, spectrophotometric and NMR results allowed to conclude that Fe(III) and Al(III) coordination takes place on the pyridinone moiety. The high steric hindrance prevents the possibility of simultaneous coordination of both groups to the same metal ion. Quantum mechanical calculations confirm this finding allowing to determine the minimal length of the linker necessary for a stable conformation of complexes in which Fe(III) is coordinated both by pyridinone and bisphosphonate groups. 相似文献
53.
Henryk Brzeskwiniewicz 《Biometrical journal. Biometrische Zeitschrift》1995,37(2):191-198
We present the idea of using multiresponse incomplete block designs when not all responses can be observed in all experimental units. For a special class of such designs, in which partial designs are PBB designs, a method for estimating natural treatment contrast is given. We also consider the problem of testing the hypotheses concerning the natural and any estimable treatment contrasts. For testing this hypothesis the Wald statistics, being asymptotically chi-square distributed, is proposed. 相似文献
54.
In the preceding paper are described the isolation and physical characterization of seven narrowly disperse fractions of calf thymus DNA in the molecular weight range 0.3 to 1.3 × 106 daltons. Herein, we have determined by light scattering the molecular weights and root mean square radii of these fractions in a solvent comprising 0.2 M NaCl, 2 mM EDTA, 2m MNa-PO4, pH 7. Measurements were made in a modified Wippler—Scheibling photometer to a 20° lower limit of scattering angle on solutions rendered virtually dust-free by procedures described. The optical aniso tropics of the DNA fractions were measured permitting the experimental molecular weights and root mean square radii to be corrected to their true values. From these values, with appropriate polydispersity corrections, we calculate a Kratky—Porod persistence length, a, of 54.0 ± 5.6 nm which is invariant over the molecular weight range examined. From the sedimentation coefficients (preceding paper) and the theory of Yamakawa and Fujii, we calculate a to be 66 nm, a value found to apply equally well to several DNA samples of various origins whose sedimentation rates are known in the molecular weight range from about 4 × 104 to 108 daltons. Similarly, from the intrinsic viscosities and the theory of Yamakawa and Fujii, we calculate a to be 59 nm, which again adequately applies to a number of DNA samples whose viscosities have been measured by other workers in the molecular weight range 3 × 105 to 108 daltons. The Flory—Mandelkern parameter, β, was found to vary with molecular weight in the manner predicted by the theory of Yamakawa and Fujii. The average value of a from the three sets of measurements is 60 ± 6 nm, which we believe applies to double-stranded DNA molecules, independent of chain length, over the whole range of molecular weights for which reliable data exist. 相似文献
55.
56.
Henryk Brzeskwiniewicz 《Biometrical journal. Biometrische Zeitschrift》1989,31(5):631-635
In this paper an inequality for the smallest positive eigenvalues of the C-matrix of a block design are derived. This inequality is a generalization of a result by Constantine (1982) to the case of unequal block sizes. On the basis of the above result a certain E-optimality criterium of block designs is given. Furthermore coefficient ed has been introduced which permits to assess how close the block design is from the optimal one. 相似文献
57.
Commonly observed chemical modifications that occur in proteins during their in vitro purification, storage, and handling
are discussed. Covalent modifications described include deamidation and isoaspartate formation, cleavage of peptide bonds
at aspartic acid residues, cystine destruction and thioldisulfide interchange, oxidation of cysteine and methionine residues,
and the glycation and carbamylation of amino groups. 相似文献
58.
59.
Keith Stokes Mary Nevill Jan Frystyk Henryk Lakomy George Hall 《Journal of applied physiology》2005,99(4):1254-1261
This study examined the growth hormone (GH) response to repeated bouts of sprint cycling. Eight healthy men completed three trials consisting of two 30-s sprints on a cycle ergometer separated by either 60 min (Trial A) or 240 min (Trial B) of recovery and a single 30-s sprint carried out the day after Trial B (Trial C). Trials A and B were separated by at least 7 days. Blood samples were obtained at rest and during recovery from each sprint. In Trial A, GH was elevated immediately before sprint 2, and there was no further increase in GH following the second sprint [area under the curve: 460 (SD 348) vs. 226 min.mug(-1).l(-1) (SD 182), P = 0.05]. Free insulin-like growth factor I tended to be lower immediately before sprint 2 than sprint 1 (P = 0.06). Serum free fatty acids were not different immediately before each of the sprints. In Trial B, there was a trend for a smaller GH response to the second sprint [GH area under the curve: 512 (SD 396) vs. 242 min.mug(-1).l(-1) (SD 190), P = 0.09]. Free insulin-like growth factor I tended to be lower (P = 0.06), and serum free fatty acids were higher (P = 0.01) immediately before sprint 2 than sprint 1. There was no difference in the GH response to sprinting on consecutive days (Trials B and C). In conclusion, repeated bouts of sprint cycling on the same day result in an attenuation or even ablation of the exercise-induced increase in GH, depending on the recovery interval between sprints. 相似文献
60.
The prion protein is a membrane attached glycoprotein that is involved in binding of divalent copper ions. In vivo human and chicken PrPs exhibit SOD-like activity associated with octarepeat and hexarepeat regions, respectively, when bind Cu(II) ions. However, the species of Cu(II)-PrP involved in the Cu(II) center which determines the highest SOD-like activity is still unknown. The data presented here clearly show that the single Cu(II) ion bound to PrP octapeptide repeat region of mammalian prion and hexapeptide repeat region of avian prion via 4 His side-chain imidazoles reveals the highest SOD activity. 相似文献