Transcriptional response of Arabidopsis thaliana's root-tip to spaceflight.

Plants are expected to play a critical role in the biological life support systems of crewed spaceflight missions, including in the context of upcoming missions targeting the Moon and Mars. Therefore, understanding the response of plants to spaceflight is essential for improving the selection and engineering of plants and spaceflight conditions. In particular, understanding the root-tip's response to spaceflight is of importance as it is the center of orchestrating the development of the root, the primary organ for the absorption of nutrients and anchorage. GLDS-120 is a pioneering study by Paul et al. that used transcriptomics to evaluate the spaceflight response of the root-tip of the model plant Arabidopsis thaliana in dark and light through separate analyses of three genotype groups (Wassilewskija, Columbia-0, and Columbia-0 PhyD) and comparison of genotype responses. Here, we provide a complementary analysis of this dataset through a combined analysis of all samples while controlling for the genotypes in a paired analysis. We identified a robust transcriptional response to spaceflight with 622 DEGs in light and 200 DEGs in dark conditions. Gene enrichment analysis identified 37 and 13 significantly enriched terms from biological processes in light and dark conditions, respectively. Prominent enrichment for hypoxia-related terms in both conditions suggests hypoxia is a key stressor for root development during spaceflight. Additional enriched terms in light conditions include the circadian cycle, light response, and terms for the metabolism of flavonoid and indole-containing compounds. These results further our understanding of plants' responses to the spaceflight environment.

Biochemistry of microwave controlled Heracleum sosnowskyi (Manden.) roots with an ecotoxicological aspect.

Sosnowski hogweed is an invasive weed in eastern-middle Europe that is dangerous to human health and the environment. The efficacy of its control using chemical and mechanical methods is limited. Electromagnetic radiation (microwaves) could be an environmentally friendly alternative for controlling this species. This study aims to: (1) Determine the effect of varying microwave treatment (MWT) durations on the control of S. hogweed using a device emitting microwaves at 2.45 GHz, 32.8 kW/m2; (2) Evaluate the impact of MWT on soil by an ecotoxicological bioassays; (3) Analyze biochemical changes occurring in the roots during the process. A field study was performed to assess the efficacy of S. hogweed control using MWT in times from 2.5 to 15 min. The MWT-treated soil was collected immediately after treatment (AT) and tested using bioassays (Phytotoxkit, Ostracodtoxkit, and Microtox). Fourteen days AT, the MWT hogweed roots were dug out, air-dried, and analyzed for the content and composition of essential oil, sugars, and fatty acids. According to the ecotoxicological biotests, the MWT soils were classified as non-toxic or low-toxic. The regeneration of hogweed was observed only in non-treated plants (control). Hogweed MWT for 2.5-15 min did not regenerate up to 14 days AT. The average weight of roots in hogweed MWT for 15.0 min was ca. two times smaller than the control plants. Those roots contained significantly higher amounts of sugars and saturated fatty acids than the control. We did not find a correlation between S. hogweed root essential oil content and composition and MWT time. The main compounds of essential oil were p­cymene and myristicin. No highly photosensitizing compounds were identified in the tested root oil. We conclude that MWT of S. hogweed could be an environmentally safe and prospective control method, but more studies are needed.

HY5 regulates light-dependent expression and accumulation of miR858a-encoded peptide, miPEP858a.

microRNA encoded peptide (miPEP) has been shown to have potential to regulate corresponding miRNA and associated function. miPEP858a regulate phenylpropanoid pathway and plant development. Several studies have suggested that various factors like light, temperature, heavy metals etc. can regulate gene and their associated functions. However, what are the regulators of miPEP are not reported till date. In this study we have reported that light directly regulates miPEP858a accumulation in Arabidopsis thaliana. Peptide assay in light and dark clearly showed the essential requirement of light. Along with this, we have reported that HY5 a shoot-to-root mobile, light-mediated transcription factor plays a crucial role in the function of miPEP858a. The transcript and endogenous protein accumulation of miPEP858a in hy5-215, OXHY5/hy5, and cop1-4 suggested that the HY5 positively regulates miPEP858a. In addition to that this study also include grafting assay between shoot of different mutant and transgenic lines with root of miPEP858a promoter:reporter lines and promoter deletion construct experiment clearly suggested that HY5 a transcription factor regulates light-dependent expression and accumulation of miPEP858a.

