Differences in particulate matter retention and leaf microstructures of 10 plants in different urban environments in Lanzhou City.

Particulate matter (PM) is a major primary environmental air pollutant and poses a threat to human health. Differences in the environment and leaf microstructures of plants will result in varying abilities to retain PM, but the effects of changes in these factors on PM retention are not yet well understood. This study selected 10 plant species in four urban areas (sports field, park, residential green space, and greenway) as the study objects. The amount of retained PM by the different species was measured, and the leaf microstructures were observed. It was found that the environment significantly affected both PM retention and leaf microstructure. The ranking of PM retention in the 10 species in four areas was greenway > residential green space > park > sports field. The ranking of average stomatal width and length was park > sports field > residential green space > greenway, while that of average stomatal density was greenway > residential green space > park > sports field. Different environments affected the length and density of trichomes in the leaves. These changes represented the adaptation of plant species to the growth environment. The stomata and grooves of the leaf surface significantly affected the ability of plants to retain PM. The amount of PM retained by different species varied. In all four urban areas, Prunus × cistena N. E. Hansen ex Koehne (purple leaf sand cherry), Prunus cerasifera Ehrhart f. atropurpurea (Jacq.) Rehd. (cherry plum), Buxus sinica var. parvifolia M. Cheng (common boxwood), and Ligustrum × vicaryi Rehder (golden privet) showed strong PM retention. The results of this study will provide information for planners and urban managers for the selection of plant species.

Phytochemical profiling of Symplocos tanakana Nakai and S. sawafutagi Nagam. leaf and identification of their antioxidant and anti-diabetic potential.

Symplocos sp. contains various phytochemicals and is used as a folk remedy for treatment of diseases such as enteritis, malaria, and leprosy. In this study, we discovered that 70% ethanol extracts of Symplocos sawafutagi Nagam. and S. tanakana Nakai leaves have antioxidant and anti-diabetic effects. The components in the extracts were profiled using high-performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry; quercetin-3-O-(6''-O-galloyl)-ß-d-galactopyranoside (6) and tellimagrandin II (7) were the main phenolic compounds. They acted as strong antioxidants with excellent radical scavenging activity and as inhibitors of non-enzymatic advanced glycation end-products (AGEs) formation. Mass fragmentation analysis demonstrated that compounds 6 and 7 could form mono- or di-methylglyoxal adducts via reaction with methylglyoxal, which is a reactive carbonyl intermediate and an important precursor of AGEs. In addition, compound 7 effectively inhibited the binding between AGE2 and receptor for AGEs as well as the activity of α-glucosidase. Enzyme kinetic study revealed that compound 7 acts as a competitive inhibitor of α-glucosidase, through interaction with the active site of the enzyme. Therefore, compounds 6 and 7, the major constituents of S. sawafutagi and S. tanakana leaves, are promising for developing drugs for preventing or treating diseases caused by aging and excessive sugar consumption.

Chemical profiling and unraveling of anti-COVID-19 biomarkers of red sage (Lantana camara L.) cultivars using UPLC-MS/MS coupled to chemometric analysis, in vitro study and molecular docking.

