What We Know and What We Do Not Know about Dragon Trees?

Screening and validation of reference genes in Dracaena cochinchinensis using quantitative real-time PCR

Dragon's blood, the red resin derived from the wounded Dracaena, is a precious traditional medicine used by different culture. Dracaena cochinchinensis is one of the main species of Dracaena, and is the endangered medicinal plants in China. The vulnerable status severely limits the medicinal value and wide application of dragon's blood. Therefore, it's essential to analyze the mechanisms that form dragon's blood in order to increase artificial production. To clarify the mechanisms forming dragon's blood, understanding gene expression in the flavonoid biosynthesis pathway is the foundation. However, reference genes of D. cochinchinensis haven't been analyzed. In this study, expression profiles of seven commonly used housekeeping genes (Actin, α-EF, UBC, β-tubulin, 18S, GAPDH, His) were evaluated by using quantitative real-time PCR combined with the algorithms geNorm, NormFinder, BestKeeper, and RefFinder. On the basis of overall stability ranking, the best reference genes were the combinations β-tubulin +UBC for wounded stems and α-EF +18S + Actin for different organs. Reliability of the recommended reference genes was validated by normalizing relative expression of two key enzyme genes PAL1 and CHI1 in the flavonoid biosynthesis pathway. The results provide a foundation to study gene expression in future research on D. cochinchinensis or other Dracaena.

Plant secondary metabolites involved in the stress tolerance of long-lived trees

Ancient trees are natural wonders because of their longevity, having lived for hundreds or thousands of years, and their ability to withstand changing environments and a variety of stresses. These long-lived trees have sophisticated defense mechanisms, such as the production of specialized plant metabolites (SPMs). In this review, we provide an overview of the major biotic and abiotic stresses that long-lived trees often face, as well as an analysis of renowned ancient tree species and their unique protective SPMs against environmental stressors. We also discuss the synthesis and accumulation of defensive SPMs induced by environmental factors and endophytes in these trees. Furthermore, we conducted a comparative genomic analysis of 17 long-lived tree species and discovered significant expansions of SPM biosynthesis gene families in these species. Our comprehensive review reveals the crucial role of SPMs in high resistance in long-lived trees, providing a novel natural resource for plant defense, crop improvement and even the pharmaceutical industry.

Longevity Estimates of Canary Palms and Dragon Trees via Radiocarbon Dating: Initial Results

Correctly estimating the maximum lifespan of plant species is a necessary component of demographic and life-history studies, which, in turn, are needed for understanding climatic impacts. Arboreal monocotyledons, which can grow to >30 m in height and >5 m in trunk perimeter, are difficult to age because they do not undergo seasonal dormancy; hence, their longevity has been estimated using various size-related methods. In this study, we tested radiocarbon (14C) dating with Accelerator Mass Spectrometry (AMS) as an additional tool for determining the age of two iconic monocotyledons: the Canary Island palm and the dragon tree. A total of 25 samples were collected from the basal stem of four palms and five dragon trees on Gran Canaria and Tenerife and then processed using the most advanced 14C-AMS analysis available. Calibration curves provided by the "IntCal group" were used to determine the oldest possible age of each sample, and 16 of them were found to be "modern", i.e., formed after the 1950s. Nine samples that were either collected from exterior, but lignified, palm tissues or from interior, and lignified, dragon tree tissues suggested ages > 300 years. Given the constant improvement of 14C-AMS tools, they can contribute to the further refinement of existing scientific knowledge on Macaronesian charismatic megaflora.

Structure and histochemistry of the stem of Dracaena cambodiana Pierre ex Gagnep

Dracaena cambodiana Pierre ex Gagnep is an important plant resource for producing dragon's blood and one of most popular ornamental trees in China. For a better understanding of the physiological function of the stem, the structural characteristics and main substance histological location of the stems of D. cambodiana were studied. The structural characteristics of the different developmental stages of stems of D. cambodiana were observed and described detailly. And then a schematic diagram of the mature stem was created. Histochemical staining showed that two kinds of polysaccharides distributed in parenchymal cells. Saponins distributed mainly in ground tissue and phenolic compounds distributed mainly in the thick cell walls. An abundant of calcium oxalate raphide bundles were identified in cortex and primary tissue. Finally, the role of the above results in the taxonomy of Dracaena species and in their strong adaptability was discussed.