Lessons Learned from the Studies of Roots Shaded from Direct Root Illumination.

The root is the below-ground organ of a plant, and it has evolved multiple signaling pathways that allow adaptation of architecture, growth rate, and direction to an ever-changing environment. Roots grow along the gravitropic vector towards beneficial areas in the soil to provide the plant with proper nutrients to ensure its survival and productivity. In addition, roots have developed escape mechanisms to avoid adverse environments, which include direct illumination. Standard laboratory growth conditions for basic research of plant development and stress adaptation include growing seedlings in Petri dishes on medium with roots exposed to light. Several studies have shown that direct illumination of roots alters their morphology, cellular and biochemical responses, which results in reduced nutrient uptake and adaptability upon additive stress stimuli. In this review, we summarize recent methods that allow the study of shaded roots under controlled laboratory conditions and discuss the observed changes in the results depending on the root illumination status.

Decoupling of Plant Growth and Accumulation of Biologically Active Compounds in Leaves, Roots, and Root Exudates of Hypericum perforatum L. by the Combination of Jasmonate and Far-Red Lighting.

The plant hormone jasmonic acid (JA) fine tunes the growth-defense dilemma by inhibiting plant growth and stimulating the accumulation of secondary compounds. We investigated the interactions between JA and phytochrome B signaling on growth and the accumulation of selected secondary metabolites in Hypericum perforatum L., a medically important plant, by spraying plants with methyl jasmonate (MeJA) and by adding far-red (FR) lighting. MeJA inhibited plant growth, decreased fructose concentration, and enhanced the accumulation of most secondary metabolites. FR enhanced plant growth and starch accumulation and did not decrease the accumulation of most secondary metabolites. MeJA and FR acted mostly independently with no observable interactions on plant growth or secondary metabolite levels. The accumulation of different compounds (e.g., hypericin, flavonols, flavan-3-ols, and phenolic acid) in shoots, roots, and root exudates showed different responses to the two treatments. These findings indicate that the relationship between growth and secondary compound accumulation is specific and depends on the classes of compounds and/or their organ location. The combined application of MeJA and FR enhanced the accumulation of most secondary compounds without compromising plant growth. Thus, the negative correlations between biomass and the content of secondary compounds predicted by the growth-defense dilemma were overcome.

Consequences of LED Lights on Root Morphological Traits and Compounds Accumulation in Sarcandra glabra Seedlings.

This study evaluated the effects of different light spectra (white light; WL, blue light; BL and red light; RL) on the root morphological traits and metabolites accumulation and biosynthesis in Sarcandra glabra. We performed transcriptomic and metabolomic profiling by RNA-seq and ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS), respectively. When morphological features were compared to WL, BL substantially increased under-ground fresh weight, root length, root surface area, and root volume, while RL inhibited these indices. A total of 433 metabolites were identified, of which 40, 18, and 68 compounds differentially accumulated in roots under WL (WG) vs. roots under BL (BG), WG vs. roots under RL (RG), and RG vs. BG, respectively. In addition, the contents of sinapyl alcohol, sinapic acid, fraxetin, and 6-methylcoumarin decreased significantly in BG and RG. In contrast, chlorogenic acid, rosmarinyl glucoside, quercitrin and quercetin were increased considerably in BG. Furthermore, the contents of eight terpenoids compounds significantly reduced in BG. Following transcriptomic profiling, several key genes related to biosynthesis of phenylpropanoid-derived and terpenoids metabolites were differentially expressed, such as caffeic acid 3-O-methyltransferase) (COMT), hydroxycinnamoyl-CoA shikimate hydroxycinnamoyl transferase (HCT), O-methyltransferase (OMT), and 1-deoxy-D-xylulose-5-phosphate synthetase (DXS). In summary, our findings showed that BL was suitable for growth and accumulation of bioactive metabolites in root tissue of S. glabra. Exposure to a higher ratio of BL might have the potential to improve the production and quality of S. glabra seedlings, but this needs to be confirmed further.

