Production of indole alkaloids by selected hairy root lines of Catharanthus roseus

Hairy root cultures of Catharanthus roseus were established by infection of seedlings with Agrobacterium rhizogenes 15834. Approximately 150 transformants from four different. C. roseus cultivars were screened for desirable traits in growth and indole alkaloid production. Five hairy root clones grew well in liquid culture with doubling times similar to those reported for cell suspensions. Fast growing clones had similar morphologies, characterized by thin, straight, and regular branches with thin tips. The levels of key alkaloids, ajmalicine, serpentine, and catharanthine, in these five clones, also compared well with literature data from cell suspensions, yet HPLC and GC-MS data indicate the presence of vindoline in two clones at levels over three orders of magnitude greater than the minute amounts reported in cell culture. These results suggest that further optimization may result in hairy roots as a potential source of vindoline and catharanthine, the two monomers necessary to synthesize that antineoplastic drug, vinblastine.

Elucidation of the cytoplasmic and vacuolar components in the inorganic phosphate region in the 31P NMR spectrum of yeast

Subcellular compartments, such as the vacuole in yeast, play important roles in cell metabolism and in cell response to external conditions. Concentrations of inorganic phosphate and pH values of the vacuole and cytoplasm were determined for anaerobic Saccharomyces cerevisiae cells based upon (31)P NMR spectroscopy. A new approach allows the determination of these values for the vacuole in cases when the resonance for inorganic phosphate in the cytoplasm overlaps with the resonance for inorganic phosphate in the vacuole. The intracellular inorganic phosphate resonance was first decomposed into two components by computer analysis. The assignments of the components were determined from in vivo correlations of P(i) chemical shift and the chemical shifts of the cytoplasmic sugar phosphates, and the pH dependency of the resonance of pyrophosphate and the terminal phosphate of poly-phosphate (PP(1)) which reside in the vacuole. An in vivo correlation relating PP(1) and P(i) (vac) chemical shifts was established from numerous evaluations of intracellular compositions for several strains of S. cerevisiae. This correlation will aid future analysis of (31)P NMR spectra of yeast and will extend NMR studies of compartmentation to cellular suspensions in phosphate-containing medium. Application of this method shows that both vacuolar and extracellular P(i) were phosphate reserves during glycolysis in anaerobic S. cerevisiae. Net transport of inorganic phosphate across the vacuolar membrane was not correlated with the pH gradient across the membrane.

Estimation of intracellular sugar phosphate concentrations in Saccharomyces cerevisiae using 31P nuclear magnetic resonance spectroscopy

A systematic procedure has been formulated for estimating the relative intracellular concentrations of sugar phosphates in Saccharomyces cerevisiae based upon (31)P nuclear magnetic resonance (NMR) measurements. The sugar phosphate region of the (31)P NMR spectrum is first decomposed by computer analysis, and the decomposition consistency and identification of individual sugar phosphate resonances are established based on in vitro chemical shift calibrations determined in separate experiments. Numerous evaluations of intracellular S. cerevisiae compositions for different strains and different cell environments provide the basis for in vivocorrelations of inorganic phosphate chemical shift with the chemical shifts of 3-phosphoglycerate, beta;-fructose 1,6-diphosphate, fructose 6-phosphate, and glucose 6 phosphate. Relative intracellular sugar phosphate concentrations are obtained by correcting peak areas for partial saturation during transient in vivo experiments. In vivo concentrations estimated by this method agree well with estimates for similar systems based on other techniques. This approach does not require costly la belled compounds, and has the advantage that other important metabolic state variables such-as internal and external pH and intracellular levels of phosphate, ATP, ADP, NAD(H), and polyphosphate may be determined from the same (31)P spectrum. Extension of this strategy to other cellular systems should be straightforward.

