Turnip (Brassica rapa L.) plants were grown in Perlite with low (< 2.5 μM) or adequate (25 μM) boron supply under well-watered and drought conditions for 12 weeks. Dry mass of leaves and roots was reduced under drought by about 61 and 56 % in plants supplied adequately with B, while up to 84 and 74 % under B starvation. Drought reduced B content by about 70 and 82 % for B-sufficient and B-deficient plants, respectively. According to the chlorophyll fluorescence parameters, the photosynthesis processes conserved their normal activities under low B supply in well-watered plants, while a serious damage to photosystem 2 occurred under drought stress. Stomatal limitation was the most important cause for a 17 % lower net photosynthetic rate (P_N) of drought stressed B-sufficient plants. In B-deficient plants, however, both stomatal and non-stomatal limitations were involved in 53 % reduction of P_N. Low B supply reduced strongly leaf water potential.

This work was performed to find out if metal resistant clones of Salix viminalis L. are capable to achieve high resistance to the metals by regulating their net accumulation. Salix clones with low or high resistance in combination with low or high accumulation capacity of either Zn or Cd were cultivated from cuttings in nutrient solution. The investigation included leakage and uptake experiments using ⁶⁵Zn or ¹⁰⁹Cd and analysis of root cation exchange capacity (CEC). Some plants were pre-treated with unlabeled 0.5 μM Cd or 2.5 μM Zn 24 h prior to the experiments to induce possible tolerance mechanisms. To find out if the regulation was a metabolic process, experiments were also performed with 2,4-dinitrophenol (DNP). Clones with high resistance and low Cd accumulation had higher efflux of Cd compared to the other clones, in both untreated and Cd pre-treated plants. This indicates a constitutive property to lower Cd accumulation by high Cd leakage. Pre-treatment with 0.5 μM Cd diminished the Cd net uptake to a level near zero in all clones, likely to be due to decreased the Cd uptake. In contrast, resistant clones with high Cd accumulation had the highest root CEC, which may be used to bind up Cd in the free space. No clear regulation of Zn net uptake was found in Zn-resistant clones. Pre-treatment with Zn decreased the uptake of Zn into the free space in Zn-resistant clones. The resistant high-accumulating clones, however, showed the highest leakage of Zn in both untreated and pre-treated plants, a constitutive process not related to high accumulation. Neither the influx nor the efflux of Cd or Zn was affected by DNP indicating passive transport across the plasma membrane.

Floral initiation in apple (Malus domestica Borkh) was studied by a novel morphogenetic approach. Developmental stages of apices were evaluated based on the morphology of shoot apical meristem (SAM) from various collection dates. Besides, the frequency of each stage was calculated within apices populations after full blooming (DAFB). Prior to doming of apex, three marked phases were found based on SAM morphology: 1) narrow appearance (vegetative phase), 2) broadened form (transition phase), and 3) prominent shape (commitment phase). A furrow region was formed at the base of leaf primordium during the bract initiation, while significant broadening of SAM was observed. Cell division patterns manifested in modification of anisotropic clusters from isotropic cellular packets, as a result of which profound morphological changes of apices occurred. Based on these findings, we propose that the structural alterations prior to doming may be taken into account for determination of the initial development and reproduction signs in apple trees.

Polygalacturonases are enzymes involved in plant cell wall growth and reorganization. Transgenic Arabidopsis thaliana plants with a Saccharomyces cerevisiae endopolygalacturonase gene (PGU1) were obtained. The yeast gene was properly expressed in the plants as it has been shown by RT-PCR as well as by the increase in the endopolygalacturonase activity. The transgenic plants showed conspicuous malformations in early stages of development probably due to a weak cell adhesion. On the other hand, adult plants exhibited almost no phenotypic differences as compared to the wild type plants, this suggesting the appearance of some mechanisms on the plant side to counteract the effect of the overexpressed polygalacturonase.

