Alba Seedlings Research Articles

Determinants of mangrove seedling survival incorporated within hybrid living shorelines

Many communities around the world face a pressing need to increase coastal resilience due to widespread coastal erosion and rising sea levels. Natural habitats such as mangrove forests have been increasingly recognised for their ability to protect coastlines through wave attenuation and sediment deposition and stabilisation. However, attempts to rehabilitate mangroves for coastal protection have been met with difficulties due to smaller windows of opportunity for seedling survival at sites experiencing high wave energy and erosion. In this study, we planted the mangrove Avicennia alba in planting pods (n = 348) deployed on an eroding shoreline in Singapore and compared survival to those planted in control plots. Several ecological factors that might influence A. alba survival were manipulated, such as life stage during planting, reduction of wrack accumulation, elevation, and post-planting maintenance. We found that mangrove pods significantly increased mangrove seedling survival. Planting older A. alba seedlings, reducing wrack accumulation, and deploying the pods at a higher elevation further increased survival. Additionally, pressure gauges deployed showed that the pods were able to attenuate wave energy, thus providing hydrodynamic shelter to mangroves. Hybrid living shorelines have the potential to facilitate mangrove rehabilitation through the alleviation of adverse environmental conditions, but other ecological requirements for mangrove seedling survival will need to be met to optimise rehabilitation efforts.

Integrative Physiological and Transcriptome Analysis Reveals the Mechanism of Cd Tolerance in Sinapis alba.

Recently, pollution caused by the heavy metal Cd has seriously affected the environment and agricultural crops. While Sinapis alba is known for its edible and medicinal value, its tolerance to Cd and molecular response mechanism remain unknown. This study aimed to analyze the tolerance of S. alba to Cd and investigate its molecular response mechanism through transcriptomic and physiological indicators. To achieve this, S. alba seedlings were treated with different concentrations of CdCl2 (0.25 mmol/L, 0.5 mmol/L, and 1.0 mmol/L) for three days. Based on seedling performance, S. alba exhibited some tolerance to a low concentration of Cd stress (0.25 mmol/L CdCl2) and a strong Cd accumulation ability in its roots. The activities and contents of several antioxidant enzymes generally exhibited an increase under the treatment of 0.25 mmol/L CdCl2 but decreased under the treatment of higher CdCl2 concentrations. In particular, the proline (Pro) content was extremely elevated under the 0.25 and 0.5 mmol/L CdCl2 treatments but sharply declined under the 1.0 mmol/L CdCl2 treatment, suggesting that Pro is involved in the tolerance of S. alba to low concentration of Cd stress. In addition, RNA sequencing was utilized to analyze the gene expression profiles of S. alba exposed to Cd (under the treatment of 0.25 mmol/L CdCl2). The results indicate that roots were more susceptible to disturbance from Cd stress, as evidenced by the detection of 542 differentially expressed genes (DEGs) in roots compared to only 37 DEGs in leaves. GO and KEGG analyses found that the DEGs induced by Cd stress were primarily enriched in metabolic pathways, plant hormone signal transduction, and the biosynthesis of secondary metabolites. The key pathway hub genes were mainly associated with intracellular ion transport and cell wall synthesis. These findings suggest that S. alba is tolerant to a degree of Cd stress, but is also susceptible to the toxic effects of Cd. Furthermore, these results provide a theoretical basis for understanding Cd tolerance in S. alba.

Phenolic Antioxidant Protection in the Initial Growth of Cryptocarya alba: Two Different Responses against Two Invasive Fabaceae.

