Plant-Growth Promoting Microbes Change the Photosynthetic Response to Light Quality in Spinach

In this study, the combined effect of plant growth under different light quality and the application of plant-growth-promoting microbes (PGPM) was considered on spinach (Spinacia oleracea L.) to assess the influence of these factors on the photosynthetic performance. To pursue this goal, spinach plants were grown in a growth chamber at two different light quality regimes, full-spectrum white light (W) and red-blue light (RB), with (I) or without (NI) PGPM-based inoculants. Photosynthesis-light response curves (LRC) and photosynthesis-CO₂ response curves (CRC) were performed for the four growth conditions (W-NI, RB-NI, W-I, and RB-I). At each step of LRC and CRC, net photosynthesis (P_N), stomatal conductance (g_s), C_i/C_a ratio, water use efficiency (WUE_i), and fluorescence indexes were calculated. Moreover, parameters derived from the fitting of LRC, such as light-saturated net photosynthesis (P_Nmax), apparent light efficiency (Q_pp), and dark respiration (R_d), as well as the Rubisco large subunit amount, were also determined. In not-inoculated plants, the growth under RB- regime improved P_N compared to W-light because it increased stomatal conductance and favored the Rubisco synthesis. Furthermore, the RB regime also stimulates the processes of light conversion into chemical energy through chloroplasts, as indicated by the higher values of Q_pp and P_Nmax in RB compared to W plants. On the contrary, in inoculated plants, the P_N enhancement was significantly higher in W (30%) than in RB plants (17%), which showed the highest Rubisco content among all treatments. Our results indicate that the plant-growth-promoting microbes alter the photosynthetic response to light quality. This issue must be considered when PGPMs are used to improve plant growth performance in a controlled environment using artificial lighting.

Light Intensity Affects the Assimilation Rate and Carbohydrates Partitioning in Spinach Grown in a Controlled Environment

The cultivation of spinach (Spinacia oleracea L.) has been increasing during the last years in controlled environment agriculture, where light represents a key factor for controlling plant growth and development and the highest energetic costs. The aim of the experiment was to evaluate the plant's response to two light intensities, corresponding to an optimal and a reduced level, in terms of the photosynthetic process, photoassimilates partitioning, and the biosynthesis of sucrose and starch. Plants of spinach cv. 'Gigante d'Inverno' were grown in a phytotron under controlled conditions, comparing two values of photosynthetic photon flux density (PPFD), 800 μmol m^-2 s^-1 (800 PPFD) and 200 μmol m^-2 s^-1 (200 PPFD), at a 10 h light/14 h dark regime. Compared to 800 PPFD, under 200 PPFD, plants showed a reduction in biomass accumulation and a redirection of photoassimilates to leaves, determining a leaf expansion to optimize the light interception, without changes in the photosynthetic process. A shift in carbon partitioning favouring the synthesis of starch, causing an increase in the starch/sucrose ratio at the end of light period, occurred in low-light leaves. The activity of enzymes cFBAse, SPS, and AGPase, involved in the synthesis of sucrose and starch in leaves, decreased under lower light intensity, explaining the rate of accumulation of photoassimilates.

Impact of Ecklonia maxima Seaweed Extract and Mo Foliar Treatments on Biofortification, Spinach Yield, Quality and NUE

Seaweed extract (SE) application is a contemporary and sustainable agricultural practice used to improve yield and quality of vegetable crops. Plant biofortification with trace element is recognized as a major tool to prevent mineral malnourishment in humans. Mo deficiency causes numerous dysfunctions, mostly connected to central nervous system and esophageal cancer. The current research was accomplished to appraise the combined effect of Ecklonia maxima brown seaweed extract (SE) and Mo dose (0, 0.5, 2, 4 or 8 µmol L^-1) on yield, biometric traits, minerals, nutritional and functional parameters, as well as nitrogen indices of spinach plants grown in a protected environment (tunnel). Head fresh weight (FW), ascorbic acid, polyphenols, N, P, K, Mg and nitrogen use efficiency (NUE) were positively associated with SE treatment. Moreover, head FW, head height (H), stem diameter (SD), ascorbic acid, polyphenols, carotenoids as well as NUE indices were enhanced by Mo-biofortification. A noticeable improvement in number of leaves (N. leaves), head dry matter (DM) and Mo concentration in leaf tissues was observed when SE application was combined with a Mo dosage of 4 or 8 µmol L^-1. Overall, our study highlighted that E. maxima SE treatment and Mo supply can improve both spinach production and quality via the key enzyme activity involved in the phytochemical homeostasis of SE and the plant nutritional status modification resulting in an enhanced spinach Mo tolerance.