Circadian rhythms driving a fast-paced root clock implicate species-specific regulation in Medicago truncatula.

Plants have a hierarchical circadian structure comprising multiple tissue-specific oscillators that operate at different speeds and regulate the expression of distinct sets of genes in different organs. However, the identity of the genes differentially regulated by the circadian clock in different organs, such as roots, and how their oscillations create functional specialization remain unclear. Here, we profiled the diurnal and circadian landscapes of the shoots and roots of Medicago truncatula and identified the conserved regulatory sequences contributing to transcriptome oscillations in each organ. We found that the light-dark cycles strongly affect the global transcriptome oscillation in roots, and many clock genes oscillate only in shoots. Moreover, many key genes involved in nitrogen fixation are regulated by circadian rhythms. Surprisingly, the root clock runs faster than the shoot clock, which is contrary to the hierarchical circadian structure showing a slow-paced root clock in both detached and intact Arabidopsis thaliana (L.) Heynh. roots. Our result provides important clues about the species-specific circadian regulatory mechanism, which is often overlooked, and possibly coordinates the timing between shoots and roots independent of the current prevailing model.

HY5 regulates light-responsive transcription of microRNA163 to promote primary root elongation in Arabidopsis seedlings.

MicroRNAs (miRNAs) play key roles in the post-transcriptional regulation of gene expression in plants. Many miRNAs are responsive to environmental signals. Light is the first environmental signal perceived by plants after emergence from the soil. However, less is known about the roles and regulatory mechanism of miRNAs in response to light signal. Here, using small RNA sequencing, we determined that miR163 is significantly rapidly induced by light signaling in Arabidopsis thaliana seedlings. The light-inducible response of miR163 functions genetically downstream of LONG HYPOCOTYL 5 (HY5), a central positive regulator of photomorphogenesis. HY5 directly binds to the two G/C-hybrid elements in the miR163 promoter with unequal affinity; one of these elements, which is located next to the transcription start site, plays a major role in light-induced expression of miR163. Overexpression of miR163 rescued the defective primary root elongation of hy5 seedlings without affecting lateral root growth, whereas overexpressing of miR163 target PXMT1 inhibited primary root elongation. These findings provide insight into understanding the post-transcriptional regulation of root photomorphogenesis mediated by the HY5-miR163-PXMT1 network.

Differential root and shoot magnetoresponses in Arabidopsis thaliana.

The geomagnetic field (GMF) is one of the environmental stimuli that plants experience continuously on Earth; however, the actions of the GMF on plants are poorly understood. Here, we carried out a time-course microarray experiment to identify genes that are differentially regulated by the GMF in shoot and roots. We also used qPCR to validate the activity of some genes selected from the microarray analysis in a dose-dependent magnetic field experiment. We found that the GMF regulated genes in both shoot and roots, suggesting that both organs can sense the GMF. However, 49% of the genes were regulated in a reverse direction in these organs, meaning that the resident signaling networks define the up- or downregulation of specific genes. The set of GMF-regulated genes strongly overlapped with various stress-responsive genes, implicating the involvement of one or more common signals, such as reactive oxygen species, in these responses. The biphasic dose response of GMF-responsive genes indicates a hormetic response of plants to the GMF. At present, no evidence exists to indicate any evolutionary advantage of plant adaptation to the GMF; however, plants can sense and respond to the GMF using the signaling networks involved in stress responses.

Carotenoid Biosynthesis and Plastid Development in Plants: The Role of Light.

