High temperature pyrolysis of 2-methyl furan.

The dissociation of 2-methyl furan at high temperatures has been studied in a combined experimental and theoretical approach to elucidate the details of this multi-channel unimolecular reaction. Laser schlieren densitometry studies were performed in a diaphragmless shock tube over the range 1600 < T < 2300 K and three pressures 60, 120 and 240 Torr. The theoretical study identified many reaction paths, most of which are initiated by the formation of carbenes. Of these paths, five account for 99% consumption of 2MF, and three account for 95% consumption. Simulations of the experimental results with a model that incorporated the theoretical predictions of reaction paths failed to reproduce the experimental data. This was resolved by increasing the rate of loss of an H-atom from the methyl group in 2-methyl furan by a factor of 2-4. The resulting model provides good simulations of the complete set of experimental data. The branching fractions for the three key reactions are both temperature and pressure dependent.

Optimization of Water Content for the Cryopreservation Of Allium sativum In Vitro Cultures by Encapsulation-Dehydration.

BACKGROUND: There is a general requirement to determine and correlate water content to viability for the standardization of conservation protocols to facilitate effective cryostorage of plant germplasm. OBJECTIVE: This study examined water content as a critical factor to optimize the cryostorage of Allium sativum. MATERIALS AND METHODS: Stem discs were excised from post-harvest, stored bulbs prior to cryopreservation by encapsulation-dehydration and water content was determined gravimetrically. RESULTS: Survival of cryopreserved stem discs was 42.5 %, with 22.5 % exhibiting shoot regrowth following 6 h desiccation. Gravimetric data demonstrated a correlation between water content corresponding with survival / regrowth from desiccated, cryopreserved stem discs. For encapsulated stem discs a 25 % residual moisture and corresponding water content of 0.36 g H2O g-1 d.wt correlated with maximal survival following ~6.5 h of desiccation. CONCLUSION: The data concurs with the literature suggesting the formation of a stable vitrified state and a 'window' for optimal survival and regrowth that is between 6 - 10 h desiccation. Further studies using differential scanning calorimetry (DSC) are suggested to substantiate these findings.

Note: An improved solenoid driver valve for miniature shock tubes.

A solenoid driver valve has been built to improve the operating performance of diaphragmless shock tubes, which are used for high pressure, high temperature chemical kinetics, and fluid mechanics studies. For shock tube driver application, the most important characteristics are those of sealing, strength, and quality of the generated shock waves and repeatability of opening characteristics and therefore subsequent post-shock conditions. The main features of the new driver valve are a face o-ring sealing design of the valve, the large internal volume, and through inserts near the solenoid core: adjustable opening characteristics of the valve.

Cryopreservation of quince (Cydonia oblonga Mill.).

BACKGROUND: Quince (Cydonia oblonga Mill.) has great potential for utilisation in pharmaceutical and food industries. OBJECTIVE: The study was to develop an efficient cryopreservation approach for quince. METHODS: Factors on the survival and regrowth such as cold acclimation, explant type and recovery media composition were assessed. The effectiveness of the resultant protocols for a number of quince cultivars was determined. RESULTS AND CONCLUSION: Quince shoot tips and nodal sections are successfully cryopreserved. Sustained regrowth of quince Angers A was observed after encapsulation-osmoprotection/dehydration, encapsulation-dehydration and PVS2 vitrification. The highest regrowth rate (80%) was obtained from explants excised from cold hardened shoots and cryopreserved using encapsulation-osmoprotection/dehydration and vitrification protocols. The optimised vitrification protocol in combination with shoot cold hardening and a MS recovery medium without activated charcoal and auxin resulted in satisfactory regrowth of shoots from six quince cultivars. The morphology of acclimatised plants derived from cryopreserved shoots was comparable with non-cryopreserved plants.

A miniature high repetition rate shock tube.

A miniature high repetition rate shock tube with excellent reproducibility has been constructed to facilitate high temperature, high pressure, gas phase experiments at facilities such as synchrotron light sources where space is limited and many experiments need to be averaged to obtain adequate signal levels. The shock tube is designed to generate reaction conditions of T > 600 K, P < 100 bars at a cycle rate of up to 4 Hz. The design of the apparatus is discussed in detail, and data are presented to demonstrate that well-formed shock waves with predictable characteristics are created, repeatably. Two synchrotron-based experiments using this apparatus are also briefly described here, demonstrating the potential of the shock tube for research at synchrotron light sources.

Cryopreservation of Helianthus tuberosus cell suspension cultures: the effect of preculture treatments on cytoskeletal proteins and transglutaminase activity.

Helianthus tuberosus cell suspension cultures were subjected to cryopreservation 24h preculture treatments with 0.5M sucrose or mannitol. Extracts were assayed for transglutaminase activity and the level of alpha-tubulin tyrosination. There was a significant reduction (compared with the non-precultured controls) in transglutaminase activity and alpha-tubulin tyrosination state after mannitol preculture treatment, whereas sucrose preculture treatment produced no significant effect. The results suggest that reduced levels of transglutaminase activity and alpha-tubulin tyrosination are associated with a lack of post-thaw recovery observed following mannitol preculture treatment of cell culture suspensions. These activities may represent useful molecular markers of the success of preculture treatments in cryopreservation protocols.

Preliminary evidence for the metabolism of benzo(a) pyrene by Plantago lanceolata.

