Effects of light and photoperiodic conditions on abscisic acid in leaves and roots of Acer pseudoplatanus L.

Roots of Acer pseudoplatanus seedlings grown in liquid nutrient medium contained much lower levels of both free and bound abscisic acid than did leaves. The levels of free abscisic acid were similar in young expanding and of mature leaves, but lower in older senscing leaves. Growing plants under long days or short days did not influence the levels of free and bound abscisic acid in leaves. However, under both long days and short days, levels of bound abscisic acid were lower at the end of the dark period than 8 h later during the light period. Phaseic acid was also detected during the light period but never at the end of the dark period.Abbreviations ABA abscisic acid - PA phaseic acid - SD short day - GLC gas-liquid chromatography - LD long day     

Effect of chlorambucil and indomethacin on growth and prostaglandin levels in sensitive and resistant walker carcinoma

An analysis of the effect of combinations of chlorambucil and indomethacin, or chlorambucil and prostaglandin E₂ (PGE₂) on the growth of alkylating agent sensitive and resistant Walker carcinoma in vitro has been made by the isobologram approach. Indomethacin alone acts as a growth inhibitor of the Walker carcinoma. High concentrations of indomethacin (5 μg/ml) act to inhibit the growth of the resistant line sub-additively with chlorambucil, whereas low concentrations act additively. For the sensitive line indomethacin acts either additively or supra-additively with chlorambucil at all concentrations employed. Both indomethacin and low concentrations of chlorambucil alone inhibit PGE₂ secretion into the culture medium of both cell lines and an enhanced inhibition is seen with the combination. PGE₂ itself acts as a growth inhibitor of both cell lines, although it causes greater growth inhibition of chlorambucil resistant Walker carcinoma (LD₅₀ 1.8 μg/ml) than of the sensitive line. This correlates with a greater PGE₂ secretion capacity by the resistant cell line (40 pg PGE₂/ml medium/10⁵ cells for the resistant tumour and 17 pg PGE₂/ml medium/10⁵ cells for the sensitive tumour). Combinations of PGE₂ with chlorambucil inhibit growth either additively or sub-additively. It seems unlikely that inhibition of PGE₂ secretion is responsible for the interactive effects of chlorambucil and indomethacin, since growth inhibition produced by the combination is not reversed by PGE₂ at any of the concentrations employed. Possible mechanisms of the interactive effects are discussed.     

Depolymerization of cortical microtubules is not a primary cause of chilling injury in corn (Zea mays L. cv Black Mexican Sweet) suspension culture cells

Cold-induced depolymerization of cortical microtubules were examined in suspension culture cells of corn (Zea mays L. cv Black Mexican Sweet) at various stages of chilling. In an attempt to determine whether microtubule depolymerization contributes to chilling injury, experiments were carried out with and without abscisic acid (ABA) pretreatment, since ABA reduces the severity of chilling injury in these cells. Microtubule depolymerization was detectable after 1 h at 4°C and became more extensive as the chilling was prolonged. There was little chilling injury after 1 d at 4°C in either ABA-treated or non-ABA-treated cells. After 3 d at 4°C, there was about 26% injury for ABA-treated and 40% injury for non-ABA-treated cells, as evaluated by 2,3,5-triphenyl-tetrazolium chloride reduction and by regrowth. After 1d at 4°C, less than 10% of cells retained full arrays of microtubules in both ABA-treated and non-ABA-treated cells, the remainder having either partial arrays or no microtubules. After 3d at 4°C, about 90% of cells showed complete or almost complete depolymerization of microtubules in both ABA-treated and non-ABA-treated cells. ABA did not stabilize the cortical microtubules against cold-induced depolymerization. In about 66% of ABA-treated cells and 57% of non-ABA-treated cells that had been held at 4°C for 3d, repolymerization of cortical microtubules occurred after 3h at 28°C. These results argue against the hypothesis that depolymerization of cortical microtubules is a primary cause of chilling injury.     