Light is an important cue that stimulates both plastid development and biosynthesis of carotenoids in plants. During photomorphogenesis or de-etiolation, photoreceptors are activated and molecular factors for carotenoid and chlorophyll biosynthesis are induced thereof. In fruits, light is absorbed by chloroplasts in the early stages of ripening, which allows a gradual synthesis of carotenoids in the peel and pulp with the onset of chromoplasts' development. In roots, only a fraction of light reaches this tissue, which is not required for carotenoid synthesis, but it is essential for root development. When exposed to light, roots start greening due to chloroplast development. However, the colored taproot of carrot grown underground presents a high carotenoid accumulation together with chromoplast development, similar to citrus fruits during ripening. Interestingly, total carotenoid levels decrease in carrots roots when illuminated and develop chloroplasts, similar to normal roots exposed to light. The recent findings of the effect of light quality upon the induction of molecular factors involved in carotenoid synthesis in leaves, fruit, and roots are discussed, aiming to propose consensus mechanisms in order to contribute to the understanding of carotenoid synthesis regulation by light in plants.

Red laser-mediated alterations in seed germination, growth, pigments and withanolide content of Ashwagandha [Withania somnifera (L.) Dunal].

Withania somnifera (L.) Dunal, generally well-known as Ashwagandha, is part of Indian traditional medicinal systems like Ayurveda, Siddha, and Unani for over 3000 years for treating an array of disorders. The chief bioactive component of this plant is the withanolides, a group of C28-steroidal lactone triterpenoids. These compounds are present in very low concentrations and hence cell culture methods have been used to enhance their production. Low-level laser irradiation has been reported to have elicited the seed germination, agronomical characters, biosynthesis of bioactive compounds in some plants. Therefore, the objective of the study was to investigate the effect of red (He-Ne) laser irradiation on seed germination, growth characters, pigment contents and withanolide content in W. somnifera. The seeds were inoculated onto two different combinations of Murashige and Skoog (MS) media and incubated for germination. The highest germination percentage was observed in ½ MS with pH 6.5 and GA3 presoaking followed by ½ MS with different pH. Four different doses of Helium-Neon (He-Ne) laser (10, 15, 20 and 25 J/cm2) were used to irradiate the seeds at 632.8 nm and germinated in vitro on ½ MS with pH 6.5. The maximum germination percentage, 63.88% was noted from seeds irradiated with 25 J/cm2 (P = 0.04). The highest total length of 13.33 cm was observed in the seedlings irradiated with 25 J/cm2 groups (P = 0.008). The highest total chlorophyll content of 329.5 µg/g fresh weight (FW) was observed for seedlings irradiated with 15 J/cm2 (P = 0.02) and the highest carotenoid content of 49.6 µg/g FW was observed for 25 J/cm2 treated seedlings. Further, primary root length was measured and found to be highest (11.14 cm) in seedlings irradiated with 10 J/cm2 and the highest number of lateral roots were observed for 15 and 25 J/cm2 groups. The significant amount of Withanolide A (WA) 0.52 µg/g dry weight (DW) and 0.60 µg/g DW was noted in 15 (P = 0.01) and 20 J/cm2 (P = 0.002) groups, respectively than control. The present investigation thus reveals the positive impact of red laser on the germination of seeds, growth characters and withanolide contents under in vitro environment.

Light contributes to salt resistance through GAI protein regulation in Arabidopsis thaliana.

