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In this study, the impact of light-emitting diodes (LEDs) in different spectrums was investigated on the seed germination and post-germinative performance of Capsicum frutescens seedlings. The seeds were exposed to different LED lights (full spectrum, white, red, blue, and red-blue) for 0, 1, 2, and 4 h (h). The seeds were placed for a week in darkness to investigate germination, and then the growth mechanisms were studied in four-week-old seedlings. Results indicated that germination percentage was promoted markedly under 2 h red and full lights and also in 1 h blue, which was accompanied by the regulation of H 2 O 2 level and NADPH oxidase (NOX) activity. Sprout growth and height were more heightened under 2 h red light, but their contents decreased considerably under blue light with a rising incubation time. Red light induced more biomass yield, chlorophyll (Chl) pigments, Chl a/b ratio and florescence in four-week-old seedlings. Blue light also increased Chl pigments, but decreased biomass yield by enhancing malondialdehyde (MDA) level. Increased growth in seedlings treated to red light was associated with upregulating Rubisco gene expressions ( rbcL and rbcS ) and its activity. Red and red-blue lights promoted the activity of superoxide dismutase, glutathione reductase, and ascorbate peroxidase enzymes to increase ascorbic acid (ASA) production in the ascorbate–glutathione cycle. Total phenolic (0.22 mg DAG g − 1 DW), ASA (89.58 mg 100 g − 1 FW) and capsaicinoids (2.73 mg g − 1 DW) contents were heightened under red light, while carotenoid (11.78 µg g − 1 FW) content was more accumulated under blue light. The findings of this study suggest red light modulates NOX activity and H 2 O 2 level for inducing seed germination and seedling quality in C . frutescens , which can create important implications for the production of antioxidant metabolites and increase the cultivation area of this plant.

Physalis alkekengi L. is a valuable medicinal plant from the Solanaceae family and has multiple therapeutic applications. This study aimed to develop an optimized protocol for callogenesis in P. alkekengi to obtain friable calluses with high biomass. The effect of different concentrations of picloram, casein hydrolysate (CH), basal media (Murashige and Skoog (MS) and Gamborg (B5)), and static magnetic field (SMF) were investigated on the callus induction and growth, signaling molecules, and enzymatic and non-enzymatic antioxidants. Results showed that CH (200 mgL −1 ) and SMF4 mT for 90 min increased callus induction and fresh weight in P. alkekengi , while different concentrations of picloram reduced callogenesis. Hypocotyl explants showed various callogenesis and metabolic responses depending on the basal medium type. The 2B5 medium supplied with CH 200 (mgL −1 ) induced friable and cream calluses with high biomass (0.62 g) compared to the MS medium (control). The maximum activity of superoxide dismutase and catalase activities was identified in the 2B5 medium and peroxidase in the 2MS medium. The highest total phenolic (129.44 µg g −1 DW) content and phenylalanine-ammonia lyase activity were obtained in the 2MS medium, and total withanolides (49.86 µg g -1 DW) and DPPH radical scavenging activity were observed in the 2B5 medium. The 2MS medium boosted the hydrogen peroxide and nitric oxide levels, while their contents alleviated in the 2B5 medium, although these parameters were higher than the control. The findings of this study suggest that an effective protocol for successful callogenesis in P. alkekengi and the nutrient composition of culture medium by affecting the level of signaling molecules can control the antioxidant defense system and callus growth.

This study represents an optimized protocol for callus establishment and cell suspension culture of Matricaria chamomilla, and the impact of the static magnetic field (SMF) on flavonoid metabolism and antioxidant activity were examined for the first time. The effect of growth regulators was investigated to enhance biomass growth and apigenin production. Murashige and Skoog medium supplemented with 2,4-D (1.5 mg l−1) and Kinetin (0.5 mg l−1) showed the highest callus induction rate (100%), fresh weight, apigenin (0.82%) and apigenin-7-glucoside (1.57%) contents. Cell suspension culture was established, and the optimum subculture time was found to 13–15 days. SMF induced cell leaching and oxidative stress in all treated cells by an increase in H2O2 content and more stimulation of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) enzymes activities. Total phenolic, flavonoid and DPPH activity increased in cells treated to SMF, and the maximum content of apigenin (1.3%) and apigenin-7-glucoside (2.1%) were identified in cell treated to 4 mT. These results provided an effective method for the regulation of flavonoid biosynthesis in M. chamomilla cell suspension culture, and the use of SMF as a tool for the induction of apigenin production.Key messageCell suspension cultures of Matricaria chamomilla contain valuable medicinal flavonoids. Static magnetic field promoted apigenin production and antioxidative enzyme activities in M. chamomilla cell suspension.