An arrangement of secretory cells involved in the formation and storage of resin in tracheid-based secondary xylem of arborescent plants

The evolution of the vascular system has led to the formation of conducting and supporting elements and those that are involved in the mechanisms of storage and defense against the influence of biotic and abiotic factors. In the case of the latter, the general evolutionary trend was probably related to a change in their arrangement, i.e. from cells scattered throughout the tissue to cells organized into ducts or cavities. These cells, regardless of whether they occur alone or in a cellular structure, are an important defense element of trees, having the ability to synthesize, among others, natural resins. In the tracheid-based secondary xylem of gymnosperms, the resin ducts, which consist of secretory cells, are of two types: axial, interspersed between the tracheids, and radial, carried in some rays. They are interconnected and form a continuous system. On the other hand, in the tracheid-based secondary xylem of monocotyledons, the resin-producing secretory cells do not form specialized structures. This review summarizes knowledge on the morpho-anatomical features of various types of resin-releasing secretory cells in relation to their: (i) location, (ii) origin, (iii) mechanism of formation, (iv) and ecological significance.

A chromosome-level genome assembly for Dracaena cochinchinensis reveals the molecular basis of its longevity and formation of dragon's blood

Dracaena, a remarkably long-lived and slowly maturing species of plant, is world famous for its ability to produce dragon's blood, a precious traditional medicine used by different cultures since ancient times. However, there is no detailed and high-quality genome available for this species at present; thus, the molecular mechanisms that underlie its important traits are largely unknown. These factors seriously limit the protection and regeneration of this rare and endangered plant resource. Here, we sequenced and assembled the genome of Dracaena cochinchinensis at the chromosome level. The D. cochinchinensis genome covers 1.21 Gb with a scaffold N50 of 50.06 Mb and encodes 31 619 predicted protein-coding genes. Analysis showed that D. cochinchinensis has undergone two whole-genome duplications and two bursts of long terminal repeat insertions. The expansion of two gene classes, cis-zeatin O-glucosyltransferase and small auxin upregulated RNA, were found to account for its longevity and slow growth. Two transcription factors (bHLH and MYB) were found to be core regulators of the flavonoid biosynthesis pathway, and reactive oxygen species were identified as the specific signaling molecules responsible for the injury-induced formation of dragon's blood. Our study provides high-quality genomic information relating to D. cochinchinensis and significant insight into the molecular mechanisms responsible for its longevity and formation of dragon's blood. These findings will facilitate resource protection and sustainable utilization of Dracaena.

Theoretical considerations regarding the functional anatomical traits of primary and secondary xylem in dragon tree trunk using the example of Dracaena draco

In Dracaena draco trunks, the primary and secondary xylem conduits co-function. Both are resistant to embolism; however, secondary conduits are mainly involved in mechanical support. Monocotyledonous dragon trees (Dracaena spp., Asparagaceae) possess in their trunks both primary and secondary xylem elements, organized into vascular bundles, that for dozens of years co-function and enable the plant to transport water efficiently as well as provide mechanical support. Here, based on the modified Hagen-Poiseuille's formula, we examined the functional anatomical xylem traits of the trunk in two young D. draco individuals to compare their function in both primary and secondary growth. We provided analyses of the: (i) conduits surface sculpture and their cell walls thickness, (ii) conduit diameter and frequency, (iii) hydraulically weighted diameter, (iv) theoretical hydraulic conductivity, (v) area-weighted mean conduit diameter, as well as (vi) vulnerability index. The conduits in primary growth, located in the central part of the trunk, were loosely arranged, had thinner cell walls, larger mean hydraulically weighted diameter, and significantly larger value of the theoretical hydraulic conductivity than conduits in secondary growth, which form a rigid cylinder near the trunk surface. Based on the vulnerability index, both primary and secondary conduits are resistant to embolism. Taking into account the distribution within a trunk, the secondary growth conduits seems to be mainly involved in mechanical support as they are twisted, form structures similar to sailing ropes and have thick cell walls, and a peripheral localization. D. draco has been adapted to an environment with water deficit by distinctive, spatial separation of the xylem elements fulfilling supportive and conductive functions.