The role of DELLAs in response to light intensity under salt stress is largely unknown. Therefore, the effect of three light intensities-low (35), medium (60), and high (155) µmol m-2 s-1 on Arabidopsis plants growth under saline condition (150 mM NaCl) was evaluated. High light intensity exhibited significant growth in the number of lateral roots related to the low light. Immunoblot assay revealed increased DELLA accumulation at the seedling stage under high light intensity. High light promotes seed germination by 24-44%, whilst, lateral roots by 25-90% in wild-type ecotypes. The lateral roots increased significantly in gai (gibberellic acid insensitive mutant) as compared with gai-t6 (wild type like gibberellic acid insensitive mutant) in response to low to medium and high to medium light intensity. High light increased seedling survival rate by 67% in Col-0 (Columbia) and 60% in Ler (Landsberg erecta) and showed a 28% increase in survival rate in gai mutant under salt stress as compared to gai-t6. Furthermore, salt-stress responsive genes' expression in gai-mutant establishes the relationship of DELLA proteins with salt resistance. Together, light is a cardinal element, its optimum quantity is highly beneficial and promotes salt stress resistance through DELLA protein at seedling stage in plants.

Effects of supplemental LED light quality and reduced growth temperature on swede (Brassica napus L. ssp. rapifera Metzg.) root vegetable development and contents of glucosinolates and sugars.

BACKGROUND: Low growth temperatures and the special light qualities of midnight sun in northern Scandinavia, have both been shown to improve eating quality of swede root bulbs. To study the combined effect of these factors on root development and sensory-related compounds, plants were grown in phytotron under different 24 h supplemental light-emitting diode (LED) light colours, at constant 15 °C, or reduced end-of-season temperature at 9 °C. RESULTS: Far-red LED (740 nm) light induced longer leaves and produced more roundly shaped bulbs, than the other light quality treatments. At constant 15 °C, supplemental light of far-red LED also produced a stronger purple crown skin colour than the other LED treatments. This difference between light quality treatments disappeared at 9 °C, as all bulb crowns developed a purple colour. There were no significant effects of LED-supplements on sugar concentrations, while the reduced temperature on average did increase concentrations of d-fructose and d-glucose. Total glucosinolate concentrations were not different among treatments, although the most abundant glucosinolate, progoitrin, on average was present in highest concentration under LEDs containing far-red light, and in lower concentration at 9 °C compared to 15 °C. CONCLUSION: The light quality of 24 h photoperiods in combination with temperature appears primarily important for growth and morphological traits in swede root bulbs. Influence of light quality and low temperature on appearance and sensory-related compounds may be utilized in marketing of root vegetables with special quality related to growth conditions of high latitude origin. © 2020 Society of Chemical Industry.

Rooting ability of rice seedlings increases with higher soluble sugar content from exposure to light.

Rooting ability of rice seedling for mechanical transplanting has a large impact on grain yield. This study explored the relationship between endogenous soluble sugar content and rooting ability of rice seedlings. We placed 15-day-old rice seedlings in controlled environment cabinets with stable light and sampled after 0, 3, 6, 9, 12, and 24 hours of light to measure their soluble sugar content, nitrate content, starch content, soluble protein content and rooting ability. The soluble sugar content of the rice seedlings before rooting increased rapidly from 65.1 mg g-1 to 126.3 mg g-1 in the first 9 hours of light and then tended to stabilize; however, few significant changes in the other physiological indices were detected. With the light exposure time increasing from 3 hours to 12 hours, the rooting ability measured with fresh weight, dry weight, total length, and number of new roots increased by 91.7%, 120.0%, 60.6% and 30.3%, respectively. Rooting ability was related more closely to soluble sugar content than to nitrate-nitrogen content of rice seedlings before rooting and their correlation coefficients were 0.8582-0.8684 and 0.7045-0.7882, respectively. The stepwise regression analysis revealed that the soluble sugar content before rooting explained 73.6%-75.4% of the variance, and the nitrate-nitrogen content explained an additional 7.3%-14.2% of the variance in rooting ability, indicating that compared with nitrate-nitrogen content, soluble sugar content of rice seedlings before rooting was more dominant in affecting rooting ability. This study provides direct evidence of the relationship between the rooting ability and endogenous soluble sugar content of rice seedlings.

Gene expression profiling reveals the effects of light on adventitious root formation in lotus seedlings (Nelumbo nucifera Gaertn.).

