Hydroponic Growth System Research Articles

Expression of Arabidopsis thaliana Thioredoxin-h2 in Brassica napus enhances antioxidant defenses and improves salt tolerance

Salt stress limits crop productivity worldwide, particularly in arid and heavily irrigated regions. Salt stress causes oxidative stress, in which plant cells accumulate harmful levels of reactive oxygen species (ROS). Thioredoxins (Trxs; EC 1.8.4.8) are antioxidant proteins encoded by a ubiquitous multigene family. Arabidopsis thaliana Trx h-type proteins localize in the cytoplasm and other subcellular organelles, and function in plant responses to abiotic stresses and pathogen attack. Here, we isolated the Arabidopsis genes encoding two cytosolic h-type Trx proteins, AtTrx-h2 and AtTrx-h3 and generated transgenic oilseed rape (Brassica napus) plants overexpressing AtTrx-h2 or AtTrx-h3. Heterologous expression of AtTrx-h2 in B. napus conferred salt tolerance with plants grown on 50 mM NaCl having higher fresh weight and chlorophyll contents compared with controls in hydroponic growth system. By contrast, expression of AtTrx-h3 or the empty vector control did not improve salt tolerance. In addition, AtTrx-h2-overexpressing transgenic plants exhibited lower levels of hydrogen peroxide and higher activities of antioxidant enzymes including peroxidase, catalase, and superoxide dismutase, compared with the plants expressing the empty vector control or AtTrx-h3. These results suggest that AtTrx-h2 is a promising candidate for engineering or breeding crops with enhanced salt stress tolerance.

A Flexible Low Cost Hydroponic System for Assessing Plant Responses to Small Molecules in Sterile Conditions.

A wide range of studies in plant biology are performed using hydroponic cultures. In this work, an in vitro hydroponic growth system designed for assessing plant responses to chemicals and other substances of interest is presented. This system is highly efficient in obtaining homogeneous and healthy seedlings of the C3 and C4 model species Arabidopsis thaliana and Setaria viridis, respectively. The sterile cultivation avoids algae and microorganism contamination, which are known limiting factors for plant normal growth and development in hydroponics. In addition, this system is scalable, enabling the harvest of plant material on a large scale with minor mechanical damage, as well as the harvest of individual parts of a plant if desired. A detailed protocol demonstrating that this system has an easy and low-cost assembly, as it uses pipette racks as the main platform for growing plants, is provided. The feasibility of this system was validated using Arabidopsis seedlings to assess the effect of the drug AZD-8055, a chemical inhibitor of the target of rapamycin (TOR) kinase. TOR inhibition was efficiently detected as early as 30 min after an AZD-8055 treatment in roots and shoots. Furthermore, AZD-8055-treated plants displayed the expected starch-excess phenotype. We proposed this hydroponic system as an ideal method for plant researchers aiming to monitor the action of plant inducers or inhibitors, as well as to assess metabolic fluxes using isotope-labeling compounds which, in general, requires the use of expensive reagents.

Novel bioprocess for the cultivation of microalgae in hydroponic growing system of tomato plants

Hydroponic growing systems and the application of natural biostimulant substances are becoming very attractive option for crop cultivation due to their economic relevance since they allow reduction in the use of fertilizer and increase the yield. In order to perform a hydroponic co-cultivation system of microalgae (Chlorella vulgaris or Scenedesmus quadricauda) and tomato plants, grown in Hoagland nutrient solution, their mutual effect and the influence of a natural biostimulant obtained by alkaline extraction from a digestate of agro-livestock residues (DHL) were evaluated. The results showed that the co-cultivation system positively affected the growth of both tomato plants and microalgae. The best option, aimed to a mutual benefit for both cultures, resulted to be the co-cultivation system of tomato plants and S. quadricauda in the presence of DHL, positively affecting the growth of tomato plants along with a great increase in microalgal biomass.

A New Suite of Plasmid Vectors for Fluorescence-Based Imaging of Root Colonizing Pseudomonads.