Characterization of the Complete Chloroplast Genome Sequence of the Socotra Dragon`s Blood Tree (Dracaena cinnabari Balf.)

The Socotra dragon`s blood tree (Dracaena cinnabari Balf.) is endemic to the island of Socotra in Yemen. This iconic species plays an essential role in the survival of associated organisms, acting as an umbrella tree. Overexploitation, overgrazing by livestock, global climate change, and insufficient regeneration mean that the populations of this valuable species are declining in the wild. Although there are many studies on the morphology, anatomy, and physiology of D. cinnabari, no genomic analysis of this endangered species has been performed so far. Therefore, the main aim of this study was to characterize the complete chloroplast sequence genome of D. cinnabari for conservation purposes. The D. cinnabari chloroplast genome is 155,371 bp with a total GC content of 37.5%. It has a quadripartite plastid genome structure composed of one large single-copy region of 83,870 bp, one small single-copy region of 18,471 bp, and two inverted repeat regions of 26,515 bp each. One hundred and thirty-two genes were annotated, 86 of which are protein-coding genes, 38 are transfer RNAs, and eight are ribosomal RNAs. Forty simple sequence repeats have also been identified in this chloroplast genome. Comparative analysis of complete sequences of D. cinnabari chloroplast genomes with other species of the genus Dracaena showed a very high conservativeness of their structure and organization. Phylogenetic inference showed that D. cinnabari is much closer to D. draco, D. cochinchinensis, and D. cambodiana than to D. terniflora, D. angustifolia, D. hokouensis, and D. elliptica. The results obtained in this study provide new and valuable omics data for further phylogenetic studies of the genus Dracaena as well as enable the protection of genetic resources of highly endangered D. cinnabari.

Phytochemistry and Pharmacological Activities of Dracaena cinnabari Resin

Dracaena cinnabari (D. cinnabari) is an endemic plant located in Socotra Island, Yemen. Deep red resin attained from different plant species including D. cinnabari is commonly known as dragon's blood. In folk medicine, it is prescribed for the treatment of traumatic dermal, dental, and eye injuries as well as blood stasis, pain, and gastrointestinal diseases in humans. Numerous studies have investigated that this resinous medicine has antidiarrheal, antiulcer, antimicrobial, antiviral, antitumor, anti-inflammatory, analgesic, wound healing, and antioxidant activity. Several phytochemicals have been isolated from D. cinnabari, including the biflavonoid cinnabarone, triflavonoids, metacyclophanes, chalcones, chalcanes, dihydrochalcones, sterols, and terpenoids. The present review highlights the structures and bioactivities of main phytochemicals isolated from D. cinnabari regarding the botany and pharmacological effects of the resin derived from this plant.

Dragon's Blood from Dracaena Worldwide: Species, Traditional Uses, Phytochemistry and Pharmacology

Dragon's blood (DB) refers mainly to the crimson resin of many Dracaena spp. DB has been used by different traditional medicine systems worldwide, including Arabic medicine, African medicine, traditional Chinese medicine, Thai medicine, etc. DB are mainly used to heal wounds, kill pain, stop bleeding, and cure various diseases such as diarrhea, dysentery and ulcers for over 1000 years. 11 Dracaena spp. and 3 subspecies are reported to be able to produce red resin. However, the resources are extremely deficient. Several Dracaena spp. are in threatened status. Over 300 compounds have been isolated from Dracaena spp., mainly including flavonoids, steroids, and phenolics. DB exhibits anti-inflammatory, analgesic, antithrombotic, anti-oxidant, antimicrobial, antidiabetic, and anticancer properties, which explain its wound healing effects, preventive effects on cardiovascular and cerebrovascular diseases, dual-directional regulation of blood flow, neuroprotection and radioprotective effects. No apparent side effects or toxicity have been reported. DB are restricted from being exploited due to limited resources and unclear resin formation mechanism. It is necessary to expand the cultivation of Dracaena spp. and fully understand the mechanism underlying the resin formation process to develop an effective induction method for the sustainable utilization of DB.

