Effetto dell'eccesso di boro sullo stato azotato del basilico in coltura idroponica

Riassunto: L’azoto (N) è un elemento essenziale per la vita e l’accrescimento delle piante entrando a far parte della struttura degli aminoacidi e di conseguenza delle proteine. Le piante assorbono N attraverso le radici principalmente come nitrato (NO3-) e secondariamente come ammonio (NH4+). Nelle cellule, l’ NO3- è suddiviso in due frazioni: quella metabolica nel citosol e quella di riserva nel vacuolo. L’ NO3- presente nel citosol è ridotto, ad opera della nitrato riduttasi (NR), a nitrito (NO2-), che a sua volta è ridotto a NH4+, dalla nitrito riduttasi (NiR) nei plastidi. L’ NH4+ così formato è incorporato negli aminoacidi attraverso una serie di reazioni catalizzate dalla glutammina sintetasi (GS) e dalla glutammato sintetasi (GOGAT). L’enzima chiave per la regolazione di tutto il processo di assimilazione dell’N è la NR. L’attività di quest’enzima (NRA) è stimolata dall’NO3- e dalla luce mentre è inibita dall’NO2-, dall’ NH4+, dalla glutammina e dagli altri aminoacidi. Se consumato in quantità eccessive l’NO3- può avere un effetto negativo sulla salute umana. L’accumulo di NO3- nei tessuti vegetali risulta favorito da condizioni di scarsa illuminazione, basse temperature e abbondante disponibilità di NO3- nel substrato di crescita. Il boro (B) è un elemento essenziale per le piante entrando a far parte della struttura della parete cellulare e ricoprendo altre funzioni metaboliche. Un suo eccesso, però, può portare a fenomeni di tossicità nelle piante, che sviluppano clorosi e necrosi a livello fogliare, con conseguente riduzione di crescita. In questa tesi, sono stati studiati gli effetti di diverse concentrazioni di B (0,25 e 20 mg/L) e di NO3- (10 mM e 20 mM) nella soluzione nutritiva su piante di basilico (Ocimum basilicum L.) coltivate in idroponica (floating system). Per gli esperimenti sono state impiegate due varietà di basilico, una con foglie verdi (“Tigullio”), generalmente usata come pianta aromatica, e una a foglie viola (“Red Rubin”), solitamente usata a fini ornamentali. La varietà viola presenta una maggiore concentrazione fogliare di antociani (nell’epidermide) e di altri composti antiossidanti, che hanno un ruolo fondamentale nella fotoprotezione (effetto sun-screen degli antociani) e nella tolleranza ai vari tipi di stress, compreso l’eccesso di B come dimostrato in precedenti studi (Landi et al, 2013a, 2013b, 2014; Ziliani, 2013). Ziliani (2013) aveva riscontrato un maggior contenuto di NO3- nelle foglie delle piante, di entrambe le varietà, quanto erano allevate in presenza di un eccesso di B (20 mg/L) nel mezzo di crescita rispetto ai livelli di NO3- rilevati nelle piante di controllo. I tre esperimenti riportati in questa tesi sono stati condotti per confermare o meno la relazione fra l’eccesso di B (20 mg/L) e il contenuto fogliare di NO3- verificando anche l’effetto della concentrazione di NO3- (10 mM e 20 mM) nel mezzo di crescita, e del genotipo sulla NRA determinata in vivo. Tutti gli esperimenti sono stati condotti con piante di 3-5 settimane dalla germinazione. Lo studio ha confermato la maggiore tolleranza all’eccesso di B della varietà “Red Rubin” rispetto a “Tigullio”. Non è stato confermato invece il maggior contenuto di NO3- nelle piante coltivate in presenza di un eccesso di B, osservato negli esperimenti di Ziliani (2013). Contrariamente a quanto inizialmente ipotizzato, l’eccesso di B non ha determinato una riduzione della NRA e addirittura in “Red Rubin” la NRA è stata minore nelle piante di controllo rispetto a quelle coltivate con 20 g/L nella soluzione nutritiva. Summary Nitrogen (N) is an essential element for plant life and growth since it is contained in amino acids and then in proteins. Principally, plant roots take up N as nitrate (NO3-) and secondly ammonium (NH4+). NO3- is divided into two fractions within cell: a metabolic fraction in the cytosol and storage fraction in the vacuole. Cytosolic NO3- is reduced by nitrate reductase (NR) to nitrite (NO2-), which is then reduced to NH4+ by nitrite reductase (NiR) in the plastids. NH4+ formed in this way is built-in amino acids by a series of reactions, which are catalyzed by glutamine synthetase (GS) and glutamate synthetase (GOGAT). NR is the most important enzyme for regulation of N assimilation as a whole. The activity of this enzyme (NRA) is enhanced by NO3- and light while is inhibited by NO2-, NH4+, glutamine and other amino acids. NO3- may have a negative effect on human health when taken in excessive quantities. NO3- accumulation in plant tissues is favored by low light conditions, low temperatures and abundant availability of NO3- in the growth substrate. Boron (B) is an essential element for plants, taking part in the wall cell structure and performing other metabolic functions. However, high B concentration can be toxic and induce foliar chlorosis and necrosis, with consequent growth reduction. In this thesis, the effects of different concentrations of B (0,25 e 20 mg/L) and NO3- (10 mM e 20 mM) in the nutrient solution were investigated in sweet basil plants (Ocimum basilicum L.) grown in hydroponics (floating system). The experiments were conducted with two cultivars of basil with green (“Tigullio”)or purple leaves (“Red Rubin”, usually used for ornamental purposes). The purple cultivar has a higher concentration of anthocyanins (within epidermis) and other antioxidants, which have a fundamental role in the photoprotection (anthocyanins’ sun-screen effect) and in the tolerance to other type of stress, including B toxicity as demonstrated in previous studies (Landi et al, 2013a, 2013b, 2014; Ziliani, 2013). Ziliani (2013) also found higher content of NO3- in the leaves of both varieties when the plants was grown with an excess of B (20 mg/L) in growth medium compared to the NO3- levels detected in the control plants. Three experiments were conducted to confirm the relationship between B excess and foliar content of NO3- found by Ziliani (2013) and to verify the effect of NO3- concentration (10 mM e 20 mM) in the growth medium and genotype on in vivo NRA. All experiments were been performed with 3 to 5-week old plants. The study confirmed that “Red Rubin” was more tolerance to B excess than “Tigullio”.In contrast, it was not found an higher leaf content of NO3- in the plants grown with an excess of B, as reported by Ziliani (2013). Contrary to the initial hypothesis, the excess of B did not result in a reduction of NRA and in “Red Rubin” NRA was even less in the control plants than in those grown with a B concentration of 20 mg/L in the nutrient solution

