The possible involvement of gibberellins and calcium in tipburn of Chinese cabbage: Study of intact plants and detached leaves

Spraying Chinese cabbage seedlings [Brassica pekinensis (Lour.) Rupr.] with the growth retardant daminozide (succinic acid-2,2-dimethylhydrazide) reduced tipburn of the mature plants. As the concentration of daminozide increased, the reduction in tipburn damage was correlated with increased calcium content in young susceptible leaves. This effect was much more pronounced in plants that were misted once a day during the head formation period.Incubation of detached Chinese cabbage leaves for 48 h (in the dark) in solutions which contained either EDTA or EGTA caused characteristic lesions at the leaf tips. The extent of the damage was reduced by including CaCl₂ in the solutions. Leaves which were incubated in a solution of EDTA+GA₃ or EGTA+GA₃ were severely affected, with the latter solution being the more harmful. GA₃ alone did not enhance tipburn. CaCl₂ greatly reduced the effect of a complex of chelating agents and GA₃. Leaves derived from daminozide-treated plants which were incubated in EDTA+GA₃ were less affected with tipburn lesions than leaves of control plants treated with the same solutions. When detached leaves were water-stressed for 24 h prior to incubation in these solutions, the severity of tipburn symptoms increased. The possible interactions between GA, calcium chelation and tipburn development are discussed.Contribution no. 1171-E, 1984 series, from the ARO, The Volcani Center Bet Dagan, Israel.     

The relationship between sister-chromatid exchange and perturbations in DNA replication in mutant EM9 and normal CHO cells

The majority of the high (12-fold elevated) baseline sister-chromatid exchanges (SCEs) that occur in the CHO mutant line EM9 appear to be a consequence of incorporated BrdUrd, and they arise during replication of DNA containing BrdUrd in a template strand. In normal CHO cells the alkaline elution patterns of DNA newly replicated on a BrdUrd-containing template are significantly altered compared with those seen during the replication on an unsubstituted template. The nascent DNA synthesized on such an altered template is delayed in reaching mature size, possibly because replication forks are temporarily blocked at sites occurring randomly along the template. Transient blockage of replication forks may be a prerequisite for SCE. The delay in replication on BrdUrd-substituted templates was greater in EM9 cells than in parental AA8 cells and was also greater in AA8 cells treated with benzamide, an inhibitor of poly(ADPR) polymerase, than in untreated AA8 cells. Under these conditions, treatment with benzamide also produced a 7-fold increase in SCEs in AA8. An EM9-derived revertant line that has a low baseline SCE frequency showed less delay in replication on BrdUrd-substituted templates than did EM9. However, under conditions where the template strand contained CldUrd, which was shown to produce 4-fold more SCEs than BrdUrd in AA8 cells, the replication delay in AA8 was not any greater in the CldUrd-substituted cells. Thus, other factors besides the delay appear to be involved in the production of SCEs by the template lesions resulting from incorporation of the halogen-substituted pyrimidine molecules.     

The effect of various inhibitors of DNA synthesis on the repair of DNA photoproducts

The effect on DNA repair of several inhibitors of DNA synthesis has been investigated in CHO cells. Three assays were employed following ultraviolet irradiation of G₁ cells: unscheduled DNA synthesis, removal of antibody binding sites and alkaline elution. Cytosine arabinoside and aphidicolin were found to reduce unscheduled DNA synthesis in a dose-dependent manner without affecting the removal of antibody-binding sites. Strand rejoining was also inhibited. These results are consistent with the hypothesis that inhibition is due to premature chain termination during repair synthesis some time after excision of the lesion. Conversely, inhibition of unscheduled DNA synthesis by novobiocin is paralleled by inhibition of excision of the lesion. However, no inhibition of incision was apparent. Since nalidixic acid, an inhibitor of topoisomerase II, did not inhibit excision, it is unlikely that the primary site of action of novobiocin is this topoisomerase. The possibility that a second topoisomerase and/or a polymerase are affected is discussed in the light of previously published data.     