Studies on plant-mediated fate of the explosives RDX and HMX

The fate of the explosives RDX and HMX on exposure to plants was investigated in 'natural' aquatic systems of Myriophyllum aquaticum for 16 days, and in axenic hairy root cultures of Catharanthus roseus for > or = 9 weeks. Exposure levels were: HMX, 5 mg/l; and RDX, approximately 8 mg/l. Exposure outcomes observed include: HMX, no transformation by aquatic plants, and minimal biological activity by axenic roots; and RDX, removal by both plant systems. In the case of RDX exposure to axenic roots, since 14C-RDX was included, removal was confirmed by the accumulation of 14C-label in the biomass. The intracellular 14C-label in these RDX studies was detected in two forms: intact RDX and bound unknown(s).

In situ NMR systems

In situ NMR is becoming an established technology for applications in bioprocessing and metabolic engineering. The in situ NMR biosensor acts as a noninvasive pH, ion, and concentration meter, with 31P and 13C as the two main isotopes of study. A substantial data base now exists for phosphorus and carbon spectra of bacteria and yeast. In situ NMR can provide many of the state variables needed for modeling glycolytic pathway function. NMR micro-reactor technology has improved significantly in the last decade. Several designs for immobilized cell reactors have been tested, and in particular, considerable gains have been made in the feasibility of studying aerobic, chemostat cultures with in situ NMR. Acquisition of 31P spectra from cell suspensions of 3-5% v/v under controlled conditions can be made in 3-7 minute time resolution in several systems.

Determination of metabolic rate-limitations by precursor feeding in Catharanthus roseus hairy root cultures

Precursors from the terpenoid and tryptophan branches were fed to Catharanthus roseus to determine which of the two branches limits metabolic flux to indole alkaloids. The feeding of tryptophan at 17 days of the culture cycle produced auxin-like effects. Addition of low levels of auxin or tryptophan resulted in significant increases in flux to the indole alkaloids. Conversely, feeding higher levels of auxin or tryptophan resulted in increased branching and thickening of the hairy root cultures. A dramatic reduction in flux to the alkaloids was also observed. However, feeding tryptamine or terpenoid precursors had no effect. Therefore, neither pathway tested revealed to be rate-limiting during the late growth phase. Feeding of either geraniol, 10-hydroxygeraniol, or loganin at 21 days each resulted in significant increases in the accumulation of tabersonine. The addition of tryptophan or tryptamine had no effect during the stationary phase of the growth cycle. Thus, during the early stationary phase of growth the terpenoid pathway appears to be rate-limiting. Combined elicitation with jasmonic acid and feeding either loganin or tryptamine did not further enhance the accumulation of indole alkaloids.

Effects of buffered media upon growth and alkaloid production of Catharanthus roseus hairy roots

The influence of buffered media upon the growth and alkaloid productivity of Catharanthus roseus hairy root culture was examined. As expected, the buffers minimized shifts in the pH of the media and had slightly negative effects upon growth. The growth of the hairy roots remained optimal in unbuffered media. The specific yield of lochnericine was significantly lower in response to the addition of buffers, while tabersonine was significantly higher. In contrast, the specific yields of ajmalicine, serpentine, and horhammericine remained unchanged.

Inhibitor studies of tabersonine metabolism in C. roseus hairy roots

The conversion of tabersonine to lochnericine and hörhammericine was investigated in C. roseus hairy root cultures. The accumulation of lochnericine and hörhammericine, like tabersonine, was associated with growth. Through the use of oxygenase inhibitors, 1-aminobenzotriazole (ABT), clotrimazole (CLOT), and 2.5-pyridinedicarboxylic acid (PCA), details of the metabolic pathway around tabersonine in hairy roots of C. roseus were elucidated. ABT specifically inhibited the formation of hörhammericine, while CLOT inhibited the accumulation of lochnericine. Using jasmonic acid in combination with the inhibitors suggests an inducible P-450 enzyme responsible for the formation of hörhammericine. The inhibitor study also revealed that both lochnericine and hörhammericine are 'turned over' in hairy root cultures.