cDNA-AFLP fingerprinting was used to identify genes with modulated expression during germination in common bean (Phaseolus vulgaris L.). The analysis was performed on the embryo axes. Nine time points covering the whole germination were considered and 800 transcript-derived fragments (PvTDFs) were scored. Among them, 80 % showed no changes during germination. The 97 PvTDFs showing differential expressions during germination were sequenced along with 14 constant transcripts that were randomly chosen. The expression of seven variable PvTDFs was confirmed by real-time RT-PCR. We observed that 92 % of the transcript changes, including 35 % of appearing mRNAs, took place before radicule protrusion, 0-17 h after imbibition (HAI). A major shift in gene expression was observed between 9 and 14 HAI, suggesting a key moment of cell re-programming. Sequence homologies were found for 52 % of the sequenced PvTDFs. The identified transcripts encode proteins belonging to several functional groups including transcription factors, proteins involved in storage compound hydrolysis, cell elongation or oxidative stress protection.

A high frequency plant regeneration system was developed for the production of high yielding elite clones of Garcinia indica via direct organogenesis. A maximum number of 86.2 shoot buds per explant were induced from the mature seed segments cultured on Woody plant medium (WPM) supplemented with 2.0 mg dm^-3 N⁶-benzyladenine and 1 mg dm^-3 indole-3-acetic acid. Rooting was achieved on half-strength WPM medium supplemented with 3 mg dm^-3 indole-3-butyric acid. Rooted plantlets were acclimatized and transferred to greenhouse for further growth. The highest survival rate of 95 % was recorded using a mixture of garden soil and sand. Histological studies clearly revealed multiple shoot formation from mature seed segments.

We study apical dominance in Alstroemeria, a plant with an architecture very different from the model species used in research on apical dominance. The standard explant was a rhizome with a tip and two vertically growing shoots from which the larger part had been excised leaving ca. 1 cm stem. The axillary buds that resumed growth were located at this 1-cm stem just above the rhizome. They were released by removal of the rhizome tip and the shoot tips. Replacement of excised tips by lanolin with indole-3-butyric acid (IBA) restored apical dominance. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and N-1-napthylphthalamic acid (NPA) reduced apical dominance. 6-Benzylaminopurine (BAP) enhanced axillary bud outgrowth but the highest concentrations (> 9 μM) caused fasciation. Thidiazuron (TDZ) did not show improvement relative to BAP. Even though the architecture of Alstroemeria and the model species are very different, their hormonal mechanisms in apical dominance are for the greater part very similar.

Microtubule cytoskeleton organization during microspore mother cell (MMC) meiosis in Allium cepa L. and microsporogenesis in Nicotiana tabacum L. was examined. The MMC microtubules (MTs) were short and well dispersed in the cytoplasm of both taxa. As the MMCs of both species entered metaphase of meiosis I, the MTs constructed a spindle that facilitated the chromosomes to orient in the meridian plane. At anaphase of meiosis I, the spindle MTs differentiated into two types: one MT type became short, pulled the chromosomes toward the two poles, and was designated as centromere MTs; the second type of MT connected the two poles, and was designated as pole MTs. In A. cepa, where successive cytokinesis was observed, pole MTs assumed a tubbish shape. Some new short MTs aggregated in the meridian plane and constricted to form a phragmoplast, which developed into a cell plate, divided the cytoplasm into two parts and produced a dyad. However, in tobacco, a phragmoplast was not generated in anaphase of meiosis I and II and cytokinesis did not occur. The spindle MTs depolymerized and reorganized the radial arrangement of MTs from the nucleate surface to the periplasm during anaphase. Following telophase of meiosis II, the cytoplasm produced centripetal furrows, which met in the center of the cell and divided it into four parts, serving as a form of cytokinesis. In this process, MTs appeared to bear no relationship to cytokinesis.

Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (P_N) ranged from 3.4 to 5.7 μmol(CO₂) m^-2 s^-1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency ranging from 0.020 to 0.043 μmol(CO₂) μmol^-1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (g_s) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (P_N/g_s) and instantaneous (P_N/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen content per unit mass.

The objective of this study was to examine the effects of different abiotic stresses on the activity of an NADP-dependent malic enzyme (NADP-ME) and the corresponding gene transcription in the leaves of the hexaploid wheat (Triticum aestivum L.) The activity of the NADP-ME enzyme was increased by water stress (20 % polyethylene glycol 6000), low temperature (4 °C), darkness, salinity (200 mM NaCl), abscisic acid and salicylic acid. The transcription of the TaNADP-ME1 gene decreased in response to all of the stresses except darkness and NaCl. In addition, the transcription of TaNADP-ME2 was down-regulated by all of the tested treatments and could not be detected under dark stress.