BACKGROUND: Lotus is an aquatic horticultural crop that is widely cultivated in most regions of China and is used as an important off-season vegetable. The principal root of lotus is degenerated, and adventitious roots (ARs) are irreplaceable for plant growth. We found that no ARs formed under darkness and that exposure to high-intensity light significantly promoted the development of root primordia. Four differential expression libraries based on three light intensities were constructed to monitor metabolic changes, especially in indole-3-acetic acid (IAA) and sugar metabolism. RESULTS: AR formation was significantly affected by light, and high light intensity accelerated AR development. Metabolic changes during AR formation under different light intensities were evaluated using gene expression profiling by high-throughput tag-sequencing. More than 2.2 × 104 genes were obtained in each library; the expression level of most genes was between 0.01 and 100 (FPKF value). Libraries constructed from plants grown under darkness (D/CK), under 5000 lx (E/CK), and under 20,000 lx (F/CK) contained 1739, 1683, and 1462 upregulated genes and 1533, 995, and 834 downregulated genes, respectively, when compared to those in the initial state (CK). Additionally, we found that 1454 and 478 genes had altered expression in a comparison of libraries D/CK and F/CK. Gene transcription between libraries D/F ranged from a 5-fold decrease to a 5-fold increase. Twenty differentially expressed genes (DEGs) were involved in the signal transduction pathway, 28 DEGs were related to the IAA response, and 35 DEGs were involved in sugar metabolism. We observed that the IAA content was enhanced after seed germination, even in darkness; this was responsible for AR formation. We also observed that sucrose could eliminate the negative effect of 150 µMol IAA during AR development. CONCLUSIONS: AR formation was regulated by IAA, even in the dark, where induction and developmental processes could also be completed. In addition, 36 genes displayed altered expression in carbohydrate metabolism and ucrose metabolism was involved in AR development (expressed stage) according to gene expression and content change characteristics.

Effects of light irradiation on essential oil biosynthesis in the medicinal plant Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim) Kitag.

Asarum heterotropoides Fr. var. mandshuricum (Maxim) Kitag (Chinese wild ginger) is an important medicinal herb. Essential oil extracted from its roots is the key ingredient and is mainly composed of phenylpropanoid compounds. As a skiophyte plant, light is a crucial factor for A. heterotropoides var. mandshuricum growth and metabolism. To investigate the effects of light irradiation on the essential oil biosynthesis in A. heterotropoides var. mandshuricum, the plants were cultivated in four light irradiation treatments (100, 50, 24 and 12% full sunlight). The photosynthetic capacity, essential oil content and composition, activities of several enzymes and levels of some secondary metabolites involved in the shikimic acid and cinnamic acid pathways were analyzed. The leaf mass per area, average diurnal net photosynthetic rate, and the essential oil content increased significantly with increasing light intensity. Phenylalanine, cinnamic acid, and p-coumaric acid in the cinnamic acid pathway were at their highest levels in plants cultivated in 100% full sunlight. The highest content of shikimic acid in the shikimic acid pathway was obtained in plants grown in 50% sunlight transmittance. The activity of the enzymes 3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase, phenylalanine ammonia lyase, cinnamate-4-hydroxylase and 4-coumarate:CoA ligase increased proportionally with light intensity. Overall, we conclude that high light irradiation promotes high net photosynthetic rate, high activity of enzymes and high amounts of phenylpropanoid precursor metabolites leading to significant biosynthesis of essential oil in A. heterotropoides var. mandshuricum.

Mutants of Citrus macrophylla rootstock obtained by gamma radiation improve salt resistance through toxic ion exclusion.