ETHNOPHARMACOLOGICAL RELEVANCE: Red sage (Lantana camara L.) (Verbenaceae) is a widely spread plant that was traditionally used in Brazil, India, Kenya, Thailand, Mexico, Nigeria, Australia and Southeast Asia for treating several ailments including rheumatism and leprosy. Despite its historical role in relieving respiratory diseases, limited studies progressed to the plant's probable inhibition to respiratory viruses especially after the striking spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. AIM OF THE STUDY: This study aimed to investigate the inhibitory activity of different L. camara cultivars to SARS-CoV-2, that was not previously inspected, and clarify their mechanisms of action in the metabolomics viewpoint, and to determine the biomarkers that are related to such activity using UPLC-MS/MS coupled to in vitro-studies and chemometric analysis. MATERIALS AND METHODS: Chemical profiling of different cultivars was accomplished via UPLC-MS/MS. Principle component analysis (PCA) and orthogonal projection to latent structures (OPLS) models were built using SIMCA® (multivariate data analysis software). Cytotoxicity and COVID-19 inhibitory activity testing were done followed by TaqMan Real-time RT-PCR (Reverse transcription polymerase chain reaction) assay that aimed to study extracts' effects on RNA-dependent RNA polymerase (RdRp) and E-genes expression levels. Detected biomarkers from OPLS analysis were docked into potential targets pockets to investigate their possible interaction patterns using Schrodinger® suite. RESULTS: UPLC-MS/MS analysis of different cultivars yielded 47 metabolites, most of them are triterpenoids and flavonoids. PCA plots revealed that inter-cultivar factor has no pronounced effect on the chemical profiles of extracts except for L. camara, cultivar Drap d'or flowers and leaves extracts as well as for L. camara cv Chelsea gem leaves extract. Among the tested extracts, flowers and leaves extracts of L. camara cv Chelsea gem, flowers extracts of L. camara cv Spreading sunset and L. camara cv Drap d'or showed the highest selectivity indices scoring 12.3, 10.1, 8.6 and 7.8, respectively, indicating their relative high safety and efficacy. Leaves and flowers extracts of L. camara cv Chelsea gem, flowers extracts of L. camara cv Spreading sunset and L. camara cv Drap d'or were the most promising inhibitors to viral plaques exhibiting IC50 values of 3.18, 3.67, 4.18 and 5.01 µg/mL, respectively. This was incremented by OPLS analysis that related their promising COVID-19 inhibitory activities to the presence of twelve biomarkers. Inhibiting the expression of RdRp gene is the major mechanism behind the antiviral activity of most extracts at almost all concentration levels. Molecular docking of the active biomarkers against RdRp revealed that isoverbascoside, luteolin-7,4'-O-diglucoside, camarolic acid and lantoic acid exhibited higher docking scores of -11.378, -10.64, -6.72 and -6.07 kcal/mol, respectively, when compared to remdesivir (-5.75 kcal/mol), thus these four compounds can serve as promising anti-COVID-19 candidates. CONCLUSION: Flowers and leaves extracts of four L. camara cultivars were recognized as rich sources of phytoconstituents possessing anti-COVID-19 activity. Combination of UPLC-MS/MS and chemometrics is a promising approach to detect chemical composition differences among the cultivars and correlate them to COVID-19 inhibitory activities allowing to pinpoint possible biomarkers. Further in-vitro and in-vivo studies are required to verify their activity.

Tectona grandis leaf extract ameliorates hepatic fibrosis: Modulation of TGF- ß /Smad signaling pathway and upregulating MMP3/TIMP1 ratio.

ETHNOBOTANICAL RELEVANCE: Tectona grandis L.f (or syn: Jatus grandis (L.f.) Kuntze Revis), from family Lamiaceae, also known as Teak, is widely recognized in ayurvedic system of medicine and confer curative potential against inflammation, liver disorders, biliousness, diabetes, bronchitis, leprosy and dysentery. Its leaves are rich source of edible food colorant and reported nontoxic for liver and various organs. AIM OF STUDY: Hepatic injury progression to liver cirrhosis and cancer is a serious health issue across the world. Currently, anti-fibrotic therapeutic options are limited and expensive with no FDA approved direct anti-hepato-fibrotic drug validated in clinic. Thus, the aim of this study was to understand ameliorative effect of Tectona grandis L.f, leaves in early liver fibrosis. METHOD AND RESULTS: C57BL/6 mice suffering from CCl4 induced liver injury, were orally administered at three different doses (50, 100 & 200 mg/kg) of Tectona grandis L.f, leaf extract, thrice a week, up to 4 and 8 weeks. Anti-fibrotic effect was evaluated through animal body/liver weight measurements, serological tests (AST, ALT, GSH, MDA and LDH assays), tissue hydroxyproline content, and histochemical analysis (H&E, Masson trichrome, Sirius red and αSMA localization). Moreover, transcriptional and post-transcriptional expression of fibrosis associated biomarkers and TGF-ß/Smad cascade were analyzed. It was observed that 100 mg/kg dose optimally downregulated TGF-ß1/Smad2 with upregulation of Smad7 and regulated αSMA, Col 1, PDGF, TIMP1 and MMP3 expression, post 8 weeks of treatment. In addition, MMP3/TIMP1 ratio was upregulated to 0.7, 2.5 and 1.7 fold at 50 mg/kg, 100 mg/kg & 200 mg/kg treatments respectively, in comparison to untreated liver fibrosis models. The extract contains gallic acid, caffeic acid, sinapinic acid and myricetin when analyzed through high performance liquid chromatography. CONCLUSION: Tectona grandis L.f, leaves have potential to ameliorate liver fibrosis induced by CCl4 in mice via modulation of TGF-ß1/Smad pathway and upregulated MMP3/TIMP1 ratio.