Revisiting the anatomy of the monocot cambium, a novel meristem

The monocot cambium is semi-storied, and its cells do not undergo rearrangement. The monocot cambium is a lateral meristem responsible for secondary growth in some monocotyledons of Asparagales. It is an unusual meristem, not homologous with the vascular cambia of gymnosperms and non-monocotyledonous angiosperms. Owing to the limited information available on the characteristics of this meristem, the aim of this study was to survey the structure of the monocot cambium in order to clarify the similarities and dissimilarities of this lateral meristem to the vascular cambium of trees. Using the serial sectioning analysis, we have studied the monocot cambium of three species of arborescent monocotyledons, i.e., Quiver Tree Aloe dichotoma, Dragon Tree Dracaena draco, and Joshua Tree Yucca brevifolia, native to different parts of the world. Data showed that in contrast to the vascular cambium, the monocot cambium is composed of a single type of short initials that vary in shape, and in tangential view display a semi-storied pattern. Furthermore, the cells of the monocot cambium do not undergo rearrangement. The criteria used in identifying monocot cambium initial cell are also discussed.

Exploring the historical distribution of Dracaena cinnabari using ethnobotanical knowledge on Socotra Island, Yemen

BACKGROUND

In this study, we present and analyze toponyms referring to Socotra Island's endemic dragon's blood tree (Dracaena cinnabari) in four areas on the Socotra Archipelago UNESCO World Heritage site (Republic of Yemen). The motivation is the understanding of the past distribution of D. cinnabari trees which is an important part of conservation efforts by using ethnobotanical data. We assumed that dragon's blood trees had a wider distribution on Socotra Island in the past.

METHODS

This research was based on field surveys and interviews with the indigenous people. The place names (toponyms) were recorded in both Arabic and the indigenous Socotri language. We grouped all toponyms into five different categories according to the main descriptor: terrain, human, plant, water, and NA (unknown). Also, this study identified current and historical Arabic names of dragon's blood trees of the genus Dracaena through literature review.

RESULTS

A total of 301 toponyms were recorded from the four study areas in Socotra Island. Among names related to plants, we could attribute toponyms to nine different plants species, of which six toponyms referred to the D. cinnabari tree, representing 14.63% of the total phytotoponyms in the category. Three historical naming periods prior to 2000 could be identified. The most commonly used name for dragon's blood trees (D. cinnabari, D. serrulata, D. ombet) appears to be "ahrieb" "إعريهب" and its resin "dum al-akhawin" "دم الأخوين," while derived (mixed-cooked) products are called "eda'a" "إيدع," while regionally different names can be found.

CONCLUSION

The place names that refer to D. cinnabari are herein suggested to represent remnant areas of once large populations. Therefore, the toponyms may support known hypotheses based on climate models that D. cinnabari had a wider distribution on Socotra Island in the past. This study also confirmed the historical importance of dragon's blood.

Structures and Bioactivities of Steroidal Saponins Isolated from the Genera Dracaena and Sansevieria

The species Dracaena and Sansevieria, that are well-known for different uses in traditional medicines and as indoor ornamental plants with air purifying property, are rich sources of bioactive secondary metabolites. In fact, a wide variety of phytochemical constituents have been isolated so far from about seventeen species. This paper has reviewed the literature of about 180 steroidal saponins, isolated from Dracaena and Sansevieria species, as a basis for further studies. Saponins are among the most characteristic metabolites isolated from the two genera. They show a great variety in structural motifs and a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-proliferative effects and, in most case, remarkable cytotoxic properties.