The allelophatic effect of the invasive Fabaceae, Ulex europaeus and Teline monspessulana, on the production of phenolic compounds in C. alba seedlings was investigated. It was expected that the oxidative stress caused by the allelochemicals released by both invaders would induce a differential response in the production of phenolic compounds in C. alba seedlings. These antioxidant mechanisms guaranteed C. alba plants' survival, even to the detriment of their initial growth. Cryptocarya alba seedlings were irrigated with T. monspessulana (TE) and U. europaeus (UE) extracts and water as a control. After eight months, morphometric variables were evaluated, and leaves were collected for histochemical analysis. The methanol extracts from treatments and control leaves were used for anthocyanin, phenol, and antioxidant activity quantifications. Both invasive species induced an inhibitory effect on the morphometric variables. Teline monspessulana induced leaf damage and increased the anthocyanin content by 4.9-fold, but did not affect the phenol content. Ulex europaeus induces root damage and a decrease in phenol content, but does not affect the anthocyanin content. Both Fabaceae extracts affected the profile and polyphenol concentration and consequently decreased the antioxidant capacity of C. alba leaves at low extract concentrations. Phenols, lignin, and ROS accumulate on C. alba leaves, but the histochemical reactions were less intense under UE. Although C. alba develops different antioxidant protection mechanisms against stress induced by UE and TE, its survival is guaranteed, even to the detriment of its initial growth.

First Report of Pseudoidium santalacearum Causing Foliar Powdery Mildew on Santalum album in Guangdong Province, China.

Santalum album Linn is an evergreen and facultative root hemiparasitic tree. It is attached to host roots through haustorium to withdraw water and nutrients. Its aromatic heartwood, honored as "Green Gold", is widely used in perfumes, incense, medicine, and skin cancer prevention (Sandeep and Manohara 2019, Polaiah et al. 2020). From February to June 2022, powdery mildew was observed on over 80% of S. album in the nursery with a mean temperature and relative humidity of 30/22°C (day/night) and 55/82% (day/night) at the Research Institute of Tropical Forestry, Chinese Academy of Forestry, Guangdong, China (23°11'N, 113°23'E). Initial symptoms were circular to irregular white colonies on the leaf surface (Fig. 1). As the disease progressed, white mycelia covered the entire leaf surface and premature defoliation of the infected leaf was observed. Then a bare stem remained and subsequently desiccated (Sundararaj et al. 2022). Infected leaves with mycelia were collected and observed under a Zeiss AX10 microscope. Foot cells of conidiophores (n = 30) were straight to slightly curved cylindrical, and the length and width of foot cells were up to 24.8 to 44.6 × 8.2 to 11.7 μm. Conidiophores (n = 30) were straight, 83.5 to 127.3 μm long × 6.6 to 7.6 μm wide and produced three immature conidia in chains. Conidia (n = 30) were elliptical to cylindrical, measured 31.3 to 41.2 μm × 11.3 to 13.7 μm. The sexual stage was not found. The morphological characterization of our samples was consistent with powdery mildew of S. album in India, termed Pseudoidium santalacearum (Patel et al. 2015). However, the molecular identification was not performed. In this study, we carefully collected the mildew and extracted the genomic DNA. The internal transcribed spacer (ITS) region of rDNA was amplified using universal primers ITS1 and ITS4 (White et al. 1990). The ITS sequences of the three samples (GenBank Accession No. OQ746371, OQ746372, and OQ746373) were all more than 99% identical with the sequence of Erysiphe palczewskii on Caragana arborescens (GenBank Accession No. LC010048) (Takamatsu et al. 2015). It is known that Erysiphe containing chasmothecia belongs to teleomorph, whereas Pseudoidium is an asexual morph of Erysiphe, belonging to anamorph (Hsiao et al. 2022, Meeboon and Takamatsu 2016). In our samples, there was no chasmothecia, and the morphological characterization was consistent with P. santalacearum (Patel et al. 2015). Therefore, we classified it as P. santalacearum. Phylogenetic analysis showed that P. santalacearum had a closer relationship with the E. palczewskii (Fig. 2). Pathogenicity tests were conducted by gently pressing the infected leaves onto five healthy S. album plants. Five non-inoculated plants were used as controls. The plants were placed in a growth chamber (Light/Dark: 16 h/8 h, temperature: 25 ± 2°C). Inoculated leaves developed powdery mildew symptoms after 7-12 days, whereas the control plants remained symptomless (Fig. 1). Morphological and molecular characters of the fungus on the inoculated plants were identical to those on naturally infected S. album, fulfilling Koch's postulates. To our knowledge, this is the first report of P. santalacearum on S. album in Guangdong, China. Powdery mildew can generally result in a high mortality of S. album seedlings. Therefore, identification of the pathogen provides a scientific basis for effective diagnosis and prevention of the disease and contribute to an appropriate nursery management of S. album seedlings.