Pea dehydrins: identification,characterisation and expression

An antiserum raised against dehydrin from maize (Zea mays) recognised several polypeptides in extracts of pea (Pisum sativum) cotyledons. A cDNA expression library was prepared from mRNA of developing cotyledons, screened with the antiserum and positive clones were purified and characterised. The nucleotide sequence of one such clone, pPsB12, contained an open reading frame which would encode a polypeptide with regions of significant amino acid sequence similarity to dehydrins from other plant species.The deduced amino acid sequence of the pea dehydrin encoded by B12 is 197 amino acids in length, has a high glycine content (25.9%), lacks tryptophan and is highly hydrophilic. The polypeptide has an estimated molecular mass of 20.4 kDa and pI=6.4. An in vitro synthesised product from the clone comigrates with one of the in vivo proteins recognised by the antiserum.A comparison of the pea dehydrin sequence with sequences from other species revealed conserved amino acid regions: an N-terminal DEYGNP and a lysine-rich block (KIKEKLPG), both of which are present in two copies. Unexpectedly, pea dehydrin lacks a stretch of serine residues which is conserved in other dehydrins.B12 mRNA and dehydrin proteins accumulated in dehydration-stressed seedlings, associated with elevated levels of endogenous abscisic acid (ABA). Applied ABA induced expression of dehydrins in unstressed seedlings. Dehydrin expression was rapidly reversed when seedlings were removed from the stress or from treatment with ABA and placed in water.During pea cotyledon development, dehydrin mRNA and proteins accumulated in mid to late embryogenesis. Dehydrin proteins were some of the most actively synthesised at about the time of maximum fresh weight and represent about 2% of protein in mature cotyledons.     

Applications of immortalized cells in basic and clinical neurology

Immortalized cell lines can serve as model systems for studies of neuronal development and restoration of function in models of neurological disease. Cell lines which result from spontaneous or experimentally-induced tumors have been used for these purposes. More recently, the techniques of genetic engineering have resulted in the production of cell lines with specific desired characteristics. This has been accomplished by insertion of a desired gene into a pre-existing immortal cell or by immortalizing primary cells. The production of immortal cell lines using temperature-sensitive immortalizing genes offers an additional method of controlling gene expression, and thereby controlling cell proliferation and differentiation. In the nervous system, these techniques have produced immortal cell lines with neuronal and glial properties.     

低温胁迫下凤眼莲叶片的适应——脱落酸和可溶性蛋白质含量升高

本文报道低温胁迫下风眼莲叶片脱落酸(ABA)、可溶性蛋白质和水势的测定结果。低温胁迫时脱落酸和可溶性蛋白质含量远高于对照,(前者含量最高可达对照的4倍,后者可达到对照的2.75倍),而且脱落酸和蛋白质含量随温度降低而升高。蛋白质的生物合成抑制剂亚胺环己酮证明,可溶性蛋白质含量升高,原因是有部分是新合成的。在各种低温处理下获得了几乎相同于对照的叶片水势。我们推测:低温胁迫下,脱落酸水平的相应变化不是由于低温诱导水分胁迫所致,而是低温胁迫本身诱导。     

Cloning and sequencing of cDNA for mouse liver metallothionein-I

Metallothionein mRNA was purified from liver of mice injected with cadmium. The corresponding double-stranded cDNA was prepared and inserted into the PstI site of plasmid pBR322. The resulting recombinant DNA was used to transform the RR1 strain of $\text{Escherichia}\text{coli}$. Clones resistant to tetracycline and sensitive to ampicillin were screened for the presence of metallothionein-specific restriction fragments in their plasmids. One plasmid, called M135, contains a cDNA insert covering the entire length of the mRNA for mouse liver metallothionein-I, except for the first 18 bases at the 5′ end.     

Causes of root growth retardation induced by ultraviolet-B irradiation of shoots in Barley seedlings

In barley seedlings (Hordeum vulgare L.) during two days after irradiation of shoots with UV-B (0.5 W/m², 6 h), the rate of elongation of primary roots decreased 2–3 times compared to that in control plants. The modulus of elasticity of roots (ε) increased at most twofold in 12 h after the onset of irradiation; the hydraulic conductivity (L _p) diminished by a factor of two in 12 h, and the root osmotic pressure gradually decreased by 0.08 MPa in 24 h. Changes in ε and L _p were shown to be related to oxidative stress in growing roots, which was evidenced from the increase in H₂O₂ level up to 15-fold increase in 6 h and in activity of guaiacol peroxidase (3.5-fold in 12 h). After 48 h, the characteristics of oxidative metabolism and root characteristics ε and L _p became identical in untreated and treated plants. On the third day, the rate of root growth in treated plants reached its initial value. It is concluded that the main causes of retardation of root growth under these conditions were as follows: the increase in cell wall rigidity related to formation of oxidative cross-links in the apoplast and the decrease in root osmotic pressure due to limited transport of assimilates from irradiated leaves. After the intensity of UV-B irradiation applied to shoots was enhanced (1.6 W/m², 4 h), another physiological status of roots was observed on the 2nd day characterized by twofold increase in L _p, tenfold decreased root elongation rate, and by a progressing increase of root diameter in growing roots. The comparison of root responses induced by irradiation of shoots with the root responses to sodium salicylate and ABA suggests that both agents might participate in the transmission of signals from irradiated leaves to roots.