The effect of drought on levels of abscisic acid,cytokinins, gibberellins and ethylene in aeroponically-grown sunflower plants

Abscisic acid (ABA), cytokinins and gibberellin-like substances (GAs) were extracted from the roots and shoots of 17-day-old sunflower seedlings which had been droughted or were unstressed. Plants were grown in an aeroponic chamber which allowed for good control over degree of water stress and easy access to roots. Following methanolic extraction of lyophilized material, cytokinins were separated from the acidic growth-regulators on a cellulose PO₄ cationic exchange column. The cytokinins were analysed by paper chromatography and HPLC and the soybean hypocotyl section assay. Semipurified acidic regulators were chromatographed on SiO₂ columns and HPLC and aliquots assayed with the dwarf rice cv. Tan-ginbozu bioassay for GAs. Fractions known to contain ABA were purified by sequential reverse-phase HPLC of the acid and then of the methyl ester forms followed by quantitation as Me-ABA on GLC-EC. ABA losses were measured by using an internal standard [³H]-ABA). Ethylene production was also monitored in stressed and unstressed seedlings.The effect of drought on GAs and ethylene was minimal. The ABA levels were markedly higher in droughted plants. Stressed roots had 32 times more ABA than controls. The levels of cytokinins in the shoots of droughted plants were about half those in unstressed shoots, and qualitative differences occurred in the roots. Under stress a large peak of activity was present similar to zeatin glucoside which was not present in the unstressed condition. The results are discussed in relation to drought-effects on metabolism.     

Secondary metabolism of hairy root cultures in bioreactors

Summary In vitro cultures are being considered as an alternative to agricultural processes for producing valuable secondary metabolites. Most efforts that use differentiated cultures instead of cell suspension cultures have focused on transformed (hairy) roots. Bioreactors used to culture hairy roots can be roughly divided into three types: liquid-phase, gas-phase, or hybrid reactors that are a combination of both. The growth and productivity of hairy root cultures are reviewed with an emphasis on successful bioreactors and important culture considerations. The latter include strain selection, production of product in relation to growth phase, media composition, the gas regime, use of elicitors, the role of light, and apparent product loss. Together with genetic engineering and process optimization, proper reactor design plays a key role in the development of successful large scale production of secondary metabolites from plant cultures.     

One-step acclimatization of plantlets using a mist reactor

A mist reactor was used to grow and acclimatize carnation plants in vitro without using ex vitro acclimatization techniques. The acclimatization protocol in the reactor consisted of altering the mist-on period during the course of the culture period and a stepwise reduction in the relative humidity surrounding the plants from 98% to 70% relative humidity (RH) during the final week of in vitro growth. After transfer and further growth in a greenhouse for 5 weeks, survival was 91% for plants grown in reactors, 81% from vented boxes, and 50% from unvented boxes. Ex vitro survival directly correlated with increased in vitro rooting and decreased hyperhydration. In vitro rooting also correlated with high-quality plants, but did not significantly correlate with low hyperhydration, as normal plants often lacked roots. After 5 weeks in the greenhouse, the quantity of mid- and high-quality plants obtained from reactors and ventilated boxes was similar. Conditions in the mist reactor can be manipulated to produce plants that are readily acclimatized and are equal or better in quality and yield than plants produced using conventional methods.     

Using an aerosol deposition model to increase hairy root growth in a mist reactor

Gas-phase reactors, including the mist reactor, have distinct advantages over liquid-phase reactors including the ability to manipulate the gas composition, to allow effective gas exchange in a densely growing biomass, and to affect secondary metabolite production. Mathematical modeling suggested that roots in a mist reactor are often too sparsely packed to capture mist particles efficiently and cannot, therefore, meet the nutrient demands required to maintain high growth rates. Indeed, growth rates of Artemisia annua hairy roots increased significantly when the initial packing density increased or when a higher sucrose concentration was used in the medium. Growth kinetics for 2, 4, and 6 days, however, showed a decrease or stationary growth rate after only 4 days for both 3 and 5% sucrose feeds. Residual medium analyses indicated that carbon was not exhausted, nor were any of the other major nutrients including phosphate. Increasing the mist duty cycle at constant carbon flux through the reactor reduced the growth rates slightly. In general, the aerosol deposition model correctly predicted how to optimize hairy root growth in the mist reactor.     

Measurement of short-term nutrient uptake rates in cranberry by aeroponics

Aeroponics, a soil-less plant culture system in which fresh nutrient solutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time while maintaining a constantly refreshed nutrient solution. Although used relatively extensively in commercial installations and in root physiology research, use of aeroponics in nutrient studies is rare. The object of this study was to examine whether nutrient uptake rates could be calculated for aeroponic systems by difference using measurements of concentrations and volumes of input and efflux solutions. Data were collected from an experiment with cranberry plants (Vaccinium macrocarpon Ait. cv. Stevens) cultured aeroponically with nutrient solutions containing various concentrations of ammonium-N and isotopically labelled nitrate-N. Validation of the calculated uptake rates was sought by: (1) evaluating charge balance of the solutions and total ion uptake (including proton efflux) and (2) comparison with N-isotope measurements. Charge balance and proton efflux calculations required use of chemical modelling of the solutions to determine speciation of dissolved phosphate and acid-neutralizing capacity (ANC). The results show that charge balance requirements were acceptably satisfied for individual solution analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference were in agreement with those determined by isotopic techniques. Additional information was easily obtained from this experimental technique, including evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Use of aeroponic systems for non-destructive measurement of water and ion uptake rates for numerous other species and nutrients appears promising.     