Plant 'hairy root' culture

Due to their fast growth rates and biochemical stability, 'hairy root' cultures remain unsurpassed as the choice for model root systems and have promise as a bioprocessing system. Applications are wide-ranging, from the production of natural products and foreign proteins to a model for phytoremediation of organic and metal contaminants. Hairy roots will have a continuing role as an experimental model in plant metabolic engineering.

In vivo 31P and multilabel 13C NMR measurements for evaluation of plant metabolic pathways

Reliable measurements of intracellular metabolites are useful for effective plant metabolic engineering. This study explored the application of in situ 31P and 13C NMR spectroscopy for long-term measurements of intracellular pH and concentrations of several metabolites in glycolysis, glucan synthesis, and central carbon metabolic pathways in plant tissues. An NMR perfusion reactor system was designed to allow Catharanthus roseus hairy root cultures to grow for 3-6 weeks, during which time NMR spectroscopy was performed. Constant cytoplasmic pH (7.40+/-0.06), observed during the entire experiment, indicated adequate oxygenation. 13C NMR spectroscopy was performed on hairy root cultures grown in solutions containing 1-13C-, 2-13C-, and 3-13C-labeled glucose in separate experiments and the flow of label was monitored. Activities of pentose phosphate pathways, nonphotosynthetic CO2 fixation, and glucan synthesis pathways were evident from the experimental results. Scrambling of label in glucans also indicated recycling of triose phosphate and their subsequent conversion to hexose phosphates.

Transient studies of light-adapted cultures of hairy roots of Catharanthus roseus: growth and indole alkaloid accumulation

Cultures of C. roseus transgenic ("hairy") root clones LBE-6-1 and LBE-4-2 were adapted with periodic daily illumination to investigate the effect of light on growth and nutrient utilization, and the accumulation of the indole alkaloids. Light-adapted roots appeared green and had radially thickened morphology compared with dark-grown controls. Their growth rates were higher than dark-grown controls, with 45% lower doubling times: LBE-6-1, 3.6 days; LBE-4-2, 2.8 days. Relative to dark-grown controls, light-adapted growth increased the biomass (DW) of LBE-6-1 by 25%, but had no effect on the DW of LBE-4-2. The macronutrients NH4+, NO3-, Pi, and sugars, were depleted completely by light-adapted root cultures in that order. The specific and total levels of the indole alkaloid serpentine was enhanced and of tabersonine was lowered in both root clones, while the overall trends of growth and non-growth association of tabersonine and serpentine, respectively, remained unaltered by light adaptation. Ajmalicine accumulation was enhanced in LBE-6-1, but lowered in LBE-4-2; its accumulation was growth-associated in dark-grown LBE-6-1, but appeared non-growth associated in light-adapted cultures. The accumulation of tabersonine-related compounds, lochnericine, and hörhammericine exhibited growth-associated trends, and were either negatively affected or unaffected by light adaptation of LBE-6-1. Neither vindoline nor its precursor, deacetylvindoline, was detected.

Effect of elicitor dosage and exposure time on biosynthesis of indole alkaloids by Catharanthus roseus hairy root cultures