HBsAg重组DNA转化中国地鼠卵巢细胞二氢叶酸还原酶阴性突变株的细胞染色体变化及致瘤性

整合了含乙型肝炎病毒表面抗原(HBsAg)基因和dhfr基因的CHO-dhfr~-细胞,其染色体的畸变率和畸变类型都比亲代CHO-dhfr~-细胞高。但转化前后两系细胞的重要特性都未发生变异,即两者的染色体总数无差别,都是20条。两系细胞株接种裸鼠,均未发现有致瘤性。     

猕猴桃种间杂交结果初报

目前,国内外栽培的猕猴桃品种均为系统选育而成。采用种间杂交育种,可获得比系统选育更为理想的新型栽培品种。开展猕猴桃远缘杂交研究己见报道的国外有新西兰,国内有郑州果树研究所、北京植物园等,但至今未见有开花结果的资料报道。为了     

黄连木五倍子的生态研究与利用

一、产地自然概况黄连木五倍子最早发现于河南省南部信阳市郊贤山脚下(东经114°0′,,北纬32°10′)。该地为低山丘陵,海拔90一320m,南部紧连鸡公山厂傍依南湾水库和狮河。     

中华猕猴桃胚乳植株后代的观察

对438株定植的中华猕猴桃胚乳培.养的试管苗,经四年的田间观察,并进行连续二年结果分析。与对照的母株相比,胚乳植株在株形、叶片大小、果实形态及果实的主要营养成分含量上都有较大的变化。同时还发现,由同一块愈伤组织诱导的胚乳试管苗后代中也有雌、雄性别的分化。胚乳植株后代的多样性,可为中华猕猴桃的选种及品种繁育提供丰富的材料。     

Chinese hamster ovary cells continuously secrete a cysteine endopeptidase

Summary The protease activity in serum-free conditioned medium of chinese hamster ovary (CHO) cells was measured using peptidyl (or aminoacyl)-4-methylcoumaryl-7-amides (MCAs) as the substrates. Aminopeptidase increased in level as amounts of nonviable cells increased during cultivation in serum-free medium, indicating that the activity seems to be originated from intracellular proteases. The activity toward Boc-Leu-Arg-Arg-MCA, which was strongly inhibited by p-chloromercuribenzonate and N-ethylmaleimide, was the strongest among those toward peptidyl-MCAs in the conditioned medium within 48 h-cultivation in serum-free medium. In contrast to the case of aminopeptidase activity, the endopeptidase activity decreased in level after 48 h-cultivation although amounts of nonviable cells increases. Thus, CHO cells continuously secrete the cysteine proteases. This work was supported by the management of the Research Association for Biotechnology as a part of the R&D of Basic Technology for Future Industries sponsored by NEDO (New Energy and Industrial Technology Development Organization).     

腐霉属分类性状评价及其中国的种

本文对腐霉属Pythium Pringsheim的研究历史作了简单的回顾,对该属的分类性状和系统进行了论述和评价,最后对中国已发现的55种腐霉,以检索表的方式进行了分类、检索。     

Characterization of a cDNA encoding cysteine proteinase inhibitor from Chinese cabbage (Brassica campestris L. ssp. pekinensis) flower buds

A cDNA encoding a new phytocystatin isotype named BCPI-1 was isolated from a cDNA library of Chinese cabbage flower buds. The BCPI-1 clone encodes 199 amino acids resulting in a protein much larger than other known phytocystatins. BCPI-1 has an unusually long C-terminus. A BCPI-1 fusion protein expressed in Escherichia coli strongly inhibits the enzymatic activity of papain, a cysteine proteinase. Genomic Southern blot analysis revealed that the BCPI gene is a member of a small multi-gene family in Chinese cabbage. Northern blot analysis showed that it is differentially expressed in the flower bud, leaf and root.