Wild edible plant species grown hydroponically with crop drainage water in a Mediterranean climate: Crop yield, leaf quality, and use of water and nutrients

There is an increasing interest in the cultivation of wild edible plants (WEP) in consideration of their quality attributes and salt tolerance, which makes these species good candidates for cascade cropping systems (CCS). In these systems, saline effluents from a salt-sensitive donor crop are used to irrigate a receiving crop with greater salt tolerance. The objective of this study was to evaluate two WEP species, Picris hieracioides (PH) and Plantago coronopus (PC) as candidate crops for CCS. Both species were grown hydroponically with saline effluent from a semi-closed substrate culture of tomato (the donor crop). Both PH and PC were grown in floating system for 36 days during spring using one of the following nutrient solutions: i) standard nutrient solution (CNS, control); ii) NaCl-enriched (50 mmol L-1) standard nutrient solution (SNS); iii) effluent from tomato substrate culture (TE); iv) artificial effluent (ATE), i.e. a nutrient with ion concentrations and salinity level (approximately 50 mmol L-1 NaCl) very close to those of TE. Compared with CNS, leaf production was significantly reduced in both TE (-33.6%) and ATE (-33.6%) plants of PH, and only in TE (-23.3%) plants of PC. In both species, leaf Na content increased in SNS (+858.1% in PH; +279.4% in PC), TE (+704.7% in PH; +226.3 in PC) and ATE (+697.7% in PH; +229.4% in PC) plants compared with the controls. Leaf antioxidant capacity was positively correlated with total phenol content and, in PC, increased in SNS (+74.3%), TE (+53.9%) and ATE plants (+37.7%) compared with the controls. In conclusion, both PH and PC could be grown in CCS with saline greenhouse hydroponic effluents since the moderate reduction of leaf production could be partially compensated by reduced production costs because of zero costs for fertilisers. The growth inhibition observed in both WEPs species cultivated with the hydroponic effluent was primarily due to its high salinity with minor or no effects due to the suboptimal nutrient levels and/or the presence of phytotoxic root exudates or microbial metabolites

