Use of Brassica callus culture to induce sporulation in Alternaria brassicae (Berk.) Sacc.

A non-sporulating isolate of Alternaria brassicae, inoculated on callus culture of Brassica juncea cv. Kranti, colonized the callus and produced spores. When captafol, a fungicide, was added (100 mg/l) to the callus culture medium, if effectively checked fungal contamination and saprophytic growth of A. brassicae on culture medium, without adversely affecting callus growth or establishment of dual culture.     

Growth and activities of enzymes of primary metabolism in batch cultures of Catharanthus roseus cell suspension under different pCO2 conditions

In vitro enzyme activities of glycolysis, pentose-phosphate pathway and dark CO₂ fixation were assayed in batch cultures of heterotrophic Catharanthus roseus cells under various gassing rates and partial pressures of carbon dioxide. Detrimental effects of low pCO₂ culture conditions on the growth characteristics could be linked to marked changes in levels of enzymes of primary metabolism during growth. The enzyme levels observed during the early stages of growth were found to be more stable when a constant pCO₂ (20 mbar) was maintained and enabled exponential growth to be reached more rapidly.The importance of carbon dioxide as a conditioning factor of the culture medium is discussed.     

Effects of auxins and cytokinins on epigenetic instability of callus-propagated Kalanchoe blossfeldiana Poelln.

A main problem in the vegetative propagation of ornamental plants in vitro is the epigenetic instability of cells removed from their organized environment. With calluses of leaf explants of Kalanchoe blossfeldiana Poelln., cv. Yucatan, the role of plant growth regulators (PGRs) in the occurrence of fasciation was studied.In various combinations of auxins and cytokinins, the auxin 2,4-D (2,4-dichlorophenoxyacetic acid) gave only deformed, inseparable shoot primordia. The most rapid callus induction with regeneration of well-developed sprouts was obtained with the natural IAA (indoleacetic acid) and Z (zeatin).As a first symptom of fasciation, aberration in decussate phyllotaxis can be observed. At increasing concentrations of IAA + Z, this symptom gradually decreased but fasciation proper increased. The optimum concentration was at 1 M for both PGRs. Reduction of exposure to the PGRs from six to three weeks reduced the epigenetic instability.     

In vitro regeneration in Trifolium. 1. Direct somatic embryogenesis in T. rubens (L.)

The origin and development of zygotic and somatic embryos of Trifolium rubens L. was studied with the aid of paraffin sections and light microscopy. Zygotic embryos were collected, fixed and prepared daily from one to ten days after cross-pollination. Somatic embryos were obtained by plating petiole sections on modified L2 medium with 0.015 mgl^-1 picloram and 0.1 mgl^-1 6-BAP. Cultured petioles were collected and fixed daily from one to 25 days after plating. Two regions in the vascular bundle sheath of cultured petioles gave rise to callus. The first region was adjacent to the phloem fibers and produced friable callus. The second region gave rise to compact callus that was connected to the fascicular cambium. Somatic embryos originated from single cells in the cortex directly without intervening callus formation and from single cells in the friable callus. In addition, embryos arose from meristematic regions in compact callus. Many early stages of embryogenesis (one, two and four-celled stages) were observed in the cortex and friable callus. Zygotic embryogenesis in Trifolium differs from other legumes in that the suspensor is short and has a broad attachment. This arrangement was observed in zygotic embryos of T. rubens and in many somatic embryos. However, a continuum of somatic embryogenesis was observed where some young embryos had a Trifolium suspensor-like arrangement while others were attached to a long narrow suspensor-like structure more characteristic of Medicago.     

In vitro tuberization in white yam (Dioscorea rotundata Poir)

Nodal cuttings of white yam were induced to produce microtubers on a MS-revised medium supplemented with various concentrations of sucrose, 20 mgl^–1 L-cysteine, 0.5 mgl^–1 kinetin and 0.7% agar. The frequency of tuberization was affected by the daylength, which is optimal at 12 and 16 h of light depending on the sucrose concentration. The microtubers were planted in a seed bed and grown to maturity. The importance of in vitro tuberization of yam as a means of international germplasm distribution or exchange as well as for the propagation of planting material is discussed.     