Ca2SiO4 chemigation reduces cadmium localization in the subcellular leaf fractions of spinach (Spinacia oleracea L.) under cadmium stress

Heavy metal like cadmium (Cd) is inessential and highly toxic and is posing serious environmental problems for agriculture worldwide. Presence of Cd gives rise to several physiological and structural disorders that leads to reduction in growth and performance of agricultural plants. Evidence related to subcellular distribution and accumulation of Cd is still enigmatic. Experiment was conducted using hydroponic culture to examine the subcellular accumulation of Cd in Spinacia oleracea L. leaves under Cd stress (50 μM and 100 μM); moreover, the Cd toxicity alleviation using 5 mM silicon (Si) was investigated. Our findings suggest that fresh and dry biomass, shoot and root length, leaf area and length of leaf declined when exposed to Cd stress (50 μM and 100 μM); however, an increase was noticed when Cd treated plants were supplied with Si (5 mM). The content of Ca²⁺, Mg²⁺ and Fe²⁺ in apoplastic washing fluid and symplasm were found to be lower in plants treated with alone Cd, when compared to control. Higher Cd²⁺:Ca²⁺, Cd²⁺:Fe²⁺ and Cd²⁺:Mg²⁺ ratios were detected under cadmium stress in both apoplast and symplast of leaves which were lowered by the addition of 5 mM Si. The novelty of the current study is the detection of increased apoplastic and symplastic Cd concentration in aerial part (i.e., spinach leaves) under alone Cd treatment which was considerably reduced when supplied with Si. Moreover, a noticeable increase in spinach growth and beneficial ionic concentrations suggest that Si can ameliorate the Cd stress in crop plants.

Spinacia oleracea L. extract attenuates hippocampal expression of TNF-α and IL-1β in rats exposed to chronic restraint stress

Background: Restraint stress causes inflammation in nervous system that leads to emersion of neurodegenerative diseases. Spinach (Spinacia oleracea L.) contains different agents with antioxidant, antiapoptosis, and hepatoprotective properties. This study examined the effect of spinach hydroalcoholic extract (SHE) on TNF-α and IL-1β expression in hippocampus of male Wistar rats exposed to chronic restraint stress.

Methods: Rats were divided into 6 groups of 5: (1) control (intact); (2) nS-S200; (3) nS-S400; (4) stress; (5) stress-S200; (6) stressS400. Groups 2 and 3 and groups 5 and 6 received S. oleracea leaf hydroalcoholic extract in 200 and 400 mg/kg doses for 21 consecutive days by gavage. Groups 4, 5 and 6 were put in a restrainer 6 hours per day for 21 consecutive days. Then, the expression of IL-1β and TNF-α mRNAs and neuronal death in the hippocampus of rats were assessed by real time PCR and Nissl staining, respectively. Oneway analysis of variance was used for data analysis, and p<0.05 was considered statistically significant.

Results: The results showed that the expression of IL-1β and TNF-α was increased in hippocampus of rats exposed to stress compared to control groups (p<0.001). Furthermore, the expression of these proinflammatory cytokines was decreased in the stress-S200 and stress-S400 groups when compared to stress group (p<0.001). Immobility also caused neuronal death in CA1 region of hippocampus, and SHE reduced damage in CA1 pyramidal neurons layer in stressed rats.

Conclusion: Spinach decreases neuroinflammation in hippocampus of stressed rats, which may be due to its abundant antiinflammatory and antioxidant phytochemicals. The results of this study suggest that spinach may be effective in the prevention and treatment of neurodegenerative diseases.

The Effects of Biostimulants, Biofertilizers and Water-Stress on Nutritional Value and Chemical Composition of Two Spinach Genotypes (Spinacia oleracea L.)

In the present study, the effect of biostimulants application on the nutritional quality and bioactive properties of spinach cultivated in protected environment under water stress conditions was evaluated. For this purpose, four commercially available biostimulant products (Megafol (MEG), Aminovert (AM), Veramin Ca (V), Twin Antistress (TA), and two spinach genotypes (Fuji F1 and Viroflay) were tested under two irrigation regimes (normal irrigation (W+), and water-holding (W–). Fat and carbohydrates content was favored by water stress when Megafol (MEGW+) and Veramin (VW+) were applied on Fuji plants, while calorific value was also increased by MEGW+ treatment. In contrast, protein and ash content increased when AMW– and TAW+ were applied on Viroflay plants. Raffinose and glucose were the most abundant sugars, followed by sucrose and fructose, with the highest contents recorded for Fuji plants when AMW+ (fructose, glucose and total carbohydrates), CW– (sucrose), and TAW– (raffinose) treatments were applied. Regarding organic acids, oxalic and malic acid which had the highest contents for the TAW– (Viroflay plants) and AMW– (Fuji plants) treatments, respectively. α- and γ-tocopherol were the only isoforms detected with MEGW– and VW– inducing the biosynthesis of α-tocopherol, while AMW+ increased γ-tocopherol content in Fuji plants. The main fatty acids were α-linolenic and linoleic acids which were detected in the highest amounts in AMW–, AMW+, and TAW+ the former and in AMW–, VW–, and CW+ the latter. Regarding phenolic compounds content, peak 12 (5,3′,4′-Trihydroxy-3-methoxy-6:7-methylenedioxyflavone-4′-glucuronide) was the most abundant compound, especially in Viroflay plants under normal irrigation and no biostimulants added (CW–). The antioxidant and cytotoxic activity of the tested samples did not show promising results when compared with the positive controls, while a variable antibacterial activity was recorded depending on the tested biostimulant, irrigation regime and genotype. In conclusion, a variable effect of the tested biostimulants and irrigation regimes was observed on bioactive properties and chemical composition of both spinach genotypes which highlights the need for further research in order to make profound conclusions regarding the positive effects of biostimulants under water stress conditions.