Plant factory with artificial light: pros and cons

Plant factory with artificial lights (PFALs) could be useful to produce more food of high quality and reduce the use of agrochemical and transportation costs. PFALs is a complete controlled indoor farming system, mainly dedicated to the production of edible plants with small size and a short cultivation, that allows to provide a reliable production of high-quality vegetables. The development of PFALs was possible thanks to the steady price decline of Light Emitting Diode (LED) lights along with the rapid improvement of their photon efficacy. In typical PFALs with LED lights, electricity, labour, and depreciation are the three major components of the production costs. The energy-efficiency must be improved to an ecologically friendly development of PFALs. The reduction of energy consumption and the increase in production and commercial value can be achieved by improving the digital control of the cultivation and by applying models to predict both crop growth and development

Effect of selenium enrichment on metabolism of tomato (Solanum lycopersicum) fruit during post‐harvest ripening

BACKGROUND Selenium (Se) enrichment of plants seems effective in enhancing the health‐related properties of produce, and in delaying plant senescence and fruit ripening. The current study investigated the effects of Se on tomato fruit ripening. Tomato (Solanum lycopersicum L.) plants were grown in hydroponics with different Se‐enriched nutrient solutions. Se, as sodium selenate, was added at rate of 0 mg L‐1 (control), 1 mg L‐1, and 1.5 mg L‐1. RESULTS Selenium was absorbed by roots and translocated to leaves and fruit. Se enrichment did not significantly affect the qualitative parameters of fruit at commercial harvest, instead it delayed ripening by affecting specific ripening‐related processes (respiration, ethylene production, color evolution) during postharvest. In the current experiment 100 g of tomato hydroponically grown with a 1.5 mg Se L‐1 enriched solution provided a total of 23.7 μg Se. Selenium recommended daily intake is 60 μg for women and 70 μg for men, thus the daily consumption of 100 g of enriched tomato would not lead to Se toxicity, but would provide a good Se diet supplementation. CONCLUSIONS The cultivation of tomato plants in a Se‐enriched solution appeared effective in producing tomato fruit with improved performances during storage and postharvest shelf life, and also with greater potential health‐promoting properties

Growth and Mineral Relations of Beta vulgaris var. cicla and Beta vulgaris ssp. maritima Cultivated Hydroponically with Diluted Seawater and Low Nitrogen Level in the Nutrient Solution

There is an increasing interest in the use of seawater in horticulture. The objective of this study was to evaluate Beta vulgaris var. cicla (Swiss chard) and its wild ancestor B. vulgaris spp. maritima (sea beet) as potential crop species for seawater hydroponics or aquaponics. Both species were grown in a floating system for leaf production with recurrent harvests. The nutrient solutions contained different concentrations of nitrate (1 and 10 mM) and a synthetic sea salt (0 and 10 g L−1), in a factorial design, where the saline solution with a low nitrate level intended to mimic the typical nutritional conditions of saltwater aquaponics. In both species, increasing the salinity or reducing the N level in the nutrient solution reduced the crop yield and total dry biomass. In both Swiss chard and sea beet, the use of saline water resulted in a lower leaf concentration of K, Ca, Cu, and Mn, and a greater content of Na and Cl. In Swiss chard, an increase in Na and Cl and a decrease in K leaf content were found in successive harvests. On average, sea beet showed a higher leaf production and accumulation of nitrate than Swiss chard

Boron accumulation and tolerance in sweet basil (Ocimum basilicum L.) with green or purple leaves

Background and aims There is a wide variability in plant tolerance to boron (B) toxicity, which is often associated with the ability to limit B accumulation. This study was conducted on two cultivars of sweet basil (Ocimum basilicum L.) with different B tolerance: ‘Tigullio’, less tolerant and with green leaves; ‘Red Rubin’, more tolerant and with purple leaves. The main goal was to verify whether the greater B tolerance of ‘Red Rubin’ is attributable to an exclusion mechanism. Methods In three greenhouse experiments, plants were grown hydroponically with solution B concentration ranging from 0.25 (control) to 25 mg L−1. Results Tissue B concentration increased with increasing B supply. Boron concentrations in root and leaf tissues were comparable in ‘Tigullio’ and ‘Red Rubin’ or even higher in the purple cultivar. Boron supply did not affect the leaf concentration of total phenolic compounds and other nutrients. Leaf concentrations of total phenols and rosmarinic acid were remarkably higher in ‘Red Rubin’ than in ‘Tigullio’. Conclusions The greater B tolerance of ‘Red Rubin’ was associated with the ability to withstand higher concentrations of this element in plant tissues rather than to reduced B accumulation in the shoot. The high phenolic content was thought to contribute to the B tolerance of ‘Red Rubin’