Genome-Wide Identification of Candidate Genes Associated with Heat Stress in Mulberry (Morus alba L.)

Mulberry (Morus alba L.) is an economically important plant for the silk industry and has the possibility of contributing immensely to Chinese pharmacopeia because of its health benefits. Domesticated silkworms feed only on mulberry leaves, meaning that the worms' survival depends on the mulberry tree. Mulberry production is threatened by climate change and global warming. However, the regulatory mechanisms of mulberry responses to heat are poorly understood. We performed transcriptome analysis of high-temperature-stressed (42 °C) M. alba seedlings using RNA-Seq technologies. A total of 703 differentially expressed genes (DEGs) were discovered from 18,989 unigenes. Among these, 356 were up-regulated, and 347 were down-regulated. KEGG analysis revealed that most DEGs were enriched in valine, leucine and isoleucine degradation, and in starch and sucrose metabolism, alpha-linolenic acid metabolism, carotenoid biosynthesis and galactose metabolism, among others. In addition, TFs such as the NAC, HSF, IAA1, MYB, AP2, GATA, WRKY, HLH and TCP families were actively involved in response to high temperatures. Moreover, we used RT-qPCR to confirm the expression changes of eight genes under heat stress observed in the RNA-Seq analysis. This study provides M. alba transcriptome profiles under heat stress and provides theoretical bases to researchers for better understanding mulberry heat response mechanisms and breeding heat-tolerant mulberry plants.

Effects of salt stress on interspecific competition between an invasive alien plant Oenothera biennis and three native species.

Biological invasions and soil salinization have become increasingly severe environmental problems under global change due to sea-level rise and poor soil management. Invasive species can often outcompete native species, but few studies focus on whether invasive alien species are always superior competitors under increasing stressors. We grew an invasive grass species, Oenothera biennis L., and three native grass species (Artemisia argyi Lévl. et Vant., Chenopodium album L., and Inula japonica Thunb.) as a monoculture (two seedlings of each species) or mixture (one seedling of O. biennis and one native species seedling) under three levels of salt treatments (0, 1, and 2 g/kg NaCl) in a greenhouse. We found that invasive O. biennis exhibited greater performance over native C. album and I. japonica, but lower performance compared to A. argyi, regardless of the soil salinity. However, salinity did not significantly affect the relative dominance of O. biennis. Interspecific competition enhanced the growth of O. biennis and inhibited the growth of I. japonica. Although O. biennis seedlings always had growth dominance over C. album seedlings, C. album was not affected by O. biennis at any salt level. At high salt levels, O. biennis inhibited the growth of A. argyi, while A. argyi did not affect the growth of O. biennis. Salt alleviated the competitive effect of O. biennis on I. japonica but did not mitigate the competition between O. biennis and the other two native species. Therefore, our study provides evidence for a better understanding of the invasive mechanisms of alien species under various salinity conditions.

Host root exudates initiate a foraging preference by the root parasite Santalum album.