Arthrocnemum macrostachyum, is a perennial halophytic shrub typical of Mediterranean salt marshes. The present study aims to investigate some combinations of inter simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) primers applied in real PCR. Thereby, the potential of R-ISSR markers to detect new genomic loci in 3 genotypes of A. macrostachyum grown in the Western coast of Syria was examined. Different combinations of RAPD and ISSR primers produced bands that were absent when single ISSR or RAPD primers were used. The results have demonstrated that ISSR primer (AG)₈TC gave more informative pattern when combined with different RAPD primers comparing to other tested primers. In contrast, the tested ISSR primer (GACA)₄ gave less informative pattern when used alone. These combinations were successfully applied in real PCR to detect new genomic variability in A. macrostachyum genotypes.

In this study, 16 hairpin RNA (hpRNA) vectors were constructed, each harboring 50 bp viral RNA sequence as the stem. They all targeted the coat protein (CP) gene of Potato virus Y (PVY). Virus resistance assay revealed that hairpin constructs targeting the anterior 200 bp regions of the CP gene were unable to induce virus resistance, while the 12 hpRNA constructs targeting posterior 600 bp regions induced high virus resistance up to 77.78 %. Northern blot analysis revealed that 50 bp-length hpRNA constructs could be transcribed efficiently and processed into siRNAs; however, no correlation between siRNA accumulation and degree of antiviral defense was observed. Results presented here indicated that the middle and 3' end of the CP cDNA was important for hpRNA-mediated PVY resistance, improving the design of pathogen-derived hpRNA expression cassettes for transgenic plant against viruses.

A new cereal type II metacaspase full-length cDNA from wheat (Triticum aestivum L.) leaves, TaeMCAII, was for the first time successfully amplified and sequenced. The full-length sequence of the TaeMCAII cDNA of 1 551 bp contains a 1 218 bp open reading frame. The deduced protein encoded by the TaeMCAII cDNA consists of 405 amino acids with a calculated molecular mass of 44 kDa and an isoelectric point of 5.29. In response to wounding or heat shock, a similar sequence of ultrastructural events including the tonoplast rupture, chromatin condensation, degradation of chloroplasts and disappearance of cytoplasm and organelles were observed using transmission electron microscopy. As the observed changes in TaeMCAII mRNA level did not occur to be statistically significant wounding-induced programmed cell death (PCD) seems to be metacaspase-independent pathway. Interestingly, in PCD caused by a heat-shock treatment, the level of TaeMCAII mRNA remained unaltered until 48 h after the stress what suggests that TaeMCAII participates in later stages of PCD triggered by heat-shock. Phylogenetic analysis enabled to classify TaeMCAII as a type II metacaspase. Finally, homology modelling of the putative three-dimensional structure of the TaeMCAII protein and a topology analysis of its probable active site were performed.

Leaves of the scab-susceptible apple (Malus domestica) cultivar Golden Delicious were harvested from May to August 2008 and 2009. Some leaves were healthy and some infected with fungus Venturia inaequalis. The phenolic compounds were analysed in healthy leaves, infected leaves and in the scab spot tissue. In comparison to healthy leaves, the infected leaves showed higher contents of hydroxycinnamic acid, flavanols and phloridzin, while lower contents on procyanidins, quercetins and phloretin. The total amount of phenolic compounds in the infected tissue was 10 to 20 % higher than in the healthy leaves. Accumulation of phenolic compounds is a post-infection response, and probably their further transformation is a prerequisite for plant resistance.