Enrichment of food crops with selenium: controlled production of Se enriched plants to delay fruit ripening and plant senescence, and to increase nutritive value and health benefits.

The ability of some crops to accumulate selenium (Se) is crucial for human nutrition and health. Selenium has been identified as a cofactor of the enzyme glutathione peroxidase, which is involved in the reduction of peroxides that can damage cells and tissues, and can act as an antioxidant. Plants are the first link in the food chain, which ends with humans. Increasing the Se amount in plant products, without exceeding the toxic threshold, is thus a good way to increase animal and human Se intake, with positive effects on long-term health. In many Se-enriched plants, most Se is in its organic form. Given that this form is more available to humans and more efficient in increasing the selenium status than inorganic forms, the consumption of Se-enriched plants appears to be beneficial. An antioxidant effect of Se has been detected in Se-enriched vegetables and fruit crops. In addition, Se appears to be effective in delay fruit ripening and plant senescence. This thus highlights the possible positive effect of Se in preserving a longer shelf-life and longer-lasting quality. The main goal of the present thesis was to investigate the effects of selenium on plant metabolism in order to use the potential beneficial effects of Se to improve the quality and the shelf-life of leafy and fruity vegetables. The mechanism of Se uptake, distribution, accumulation, and the effects of Se concentration on plant growth, quality and post-harvest shelf-life in sweet basil (Ocimum basilicum L.) were investigated. The first two experiments aimed to study the ability of sweet basil to accumulate selenium, and to evaluate the possibility to obtain Se-enriched basil as a Se supplement resource for humans. Different Se concentrations (0.5, 1, 2 and 4 mg Se L-1) were tested in order to determine the optimal Se concentration in leaves that may induce benefits to human health without phytotoxic effects. Floating system was tested as a possible cultivation system for the production of Se biofortified basil plants. The results showed that the addition of selenium as sodium selenate in the nutrient solution significantly increased the Se content in basil, and could be an efficient system for providing enriched basil plants. On the basis of the results of the first two experiments, a third trial was conducted in order to understand the processes of Se uptake and accumulation in basil plants. Since the amount of Se accumulated in leaves in the previous experiments was far from the Se toxic threshold for humans, higher Se concentrations (4, 8 and 12 mg Se L-1) were tested. The Se concentration in all plant organs was measured during the growth cycle, and the relationship among Se uptake rate, Se concentration in the nutrient solution and plant growth was evaluated. Selenium was absorbed by the roots, translocated to the above-ground organs and accumulated particularly in the leaves, without affecting the plant biomass. Se concentration increased during seedling growth, was highest in the younger leaves and then declined before or upon flowering. The growing trend detected in the total Se was more dependent on the biomass, which increased throughout the experiment, than on the Se concentration, which reached the maximum values during the first part of the experiment and then decreased. The fourth experiment aimed at studying the allocation of selenium absorbed by roots in the different plants organs. The remobilization of Se accumulated in the seeds to the seedlings, and the effects of Se on the quality of sprouts were investigated. Basil plants accumulated Se mostly in leaves and roots. High amounts of Se were also accumulated in seeds and then remobilized to sprouts. The sprouts, produced by the seeds of Se-enriched plants, showed higher germination index and antioxidant capacity compared to seeds of control plants. Given the potential action of Se in ameliorating the oxidative stress and delaying senescence, the effects of Se on basil leaf quality and shelf-life were studied in the fifth experiment. The different climate conditions during the two experiments reported in the fifth chapter may have affected the amount of Se taken up by plants. Lower values of cumulative solar radiation during the second experiment may have determined a lower plants growth and transpiration rate, inducing a lower Se accumulation in basil leaves, compared to the first experiment reported in the same chapter. Se-treated plants showed increased phenolic content and antioxidant activity, thus contrasting the reduction of biomass due to the high Se concentrations added to the nutrient solution. This resulted in an improved quality of basil leaves. As final issue, the effects of Se in tomato fruit were investigated. Tomato plants were grown in solution enriched with selenium to study the effects of Se treatments on fruit ripening and shelf-life. The results obtained in this experiment confirmed the effect of Se in delaying fruit ripening, and the possibility to use Se-treatments to improve the postharvest shelf-life of fruits

Can Light Spectrum Composition Increase Growth and Nutritional Quality of Linum usitatissimum L. Sprouts and Microgreens?