Phytochemical screening, phenolic and flavonoid contents, antioxidant and cytogenotoxicity activities of Combretum leprosum Mart. (Combretaceae).

Combretum leprosum Mart. (Combretaceae), a shrub popularly known as mofumbo, is used in folk medicine for treatment of uterine bleeding, pertussis, gastric pain, and as a sedative. The aim of this study was to (1) determine the phytochemical profile,(2) identify chemical constituents and (3) examine antioxidant and cytogenotoxic activity of ethanolic extracts and fractions of stem bark and leaves. The plant material (leaf and stem bark) was submitted to extraction with ethanol, followed by partition using hexane, chloroform, and ethyl acetate. It was possible to identify and quantify the epicatechin in the ethanolic stem bark extract (0.065 mg/g extract) and rutin in the leaf extract (3.33 mg/g extract). Based upon in vitro tests a significant relationship was noted between findings from antioxidant tests and levels of total phenolic and flavonoid. Comparing all samples (extracts and fractions), the ethyl acetate fractions of stem bark (411.40 ± 15.38 GAE/g) and leaves (225.49 ± 9.47 GAE/g) exhibited higher phenolic content, whereas hexanic fraction of stem bark (124.28 ± 56 mg/g sample) and ethyl acetate fraction of leaves (238.91 ± 1.73 mg/g sample) demonstrated a higher content of flavonoids. Among the antioxidant tests, the intermediate fraction of stem bark (28.5 ± 0.60 µg/ml) and ethyl acetate fraction of leaves (40 ± 0.56 µg/ml) displayed a higher % inhibition of free radical DPPH activity, whereas intermediate fraction of stem bark (27.5 ± 0.9 µg/ml) and hydromethanol fraction of leaves (81 ± 1.4 µg/ml) demonstrated inhibition of the free radical ABTS. In biological tests (Allium cepa and micronucleus in peripheral blood), data showed that none of the tested concentrations of ethanolic extracts of leaves and stem bark produced significant cytotoxicity, genotoxicity, and mutagenic activity.Abbreviations AA%: percentage of antioxidant activity; ABTS: 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid); CEUA: Ethics Committee in the Use of Animals; TLC: Thin Layer Chromatography; DNA: deoxyribonucleic acid; DPPH: 1,1-diphenyl-2-picrylhydrazyl; ROS: Reactive oxygen species; EEB: ethanol extract of the stem bark; HFB: Hexanic fraction of stem bark; IFB: Intermediate fraction of stem bark; CFB: Chloroform fraction of stem bark; EAFB: Ethyl acetate fraction of stem bark; HMFB: Hydromethanol fraction of the stem bark; EEL: Ethanol extract from leaves; HFL: Hexane fraction of leaves; CFL: Chloroform fraction of leaves; EAFL: Ethyl acetate fraction of leaves; HMFL: Hydromethanol fraction of leaves; GAE: Gallic Acid Equivalent; IC50: 50% inhibition concentration; HCOOH: Formic acid; HCl: hydrochloric acid; HPLC: High-performance liquid chromatography; MN: micronucleus; WHO: World Health Organization; UFLC: Ultra-Fast Liquid Chromatography; UESPI: State University of Piauí.

Supercritical Fluid Chromatography development of a predictive analytical tool to selectively extract bioactive compounds by supercritical fluid extraction and pressurised liquid extraction.

Selective extraction is a great concern in the field of natural products. The interest is to apply specific conditions favouring the solubility of targeted secondary metabolites and avoiding the simultaneous extraction of unwanted ones. Different ways exist to reach selective extractions with suited conditions. These conditions can be determined from experimental studies through experimental design, but a full experimental design takes time, energy, and uses plant samples. Prediction from varied solubility models can also be applied allowing a better understanding of the final selected conditions and eventually less experiments. The aim of this work was to develop and use a chromatographic model to determine optimal extraction conditions without the need for numerous extraction experiments. This model would be applied on the selective extraction of the desired antioxidant compounds in rosemary leaves (rosmarinic and carnosic acids) vs chlorophyll pigments to limit the green colour in extracts. This model was achieved with Supercritical Fluid Chromatography (SFC) and then applied to Supercritical Fluid Extraction (SFE) and Pressurised Liquid Extraction (PLE) assays. SFC models predicted low solubility of chlorophylls for low (5%) and high (100%) percentage of solvent in carbon dioxide. Also, low solubility was predicted with acetonitrile solvent compared to methanol or ethanol. This was confirmed with different extractions performed using SFE with different percentages of solvent (5, 30, and 70%) and with the three solvents used in the SFC models (acetonitrile, methanol and ethanol). Also extractions using PLE were carried out using the same neat solvents in order to confirm the SFC models obtained for 100% of solvent. Globally, extractions validated the SFC models. Only some differences were observed between ethanol and methanol showing the complexity of plant extraction due to matrix effect. For all these extracts, the content of carnosic acid and rosmarinic acid was also monitored and selective extraction conditions of bioactive compounds could be determined.