In the terrestrial ecosystem, plant–microbe symbiotic associations are ecologically and economically important processes. To better understand these associations at structural and functional levels, different molecular and biochemical tools are applied. In this study, we have constructed a suite of vectors that incorporates several new elements into the rhizosphere stable, broad-host vector pME6031. The new vectors are useful for studies requiring multi-color tagging and visualization of plant-associated, Gram-negative bacterial strains such as Pseudomonas plant growth promotion and biocontrol strains. A number of genetic elements, including constitutive promoters and signal peptides that target secretion to the periplasm, have been evaluated. Several next generation fluorescent proteins, namely mTurquoise2, mNeonGreen, mRuby2, DsRed-Express2 and E2-Crimson have been incorporated into the vectors for whole cell labeling or protein tagging. Secretion of mTurquoise2 and mNeonGreen into the periplasm of Pseudomonas fluorescens SBW25 has also been demonstrated, providing a vehicle for tagging proteins in the periplasmic compartment. A higher copy number version of select plasmids has been produced by introduction of a previously described repA mutation, affording an increase in protein expression levels. The utility of these plasmids for fluorescence-based imaging is demonstrated by root colonization of Solanum lycopersicum seedlings by P. fluorescens SBW25 in a hydroponic growth system. The plasmids are stably maintained during root colonization in the absence of selective pressure for more than 2 weeks.

Cyanobacterial Catalase Activity Prevents Oxidative Stress Induced by Pseudomonas fluorescens DUS1-27 from Inhibiting Brassica napus L. (canola) Growth.

Plant growth-promoting bacteria (PGPB) inhabit the rhizosphere of plants and are capable of enhancing plant growth through a number of mechanisms. A strain of Pseudomonas fluorescens DUS1-27 was identified as a potential PGPB candidate based on its ability to increase the growth of Brassica napus L. (canola) over that of uninoculated control plants in a soil-based system. The same P. fluorescens isolate was found to reduce plant growth in a hydroponic growth system, with plants showing the symptoms of a microbe-associated molecular pattern (MAMP) response to the bacteria. The amperometric quantification of H2O2, fluorescence-based total peroxidase assays, and quantification of catalase gene expression levels using qRT-PCR revealed that oxidative stress reduced plant growth in the hydroponic system. The addition of the cyanobacterium Nostoc punctiforme (known to have high catalase activity levels) in the hydroponic system as a co-inoculant reduced oxidative stress (49.7% decrease in H2O2 concentrations) triggered by the addition of P. fluorescens DUS1-27, thereby enabling plants to grow larger than uninoculated control plants. These results show the advantage of inoculating with multiple bacteria to promote plant growth and, for the first time, demonstrate that N. punctiforme beneficially assists plants under oxidative stress through its catalase activity in planta.

Assessment of Electricity-Free Hydroponics in India: A Proof of Concept Field Study

Subsistence and smallholder farmers in the Deccan plateau region of India struggle with a predominantly hot and dry climate and often accumulated debt due to the cost of fertilizer that they need to increase yields for profitability. While a low-cost deep-flow technique hydroponic growing system (DFT) as a supplement to soil-based agriculture could help reduce debt, the cost of electricity needed to operate the DFT makes it inaccessible to these farmers. The objective of this project was to test the viability of electricity-free DFT which would substantially reduce production costs. Two DFT systems were set up in a shade net house and prepared with identical nutrients to grow chili pepper seedlings. Each DFT system was oxygenated for 30 minutes per day, one system using an electrical air pump, and the other system was oxygenated manually. After four weeks of growth, the dry mass of the shoots of the chili pepper seedlings in each system was measured. While the pump-oxygenated DFT system produced more dry matter, the manually-oxygenated system produced a larger number of visually healthier plants. Therefore, we conclude that electricity-free DFT hydroponics may be a viable alternative to pump-oxygenated DFT hydroponics, making hydroponic farming a cost-effective option for poor farmers.