Haustoria of root-parasitic plants draw nutrients from the roots of host species. While recent studies have assessed host preferences of parasitic plants, how root-exuded chemicals can mediate host tropism and selection by root-parasitic plants is poorly understood. Under greenhouse conditions, we performed two pot experiments to determine whether the root parasite Santalum album selectively forages for superior hosts (N2-fixing Acacia confusa Merr. or Dalbergia odorifera T. Chen) rather than for inferior hosts (non-N2-fixing Bischofia polycarpa (levl.) Airy Shaw or Dracontomelon duperreranum Pierre), and whether S. album uses host root exudates and/or specific chemicals in these root exudates to locate and trigger haustorium formation. Lateral roots and haustoria of S. album seedlings exhibited greater growth in the direction of D. odorifera roots than toward roots from the other three hosts. Comparative metabolic analysis revealed that D. odorifera root exudates were enriched in isoflavonoid, flavonoid and flavone/flavonol biosynthesis pathways, and that the relative contents of flavonoids were significantly greater in the root exudates of D. odorifera than in those of the other three hosts. Root exudates from D. odorifera significantly promoted S. album root growth, haustorium formation and reactive oxygen species accumulation in haustoria. Our results demonstrate that the key step in plant parasitism by S. album is based on root exudation by a host plant; the exudates function as a metabolite signal that activate lateral root growth and haustorium formation. Our results also indicate that flavonoids in the root exudates could play an important role in S. album foraging activity. Information on the responses of root parasites to host root exudates and/or haustorium-inducing chemicals may be useful for selecting superior host species to plant with valuable species of root parasites.

Effects of Drought and Host on the Growth of Santalum album Seedlings in Pot Culture

Santalum album is a semi parasitic plant and its growth is often restricted due to a lack of a host or water during plantation establishment. In this study, the effects of water and the host on the growth of S. album seedlings were studied in pot culture. The results showed that the net photosynthetic rate and height of S. album seedlings decreased significantly under drought stress. Compared with the seedlings of S. album grown without a host, the host could significantly increase the growth of S. album seedlings. The contents of soluble sugar and proline in S. album leaves increased significantly under drought stress. Drought stress resulted in a significant accumulation of malondialdehyde, increments of antioxidant enzymes activity, and non-enzymatic antioxidant substances. Antioxidant capacity was stronger and malondialdehyde content was lower in the seedling leaves of S. album with a host than in the seedlings without a host. RNA-seq was used to analyze the transcription expression profiles of S. album leaves and the results were consistent with the physiological data. These results indicate that the host can promote the seedling growth of S. album and it can increase the antioxidant capacity and osmotic adjustment substance content of the seedlings of S. album, alleviating the damage caused by drought.

Allelopathic Effect of Black Cherry (Prunus serotina Ehrh.) on Early Growth of White Mustard (Sinapis alba L.) and Common Buckwheat (Fagopyrum esculentum Moench): Is the Invader a Threat to Restoration of Fallow Lands?

Abandoned agricultural land present in most European countries constitutes a resource of land that can be restored to agricultural production. Fallow colonization by invasive plant species contributes to changes in the course of natural secondary succession. This may modify the possibilities of returning fallow lands to agriculture, which constitutes an issue that needs to be investigated. In this study, the phytotoxic effect of invasive black cherry (Prunus serotina Ehrh.) on two crop plants commonly used for fallow land utilization, white mustard (Sinapis alba L.) and common buckwheat (Fagopyrum esculentum Moench), was assessed. The influence of water extracts from P. serotina litter and the soil collected under the individuals of this species was investigated. Sinapis alba was found to be more sensitive to allelochemicals released by P. serotina than F. esculentum. Litter extracts and soil with residues of P. serotina significantly inhibited both germination and growth of S. alba seedlings, estimated with length and mass of the above-ground and underground parts. In the case of F. esculentum, a negative effect of the tested extracts and soil on root mass reduction was observed. Preliminary results of our laboratory tests suggest that cultivation of white mustard should be avoided in the reclamation of fallows with black cherry.

Seed Priming with ZnO and Fe3O4 Nanoparticles Alleviate the Lead Toxicity in Basella alba L. through Reduced Lead Uptake and Regulation of ROS.