Late exponential phase hairy root cultures of Catharanthus roseus were elicited with pectinase and jasmonic acid. The effects of elicitor concentration and exposure time on growth and levels of several compounds in the indole alkaloid biosynthetic pathway were monitored. Pectinase decreased the fresh weight to dry weight ratio of the roots, while addition of jasmonic acid had no significant effect. Selective effects on indole alkaloid yields were observed upon addition of elicitors. An increase of 150% in tabersonine specific yield was observed upon addition of 72 units of pectinase. Transient studies at the same level demonstrated possible catabolism as serpentine, tabersonine, and lochnericine levels decreased immediately after elicitation. The levels of these compounds recovered back to control levels or were higher than the control levels after some time. Jasmonic acid was found to be a unique elicitor leading to an enhancement in flux to several branches in the indole alkaloid pathway. Jasmonic acid addition caused an increase in the specific yields of ajmalicine (80%), serpentine (60%), lochnericine (150%), and hörhammericine (500%) in dosage studies. Tabersonine, the likely precursor of lochnericine and hörhammericine, decreased at lower levels of jasmonic acid and then increased with increasing jasmonic acid concentration. Transient studies showed that lochnericine and tabersonine levels go through a maxima, then decrease back to control levels and reduce below control levels, respectively. The yields of ajmalicine, serpentine, and hörhammericine increased continuously after the addition of jasmonic acid. The methods described in this article could generally be used in devising strategies for enhancement in productivity of secondary metabolites and for probing and studying the complex secondary metabolite pathways in plant tissue cultures.

Quantification of metabolites in the indole alkaloid pathways of catharanthus roseus: implications for metabolic engineering

In this article, we present a review of the current state of metabolic engineering in Catharanthus roseus. A significant amount of research has contributed to characterization of several individual steps in the biosynthetic pathway of medicinally valuable alkaloids. However, knowledge of the regulation of these pathways is still sparse. Using hairy root cultures, we studied the responses of alkaloid metabolism to environmental stimulation such as light and elicitation. Through precursor feeding studies, the putative rate-limiting steps of the terpenoid pathway in hairy root cultures also have been examined. Relating this knowledge to specific events at the molecular level, and the cloning of corresponding genes are the next key steps in metabolic engineering of the C. roseus alkaloids. Copyright 1998 John Wiley & Sons, Inc.

Quantification of metabolites in the indole alkaloid pathways of catharanthus roseus: implications for metabolic engineering

In this article, we present a review of the current state of metabolic engineering in Catharanthus roseus. A significant amount of research has contributed to characterization of several individual steps in the biosynthetic pathway of medicinally valuable alkaloids. However, knowledge of the regulation of these pathways is still sparse. Using hairy root cultures, we studied the responses of alkaloid metabolism to environmental stimulation such as light and elicitation. Through precursor feeding studies, the putative rate-limiting steps of the terpenoid pathway in hairy root cultures also have been examined. Relating this knowledge to specific events at the molecular level, and the cloning of corresponding genes are the next key steps in metabolic engineering of the C. roseus alkaloids. Copyright 1998 John Wiley & Sons, Inc.

Influence of aeration on cytoplasmic pH of yeast in an NMR airlift bioreactor

Nuclear magnetic resonance spectroscopy has been increasingly pursued as a tool for noninvasive, real-time studies of metabolic processes of cell suspension in bioreactors. One acute challenge in NMR bioreactor design has been supplying enough oxygen for cell respiration in a suspension that contains sufficient cells for NMR signal detection. The use of cytoplasmic pH as an intracellular marker of adequate oxygenation was evaluated from 31P NMR spectra of the yeast Saccharomyces cerevisiae at several cell densities, ranging from low (0.9% (v/v)) to very high (45% (v/v)) cell densities, in an airlift bioreactor. 31P NMR spectra were obtained for derepressed yeast cells prior to, and during, glycolysis under nongrowth conditions. During endogenous respiration, pHcyt can be used as an intracellular marker for aeration for cell densities up to 18% (v/v) based on two criteria: a value of pHcyt at least 0.2 pH units higher under aerobic than anaerobic conditions and an absolute pHcyt value of 7.1-7.2. These results were more conservative than values of the maximum cell density obtained from calculations using kLa and respiration rate estimates and highlight the utility of intracellular measurements in conjunction with engineering design calculations. During glycolysis, pHcyt values were similar under aerobic and anaerobic conditions and hence pHcyt cannot be used as a marker under these conditions. Carbon dioxide in the influent gas was observed to aid cells in maintaining physiological pHcyt at high cell densities.