A full-length cDNA clone encoding cytosolic glutamine synthetase (GS1; EC 6.3.1.2) was isolated from melon (Cucumis melo L.) for the first time by RT-PCR and RACE approach. The clone, designated as M-GS1 (accession No. DQ851867), contains 1494 nucleotides with an open reading frame (ORF) of 1068 nucleotides. The deduced 356 amino acid sequence showed high similarity with previously reported GS1s from various plant species. Sequence analysis revealed that the predicted protein contains a GS β-Grasp domain, a GS catalytic domain, and the main conserved motifs characteristic of a plant GS1. The phylogenetic analysis displayed that M-GS1 is related most closely to the GS1 from Datisca glomerata. Southern blot analysis indicated that M-GS1 belongs to a small gene family of 2 or 3 members. M-GS1 was expressed in all plant tissues without evident tissue specificity, but with different patterns when the melon plants were fed in hydroponic culture with different forms and concentration of nitrogen. Ammonium dramatically enhanced the contents of M-GS1 transcripts in all tested tissues, while nitrate stimulated M-GS1 transcription only in the roots and leaves, but not in the stems; glutamate, however, depressed M-GS1 transcripts in the roots, but resulted in no significant change to the levels of M-GS1 transcripts in the stems and leaves. Moreover, the same effects were observed at the GS enzyme activity level. These results indicated that melons respond to changes of N nutrition by regulating M-GS1 expression.

Hexokinase (HXK, EC 2.7.1.1) plays an important role in the metabolism and glucose signalling. To examine the characteristics of HXK gene family in rice, the subcellular localizations of ten hexokinases (OsHXK1 - OsHXK10) were determined using OsHXK::GFP fusion proteins in tobacco mesophyll protoplasts. As was previously demonstrated, OsHXK4 was detected in the chloroplast stroma, OsHXK5 and OsHXK6 in the mitochondria, and OsHXK7 and OsHXK10 in the cytoplasm. In the present study, OsHXKs were clearly divided into three types (A, B, C) based on their N-terminal sequences. The new type-C HXKs in plants, OsHXK1, OsHXK7 and OsHXK8, which lack the plastidic transit peptide and the membrane anchor domain, were detected not only in the cytoplasm but also in the nucleus. The type-B HXKs, OsHXK2, OsHXK3, OsHXK9 and OsHXK10, which contained a membrane anchor domain, were distinctly localized in the mitochondria. These results suggest that OsHXKs localized in different cell compartments may be involved in the glucose signalling-related gene expression during growth and development of rice.

The effect of aluminum and chromium on two barley genotypes differing in Al tolerance was studied in a hydroponic experiment. Al stress decreased plant growth, biomass production, chlorophyll content and photosynthetic efficiency determined as variable to maximum chlorophyll fluorescence ratio (F_v/F_m), net photosynthetic rate (P_N), intercellular CO₂ concentration (c_i), stomatal conductance (g_s) and transpiration rate (E) less in an Al-tolerant genotype Gebeina than in an Al-sensitive genotype Shang 70-119. Cr stress also caused marked reduction in growth and photosynthetic traits in barley plants. Higher reduction was observed at pH 4.0 as compared to pH 6.5. Combined stress of Cr and Al, caused further reduction in growth and photosynthetic parameters.

The knowledge of breeding impacts on the genetic diversity of hybrids of Eucalyptus is crucial to the exploration of genetic resources. We estimated genetic polymorphic parameters of 112 hybrids of Eucalyptus spp. using 10 genomic simple sequence repeats (SSR) markers and 10 expressed sequence tags (EST) microsatellite markers. According to Student's t-test, there were no significant differences between genomic SSR and EST-SSR markers. Our results also revealed high polymorphism in the hybrids analyzed, indicating that both markers are appropriate for use in genetic breeding programs.

The role of peroxisomes in the oxidative injury induced by the auxin herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in leaves of pea (Pisum sativum L.) plants was studied. Applications of (2,4-D) on leaves or to root substrate increased the superoxide radical production in leaf peroxisomes. Foliar application also increased H₂O₂ contents in leaf peroxisomes. Reactive oxygen species (ROS) overproduction was accompanied by oxidative stress, as shown by the changes in lipid peroxidation, protein carbonyls, total and protein thiols, and by the up-regulation of the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, catalase, glucose 6-phosphate dehydrogenase and NADP⁺-dependent isocitrate dehydrogenase. Foliar or root 2,4-D applications also induced senescence symptoms in pea leaf peroxisomes, as shown by the decrease of protein content and glycolate oxidase and hydroxypyruvate reductase activities, and by the increase of endopeptidase, xanthine oxidase, isocitrate lyase and acyl-CoA oxidase activities as well as of 3-ketoacyl-CoA thiolase and thiol-protease protein contents. 2,4-D did not induce proliferation of pea leaf peroxisomes but induced senescence-like morphological changes in these organelles. Results suggest that peroxisomes might contribute to 2,4-D toxicity in pea leaves by overproducing cell-damaging ROS and by participating actively in 2,4-D-induced leaf senescence.