Microbial Effects on the Production of Aquaponically Grown Lettuce

In the study of aquaponics, questions have risen concerning the role of microbiota upon plant growth. This experiment compared unaltered aquaponic nutrient solution at pH 7.0 (treatment A7) with sterilized aquaponic nutrient solution at pH 7.0 (treatment SA7) to quantify effects that live microorganisms had on the growth of lettuce (Lactuca sativa). Baseline comparisons were made to conventional hydroponic conditions using inorganic nutrients at pH 5.8 (treatment H5) or pH 7.0 (treatment H7), which showed a 51% reduction in lettuce fresh weight (FW) growth, indicating a strong negative effect of the higher pH nutrient solution; a similar large difference (38%) occurred for dry weight (DW) comparisons between these two treatments. No difference occurred between the sterilized aquaponic treatment (SA7) and H5 in FW or DW. H5 produced more FW and DW than the non-sterile aquaponic treatment (A7). Responses were not different in FW and DW between the two aquaponic conditions. Reduced FW and DW of A7 compared to H5 may be related to the 50 times higher microbial community living in the A7 treatment water than in H5 at the beginning of each trial. Given that the sterile aquaponic solution SA7 and the H5 hydroponic condition were not different in performance, we concluded that the beneficial effects of the microbial community in the fish recirculating aquaculture system (RAS) occurred before the water was sterilized. An interesting implication of our findings is that an RAS can be decoupled from the hydroponic growing system, since its benefits are not dependent upon continuous recirculation between the plant and fish system and its living biotic community.

Internalization and dissemination of human norovirus and Tulane virus in fresh produce is plant dependent

Human norovirus (NoV) is a leading cause of fresh produce associated outbreaks. Previous research indicates that the roots of growing leafy greens and berries internalize human NoV. However the effect of plant type and inoculum level on internalization rates has not been directly compared. In this study we compared the internalization and dissemination rates of human NoV and its surrogate, Tulane virus (TV) in green onion, radishes, and Romaine lettuce. We also evaluated the effect inoculum level and plant growth matrix on the rate of viral internalization. In the hydroponic growth system, we detected internalization and dissemination of human NoV RNA in green onions. In hydroponically growing green onions inoculated with high titer TV, we found higher rates of internalization and dissemination compared to green onions inoculated with low titer TV. In soil growth systems, no infectious TV was detected in either green onion or radishes. However, in Romaine lettuce plants grown in soil approximately 4 log10 PFU/g was recovered from all tissues on day 14 p.i. Overall, we found that the type of plant, growth matrix, and the inoculum level influences the internalization and dissemination of human NoV and TV.

Morpho-physiological analysis of tolerance to aluminum toxicity in rice varieties of North East India.

Aluminum (Al) is the third most abundant metal in earth crust, whose chemical form is mainly dependent on soil pH. The most toxic form of Al with respect to plants is Al3+, which exists in soil pH <5. Acidic soil significantly limits crop production mainly due to Al3+ toxicity worldwide, impacting approximately 50% of the world’s arable land (in North-Eastern India 80% soil are acidic). Al3+ toxicity in plants ensues root growth inhibition leading to less nutrient and water uptake impacting crop productivity as a whole. Rice is one of the chief grains which constitutes the staple food of two-third of the world population including India and is not untouched by Al3+ toxicity. Al contamination is a critical constraint to plant production in agricultural soils of North East India. 24 indigenous Indica rice varieties (including Badshahbhog as tolerant check and Mashuri as sensitive check) were screened for Al stress tolerance in hydroponic plant growth system. Results show marked difference in growth parameters (relative growth rate, Root tolerance index, fresh and dry weight of root) of rice seedlings due to Al (100 μM) toxicity. Al3+ uptake and lipid peroxidation level also increased concomitantly under Al treatment. Histochemical assay were also performed to elucidate uptake of aluminum, loss of membrane integrity and lipid peroxidation, which were found to be more in sensitive genotypes at higher Al concentration. This study revealed that aluminum toxicity is a serious harmful problem for rice crop productivity in acid soil. Based on various parameters studied it’s concluded that Disang is a comparatively tolerant variety whereas Joymati a sensitive variety. Western blot hybridization further strengthened the claim, as it demonstrated more accumulation of Glutathione reductase (GR) protein in Disang rice variety than Joymati under stressed condition. This study also observed that the emergence of lethal toxic symptoms occurs only after 48h irrespective of the dose used in the study.