The increased lead (Pb) content in the environment has an impact on all living beings, including plant growth and quality. The present study aims to investigate the protective roles of zinc (Zn)- and iron (Fe)- nanoparticles (NPs) in alleviating stress symptoms caused by lead (Pb) exposure in Basella alba seedlings. For this purpose, 15 different treatment combinations of seed priming with two NPs at 0 and 200 mg L−1, and five Pb levels (0, 4, 8, 15, 20 mM) were chosen. Pb stress (20 mM) was found to reduce seed germination by 72.8% and seedling growth, particularly root length, by 92% when compared to the control. Under different Pb concentrations, seed priming with ZnNPs (200 mg L−1) and FeNPs (200 mg L−1) increased seed germination by 34.7% and 54.9%, respectively, and root length by 152.9% and 252.9%, respectively. In 20 mM Pb stress, NPs primed seedling showed decrease in Pb content by 33.7% with ZnNPs and 32.6% with FeNPs. Increased Pb stress resulted in increased reactive oxygen species (ROS) generation (H2O2) and lipid peroxidation (MDA) compared to non-Pb stressed seedlings. However, increased antioxidants in the NPs treatments such as SOD, CAT, POD and proline content, scavenged these ROS. Considering all the parameters under study, priming alleviated Pb stress in the following order: FeNPs > ZnNPs > hydropriming > control. To summarise, seed priming with Zn- and Fe-NPs has the potential to alleviate Pb toxicity via reduced Pb uptake, ROS generation and lipid peroxidation as well as increased proline content and activation of antioxidant enzymatic system.

Biostimulants as forest protection agents: Do these products have an effect against abiotic stress on a forest native species? Aspects to elucidate their action mechanisms

Projections of climatic change pose a challenging scenario for the management and adaptation of ecosystems. It is expected that forests around the world will be exposed to severe stress conditions such as imposed for drought, heat, and weather extremes. Forest native species of great economic-ecological importance will be affected. For example, in Argentina, Prosopis alba, a native species, is essential for restoring and reforestation of degraded areas. Hence, there is an imperious demand to find sustainable strategies to promote its tolerance to environmental changes. This work aims to evaluate the potential of phytoextracts from native plant species as biostimulants that increase the abiotic stress tolerance of P. alba, contributing to the biological resilience of native forests. We tested biochemical, physiological, and morphological characteristics (BPMc) on P. alba seedlings sprayed with phytoextracts of four different species. Measurements were made in the nursery as well as in the field. Our results showed that foliar application of Ilex paraguariensis and Larrea divaricata reduced an oxidative stress biomarker in P. alba 21 days after the acclimation phase began. Both extracts had high antioxidant activity. Notably, L. divaricata at 3 % w/v (LDa3%) exhibited significant potential as a biostimulant in the nursery and field. This phytoextract enhanced the BPMc of P. alba. Foliar applications of that biostimulant positively affected plant growth, increasing diameter, height, shoot biomass and root biomass. Indeed, seedlings sprayed with LDa3% demonstrated the best performance after transplanting from the nursery to the field. According to our results, foliar applications of LDa3% could stimulate the activity of cell antioxidants under abiotic stress conditions. Our results suggest that phytoextracts may be used as innovative products that improve the abiotic stress tolerance of P.alba, but the applied doses must be considered and evaluated. In the appropriate doses, we could observe that these products stimulate growth and activate plant defences against abiotic stress conditions on this forest species. Even though most of the research on biostimulants focuses on agricultural production, according to our results, these products have the potential to become a part of sustainable forestry during nursery production.