Polycyclic aromatic hydrocarbons (PAHs) have long been recognised as potential carcinogens in animals in which biotransformation into reactive metabolites can lead to DNA damage. In animals PAHs metabolism mainly occurs in hepatic microsomes and is associated with the cytochrome p-450 mediated mixed functional oxidase (MFO) system. PAH metabolism in plants has been shown to occur via a similar enzyme system, but has received relatively little attention. This study is looking at how the plant species Plantago lanceolata metabolizes benzo(a)pyrene (B(a)P), which is one of the PAHs whose metabolism has been studied extensively in animals. The aim of the work is to establish firstly that the B(a)P is taken up and secondly that it is biotransformed by the plant to products possibly similar to those found in animals. This work is achieved by using C-14-B(a)P along with whole body autoradiography, scintillation analysis and chromatography techniques to locate the B(a)P and its metabolites.

Mechanisms of copper tolerance by Armeria maritima in Dolfrwyong Bog, north Wales--initial studies.

Preliminary field studies were carried out at Dolfrwynog Bog in July 2000. Replicate samples of water, Armeria maritima plants and the soils adhering to its roots were collected and analysed for copper. Concentrations of up to 6486 mg kg-1 of copper in the soils were recorded. Accumulation of copper by the plant as expressed by concentration factors (CF) show that it is acting mainly as a copper excluder. Of the copper that is taken up, most of it is retained within the roots with very little being transported to the shoots of the plant. Moreover, a further possible mechanism of tolerance is exhibited by the excretion of copper through its decaying leaves. Towards the use of in vitro cultures to study the copper tolerance mechanisms in A. maritima a micropropagation protocol has been developed. The ex vitro plants have been rooted and established in compost.

Cryopreservation of auricula shoot tips using the encapsulation/dehydration technique.

Calcium alginate encapsulated, in vitro culture derived shoot tips of the florist's auricula, cultivar Embley, were successfully cryopreserved using the encapsulation/dehydration technique. The use of preculture media containing both sucrose and mannitol was essential for post-thaw growth. After 2 weeks cold acclimatisation at 10 degrees C, shoot tips were encapsulated and incubated in culture medium containing 0.25 M sucrose and 0.25 M mannitol for 48h, followed by 23h dehydration with silica gel (water content of beads approximately 16%) prior to plunging into liquid nitrogen. Post-thaw growth of the shoot tips was without callus formation. The morphology of frozen and non-frozen shoots was comparable.

Cryopreservation of plumular explants of coconut (Cocos nucifera L.) to support programmes for mass clonal propagation through somatic embryogenesis.

Callus growth has been observed from plumules of ecotype Laguna Tall after cryopreservation using an encapsulation/dehydration protocol. Sucrose preculture treatment and silica gel dehydration both significantly influenced the frequency of callus formation from non-frozen and frozen plumules. The greatest frequency of post-thaw callus growth occurred after incubation of the encapsulated plumules for 72-96 h in medium containing 0.75 M sucrose followed by desiccation over silica gel for 7-8 h down to approximately 30% moisture content (fresh weight basis). Freezing and thawing were carried out rapidly. Post-thaw recovery rates in excess of 80% were recorded.

Equipment for the large-scale electromanipulation of plant protoplasts.

Electric fields are now used extensively for the genetic manipulation of plant cells through protoplast fusion and direct gene uptake. The cost of commercially available electrofusion and electroporation equipment remains prohibitive for many laboratories. This paper describes an electronic apparatus, suitable for the large-scale electrofusion and electroporation of plant protoplasts that is compatible in both function and cost with commercially available equipment.

Variation in free-radical damage in rice cell suspensions with different embryogenic potentials.

Levels of free-radical-mediated lipid peroxidation were monitored in cell-suspension cultures of Oryza sativa L. possessing different embryogenic potentials. Oxidative stress was evaluated using assays which sequentially assessed the stages of lipid peroxidation (diene conjugation, peroxidation, and the formation of secondary lipid-peroxidation products). Lipid peroxidation was significantly higher in a cell line which had lost embryogenic ability compared with lines which still retained this capacity. Superoxide dismutase (EC 1.15.1.1) activity did not vary significantly between the embryogenic and previously embryogenic lines; however, catalase (EC 1.11.1.6) and peroxidase (EC 1.11.1.7) activities were significantly lower in the line which had lost embryogenic ability. Metabolic activity as estimated by reduction of triphenyl tetrazolium chloride decreased with diminishing embryogenic potential and was especially low in cell lines which never exhibited embryogenic capabilities. The possible involvement of free radicals in the loss of embryogenic potential of rice cells is discussed.

Electrofusion of protoplasts from celery (Apium graveolens L.) with protoplasts from the filamentous fungus Aspergillus nidulans.

A method was developed for electrofusion of higher-plant protoplasts from celery and protoplasts from the filamentous fungus Aspergillus nidulans. Initially, methods for the fusion of protoplasts from ecch species were determined individually and, subsequently, electrical parameters for fusion between the species were determined. Pronase-E treatment and the presence of calcium ions markedly increased celery protoplast stability under the electrical conditions required and increased fusion frequency with A. nidulans protoplasts. A reduction in protoplast viability was observed after electrofusion but the majority of the protoplasts remained viable over a 24-h incubation period. A small decline in protoplast respiration rate occurred during incubation but those celery protoplasts fused with A. nidulans protoplasts showed elevated respiration rates for 3 h after electrofusion.