Flavonoids and Stilbenoids of the Genera Dracaena and Sansevieria: Structures and Bioactivities

The genera Dracaena and Sansevieria (Asparagaceae, Nolinoideae) are still poorly resolved phylogenetically. Plants of these genera are commonly distributed in Africa, China, Southeast Asia, and America. Most of them are cultivated for ornamental and medicinal purposes and are used in various traditional medicines due to the wide range of ethnopharmacological properties. Extensive in vivo and in vitro tests have been carried out to prove the ethnopharmacological claims and other bioactivities. These investigations have been accompanied by the isolation and identification of hundreds of phytochemical constituents. The most characteristic metabolites are steroids, flavonoids, stilbenes, and saponins; many of them exhibit potent analgesic, anti-inflammatory, antimicrobial, antioxidant, antiproliferative, and cytotoxic activities. This review highlights the structures and bioactivities of flavonoids and stilbenoids isolated from Dracaena and Sansevieria.

Germination of Dracaena cinnabari Balf.f. Seeds under Controlled Temperature Conditions

Research highlights: This study is focused on the germination of Dracaena cinnabari seeds in order to discover the possibility of natural and artificial regeneration of this species. Background and Objectives: This study aimed to determine the optimal temperature for D. cinnabari seed germination, e.g., the temperature at which the germination percentage and germination rate (vitality) are the highest. The objectives of this study are to: (1) determine the optimal temperature for the germination of D. cinnabari seeds, (2) compare the suitability of different seed collection methods, and (3) compare the germination parameters of seeds that were collected from different localities. The results of this study will contribute to obtaining the highest number of seedlings from limited seed material for reforestation of the most endangered localities of D. cinnabari species. Materials and methods: Four seed sections were employed. These sections were directly collected from either the fruits of a cut panicle or the ground and were obtained from different localities that differ in altitude. The seeds were tested in a greenhouse while using Petri dishes at three different temperatures—22, 26, and 30 °C—with four replicates of 25 seeds of each section. ANOVA and the t-test were employed for data analysis. Results: The highest germination percentages (GPs) were achieved at 26 °C and 30 °C, which were 84.6% and 82.5%, respectively. The ANOVA and t-test results showed that the germination index (GI) of the species was relatively higher at a temperature of 30 °C relative to that at other temperatures in the study. Although seeds that were collected from the tree achieved a higher GP, the t-test result showed no significant differences in the GI of D. cinnabari seeds that were collected from the ground and from the tree (p > 0.05). Overall, the findings of this study show that temperature has substantial influence on the germination of seeds of D. cinnabari. Therefore, we recommend a temperature of 30 °C to facilitate the germination of D. cinnabari, as it achieved the highest GI at this temperature relative to that at the other temperatures (22 °C, 26 °C) applied in this study.

Complete Chloroplast Genome Sequence and Phylogenetic Inference of the Canary Islands Dragon Tree (Dracaena draco L.)

Dracaena draco, which belongs to the genus Dracaena, is an endemic succulent of the Canary Islands. Although it is one of the most popular and widely grown ornamental plants in the world, little is known about its genomic variability. Next generation sequencing, especially in combination with advanced bioinformatics analysis, is a new standard in taxonomic and phylogenetic research. Therefore, in this study, the complete D. draco chloroplast genome (cp) was sequenced and analyzed in order to provide new genomic information and to elucidate phylogenetic relationships, particularly within the genus Dracaena. The D. draco chloroplast genome is 155,422 bp, total guanine-cytosine (GC) content is 37.6%, and it has a typical quadripartite plastid genome structure with four separate regions, including one large single copy region of 83,942 bp length and one small single copy region of 18,472 bp length, separated by two inverted repeat regions, each 26,504 bp in length. One hundred and thirty-two genes were identified, 86 of which are protein-coding genes, 38 are transfer RNAs, and eight are ribosomal RNAs. Seventy-seven simple sequence repeats were also detected. Comparative analysis of the sequence data of various members of Asparagales revealed mutational hotspots potentially useful for their genetic identification. Phylogenetic inference based on 16 complete chloroplast genomes of Asparagales strongly suggested that Dracaena species form one monophyletic group, and that close relationships exist between D. draco, D. cochinchinensis and D. cambodiana. This study provides new and valuable data for further taxonomic, evolutionary and phylogenetic studies within the Dracaena genus.