This study represents an optimized protocol for cell line culture of Matricaria chamomilla and the impact of clino-rotation on cell division, cell growth, and antioxidant enzyme activities for the first time. The cell suspension was transferred in the solid MS medium supplied with 2, 4-D, and KIN. Then the calli produced from a cell line were selected for callus subculture and clino-rotation treatment for 7 days by a 2D-clinostat. A significant rise of fresh and dry weights, cell division, total soluble sugar, reducing sugar, and starch contents were detected under clino-rotation. Protein content approximately unchanged in microgravity-treated calli. Antioxidant enzymes activities, such as peroxidase, catalase (CAT), and superoxide dismutase were elevated in calli exposed to microgravity. CAT activity showed a more than three-fold increase than that of control. According to native polyacrylamide gel electrophoresis, all the antioxidant enzymes isoforms were stronger in clino-rotated calli than that of the untreated control. Microgravity also stimulated H2O2 production and markedly adjusted lipid peroxidation in calli exposed to clino-rotation. These findings suggest that clino-rotation with stimulation of carbohydrate accumulation and antioxidant enzymes mitigates oxidative stress and improves growth and cell division.Key messageThe isolation of M. chamomilla cell line with high growth was conducted to study the impact of clino-rotation on some cellular and antioxidative enzyme responses. Clino-rotation stimulated the cell division and growth by induction of antioxidant enzyme activities.

Fulvic acid (FA) is an active humic substance and is found to improve the antioxidant defence system under unfavourable conditions. Dunaliella salina is a unicellular microalga and is a rich source of β -carotene. In this study the impact of fulvic acid (FA) was investigated on some physiological parameters, H 2 O 2 production, antioxidant metabolites, and enzymatic responses related to the ascorbate (ASA)-glutathione (GSH) pathway in D. salina . Results showed that 100 mg FA L −1 maintained the D. salina cell growth compared to control, and exhibited as a suitable treatment to induce carotenoids compared to 50 FA mg L −1 . However, 200 FA mg L −1 significantly decreased the cell biomass. FA (100 mg L −1 ) enhanced the total carotenoids (3.92 pg cell −1 ), β -carotene (2.46 pg cell −1 ), and lutein (0.81 pg cell −1 ) after 7 days, which was accompanied by a reduction in the chlorophyll a and b . Cell number did not change significantly under FA and cells trended to be round in shape after 7 days. Protein content showed an insignificant change, while H 2 O 2 level was promoted by FA treatment, which was related to the regulation of the ASA-GSH pathway. The activity of ascorbate peroxidase, superoxide dismutase, and dehydroascorbate reductase was more promoted in the FA-treated cells, while glutathione reductase activity and glutathione content were just induced under Sevier oxidative conditions. The findings of this research suggest new insights into the inducing impact of FA on the ASA-GSH pathway and carotenoid biosynthesis to regulate the ROS level in D. salina .

LED (light-emitting diode) light is an economical and effective light source for inducing plant growth and development. The impact of different LED lights was investigated on callus growth, antioxidant enzymes, oxidative damage, and secondary metabolite production of H. reticulatus. The in vitro callus initiated from hypocotyl were subcultured on Murashige and Skoog (MS) medium and transferred to shelves with different LED lights (white, red, blue, and red-blue) and darkness for 3 wk. Results showed darkness and red-blue light were the best for maximum biomass, protein content, and cell viability. Red and blue LED lights motivated cells to be round in shape and non-viable, and induced more lipoxygenase activity, lipid peroxidation, and hydrogen peroxide contents as compared to darkness and red-blue light. Different LED lights enhanced total sugar content as compared to darkness. The maximum activities of superoxide dismutase (SOD) and catalase (CAT) were observed in calluses treated to red-blue light and darkness, while peroxidase (POX) activity was more induced under blue and red lights. LED light also enhanced the accumulation of total phenol, flavonoid, alkaloid, secondary metabolites, and DPPH scavenging activity, especially in red-blue light. This research may establish new strategies by red-blue LED light for sustainable production of secondary metabolite and biomass in H. reticulatus callus.

Cell suspension culture has the potential to be a valuable source for the bioactive compound productions. In this study, an optimized procedure was established for callus and cell suspension culture of Physalis alkekengi for the first time, and the impact of static magnetic field (SMF, 6 mT) was studied on the high-value metabolic compounds through investigation of signaling molecules and gene expressions at the late log-to-stationary phase. Results showed that the growth regulators of 6-benzyl amino purine (BAP, 1.5 mg−1 L) and 1-naphthaleneacetic acid (NAA, 0.4 mg−1 L) induced the highest fresh weight, callus rate, callus index, and total withanolides. Cell suspension culture was established in the liquid MS medium supplied with BAP (1.5 mg−1 L) and NAA (0.1 mg−1 L). SMF application decreased slightly the cell growth and viability and enhanced the number of round-shaped cells. The hydrogen peroxide (H2O2) and nitric oxide (NO) levels increased at an all-time series after SMF exposure, and their maximum contents were observed after 12 h. A significant alteration of malondialdehyde content was also identified after 12 h of SMF exposure. The expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), 1-deoxyD-xylulose 5-phosphate synthase (DXS), squalene synthase (SQS), sterol Δ7-reductase (DWF5), and C-7,8 sterol isomerase (HYD1) genes was upregulated significantly after 24 and 48 h. An increase in the total withanolides was related to more activity of HMGR and DXS enzymes in SMF-exposed cells and the maximum physalin A (12.8 mg g−1 DW) and physalin B (1.92 mg g−1 DW) obtained after 24 h compared to controls. Findings suggest that SMF can play a supportive factor in inducing steroidal compounds in P. alkekengi through modulating H2O2 and NO levels and the related-gene expressions.