Cloning and functional analysis of 1-deoxy-d-xylulose-5-phosphate synthase (DXS) in Santalum album L

The commercial value of Santalum album L. lies in its aromatic heartwood and essential oil. Sesquiterpenes are the main components of sandal essential oil, and these are synthesized through the plant’s mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. In this study, the first key rate-limiting enzyme, 1-deoxy-d-xylulose-5-phosphate synthase (SaDXS), was investigated to provide a theoretical molecular basis for the sandalwood MEP sesquiterpene biosynthetic pathway. The biofunctions of SaDXS were also analyzed. SaDXS promoters were successfully cloned from a seven-year-old S. album tree. SaDXS1A/1B promoter activity was verified by a β-glucuronidase (GUS) assay and by analyzing cis-acting elements of the promoters, which carried light- and methyl jasmonate (MeJA)-responsive signals. In an experiment involving yellow S. album seedlings, exposure to light upregulated SaDXS1A/1B expression and increased chlorophyll and carotenoid contents when overexpressed in Arabidopsis thaliana. Analysis of the expression of SaDXS1A/1B and SaSSy, key genes of santalol biosynthesis, revealed SaDXS1A expression in all tissues whereas SaDXS1B was expressed in tissues that contained photosynthetic pigments, such as stems, leaves and flowers. Sandal seedlings exogenously treated with two hormones, MeJA and ethylene, revealed similar expression patterns for SaDXS1A/1B and SaSSy. Sandal seedlings were treated with an inhibitor of DXS, clomazone, but showed no significant changes in the contents of α-santalene, β-santalene and α-santalol between treatment and control groups. These results suggest that SaDXS1A/1B play a role in the synthesis of sandalwood sesquiterpenes, providing carbon for downstream secondary metabolites. SaDXS1A/1B also play a role in the biosynthesis of chlorophyll, carotenoids, and primary metabolites.

Growth characteristics of Abies alba seedlings in Voronezh

ISHS VIII International Scientific and Practical Conference on Biotechnology as an Instrument for Plant Biodiversity Conservation (Physiological, Biochemical, Embryological, Genetic and Legal Aspects) Growth characteristics of Abies alba seedlings in Voronezh

Pengaruh Media Tanam dan Intensitas Naungan Terhadap Pertumbuhan Bibit Api-Api (Avicennia alba)

Mangrove forests are ecosystems located in tidal areas in coastal areas, beaches, and small islands. The area of ​​mangrove forests is decreasing due to the conversion of mangrove forests into fishponds, plantations, and timber exploitation. Mangrove ecosystem rehabilitation activities need to be carried out through planting. Avicennia alba is a pioneer mangrove species that grows in mangrove swamp habitats on sheltered coastal locations, as well as in the saltier parts of the coastline. The objectives of this research is to analyze the effect of planting media and shade intensity on the seedling growth of Avicennia alba. The study used a two-factor experimental design in a complete randomized design. The first factor is planting media and the second one in shade intensity. The results showed that the shading intensity most influenced the growth of Avicennia alba seedlings. The variables affected include height, diameter, number of leaves, total wet weight, and total dry weight. The treatment combination that gave the best results was A2N0, that means the planting medium in the form of a mixture of mud, sand and compost and without shade (0% shade).
 Keywords: Avicennia alba, growth, photosynthesis, planting media, shade intensity

THE EFFECT OF PARANET SHADE ON THE GROWTH AND MORPHOLOGICAL CHARACTERISTICS IN SIX SPECIES OF MANGROVE SEEDLING

In mangrove rehabilitation, nursery operation was required to enhance survival of seedlings prior to field planting. Healthy and mature seed and propagules of six mangroves namely Ceriops tagal, Sonneratia alba, Rhizophora apiculata, S. caseolaris, R. mucronata, and Xylocarpus granatum were planted in paranet shade (0%, 25%, 50%, 75% and 100%) for three months. The research purpose was to study the impact of paranet shade on the growth, and morphologic characteristic in all six mangrove seedlings. Results indicated that 50% paranet shade intensity supported C. tagal, R. mucronata, and S. caseolaris seedlings for the best growth (height and diameter). By contrast, 75% intensity of the shade displayed in the optimal growth, number of leaves, and the leaves area of R. apiculata seedlings. We determined that the best growth of seedlings of X. granatum was acquired in the intensity of shade 100%, contrary with S. alba seedling, showing 0% shade intensity as the best for growth. The tolerance to paranet of mangrove shade plants preceded the sequence of X. granatum (landward species) > R. apiculata > R. mucronata; C. tagal, and S. caseolaris > S. alba (seaward species). The present works generates useful information for restoration efforts in North Sumatra and indicates the value for representative mangrove species of intensely shaded nurseries based on optimum growth and morphological characteristics.