Hydroponics: A Versatile System to Study Nutrient Allocation and Plant Responses to Nutrient Availability and Exposure to Toxic Elements.

Hydroponic systems have been utilized as one of the standard methods for plant biology research and are also used in commercial production for several crops, including lettuce and tomato. Within the plant research community, numerous hydroponic systems have been designed to study plant responses to biotic and abiotic stresses. Here we present a hydroponic protocol that can be easily implemented in laboratories interested in pursuing studies on plant mineral nutrition.This protocol describes the hydroponic system set up in detail and the preparation of plant material for successful experiments. Most of the materials described in this protocol can be found outside scientific supply companies, making the set up for hydroponic experiments less expensive and convenient.The use of a hydroponic growth system is most advantageous in situations where the nutrient media need to be well controlled and when intact roots need to be harvested for downstream applications. We also demonstrate how nutrient concentrations can be modified to induce plant responses to both essential nutrients and toxic non-essential elements.

Hydroponics: A Versatile System to Study Nutrient Allocation and Plant Responses to Nutrient Availability and Exposure to Toxic Elements

Hydroponic systems have been utilized as one of the standard methods for plant biology research and are also used in commercial production for several crops, including lettuce and tomato. Within the plant research community, numerous hydroponic systems have been designed to study plant responses to biotic and abiotic stresses. Here we present a hydroponic protocol that can be easily implemented in laboratories interested in pursuing studies on plant mineral nutrition. This protocol describes the hydroponic system set up in detail and the preparation of plant material for successful experiments. Most of the materials described in this protocol can be found outside scientific supply companies, making the set up for hydroponic experiments less expensive and convenient. The use of a hydroponic growth system is most advantageous in situations where the nutrient media need to be well controlled and when intact roots need to be harvested for downstream applications. We also demonstrate how nutrient concentrations can be modified to induce plant responses to both essential nutrients and toxic non-essential elements.

Vertical farming increases lettuce yield per unit area compared to conventional horizontal hydroponics.

Vertical farming systems (VFS) have been proposed as an engineering solution to increase productivity per unit area of cultivated land by extending crop production into the vertical dimension. To test whether this approach presents a viable alternative to horizontal crop production systems, a VFS (where plants were grown in upright cylindrical columns) was compared against a conventional horizontal hydroponic system (HHS) using lettuce (Lactuca sativa L. cv. “Little Gem”) as a model crop. Both systems had similar root zone volume and planting density. Half‐strength Hoagland's solution was applied to plants grown in perlite in an indoor controlled environment room, with metal halide lamps providing artificial lighting. Light distribution (photosynthetic photon flux density, PPFD) and yield (shoot fresh weight) within each system were assessed. Although PPFD and shoot fresh weight decreased significantly in the VFS from top to base, the VFS produced more crop per unit of growing floor area when compared with the HHS. Our results clearly demonstrate that VFS presents an attractive alternative to horizontal hydroponic growth systems and suggest that further increases in yield could be achieved by incorporating artificial lighting in the VFS.

Evolving technologies for growing, imaging and analyzing 3D root system architecture of crop plants.