Oxygen Availability during Growth Modulates the Phytochemical Profile and the Chemo-Protective Properties of Spinach Juice

Fruits and vegetables are a good source of potentially biologically active compounds. Their regular consumption in the human diet can help reduce the risk of developing chronic diseases such as cardiovascular diseases and cancer. Plants produce additional chemical substances when subject to abiotic stress or infected by microorganisms. The phytochemical profile of spinach leaves (Spinacia oleracea L.), which is a vegetable with widely recognized health-promoting activity, has been affected by applying root hypoxic and re-oxygenation stress during plant growth. Leaf juice at different sampling times has been subject to liquid chromatography mass spectrometry (LC-MSn) analysis and tested on the human colorectal adenocarcinoma cell line HT29 by using the Comet assay. The cells were previously treated with H₂O₂ to simulate the presence of an oxidative stress (as in colon cancer condition) and the leaf juice application resulted in a significant antioxidant and protective in vitro effect. The duration of the hypoxic/re-oxygenation stress imposed on the plant reflects the antioxidant leaf juice content. After hypoxic stress (24 h) and reoxygenation (2 h), we show a decrease (50%) of the relative abundance of the principal identified antioxidant molecules but a higher antioxidant activity of the spinach juice on HT29 cells (20%). Data shows a complex relation between plant growing conditions and the modulation of secondary metabolites content in leaf juice that results in different chemo-protective activities in colon cancer cells.

Genetic diversity and association mapping of mineral element concentrations in spinach leaves

BACKGROUND

Spinach is a useful source of dietary vitamins and mineral elements. Breeding new spinach cultivars with high nutritional value is one of the main goals in spinach breeding programs worldwide, and identification of single nucleotide polymorphism (SNP) markers for mineral element concentrations is necessary to support spinach molecular breeding. The purpose of this study was to conduct a genome-wide association study (GWAS) and to identify SNP markers associated with mineral elements in the USDA-GRIN spinach germplasm collection.

RESULTS

A total of 14 mineral elements: boron (B), calcium (Ca), cobalt (Co), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na), nickel (Ni), phosphorus (P), sulfur (S), and zinc (Zn) were evaluated in 292 spinach accessions originally collected from 29 countries. Significant genetic variations were found among the tested genotypes as evidenced by the 2 to 42 times difference in mineral concentrations. A total of 2402 SNPs identified from genotyping by sequencing (GBS) approach were used for genetic diversity and GWAS. Six statistical methods were used for association analysis. Forty-five SNP markers were identified to be strongly associated with the concentrations of 13 mineral elements. Only two weakly associated SNP markers were associated with K concentration. Co-localized SNPs for different elemental concentrations were discovered in this research. Three SNP markers, AYZV02017731_40, AYZV02094133_57, and AYZV02281036_185 were identified to be associated with concentrations of four mineral components, Co, Mn, S, and Zn. There is a high validating correlation coefficient with r > 0.7 among concentrations of the four elements. Thirty-one spinach accessions, which rank in the top three highest concentrations in each of the 14 mineral elements, were identified as potential parents for spinach breeding programs in the future.

CONCLUSIONS

The 45 SNP markers strongly associated with the concentrations of the 13 mineral elements: B, Ca, Co, Cu, Fe, Mg, Mn, Mo, Na, Ni, P, S, and Zn could be used in breeding programs to improve the nutritional quality of spinach through marker-assisted selection (MAS). The 31 spinach accessions with high concentrations of one to several mineral elements can be used as potential parents for spinach breeding programs.

Phytoextraction and dissipation of lindane by Spinacia oleracea L

Remediation and management of organochlorine pesticide (OCPs) contaminated soil is becoming a global priority as they are listed in the Stockholm list of persistent organic pollutants (POPs) for global elimination. Lindane is a OCPs candidate recently included in the Stockholm list. However, India has an exemption to produce lindane for malaria control. Because of its widespread use during the last few decades, lindane contaminated soils are found in almost all parts of India. Since phytoremediation is widely acknowledged as an innovative strategy for the clean-up of contaminated soils; the present study was aimed to evaluate the phytoextraction and dissipation of lindane by a leafy vegetable Spinacia oleracea L (Spinach). The test plant was grown in different concentrations of lindane (5, 10, 15 and 20 mg kg(-1)) and harvested at 10, 30 and 45 days. At 45 days, the concentrations of lindane in root and leaf of Spinach growing in four different concentrations were reached up to 3.5, 5.4, 7.6 and 12.3 mg kg(-1) and 1.8, 2.2, 3 and 4.9 mg kg(-1), respectively. There was a significant difference (p<0.01) in the dissipation of lindane in vegetated and non-vegetated soil. Moreover, the residual lindane in four experiments was reduced to 81, 76, 69 and 61 percent, respectively. The experimental results indicate that Spinach can be used for the phytoremediation of lindane. However, more studies are required to prevent the toxicity of harvested parts.