Culture of amebocytes in a nutrient mist bioreactor

Summary We report the first use of nutrient mist bioreactor (NMB) technology to culture animal cells. The nutrient mist approximated the amebocyte stem tissue’s natural environment, which is a thin layer of fluid in the gill leaflets of the horseshoe crabLimulus polyphemus. NMB culture was tried in an attempt to increase production of amebocytes, which are the source of theLimulus Amebocyte Lysate (LAL), the basis for a sensitive and commercially valuable endotoxin assay. Amebocyte growth in the nutrient mist bioreactor is comparable to growth in liquid medium. However, the current design of the bioreactor presents problems for primary cultures such as ours where a pyrogen-free environment is necessary and fungal decontamination is difficult.     

番茄基质通气栽培模式的效果

针对雾培模式在提高作物产量同时增加无土栽培成本的问题,研制了一种新型的珍珠岩通气栽培模式,探讨了其对番茄的栽培效果.试验设计3种栽培方式:全珍珠岩栽培(CK),珍珠岩通气栽培(T1)和气雾培(T2).结果表明:T1可显著改善番茄根际通气环境,其中根际CO2浓度仅为CK的1/5,O2浓度则为CK的1.17倍;显著增加了番茄的株高和茎粗,在定植后60d时,株高和茎粗分别比CK增加了5.1%和8.4%;植株净光合速率显著高于CK,在净光合速率达到最大值(定植后45d)时,比CK提高了13%;显著提高了植株根系活力和吸收能力,在定植后45d时,其根系活力为CK的1.23倍,在定植后60d时,根系钾、钙、镁含量分别比CK增加了31%、37%和27%,番茄产量为CK的1.16倍.且T1上述指标均与T2无显著差异;而CK、T1和T2在果实的可溶性糖、有机酸、糖酸比方面无显著差异.表明以珍珠岩为基质的通气栽培模式简便易行且可显著提高番茄产量.     

Regeneration of plants using nutrient mist culture

Summary A nutrient mist was used forin vitro culture of plant tissue in a novel bioreactor, wherein the tissues were grown on a biologically inert screen within a sterile chamber which allows excess media to drain away from the tissue. Plants tested includedDaucus, Lycopersicon, Ficus, Cinchona, andBrassica. The latter 4 genera were fully regenerated within the bioreactor. Tissue inocula included callus, anthers, and shoot meristems. All plants grew at least as well in nutrient mists as in agar and always produced a greater quantity of shoots of a higher quality and often faster than agar cultures. Cost analysis estimates showed up to a 65% savings in production costs (labor and materials) could be realized using nutrient mist culture. Nutrient mist culture offers significant improvements in the micropropagation of plants.     

Allometric relationships in young seedlings of faba bean (Vicia faba L.) following removal of certain root types

Sink-source relationships and allometric ratios were studied in young seedlings of faba bean (Vicia faba L.) following pruning of some root types. The plants were grown in an aeroponic system allowing an easy access to each part of the root system, throughout the experiment, without disturbing the others. Root, leaf and stem growth as well as their mineral content were determined in one group of undisturbed plants (CTRL) and in four groups of plants treated as follows: TAP – the distal-free portion of the taproot was removed; HALF – half the laterals were removed; ALL – all lateral roots were removed, and TAP+HALF – both the distal part of the taproot and half of the laterals were removed. Removal of all the lateral roots (ALL) induced the development of a longer taproot but severely arrested shoot growth. Phosphorus, potassium and calcium contents were lower in the plants of the ALL treatment. However, the content of Mg was practically unaffected. The effect of the HALF treatment was hardly noticeable but the effects of TAP+HALF treatment were cumulative. The allometric relationships between the surface area of the roots and that of the leaves were restored within the experimental period, apparently due to reduction in shoot growth. Removal of the distal parts of the taproot did not cause an increase in shoot growth. This indicates that the strength of the sinks (mostly of lateral roots) rather than that of the source determines these relationships.     

Novel temporal, fine-scale and growth variation phenotypes in roots of adult-stage maize (Zea mays L.) in response to low nitrogen stress

There is interest in discovering root traits associated with acclimation to nutrient stress. Large root systems, such as in adult maize, have proven difficult to be phenotyped comprehensively and over time, causing target traits to be missed. These challenges were overcome here using aeroponics, a system where roots grow in the air misted with a nutrient solution. Applying an agriculturally relevant degree of low nitrogen (LN) stress, 30-day-old plants responded by increasing lengths of individual crown roots (CRs) by 63%, compensated by a 40% decline in CR number. LN increased the CR elongation rate rather than lengthening the duration of CR growth. Only younger CR were significantly responsive to LN stress, a novel finding. LN shifted the root system architectural balance, increasing the lateral root (LR)-to-CR ratio, adding ～70 m to LR length. LN caused a dramatic increase in second-order LR density, not previously reported in adult maize. Despite the near-uniform aeroponics environment, LN induced increased variation in the relative lengths of opposing LR pairs. Large-scale analysis of root hairs (RHs) showed that LN decreased RH length and density. Time-course experiments suggested the RH responses may be indirect consequences of decreased biomass/demand under LN. These results identify novel root traits for genetic dissection.