Antinociceptive activity of 3ß-6ß-16ß-trihydroxylup-20 (29)-ene triterpene isolated from Combretum leprosum leaves in adult zebrafish (Danio rerio).

Drugs used to treat pain are associated with adverse effects, increasing the search for new drugs as an alternative treatment for pain. Therefore, we evaluated the antinociceptive behavior and possible neuromodulation mechanisms of triterpene 3ß, 6ß, 16ß-trihydroxylup-20(29)-ene (CLF-1) isolated from Combretum leprosum leaves in zebrafish. Zebrafish (n = 6/group) were pretreated with CLF-1 (0.1 or 0.3 or 1.0 mg/mL; i.p.) and underwent nociception behavior tests. The antinociceptive effect of CFL-1 was tested for modulation by opioid (naloxone), nitrergic (L-NAME), nitric oxide and guanylate cyclase synthesis inhibitor (methylene blue), NMDA (Ketamine), TRPV1 (ruthenium red), TRPA1 (camphor), or ASIC (amiloride) antagonists. The corneal antinociceptive effect of CFL-1 was tested for modulation by TRPV1 (capsazepine). The effect of CFL-1 on zebrafish locomotor behavior was evaluated with the open field test. The acute toxicity study was conducted. CLF-1 reduced nociceptive behavior and corneal in zebrafish without mortalities and without altering the animals' locomotion. Thus, CFL-1 presenting pharmacological potential for the treatment of acute pain and corneal pain, and this effect is modulated by the opioids, nitrergic system, NMDA receptors and TRP and ASIC channels.

Nanoencapsulation of triterpene 3ß,6ß,16ß-trihydroxylup-20(29)-ene from Combretum leprosum as strategy to improve its cytotoxicity against cancer cell lines.

The pentacyclic triterpene 3ß,6ß,16ß-tri-hydroxilup-20(29)-ene is a natural product produced by the Brazilian medicinal plant Combretum leprosum. Its cytotoxicity has been previously reported against breast cancer cell lines. The low water solubility of this natural product, that hampers its bioavailability, motivated the investigation of a new nanoparticle formulation containing the triterpene in order to improve its bioactivity. The triterpene was encapsulated in polycaprolactone (PCL) polymer by nanoprecipitation, producing homogenic nanoparticles with nanometer sizes (122.7 ± 2.06 nm), which were characterized by FT-IR, SEM imaging and DSC. The cytotoxicity (MTT method) of the nanoparticle containing the triterpene 1, besides the free natural product and the nanoparticle control (without 1), was assayed against three human tumor cell lines [human colon carcinoma line (HCT116), prostate (PC3) and glioblastoma (SNB19)] and the normal epithelial embryo kidney human cell line (Hek293T). The nanocarrier produced a significative effect in the cytotoxicity of the natural product in the nanoformulation (IC50 0.11-0.26 µg mL-1) when compared with its free form (IC50 1.07-1.44 µg mL-1). Additionally, higher selectivity of the triterpene to the tumor cells was found when it was encapsulated (SI 1.92-4.54) than in its free form (SI 0.42-0.56). In this case, the nanoencapsulated triterpene was more selective to PC3 (SI 3.33) and SNB19 (SI 4.54) tumor cells.

Antimicrobial activity of the lupane triterpene 3ß,6ß,16ß-trihydroxylup-20(29)-ene isolated from Combretum leprosum Mart.