Salinity is one of the biggest challenges that need to be faced in crop production. Citrus is highly sensitive to salt stress and obtaining rootstocks with improved resistance to salinity is key for the citrus growing industry. In this study, five mutants of Citrus macrophylla rootstock, obtained through gamma radiation and in vitro pre-selected for their resistance to salinity, were irrigated with a solution containing 100 mM of NaCl. After 8 weeks of exposure, the mutants were evaluated for their performance (growth, visual leaf damage) and chlorophyll, proline, starch, soluble sugars and ion contents to determine their degree of resistance to this salinity level. In the saline conditions assayed, all the mutants showed better performance and less leaf damage than Citrus macrophylla. Our data suggest that this improved resistance to salinity was based on their capacity to accumulate less Na (MM4B and MMN1) or Cl- (MM1A, MM4A and MM3B). Besides having the lowest Cl- content, the mutants MM1A, MM4A and MM3B, had the highest NO3- concentrations in salinity. Furthermore, mutants did not show chlorophyll degradation and showed less leaf damage and acceptable plant growth. Other parameters including proline and soluble sugars, did not prove decisive in the salinity resistance of these genotypes.

Subject: UV-B radiation and low temperature promoted hypericin biosynthesis in adventitious root culture of Hypericum perforatum.

The hypericin is assumed as a highly demanded and key bioactive compound, which has antiviral, antimicrobial, antioxidant, and antitumor properties isolated from Hypericum perforatum. Nowadays, increasing bioactive molecules' contents through generating novel compounds is one of the major research objectives of H. perforatum biotechnology; however, this plant remains recalcitrant and unmanageable to Agrobacterium mediated transformation and genetic improvement programs. In order to overcome these challenges, many researchers have focused on this unruly herb using biotic and abiotic eliciting strategies. Therefore, two experiments were separately designed for the evaluation of two types of abiotic elicitors, aiming at increasing the productivity of hypericin in the adventitious root suspension culture of H. perforatum. The first one was accomplished to evaluate the effect of UV-B light elicitors (the exposure time of 30, 60, and 90 min) and the recovery treatment (with or without) on hypericin content while the second one was assessed the effect of various temperatures (4°C, 8°C, 16°C, and 25°C) in three different exposure times (24 h, 72 h, and 7 d). Based on the results, UV-B (60 min) treatment followed by the recovery produced 0.430 µg/g DW hypericin and was distinguished as the most effective UV-B elicitation treatment. In addition, a temperature of 4°C for a period of 72 hours is required to get the highest amount of hypericin content. These findings indicate the fact that hypericin biosynthesis is notably affected by UV-B exposure time and Low-temperature. The data also clearly elucidate further mechanisms of hypericin production in H. perforatum adventitious root culture.

Response of young Nerium oleander plants to long-term non-ionizing radiation.

MAIN CONCLUSION: Although exposure to low frequency electromagnetic radiation is harmful to plants, LF-EM irradiated Nerium oleander seedlings exhibited enhanced development and growth, probably taking advantage of defined structural leaf deformations. Currently, evidence supports the undesirable, often destructive impact of low frequency electromagnetic (LF-EM) radiation on plants. The response of plants to LF-EM radiation often entails induction in the biosynthesis of secondary metabolites, a subject matter that is well documented. Nerium oleander is a Mediterranean plant species, which evolved remarkable resistance to various environmental stress conditions. In the current investigation, cultivated N. oleander plants, following their long-term exposure to LF-EM radiation, exhibited major structural modifications as the flattening of crypts, the elimination of trichomes and the reduction of the layers of the epidermal cells. These changes co-existed with an oxidative stress response manifested by a significant increase in reactive oxygen species at both the roots and the above ground parts, a decline in the absorbance of light by photosynthetic pigments and the substantially increased biosynthesis of L-Dopa decarboxylase (DDC), an enzyme catalyzing the production of secondary metabolites that alleviate stress. The exposed plants exhibited greater primary plant productivity, despite a manifested photosynthetic pigment limitation and the severe oxidative stress. This unique response of N. oleander to severe abiotic stress conditions may be owed to the advantage offered by a structural change consistent to an easier diffusion of CO2 within the leaves. A major plant response to an emerging "pollutant" was documented.