A plant's ability to maintain or improve its yield under limiting conditions, such as nutrient deficiency or drought, can be strongly influenced by root system architecture (RSA), the three-dimensional distribution of the different root types in the soil. The ability to image, track and quantify these root system attributes in a dynamic fashion is a useful tool in assessing desirable genetic and physiological root traits. Recent advances in imaging technology and phenotyping software have resulted in substantive progress in describing and quantifying RSA. We have designed a hydroponic growth system which retains the three-dimensional RSA of the plant root system, while allowing for aeration, solution replenishment and the imposition of nutrient treatments, as well as high-quality imaging of the root system. The simplicity and flexibility of the system allows for modifications tailored to the RSA of different crop species and improved throughput. This paper details the recent improvements and innovations in our root growth and imaging system which allows for greater image sensitivity (detection of fine roots and other root details), higher efficiency, and a broad array of growing conditions for plants that more closely mimic those found under field conditions.

Monitoring generic Escherichia coli in reclaimed and surface water used in hydroponically cultivated greenhouse peppers and the influence of fertilizer solutions

Systematic monitoring of indicator microorganisms, such as Escherichia coli, can help to identify potential risk factors for faecal contamination in the agricultural environment. In this study, levels of E. coli in irrigation water (both reclaimed and surface water), water sprayed in humidifiers to regulate ambient humidity, and pepper fruits were assessed in a commercial greenhouse of hydroponically cultivated crops. Additionally, the role of fertilizer solutions as a potential vector of contamination was investigated. Lab-scale studies were also performed to evaluate the influence of fertilizer solutions on the growth/survival of E. coli in irrigation water. As expected, higher levels of E. coli were detected in reclaimed water compared with surface water. No link between E. coli prevalence in irrigation water and presence in fruit could be established. Regarding the fertilizer solutions, E. coli was detected more frequently and in higher levels in the fertilizer solution richer in micronutrients. Low concentrations of E. coli were also present in pulverized water sprayed inside the greenhouse to control humidity. In lab-scale experiments, E. coli showed potential for surviving but not for growing in most fertilizer solutions and irrigation water. Fertilizer solution of HNO3, was the only solution in which no E. coli were able to survive in the irrigation head and a rapid inactivation was observed in lab-scale tests. These results suggest that there is a low risk of contamination in this agricultural system despite the combination of higher risk irrigation water sources (reclaimed and surface water) and the hydroponic growing system. Nevertheless, special care should be taken regarding the microbiological quality of the agricultural solutions in direct contact with the edible parts of the crop.

Vegetable production using a simplified hydroponics system inside City of Dead (Cairo)

This research work was performed in the poorest urban area of Cairo (Egypt) in a slum area called Al-Quarafa. The aim was to develop and evaluate a simplified hydroponics system (HS) to grow vegetables for the local inhabitants who live in an extreme status of food unsafety. In the hydroponic growing system the tomato plants were cultivated and two substrates were compared: peat:perlite (70/30 W/w) and sand:coir (50:50 W/w). This technique guarantees high levels of production and low contamination by avoiding the use of polluted urban soils which are often common in slum areas. Macro and microelements in tomato fruits were analysed by ICP-MS. Results showed low concentrations of heavy metals (Cd, Sr, As, Cr, Mo) with all heavy metals under the levels set by European Community laws. Lack of food safety in slums is more closely linked with malnutrition than starvation, so it is also important to understand mineral availability (both micro and macro) and nutritional significance for health. For this reason micro and macro elements (K, Ca, Na, Fe, Mn, Mg, Cu, Zn) were analysed in the harvested fruits. This study showed that HS is a valid method to grow vegetables in urban areas to improve food security in Middle East cities.

Nutritional status and ion uptake response of Gynura bicolor DC. between Porous-tube and traditional hydroponic growth systems

