In barley leaves a group of genes is expressed in response to treatment with jasmonates and abscisic acid (ABA) [21]. One of these genes coding for a jasmonate-induced protein of 23 kDa (JIP-23) was analyzed to find out the link between ABA and jasmonates by recording its expression upon modulating independently, the endogenous level of both of them. By use of inhibitors of JA synthesis and ABA degradation, and the ABA-deficient mutant Az34, as well as of cultivar-specific differences, it was shown that endogenous jasmonate increases are necessary and sufficient for expression of this gene. The endogenous rise of ABA did not induce synthesis of JIP-23, whereas exogenous ABA did not act via jasmonates. Different signalling pathways are suggested and discussed. 相似文献
Summary The frequency of sister chromatid exchange (SCE) was determined in a nontransformed diploid rat cell line, FR3T3, under several
tissue culture variables such as cultivation temperature, growth conditions of cells, and concentrations of 5-bromo-2′-deoxyuridine
(BrdU).
The conclusions to be drawn from these experiments are: (a) The cell growth and mechanism(s) of SCE formation in FR3T3 cells
are largely temperature independent (or efficiently regulated) in the range between 33 and 40.5°C. (b) The concentration limits
for BrdU incorporation are 5 to 100 μM; baseline frequency is about 11 SCE/metaphase (constant up to 20 μM BrdU) and increases only moderately at higher BrdU concentrations. (c) Toxic levels of BrdU (150 μM) cause a decrease of SCE rates below that found at 100 μM, presumably due to selective cell death. (d) Keeping cells growth arrested over a long period causes substantial SCE induction
after replating. (e) Induced increase of SCEs probably occurs in this manner during the first cell cycle after release from
growth arrest. It is no longer detectable after the fourth consecutive cell division.
This work was supported by a grant from the Medizinisch-wissenschaftlicher Fond des Bürgermeisters der Bundeshauptstadt Wien. 相似文献
The data accumulated during the past twenty years suggest that thyroid hormones have a direct effect on the differentiation of both the neurons and the glial cell during the critical period of brain development. A fast survey of the available data (which is presented in the introduction of this article) on the mechanism of action of thyroid hormones and on their different effects during brain development suggests that the most dramatic effect of hypothyroidism is a hypoplastic neuropile. Both in vivo, during the critical period of nerve cell differentiation and in vitro, when added to primary cultures of embryonic nerve cells thyroid hormones stimulate neurite outgrowth. Since neurite outgrowth requires massive microtubule assembly the assumption was made that thyroid hormones stimulate nerve cell differentiation by changing the concentration and/or activity of the different proteins (tubulin and “microtubule associated proteins”, MAPs) which co-polymerize to form microtubules.
Preliminary information was obtained by following the kinetics of microtubule assembly in crude brain supernatants. The data showed that: (1) the rate of in vitro microtubule assembly increases with age during brain development; (2) hypothyroidism, when produced in the rat at late pregnancy, slows this evolution; (3) early replacement therapy with thyroid hormones restores normal rates of assembly; (4) the addition of purified MAPs to normal young or 15-day-old hypothyroid brain preparations restores normal rates of polymerization. These and other data suggested that thyroid hormones regulate microtubule assembly by changing the concentration and/or activity of one or more of the MAPs.
Further analysis revealed that striking qualitative changes in MAPs composition occur during brain development. For instance, the TAU fraction, a group of 4–5 proteins with a molecular weight of 60–68 K which is present in adult brain, is absent at early stages of postnatal development: two other entities are present, TAU slow and TAU fast, with different molecular weights, lower activity and different peptide mapping. This latter observation suggests that different TAU genes are expressed during brain development; a conclusion which has been confirmed by cell-free translation of the mRNas coding for these proteins. Analysis of the TAU fraction prepared from hypothyroid rat brains also revealed that a group of TAU proteins. “TAU3”, is almost missing, whereas thyroid hormone administration markedly increases its concentration. Two-dimensional gel electrophoresis showed that the TAU fraction is composed with more than 15 entities, with at least five of them being under thyroid hormone control.
The precise physiological significance of the heterogeneity of MAPs and of the changes in MAPs composition seen during development and in hypothyroid rat brain remains to be determined. The assumption is made that these changes might be of utmost importance to regulate the number and length of the microtubules, and therefore the number and length of the neurites which are formed during the differentiation process of the different neurons. Thyroid hormones would be in these respects one of the epigenic factors required to synchronize sequentially the expression of the genes coding for these proteins in the different nerve cells. 相似文献
Microsomal membranes isolated by sucrose density gradient centrifugation from mature toad ovary has been found to vary significantly
in lipid composition and various enzyme activities in different seasons. Na+, K+—ATPase activity is the highest in breeding season (rainy season). Significantly the optimum temperature for enzyme activity
is 30°C. The other enzyme Δ5-3β-hydroxysteroid dehydrogenase activity is also lower in hibernation period than other seasons. The total phospholipid,
sterol and fatty acid contents differ significantly between seasons. The poly-unsaturated fatty acid, except arachidonic acid
content in hibernation period is much lower than that during other seasons. The sterol content is also the lowest in this
season. The present findings indicate that during hibernation period the membrane is more rigid and the metabolic activity
of the animal is slow because of a lower level of various functionally important enzyme activities.
Part of this work was presented at the 13th International Union of Biochefstry Congress, held at Amsterdam in August 1985. 相似文献