Melatonin enhances nitrogen metabolism and haustorium development in hemiparasite Santalum album Linn.

The facultative hemiparasite Santalum album can rely entirely on its own roots to obtain nutrients when growing without a host or can use its haustoria to partially rely on host plants for water and nutrients, especially nitrogen (N). However, how S. album responds to different N conditions has not been determined and no attempt has been made to improve N use by S. album. Our previous studies showed that melatonin, which is known to promote tolerance to abiotic stresses in plants, enhances S. album growth. Here, we investigated the mechanisms and key pathways by which melatonin affects N uptake and assimilation in S. album. We evaluated changes in the physiology, transcriptional profiles, and chromatin accessibility in S. album seedlings exposed to low N (LN) or high N (HN) with or without 1 μM melatonin addition. Without melatonin addition, LN disturbed the homeostasis of N metabolism, reducing both N uptake and assimilation. Melatonin addition, in contrast, significantly increased NH4+ uptake under LN and increased NO3− uptake under HN. Melatonin also increased the activities of NR and GS enzymes under LN, resulting in accelerated N metabolism and enhanced haustorium development via a mechanism associated with auxin accumulation. Using global RNA-seq and ATAC-seq, we found that many genes were differentially expressed in response to melatonin addition. The upregulated genes were enriched in N metabolism and hormone signal transduction (auxin) pathways, suggesting that they have key roles in improving N use by S. album. These results strongly suggest that the application of melatonin may enhance S. album growth via accelerated N metabolism and haustorium formation.

Survival, growth and photochemical efficiency of silver fir seedlings produced with different technologies

Forest tree seedling production technologies impact reforestation success determined with survival and quality of seedlings. Five Abies alba seedling production technologies were tested: (1) bare-root seedling, three years in the open (3/0); (2) bare-root seedling, two years under a shading net (40% of full light), a year in the open (2/g); (3) ball root seedling, two years under a shading net (40%), a year in the open (2/K); (4) bare-root seedling grown in an opening in a Norway spruce stand (3/Pic); (5) bare-root seedling, three years under Scots pine canopy (3/Pin). Silver fir seedlings acclimatized their growth rates to the common growing environment in relation to the seedling production technology used in the nurseries. The height and diameter at root collar were positively correlated with survival. The 3/Pic seedlings manifested the lowest survival and were lower than other seedlings in terms of height and photochemical efficiency. The needle photochemistry of seedlings growing two years in plantation was determined by their earlier acclimation to the nursery light conditions. The production technology determined the ability of A. alba seedlings to acclimatize to the natural environment. Ball root seedlings grown two years in shade and a year in the open (2/K) acclimatized better to the full light environment compared with bare-root seedlings produced in canopy shade, and they are likely more suitable to be planted after clearcutting.

Cloning, characterization, and functional analysis of acetyl-CoA C-acetyltransferase and 3-hydroxy-3-methylglutaryl-CoA synthase genes in Santalum album