Hydroponic culture has traditionally been used for Bioregenerative Life Support Systems (BLSS) because the optimal environment for roots supports high growth rates. Recent developments in Porous-tube Nutrient Delivery System (PTNDS) also offer high control of the root environment which is designed to provide a means for accurate environmental control and to allow for two-phase flow separation in microgravity. This study compared the effects of PTNDS and traditional hydroponic cultures on biomass yield, nutritional composition and antioxidant defense system (T-AOC, GSH, H2O2 and MDA) of G. bicolor, and ionic concentration (NH4+, K+, Mg2+, Ca2+, NO3−, H2PO4−, SO42−) of nutrient solution during planting period in controlled environment chambers. The results indicated that the biomass production and yield of G. bicolor grown in PTNDS were higher than in hydroponic culture, although Relative water content (RWC), leaf length and shoot height were not significantly different. PTNDS cultivation enhanced calories from 139.5 to 182.3kJ/100g dry matter, and carbohydrate from 4.8 to 7.3g/100g dry matter and reduced the amount of protein from 7.3 to 4.8g/100g dry matter and ash from 1.4 to1.0g/100g dry matter, compared with hydroponic culture. PTNDS cultivation accumulated the nutrition elements of Ca, Cu, Fe and Zn, and reduced Na concentration. T-AOC and GSH contents were significantly lower in PTNDS than in hydroponic culture in the first harvest. After the first harvest, the contents of MDA and H2O2 were significantly higher in PTNDS than in hydroponic culture. However, the activity of T-AOC and GSH and H2O2 and MDA contents had no significant differences under both cultures after the second and third harvest. Higher concentrations of K+, Mg2+ and Ca2+ were found in nutrient solution of plants grown in hydroponics culture compared to PTNDS, wherein lower concentrations of NO3−, H2PO4− and SO42− occurred. Our results demonstrate that PTNDS culture has more potential to maintain nutritional quality and the optimal root zone environment for G. bicolor compared with hydroponic culture. And further refinements in PTNDS culture would make it a viable alternative for achieving high productivity in a BLSS.

Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits.

Phosphorus (P) is an important element for crop productivity and is widely applied in fertilizers. Most P fertilizers applied to land are sorbed onto soil particles, so research on improving plant uptake of less easily available P is important. In the current study, we investigated the responses in root morphology and root-exuded organic acids (OAs) to low available P (1 μM P) and sufficient P (50 μM P) in barley, canola and micropropagated seedlings of potato-three important food crops with divergent root traits, using a hydroponic plant growth system. We hypothesized that the dicots canola and tuber-producing potato and the monocot barley would respond differently under various P availabilities. WinRHIZO and liquid chromatography triple quadrupole mass spectrometry results suggested that under low P availability, canola developed longer roots and exhibited the fastest root exudation rate for citric acid. Barley showed a reduction in root length and root surface area and an increase in root-exuded malic acid under low-P conditions. Potato exuded relatively small amounts of OAs under low P, while there was a marked increase in root tips. Based on the results, we conclude that different crops show divergent morphological and physiological responses to low P availability, having evolved specific traits of root morphology and root exudation that enhance their P-uptake capacity under low-P conditions. These results could underpin future efforts to improve P uptake of the three crops that are of importance for future sustainable crop production.

Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L.

Pedneault, K., Dorais, M., Leonhart, S., Angers, P. and Gosselin, A. 2014. Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L. Can. J. Plant. Sci. 94: 383-395. In recent decades, the use of plant-based medicines as health products has increased considerably all over the world. As greenhouse hydroponic culture allows standardized cultural methods to be used, it may be valuable for reducing the risks associated with harvesting medicinal plants from the wild, such as species dissemination, species misidentification, adulteration, and non-hygienic handling, while allowing the production of high yields of clean, standardized biomass year-round. To evaluate the potential of hydroponic culture for medicinal plant production, the present study investigated the accumulation patterns of apigenin, luteolin, apigenin glycosides, and the chlorogenic acid 5-caffeoylquinic acid in the plant organs of A. millefolium at five phenological stages from 35 to 102 d after sowing, and drew a comparison with outdoor-grown plants at 122 d after sowing. The results showed two flavonoid accumulation peaks: one at the early growth stage (35 d after sowing) and one at early flowering (87 d after sowing). At 87 d after sowing, most of the apigenin glycosides were concentrated in the roots (3.80% wt/wt, dry weight basis), whereas free apigenin and luteolin were located mainly in the flower heads (1.25 and 0.86% wt/wt, dry weight basis, respectively). Early flowering was the best harvesting stage for optimal flavonoid production in terms of active compounds per plant and kilograms of plant biomass per cultivated area. At 122 d after sowing (phenological stage 4), the outdoor-grown plants were nine times smaller than the early flowering plants (87 d after sowing) from the hydroponic system and had a root-tissue apigenin glycoside level that was five times lower than that of the hydroponically grown plants. In conclusion, the use of a hydroponic growing system reduced by 29% the time required to reach phenological stage 4, which corresponds to maximum plant bioactive concentration, in comparison with field production. Therefore, hydroponic culture represents an effective alternative to outdoor production and can result in standardized, high-quality medicinal plant biomass with potential flavonoid yields approximating 515 mg per plant.

Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L.

Pedneault, K., Dorais, M., Léonhart, S., Angers, P. and Gosselin, A. 2014. Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L. Can. J. Plant. Sci. 94: 383–395. In recent decades, the use of plant-based medicines as health products has increased considerably all over the world. As greenhouse hydroponic culture allows standardized cultural methods to be used, it may be valuable for reducing the risks associated with harvesting medicinal plants from the wild, such as species dissemination, species misidentification, adulteration, and non-hygienic handling, while allowing the production of high yields of clean, standardized biomass year-round. To evaluate the potential of hydroponic culture for medicinal plant production, the present study investigated the accumulation patterns of apigenin, luteolin, apigenin glycosides, and the chlorogenic acid 5-caffeoylquinic acid in the plant organs of A. millefolium at five phenological stages from 35 to 102 d after sowing, and drew a comparison with outdoor-grown plants at 122 d after sowing. The results showed two flavonoid accumulation peaks: one at the early growth stage (35 d after sowing) and one at early flowering (87 d after sowing). At 87 d after sowing, most of the apigenin glycosides were concentrated in the roots (3.80% wt/wt, dry weight basis), whereas free apigenin and luteolin were located mainly in the flower heads (1.25 and 0.86% wt/wt, dry weight basis, respectively). Early flowering was the best harvesting stage for optimal flavonoid production in terms of active compounds per plant and kilograms of plant biomass per cultivated area. At 122 d after sowing (phenological stage 4), the outdoor-grown plants were nine times smaller than the early flowering plants (87 d after sowing) from the hydroponic system and had a root-tissue apigenin glycoside level that was five times lower than that of the hydroponically grown plants. In conclusion, the use of a hydroponic growing system reduced by 29% the time required to reach phenological stage 4, which corresponds to maximum plant bioactive concentration, in comparison with field production. Therefore, hydroponic culture represents an effective alternative to outdoor production and can result in standardized, high-quality medicinal plant biomass with potential flavonoid yields approximating 515 mg per plant.

Identification of QTLs for shoot and root growth under ionic–osmotic stress in Lotus, using a RIL population

The genus Lotus includes a group of forage legume species including genotypes of agronomic interest and model species. In this work, an experimental hydroponic growth system allowed the discrimination of growth responses to ionic–osmotic stress in a population of recombinant inbred lines (RILs) developed from L. japonicus × L. burttii and the identification of the associated quantitative trait loci (QTLs). The analyses led to the identification of eight QTLs: three for shoot growth localised on chromosome 3, 5 and 6; one for root growth on chromosome 1; three for total growth on chromosome 1, 4 and 5; and one associated with shoot/root ratio on chromosome 3. An interaction of QTL × stress condition was established and the effect of the environment quantified. In summary, it was established that the allele from L. burttii explained most responses to osmotic stress, while the alleles of L. japonicus explained the responses related to ionic stress conditions. Of 49 markers linked to all QTLs identified, 41 expressed superiority of the L. burttii parental allele in the osmotic stress condition, but when an iso-osmotic concentration of NaCl was applied, L. burttii lost superiority in 21 of these markers. This shows the superiority of the L. japonicus parental allele in ionic stress conditions. This study is the first report in which a RIL population of lotus is analysed with the aim of providing molecular markers associated with plant responses to ionic or osmotic stress.