Introduction. Combretum leprosum (Combretaceae) is commonly found in the Northeast Region of Brazil and is known for several bioactivities, including antimicrobial ones. Because of increasing bacterial antibiotic resistance, natural products from several plants have been studied as putative adjuvants to antibiotic activity, including products from C. leprosum. Aims. This study was carried out to investigate the structural properties, bactericidal activity and antibiotic modifying action of the lupane triterpene 3ß,6ß,16ß-trihydroxylup-20(29)-ene (CLF1) isolated from C. leprosum Mart. leaves.Methods. The CLF1 was evaluated by the Fourier transform infrared spectroscopy method and the antibacterial activity of this compound was assayed alone and in association with antibiotics by microdilution assay.Results. Spectroscopic studies confirmed the molecular structure of the CLF1 and permitted assignment of the main infrared bands of this natural product. Microbiological assays showed that this lupane triterpene possesses antibacterial action with clinical relevance against Staphylococcus aureus. The CLF1 triterpene increased antimicrobial activity against the multidrug-resistant Escherichia coli 06 strain when associated with the antibiotics gentamicin and amikacin. Synergistic effects were observed against the S. aureus 10 strain in the presence of the CLF1 triterpene with the antibiotic gentamicin.Conclusion. In conclusion, the CLF1 compound may be useful in the development of antibacterial drugs against the aforementioned bacteria.

Evaluation of acute and subacute toxicity of aqueous extract of Crassocephalum rubens leaves in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Crassocephalum rubens is found throughout tropical Africa including the Indian Ocean islands. The leaves are commonly eaten in form of soups and sauces in South-Western Nigeria, also in other humid zones of Africa. Traditionally, it is used as an antidote against any form of poisoning; used to treat stomach and liver complaints; and externally to treat burns, sore eyes, earache, leprosy and breast cancer. In this study, acute and subacute toxicity of aqueous extract of C. rubens leaves was evaluated in rats in order to assess its safety profile. MATERIALS AND METHODS: In acute toxicity study, rats were given a single oral administration of aqueous extract of C. rubens leaves at graded doses (250-5000mg/kg). The animals were monitored for behavioural changes and possible mortality over a period of 24h and thereafter, for 14 days. In the subacute toxicity study, rats of both sexes were administered C. rubens orally at doses of 250mg/kg, 500mg/kg, 750mg/kg and 1000mg/kg body weight daily, for 28 days. Rats were observed weekly for any changes in general behaviour and body weights. In addition, other relevant parameters were assayed at the end of the main and reversibility study periods. RESULTS: There was no observed adverse effect; including mortality in the animals. The extract caused no significant difference in the body weights as well as organs weights of treated groups when compared with the control groups. Haematological and biochemical parameters also revealed no toxic effects of the extract on rats. Histological assessments were normal in liver and kidney. CONCLUSIONS: It can therefore be suggested based on the results from this study that aqueous extract of C. rubens leaves, at dosage levels up to 1000mg/kg, is non-toxic and could also offer protection on some body tissues. Aqueous extract of C. rubens could therefore, be considered safe. This study supports the application of Crassocephalum rubens in traditional medicine.

Cytotoxicity potentials of eleven Bangladeshi medicinal plants.

Various forms of cancer are rising all over the world, requiring newer therapy. The quest of anticancer drugs both from natural and synthetic sources is the demand of time. In this study, fourteen extracts of different parts of eleven Bangladeshi medicinal plants which have been traditionally used for the treatment of different types of carcinoma, tumor, leprosy, and diseases associated with cancer were evaluated for their cytotoxicity for the first time. Extraction was conceded using methanol. Phytochemical groups like reducing sugars, tannins, saponins, steroids, gums, flavonoids, and alkaloids were tested using standard chromogenic reagents. Plants were evaluated for cytotoxicity by brine shrimp lethality bioassay using Artemia salina comparing with standard anticancer drug vincristine sulphate. All the extracts showed potent to moderate cytotoxicity ranging from LC50 2 to 115 µg/mL. The highest toxicity was shown by Hygrophila spinosa seeds (LC50 = 2.93 µg/mL) and the lowest by Litsea glutinosa leaves (LC50 = 114.71 µg/mL) in comparison with standard vincristine sulphate (LC50 = 2.04 µg/mL). Among the plants, the plants traditionally used in different cancer and microbial treatments showed highest cytotoxicity. The results support their ethnomedicinal uses and require advanced investigation to elucidate responsible compounds as well as their mode of action.

Nephroprotective activity of Cocculus hirsutus leaf extract in 5/6 nephrectomized rat model.