向日葵幼胚培养中体细胞胚胎发生的观察

1.向日葵不同品种体细胞胚胎发生的情况不同。2.较高浓度的蔗糖有利于向日葵幼胚的体细胞胚胎发生。3.在同样条件下,2mm长的幼胚较其它时期的幼胚体细胞胚胎发生的频率高。4.在蔗糖浓度为17.5％并分别加入0.5—10.0ppm玉米素的Nitsch培养基中,向日葵幼胚产生体细胞胚胎发生的频率随着玉米素浓度的增高而增加。5. 2,4-D能使体细胞胚胎发生,但不能分化器官。6.切片观察表明:在含玉米素的培养基上,幼胚产生了胚性细胞团和胚状体。并多数发生于子叶与下胚轴的深层。胚性细胞团周围细胞退化,使其与周围组织之间形成间隙。     

Ionic Requirements for the Specific Binding of [3H]GBR 12783 to a Site Associated with the Dopamine Uptake Carrier

At 0°C, when Na⁺ was the only cation present in the incubation medium, increasing the Na⁺ concentration from 3 to 10 mM enhanced the affinity of [³H]l-[2-(di-phenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperazine ([³H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the 5_max. For higher Na⁺ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na⁺. In a 10 mM Na⁺ medium, the K_D and the B_max were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [³H]GBR 12783, the half-maximal specific binding occurred at 5 mM Na⁺. A similar Na⁺ dependence was observed at 20°C. Scatchard plots indicated that K⁺, Ca²⁺, Mg²⁺, and Tris⁺ acted like competitive inhibitors of the specific binding of [³H]GBR 12783. The inhibitory potency of various cations (K⁺, Ca²⁺, Mg²⁺, Tris⁺, Li⁺ and choline) was enhanced when the Na⁺ concentration was decreased from 130 to 10 mM. In a 10 mM Na⁺ medium, the rank order of inhibitory potency was Ca²⁺ (0.13 mM) > Mg²⁺ > Tris⁺ > K⁺ (15 mM). The requirement for Na⁺ was rather specific, because none of the other cations acted as a substitute for Na⁺. No anionic requirement was found: Cl^-, Br^-, and F^- were equipotent. These results suggest that low Na⁺ concentrations are required for maximal binding; higher Na⁺ concentrations protect the specific binding site against the inhibitory effect of other cations.     

Maitotoxin-Evoked γ-Aminobutyric Acid Release Is Due Not Only to the Opening of Calcium Channels

The effects of maitotoxin (MTX) on endogenous amino acid release were tested on highly purified striatal neurons differentiated in primary culture. MTX induced a large and concentration-dependent release of gamma-aminobutyric acid (GABA). This effect was abolished when experiments were performed in the absence of external Ca2+, and restored when Ca2+ ions were added after removing the MTX-containing Ca2+-free solution. MTX-induced amino acid release was not affected by 1 microM nifedipine and only slightly inhibited by 1 mM Co2+. MTX also induced a massive accumulation of 45Ca2+ in the neurons which, in contrast to the MTX-evoked GABA release, was totally blocked in the presence of 1 mM Co2+. Whereas 500 nM tetrodotoxin was without significant effect, MTX-evoked GABA release was dependent on the presence of external Na+ and sensitive to nipecotic acid, a GABA uptake inhibitor. It is concluded that, on striatal neurons, MTX induced Na+ influx only in the presence of external Ca2+. The increase in cytoplasmic Na+ ions then triggers the release of GABA.     

A molecular and cytogenetic survey of major repeated DNA sequences in tomato (Lycopersicon esculentum)

Summary The major families of repeated DNA sequences in the genome of tomato (Lycopersicon esculentum) were isolated from a sheared DNA library. One thousand clones, representing one million base pairs, or 0.15% of the genome, were surveyed for repeated DNA sequences by hybridization to total nuclear DNA. Four major repeat classes were identified and characterized with respect to copy number, chromosomal localization by in situ hybridization, and evolution in the family Solanaceae. The most highly repeated sequence, with approximately 77000 copies, consists of a 162 bp tandemly repeated satellite DNA. This repeat is clustered at or near the telomeres of most chromosomes and also at the centromeres and interstitial sites of a few chromosomes. Another family of tandemly repeated sequences consists of the genes coding for the 45 S ribosomal RNA. The 9.1 kb repeating unit in L. esculentum was estimated to be present in approximately 2300 copies. The single locus, previously mapped using restriction fragment length polymorphisms, was shown by in situ hybridization as a very intense signal at the end of chromosome 2. The third family of repeated sequences was interspersed throughout nearly all chromosomes with an average of 133 kb between elements. The total copy number in the genome is approximately 4200. The fourth class consists of another interspersed repeat showing clustering at or near the centromeres in several chromosomes. This repeat had a copy number of approximately 2100. Sequences homologous to the 45 S ribosomal DNA showed cross-hybridization to DNA from all solanaceous species examined including potato, Datura, Petunia, tobacco and pepper. In contrast, with the exception of one class of interspersed repeats which is present in potato, all other repetitive sequences appear to be limited to the crossing-range of tomato. These results, along with those from a companion paper (Zamir and Tanksley 1988), indicate that tomato possesses few highly repetitive DNA sequences and those that do exist are evolving at a rate higher than most other genomic sequences.