Flaxseed could be suitable for obtaining high-quality sprouts and microgreens thanks to high amounts of nutrients and antioxidant, antidiabetic, and anticancer compound content in its seeds. Recent studies highlighted that seedling growth, nutritional compound, and secondary metabolite content can be strongly managed by regulation of the light spectrum used during germination. The present study intended to shed light on flaxseed as emerging and novel species for sprouts and microgreens and to evaluate the effect of light, with different spectrum compositions (100% blue, 100% red, 100% green, and red:green:blue—1:1:1) on the performance of flax microgreens and sprouts grown indoors under controlled conditions. Microgreens showed, compared to sprouts, a higher chlorophyll (+62.6%), carotenoid (+24.4%), and phenol content (+37.8%), antioxidant capacity (+25.1%) and a lower dry matter content (−30.7%). Besides, microgreens treated with 100% blue light were characterized by the highest content of flavonoids (2.48 mg CAE g−1 FW), total phenols (3.76 mg GAE g−1 FW), chlorogenic acid (1.10 mg g−1 FW), and antioxidant capacity (8.06 µmol TEAC g−1 FW). The paper demonstrates the feasibility of obtaining flax sprouts and microgreens indoors with a considerable antioxidant capacity and health-promoting compounds by modulating the light spectrum

Effects of Individual and Simultaneous Selenium and Iodine Biofortification of Baby-Leaf Lettuce Plants Grown in Two Different Hydroponic Systems

The iodine (I) and selenium (Se) deficiencies affect approximately 30% and 15%, respectively, of the global population. The biofortification of vegetables is a valid way to increase the intake of iodine and selenium through the diet. This study was carried out on baby-leaf lettuce to investigate the effects on plant growth, leaf quality, and leaf I and Se accumulation of adding potassium iodide and sodium selenate, separately and simultaneously, to the nutrient solution in a floating system and aeroponics. The effect of I and Se biofortification on post-harvest quality of lettuce leaves was also evaluated. Our results evidenced that the Se and I treatments increased the content of the two microelements in lettuce leaves without any negative interactions in the plants, when applied either separately or simultaneously. Both hydroponic systems proved to be suitable for producing Se and/or I enriched lettuce. Biofortification with Se was more effective when performed in aeroponics, whereas I biofortification was more effective in the floating system. Quality of leaves during post-harvest storage was not affected by neither of the treatments. Lettuce leaves enriched with 13 µM Se and 5 µMI could be good dietary sources of Se and I without inducing toxic effects in humans

Selenium Biofortification of Three Wild Species, Rumex acetosa L., Plantago coronopus L., and Portulaca oleracea L., Grown as Microgreens

Microgreens of wild herbs are a source of healthy compounds. Selenium (Se) biofortification of microgreens could help increase the Se content and thus contribute to Se requirements in humans. We evaluated whether three wild herbs, Rumex acetosa L., Plantago coronopus L., and Portulaca oleracea L., were suitable for biofortification in order to obtain products with high nutraceutical value. In the first experiment, the three species were enriched with Na2SeO4 at 0 and 1.5 mg Se L−1, and the effects of Se on the nutraceutical characteristics of microgreens were evaluated. In the second experiment, using P. oleracea enriched with 0, 1.5, 5, and 10 mg Se L−1, we investigated whether there was a relation between the increasing Se concentrations in the nutrient solution and the Se content in microgreens. The Se added was taken up by roots and accumulated in the aerial part. P. coronopus exhibited the highest ability to accumulate selenium, and the Se-enriched microgreens showed the highest chlorophyll and flavonoid content. The strong correlation between the Se concentration in the growth solution and the Se accumulated in P. oleracea may enable the cultivation of microgreens with the targeted Se content. The resulting Se-biofortified microgreens of wild species could represent a new vegetable product with high nutraceutical value also ensuring a sufficient dietary intake of Se