Mangrove endophytic fungi can produce impressive quantities of metabolites with promising antioxidant activities that may be useful to humans as novel physiological agents. In this study, we investigated the phylogenetic diversity and antioxidant potential of 46 fungal endophytes derived from the mangrove species Rhizophora stylosa and R. mucronata from the South China Sea. The fungal isolates were identified using a combination of morphological characteristics and phylogenetic analysis of the internal transcribed spacer (ITS) sequences. Seventeen genera belonging to 8 taxonomic orders of Ascomycota were discovered, specifically, Botryosphaeriales, Capnodiales, Diaporthales, Eurotiales, Glomerellales, Hypocreales, Pleosporales, and Xylariales. The most abundant fungal orders included Xylariales (35.49%) and Diaporthales (27.61%), which were predominantly represented by the culturable species Pestalotiopsis sp. (34.54%) and Diaporthe sp. (18.62%). The stems showed more frequent colonization and species diversity than the roots, leaves, hypocotyls, and flower tissues of the host plant. The antioxidant activities of all the isolated fungal extracts on four different culture media were assessed using improved 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) methods. A relatively high proportion (84.8%) of the isolates displayed antioxidant capacity (%RSA > 50%). Further research also provided the first evidence that HQD-6 could produce flufuran as a significant radical scavenger with IC₅₀ values of 34.85±1.56 and 9.75±0.58 μg/mL, respectively. Our findings suggest that the utilization of a biotope such as that of the endophytic fungal community thriving on the mangrove plants R. stylosa and R. mucronata may be suitable for use as a sustainable resource for natural antioxidants.

Ultrasonic-assisted extraction (UAE) was developed to extract phenolic and flavonoid antioxidants from Clerodendrum cyrtophyllum Turcz leaves. The optimal experimental parameters for antioxidant extraction from C. cyrtophyllum leaves were measured using single-factor experimentation combined with response surface methodology (RSM). Total phenolic content (TPC) and total flavonoid content (TFC) assays were used to quantify antioxidant compounds. Next, antioxidant radical scavenging capacity was measured using 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′ -azino-bis(3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) radicals. Optimized extraction conditions for UAE from C. cyrtophyllum leaves were as follows: 60.9% ethanol, 85.4 min, and 63.3°C for maximal TPC extraction (16.8±0.2 mg GAE/g DW); 67.7% ethanol, 82.9 min, and 63.0°C for maximal TFC extraction (49.3±0.4 mg RT/g DW); 48.8% ethanol, 85.1 min, and 63.9°C for maximal DPPH radical-scavenging capacity (86.8±0.2%); and 50.6% ethanol, 81.3 min, and 63.4°C for maximal ABTS radical-scavenging capacity (92.9±0.5%). Ethanol concentration was the most important factor in the extraction process. Our work offers optimal extraction conditions for C. cyrtophyllum as a potential source of natural antioxidants.

Chemical examination of Chinese mangrove Ceriops tagal endophytic Cytospora sp., yielded a new biscyclic sesquiterpene seiricardine D (1), and eight known metabolites, xylariterpenoid A (2a), xylariterpenoid B (2b) and regiolone (3) 4-hydroxyphenethyl alcohol (4), (22E, 24R)5, 8-epidioxy-5α, 8α-ergosta-6,22E-dien-3ß-ol (5), (22E, 24R)5, 8-epidioxy-5α, 8α-ergosta-6,9(11), 22-trien-3 ß-ol (6), ß-sitosterol (7) and stigmast-4-en-3-one (8). These structures were unambiguously elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. The antimicrobial activities of compounds 1–8 and their effects on a panel of plant and human pathogens were evaluated.

Understanding which factors affect the distribution pattern of extremely small populations is essential to the protection and propagation of rare and endangered plant species. In this study, we established 108 plots covering the entire Hainan Island, and measured the appearance frequency and species richness of plant species with extremely small populations, as well as the ecological environments and human disturbances during 2012–2013. We explored how the ecological environments and human activities affected the distribution pattern of these extremely small populations. Results showed that the extremely small populations underwent human disturbances and threats, and they were often found in fragmental habitats. The leading factors changing the appearance frequency of extremely small populations differed among plant species, and the direct factors making them susceptible to extinction were human disturbances. The peak richness of extremely small populations always occurred at the medium level across environmental gradients, and their species richness always decreased with increasing human disturbances. However, the appearance frequencies of three orchid species increased with the increasing human disturbances. Our study thus indicate that knowledge on how the external factors, such as the ecological environment, land use type, roads, human activity, etc., affect the distribution of the extremely small populations should be taken for the better protecting them in the future.

Chemical examination of Chinese mangrove Rhizophora mucronata endophytic Pestalotiopsis sp., yielded 11 known metabolites with various structure types, including demethylincisterol A₃ (1), dankasterone B (2), (22E, 24R)-ergosta-7,9(11), 22-triene-3β, 5α, 6α-triol (3), ergosta-5,7,22-trien-3-ol (4), 5, 8-epidioxy-5, 8-ergosta-6, 22E-dien-3-ol (5), stigmastan-3-one (6), stigmast-4-en-3-one (7), stigmast-4-en-6 -ol-3-one (8), flufuran (9), (2-cis, 4-trans)-abscisic acid (10), similanpyrone B (11). Their structures were unambiguously elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. Compounds 1, 4, 6–9 showed significant in vitro cytotoxicity against the human cancer cell lines Hela, A549 and HepG, of which compound 1 was the most potential with IC₅₀ values reaching nM degree ranging from 0.17 to 14.16 nM. Flow cytometric investigation demonstrated that compound 1 mainly inhibited cell cycle at G₀/G₁ phase in a dose-dependent manner with a significant induction of apoptosis on the three tested cell lines. The involvement of the mitochondria in compound 1 induced apoptosis was investigated using MMP. We suggested that R. mucronata endophytic Pestalotiopsis sp. contained a potential anticancer compound demethylincisterol A₃.

As the only forests situated at the transition between land and sea, mangrove forests are one of the first ecosystems vulnerable to rising sea levels. When the sea level rises, plants are exposed to increased salinity, as well as tidal flooding. The responses of mangrove forests to changing sea levels depend on the synergistic effects of tidal flooding and salinity on plants, especially seedlings. The focus of this paper is to assess the ability of different tide position on mangrove Aegiceras corniculatum (A. corniculatum) and Bruguiera sexangula (B. sexangula) seedlings to withstand tidal flooding and seawater salinity, and to investigate the effects of tidal flooding and salinity on plant growth. To accomplish this, a controlled experiment was initiated to examine the synergistic effects of tidal flooding and salinity on the growth and physiology of A. corniculatum and B. sexangula seedlings subjected to four tidal flooding times and four levels of salinity over a course of six months. The results showed that the biomass and antioxidant enzymes of A. corniculatum and B. sexangula seedlings were significantly affected by the increase in salinity and flooding time. Changes in biomass, SOD, and CAT activity of A. corniculatum seedlings show that they are more adapted to grow in an environment with high salinity and long flooding time than B. sexangula. Our results show that species growing in middle- to low-tide levels were better adapted to sea level rise than those growing at high-tide levels.