BACKGROUND: Cocculus hirsutus, commonly known as broom creeper, belongs to the family Menispermaceae. It is widely used in folk medicine to treat leprosy, skin diseases, dyspepsia, etc. Hence, an effort has been made to investigate the nephroprotective potential of C. hirsutus. METHODS: The nephroprotective activity of ethanolic C. hirsutus leaf extract (ECHE) in the 5/6 nephrectomized rat model was investigated. Different parameters like postoperative survival rate, change in body weight and levels of red blood corpuscles (RBCs), hemoglobin (Hb), triglyceride, cholesterol, creatinine, urea and uric acid were estimated in experimental rats. RESULTS: The findings revealed the postoperative survival rate of rats in the investigated novel method to be 100%. Change in the body weight of ECHE-treated groups I and II was found to be 32 and 30 g, respectively. These values suggested that ECHE treatment normalized the elevated body weight levels in experimental rats. Furthermore, ECHE treatment normalized the decreased RBC levels and the elevated Hb, triglyceride, cholesterol, creatinine, urea and uric acid levels in experimental rats. CONCLUSIONS: The results indicate that C. hirsutus has strong nephroprotective activity. However, further scrutiny is essential for isolation and characterization of the active components that can be employed to allay various human maladies.

Evaluation of wound healing activity of Lantana camara L. - a preclinical study.

Lantana camara is used in herbal medicine for the treatment of skin itches, as an antiseptic for wounds, and externally for leprosy and scabies. The objective of our study was to investigate excision wound healing activity of the leaf extract of L. camara in rats. The animals were divided into two groups of 12 each in both the models. The test group animals were treated with the aqueous extract of L. camara (100 mg/kg/day) topically and the control group animals were left untreated. Wound healing efficacy was measured by determining the morphological and biochemical parameters. Wound healing time, wound contraction and synthesis of collagen were monitored periodically. Antimicrobial activities of the extract against the microorganisms were also assessed. Treatment of the wounds with extract enhanced significantly the rate of wound contraction (98%), synthesis of collagen and decreased mean wound healing time. These studies demonstrate that L. camara is effective in healing excision wounds in the experimental animal and could be evaluated as a therapeutic agent in tissue repair processes associated with skin injuries.

Composition and antimicrobial activity of the essential oil of Actinidia macrosperma from China.

Actinidia macrosperma is a medicinal plant in China and has been well known for its attraction to cats and activities against leprosy and cancers. The compositions and the antimicrobial activity of its leaf oil were reported for the first time. The oil obtained by hydrodistillation and analyzed by GC and GC-MS, was characterized by the high content of monoterpenes. Linalool (48.14%) is the major component identified, followed by 1,2-dimethyl-lindoline (7.94%), linolenic acid methylester (6.57%) and (E)-phytol (5.29%). The antimicrobial activity of the oil was evaluated against four bacterial and three fungal species. The results showed that it exhibited a mild antibacterial activity against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), a significant activity against Gram-negative bacteria (Escherichia coli), and no activity on Pseudomonas aeruginosa. The test fungi were more sensitive to the oil, with a MIC range of 0.78-1.56 microL mL(-1) than bacteria in the range which were significantly higher from 0.78 to 25.50 microL mL(-1).

Patterns of dynamic irradiance affect the photosynthetic capacity and growth of dipterocarp tree seedlings.

In the deeply shaded understorey of S.E. Asian rain forests the growth and survival of dipterocarp seedlings is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain in understorey plants. To test the sensitivity of photosynthesis and growth to variation in the pattern of dynamic irradiance, dipterocarp tree seedlings (Shorea leprosula and Hopea nervosa) were grown for 370 days under shaded forest light treatments of equal total daily photosynthetic photon flux density (approximately 3.3 mol m(-2) day(-1)), but characterised by either long flecks (LF) or short flecks (SF). Seedling growth was more than 4-fold greater under LF, compared with SF, in both species. Variation in the relative growth rates (RGR) and light saturated rates of photosynthesis (A(max)) were strongly positively correlated with the mean duration of sunflecks. Variation in RGR was strongly correlated with greater unit leaf rate growth, indicating that photosynthetic carbon gain per unit leaf area was greater under LF. The accumulation of starch in leaves over the diurnal period was 117% greater in both species under LF, compared with SF. Greater carbon gain in seedlings under LF is likely to have resulted from the combination of (1) greater A(max) (S. leprosula 35%, H. nervosa 40%), (2) more efficient dynamic photosynthesis, and (3) greater incident photosynthetic quantum yield, compared with seedlings receiving the SF irradiance treatment. The pattern of dynamic irradiance received by seedlings may significantly impact their growth and survival to a previously unrecognised extent, with important consequences for regeneration processes and hence forest structure and composition.