Effect of mechanical vibration on salt stress alleviation was studied in pennyroyal ( Mentha pulegium L.) seedlings under in vitro and greenhouse conditions, and changes in growth, anatomical, and antioxidative responses were investigated. To determine the optimum frequency of vibration, the sterilized seeds were cultivated on Murashige and Skoog (MS) basal medium. The 14-day-old seedlings were exposed to various frequencies of sinusoidal vibration (0, 50, 100, and 150 Hz) for 30 min, and the optimum frequency was determined based on some growth, physiological, and anatomical parameters. Vibrations up to 100 Hz increased growth, shoot length, chlorophyll content, and relative water content (RWC). Vibration-induced aerenchyma formation, stele diameter, phloem, and suppressed xylem and only a few xylem vessels can be observed at 100 Hz. For evaluation of vibration effects on salt stress alleviation, the seedlings were treated by optimum vibration frequency (100 Hz) and then were subjected to salinity stress (0, 50, 100, and 150 mM NaCl). In salt-stressed plants, vibration decreased malondialdehyde (MDA), H 2 O 2 , electrolyte leakage, total carbohydrates, polyphenol oxidase (PPO) activity, and induced proline, protein, ascorbate peroxidase (APX) peroxidase (POX), and superoxide dismutase (SOD) activities. The lower contents of MDA, H 2 O 2 , and electrolyte leakage under in vitro grown seedlings comparing to that of whole plants could be associated with the higher levels of in vitro antioxidative enzyme activities. However, vibration induced more antioxidative enzyme activities.

Clinostat is a device often used for applying microgravity analogs in gravitational biology studies. It can constantly change the direction of the gravity vector through clinorotation with the possibility of speed regulation. In the present study, the impact of clinorotation (speed of 30 rpm) was investigated on the cell growth, viability, oxidative damage, and antioxidant compounds in Anthemis gilanica cell line using a two-dimensional clinostat. Cell clones were obtained from putting a cell suspension (1 ml) on the solid MS medium supplemented with 1-naphthaleneacetic acid (NAA, 0.5 mg L−1) and 6-benzylaminopurine (BAP, 1.5 mg L−1). Then, a cell line clone was transferred to a liquid MS medium for proliferation. The optimum subculture time for the cell line was found to be 14–15 days, and the cell line showed higher fresh weight compared to the control. The cell line was exposed to clinorotation (30 rpm) for 3 and 7 days. Results showed the cell growth parameters are managed with the ROS level and accumulation of antioxidant compounds in a time-dependent manner. Clinorotation increased cell growth, viability, protein content, DPPH, and antioxidant power, especially after 7 days. The level of H2O2, MDA, and protein-carbonyl increased after 3 days of clinorotation and then did not change significantly after 7 days compared to the control. Comet assay showed the weak genotoxicity impact of clinorotation on DNA damage in A. gilanica, which may relate to induction of antioxidant compounds (phenol and flavonoid) and PAL activity, especially after 7 days. But anthocyanin content did not change between treatments. The results display the potential effect of clinorotation on enhancing antioxidant capacity against oxidative damage and maintaining cell growth.Key messageCell line with a homogenous population of proliferating cells can prepare the proper situation to study various cell responses under microgravity. Improving of potential antioxidant by clinorotation mitigates oxidative damage in medicinal plant cells.

Magnetic fields are an unavoidable physical factor affecting living organisms. Lettuce seeds (Lactuca sativa var. cabitat L.) were subjected to various intensities of the static magnetic field (SMF) viz., MF0 (control), SMF1 (0.44 Tesla (T), SMF2 (0.77 T), and SMF3 (1 T) for three exposure times (1, 2, and 3 h). SMF-treated seedlings showed induction in growth parameters and metabolism comparing to control. All photosynthetic pigments were induced markedly under SMF, especially chlorophyll a. SMF at different intensities boosted osmolytes, non-enzymatic antioxidants, and the phenylalanine ammonia-lyase activity over non-magnetized seedlings. Oxidative damage criteria viz., hydrogen peroxide, superoxide radical, and lipid peroxidation, as well as polyphenol oxidase activity, were kept at low values under SMF-treated seeds relative to control, especially SMF2. Electron donors to antioxidant enzymes including nitrate reductase, nitric oxide, and hydrogen sulfide induced via SMF exposure and consequently the activities of superoxide dismutase, glutathione-S-transferases, catalase, and peroxidases family enzymes were also stimulated under SMF, whatever the intensity or the exposure period applied. All these regulations reflected on the enhancement of lettuce yield production which reached 50% over the control at SMF3. Our findings offered that SMF-seed priming is an innovative and low-cost strategy that can improve the growth, bioactive constituents, and yield of lettuce.