Desiccation of Xerophyta scabrida caused considerable damage of chloroplast ultrastructure together with a complete loss of chlorophyll. Upon rehydration, the relative water content of the pale-green leaves almost reached that of the dark-green ones, however, the Chl content and photosynthetic activity remained lower. The process of reconstitution of the photosynthetic apparatus in the re-greening leaves was accompanied by changes in fatty acid (FA) content. The amount of the FA methyl esters was more than 2-fold higher in the green leaves as compared to the dry ones and slightly increased after rehydration in the pale-green leaves. Among the three main fatty acids in the leaves, oleic, palmitic and linoleic acid, the latter increased more than 3-fold during rehydration. This acid is concentrated mainly in the glycolipids and this was an indirect indication for the restoration of the photosynthetic apparatus. Our results showed that rehydration of X. scabrida led to a decrease of the saturated FA in parallel with an increase of the unsaturated FA, thus indicating increased membrane permeability. The observed changes in the lipid content can be considered as a characteristic feature of X. scabrida and most probably of other poikilochlorophyllous species.

Somatic embryogenesis has been obtained in many citrus cultivars. However, culture synchronization is yet to be achieved and in the present work we evaluate the effect of desiccation, cold and size of cell clusters on embryo production efficiency from callus cultures of Citrus sinensis L. Osbeck, cv. Valencia. The results showed that sieving was effective in promoting somatic embryo synchronization, whether or not it was followed by cold or desiccation treatments. Histological and histochemical analyses are presented to characterize the structure of cell aggregates and protein accumulation.

Catechin is associated with several functions in animal and plant systems, with little information available regarding its role in plant growth. Low concentrations of catechin (50 and 100 μM) were found to enhance length of primary and lateral roots, number of lateral roots, fresh and dry masses of shoots and roots, leaf area, water potential of leaf and root tissues, the number of vascular bundles in the inflorescence, and leaf thickness in Arabidopsis thaliana ecotype Col-0. A significant increase in net photosynthetic rate, stomatal conductance and concentration of indole-3-acetic acid was also observed in catechin treated plants.

Protocol was developed for high frequency in vitro multiplication of an endemic species, Zingiber rubens Roxb. The sprouted buds of the rhizomes were cultured on Murashige and Skoog (MS) medium supplemented with 6-benzyladenine (BA; 0.5-5.0 mg dm^-3), indole-3-acetic acid (IAA; 0.5-2.0 mg dm^-3), kinetin (KIN; 1.0-3.0 mg dm^-3), naphthaleneacetic acid (NAA; 0.5-1.0 mg dm^-3) and adenine sulphate (ADS; 80-100 mg dm^-3). MS basal medium supplemented with 3 mg dm^-3 BA and 0.5 mg dm^-3 IAA was optimum for shoot elongation. The elongated shoots (1-2 cm) were transferred to multiplication medium containing 2 mg dm^-3 BA, 1 mg dm^-3 IAA and 100 mg dm^-3 ADS. The multiplication rate remained unchanged in subsequent subcultures. Upon ex vitro transfer, 85 % of plants survived. Genetic stability of micropropagated clones were periodically evaluated at an interval of 6 months up to 30 months in culture using random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) analysis and genetic uniformity in all regenerants was confirmed.