Sandalwood (Santalum album L.) is famous for its unique fragrance derived from the essential oil of heartwood, whose major components are santalols. To understand the mechanism underlying the biosynthesis of santalols, in this study, we cloned two related genes involved in the mevalonate pathway in S. album coding for acetyl-CoA C-acetyl transferase (AACT) and 3-hydroxy-3-methyglutary-CoA synthase (HMGS). These genes were characterized and functionally analyzed, and their expression profiles were also assessed. An AACT gene designated as SaAACT (GenBank accession No. MH018694) and a HMGS gene designated as SaHMGS (GenBank accession No. MH018695) were successfully cloned from S. album. The deduced SaAACT and SaHMGS proteins contain 415 and 470 amino acids, and the corresponding size of their open-reading frames is 1538 bp and 1807 bp, respectively. Phylogenetic trees showed that the SaAACT protein had the closest relationship with AACT from Hevea brasiliensis and the SaHMGS proteins had the highest homology with HMGS from Siraitia grosvenorii. Functional complementation of SaAACT and SaHMGS in a mutant yeast strain deficient in these proteins confirmed that SaAACT and SaHMGS cDNA encodes functional SaAACT and SaHMGS that mediate mevalonate biosynthesis in yeast. Tissue-specific expression analysis revealed that both genes were constitutively expressed in all examined tissues (roots, sapwood, heartwood, young leaves, mature leaves and shoots) of S. album, both genes showing highest expression in roots. After S. album seedlings were treated with 100 μM methyl jasmonate, the expression levels of SaAACT and SaHMGS genes increased, suggesting that these genes were responsive to this elicitor. These studies provide insight that would allow further analysis of the role of genes related to the sandalwood mevalonate pathway in the regulation of biosynthesis of sandalwood terpenoids and a deeper understanding of the molecular mechanism of santalol biosynthesis.

Distribution Dynamics and Roles of Starch in Non-photosynthetic Vegetative Organs of Santalum album Linn., a Hemiparasitic Tree

Allocation dynamics of stored starch plays essential roles in the development and growth of trees. Previous studies focused on the dynamics and the characteristics of starch in autotrophic trees. However, although starch granules have been detected in the organs or tissues of some parasitic plants, studies on the allocation dynamics and roles of storage starch in them are limited. Therefore, we determined and estimated the allocation dynamics and roles of starch in Santalum album Linn., a hemiparasitic tree, using morphological and physiological methods. Our findings showed abundant starch in the stem and root of S. album at the early seedling stage. Although S. album seedlings attached to the host showed no significant changes in starch levels throughout the experiment, unattached and host-removed seedlings exhibited a gradual decrease in the starch content over time. When the starch content of unattached seedlings was less than 1%, they started to die. Starch accumulated to high levels in developing and active haustoria; however, starch levels were low in the inactive haustoria. The present study suggests that starch may provide energy to seedlings that have no host, allowing them to survive during the unattached phase, thus increasing their chance to attach to host roots by extending their survival duration. In addition, we speculate that storage starch is potentially involved in the development of haustoria and in the physiological processes of S. album related to the absorption and transportation of water and nutrients from its host.

Functional characterization of an Indian sandalwood (Santalum album L.) dual-localized bifunctional nerolidol/linalool synthase gene involved in stress response

Essential oils extracted from the heartwood of Indian sandalwood (Santalum album L.) contain linalool and nerolidol as minor components. However, nerolidol/linalool synthase (NES/LIS), which produce linalool and nerolidol, have yet to be characterized in sandalwood. Using a transcriptomic-based approach, a terpene synthase gene was screened from unigenes of transcriptome data derived from S. album seedlings exposed to low temperature (4 °C). The enzyme encoded by these complementary DNAs belongs to the TPS-b clade. Recombinant SaNES/LIS is a bifunctional enzyme that can catalyze the formation of (E)-nerolidol from farnesyl diphosphate and linalool from geranyl diphosphate, respectively. Whereas SaNES/LIS was primarily localized in chloroplastids, both as granular fluorescence and as diffuse fluorescence, it was also detected in the cytosol of a limited number of cells. Agrobacterium tumefaciens-mediated transient gene expression in planta produced the same terpene products as those obtained in vitro. Real-time PCR analysis showed the highest expression of SaNES/LIS in fruits, with about a three-fold higher level than in leaves, followed by flowers, heartwood and roots. SaNES/LIS transcripts were differentially activated in different tissues in response to methyl jasmonate, cold, high temperature, strong illumination, and drought stress. Our results provide novel insight into the role of sandalwood terpenoids in response to various environmental stresses.