Changes in the Physical State of Membrane Lipids during Senescence of Rose Petals

Changes in the physical state of microsomal membrane lipids during senescence of rose flower petals (Rosa hyb. L. cv Mercedes) were measured by x-ray diffraction analysis. During senescence of cut flowers held at 22°C, lipid in the ordered, gel phase appeared in the otherwise disordered, liquid-crystalline phase lipids of the membranes. This was due to an increase in the phase transition temperature of the lipids. The proportion of gel phase in the membrane lipids of 2-day-old flowers was estimated as about 20% at 22°C. Ethylene may be responsible, at least in part, for the increase in lipid transition temperature during senescence since aminooxyacetic acid and silver thiosulfate inhibited the rise in transition temperature. When flowers were stored at 3°C for 10 to 17 days and then transferrd to 22°C, gel phase lipid appeared in membranes earlier than in freshly cut flowers. This advanced senescence was the result of aging at 3°C, indicated by increases in membrane lipid transition temperature and ethylene production rate during the time at 3°C. It is concluded that changes in the physical state of membrane lipids are an integral part of senescence of rose petals, that they are caused, at least in part, by ethylene action and that they are responsible, at least in part, for the increase in membrane permeability which precedes flower death.     

Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca

High Na⁺ concentrations may disrupt K⁺ and Ca²⁺ transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca²⁺ levels often counteract these consequences of salinity. The effect of supplemental Ca²⁺ on influx of Ca²⁺, K⁺, and Na⁺ in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca²⁺. Sodium influx increased proportionally to increasing salinity. At high external Ca²⁺, Na⁺ influx was less than at low Ca²⁺. Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, ⁴⁵Ca²⁺ influx increased in proportion to salt concentrations, especially with high Ca²⁺. Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca²⁺. The rate of K⁺ uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca²⁺ is related to improved Ca-status and maintenance of K⁺/Na⁺ selectivity.     

The molecular basis for rRNA-dependent spectinomycin resistance in Nicotiana chloroplasts

The chloroplast genes coding for the 16S ribosomal RNA from several spectinomycin-resistant Nicotiana mutants were analyzed. Two classes of mutants were identified. In one class, a G to A base transition is found at position 1140 of the tobacco-chloroplast 16S rRNA gene, which eliminates an AatII restriction endonuclease site. This base transition is proximal to a mutation previously described for spectinomycin resistance in Escherichia coli. In the other class, a novel G to A transition is found at position 1012 of the 16S rRNA gene. Although the mutations in the two classes are 128 nucleotides apart, the secondary structure model for 16S rRNA suggests that the two mutated nucleotides are in spatial proximity on opposite sides of a conserved stem structure in the 3' region of the molecule. Phylogenetic evidence is presented linking this conserved stem with spectinomycin resistance in chloroplasts. Perturbation of the stem is proposed to be the molecular-genetic basis for rRNA-dependent spectinomycin resistance.     

Economic assessment of plant cell culture for the production of ajmalicine

Cost estimates have been prepared for commercial-scale production of ajmalicine-rich Catnaranthus roseus biomass using plant cell culture. At the current state of the technology the cost would be approximately $7.30/lb dry biomass ($3215/kg ajmalicine). Naturally-grown C. roseus roots have a 50% lower ajmalicine concentration but would cost only ca. $0.70/lb ($619/kg ajmalicine). The principal reason for the high cost of the plant cell culture route is not the slow specific growth rate (0.35 day(-1)), but rather the slow specific product accumulation rate (0.26 mg/g day). This rate will have to be increased by a factor of 40 to make the process competitive.     

Evaluation of the effectiveness factor along immobilized enzyme fixed-bed reactors: Design of a reactor with naringinase covalently immobilized into glycophase-coated porous glass

A design equation is presented for packed-bed reactors containing immobilized enzymes in spherical porous particles with internal diffusion effects and obeying reversible one-intermediate Michaelis-Menten kinetics. The equation is also able to explain irreversible and competitive product inhibition kinetics. It allows the axial substrate profiles to be calculated and the dependence of the effectiveness factor along the reactor length to be continuously evaluated. The design equation was applied to explain the behavior of naringinase immobilized in Glycophase-coated porous glass operating in a packed-bed reactor and hydrolyzing both p-nitrophenyl-alpha-L-rhamnoside and naringin. The theoretically predicted results were found to fit well with experimentally measured values.     

A model for growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media

A major problem in the use of plasmids as recombinant vectors is the problem of plasmid-free cell generation from plasmid shedding and subsequent growth. A common technique for controlling the population of plasmidfree cells is the use of selective media against these cells using an auxotrophic host and a plasmid that has the ability to produced the essential metabolite. A distributed model describing the growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media was developed. The model allows for growth and production of a metabolite by the plasmid-carrying strain and growth of the plasmid-free cells on resulting metabolite concentrations. Through a determination of system constants and numerical solution to the equations, experimental batch and continuous culture results for cell concentration transients could be simulated by the model. The results indicated that despite selective pressure, plasmid-free cell growth was significant.     

Modeling bisubstrate removal by biofilms

A bisubstrate secondary utilization model is based on the concept that an individual substrate can be utilized not only by the biomass by its utilization but also by the biomass made from the utilization of the other substrate. When substrate concentrations are low, a key factor is having sufficient substrate to initiate biofilm growth. Modeling results for three characteristic cases demonstrate that satisfying a total S(min) concentration for a bisubstrate system is the necessary condition for initiating biofilm growth and simultaneous utilization of both substrates. Because having more than one substrate supporting biofilm growth enhances the removal of each compound, the utilization rate of a specific compound can be increased by the concentration of other compounds, and the total S(min) concentration can be less than the weighted average of individual S(min) values.