The shrub Chimonanthus praecox L. (wintersweet) which is native to Chinese montane forests produces its flowers in the midst of winter. This indicates that the floral organs of this species are adapted to growth and development under freezing temperatures. Here, we report the isolation and preliminary characterisation of a 33 kDa apoplastic antifreeze chitinase (CpCHT1) from the petals and its corresponding cDNA. The chitinase activity of CpCHT1 was confirmed by activity staining. Antifreeze activity was validated in terms of the formation of bipyramidal ice crystals and high thermal-hysteresis values. CpCHT1 was also found to affect the germination of fungal spores of four major plant pathogens. In addition, the gene and protein are expressed constitutively not only in flowers, but also in leaves, bark and root tissues. From these data we hypothesize that this protein is multifunctional and may protect wintersweet from freezing injury and provide nonspecific disease resistance.

The Nicotiana tabacum transgenic plants expressing a Cucurbita pepo antisense PHYA RNA were obtained. The seedlings of transgenic tobacco with reduced phytochrome A (PHYA) content displayed decreased sensitivity to continuous broad-band far-red radiation (λ > 680 nm). Under far-red irradiance transgenic seedlings showed less elongation of the hypocotyls, more rapid plastid development, more chlorophyll accumulation, less repression of lightdependent NADPH:protochlorophyllide oxidoreductase than wild-type plants that was in accordance with PHYA control of plant development. Dynamics of the far-red radiation dependent changes in low temperature chlorophyll fluorescence spectra for the transgenic and wild-type seedlings were consistent with the more rapid formation of photosynthetic apparatus in the seedlings with reduced PHYA.

The blue colour of Vanda coerulea petals is slowly produced during flower development but quickly disappears when the flowers are pollinated. To investigate the molecular basis of the phenomenon, we isolated a novel cytochrome P450 gene, CYP76AB1, from this plant by polymerase chain reaction (PCR) based on the conserved regions of flavonoid 3',5'-hydroxylase amino acid sequences. CYP76AB1 transcripts were detectable at low level in the late phase of flower development when the petals were light blue, but became abundant in the subsequent opening flower stage, as the petals turned blue. When the flowers were pollinated they turned white, and the CYP76AB1 transcripts returned to low level. This indicates that the expression of CYP76AB1 may regulate petal colour of V. coerulea, and be a target for developing permanently blue flowers.

In crosses between hexaploid wheat and inbred lines of rye, a small number of rye genotypes produce seeds carrying undifferentiated, non-viable embryos. Hybrids between such lines and those not showing this phenotype were used as pollen donors in crosses with bread wheat in order to determine the genetic basis of disturbed embryo development. A single gene, designated Eml-R1b, is causing this character. Molecular markers associated with F₂ genotypes derived from a contrasting rye inbred progeny were used for a linkage study. Recombinant inbred lines of an F₅ population served as testers. Eml-R1b maps to chromosome arm 6RL, along with two co-segregating microsatellite loci, Xgwm1103 and Xgwm732. Complementary interactions of deleterious genes in wheat and rye are discussed.

To improve large-scale in vitro production of Oplopanax elatus Nakai, we cultured somatic embryo-derived plantlets under a heterotrophic condition (semi-solid culture with sucrose), photoautotrophic condition (semi-solid culture without sucrose), or modified photoautotrophic condition (liquid culture with forced ventilation). The plantlets grown under the modified photoautotrophic condition had more leaves as well as higher chlorophyll content, and higher net photosynthetic rate than those grown under the conventional conditions. Further, the photoautotrophically grown plantlets acclimatized better and sooner upon ex vitro transplantation than did the conventionally cultured plantlets. Consequently, a photoautotrophic culture method with forced ventilation is effective for enhancing the growth and acclimatization of O. elatus.

Although crosstalk between cytosolic and plastidic terpenoid pathways has been validated in many plant species, we report here for the first time a striking elevation of the nucleus-encoded artemisinin biosynthesis relevant DBR2 mRNA following the incubation of plants with fosmidomycin (FM). FM decreased singlet oxygen (¹O₂) scavengers such as β-carotene and α-tocopherol and subsequently invoked ¹O₂ burst. The treatment of plants with fluridone (FD) neither decreased α-tocopherol content nor triggered ¹O₂ emission. In conclusion, FM can up-regulate ¹O₂-sensitive nuclear genes responsible for artemisinin biogenesis by mitigating the accumulation of plastidic scavenging terpenoids, thereby eliciting ¹O₂ generation and initiating ¹O₂ retrograde signaling.