Pollen limitation and xenia effects in a cultivated mass-flowering tree, Macadamia integrifolia (Proteaceae).

BACKGROUND AND AIMS: Pollen limitation is most prevalent among bee-pollinated plants, self-incompatible plants and tropical plants. However, we have very little understanding of the extent to which pollen limitation affects fruit set in mass-flowering trees despite tree crops accounting for at least 600 million tons of the 9200 million tons of annual global food production. METHODS: We determined the extent of pollen limitation in a bee-pollinated, partially self-incompatible, subtropical tree by hand cross-pollinating the majority of flowers on mass-flowering macadamia (Macadamia integrifolia) trees that produce about 200 000-400 000 flowers. We measured tree yield and kernel quality and estimated final fruit set. We genotyped individual kernels by MassARRAY to determine levels of outcrossing in orchards and assess paternity effects on nut quality. KEY RESULTS: Macadamia trees were pollen-limited. Supplementary cross-pollination increased nut-in-shell yield, kernel yield and fruit set by as much as 97, 109 and 92 %, respectively. The extent of pollen limitation depended upon the proximity of experimental trees to trees of another cultivar because macadamia trees were highly outcrossing. Between 84 and 100 % of fruit arose from cross-pollination, even at 200 m (25 rows) from orchard blocks of another cultivar. Large variations in nut-in-shell mass, kernel mass, kernel recovery and kernel oil concentration were related to differences in fruit paternity, including between self-pollinated and cross-pollinated fruit, thus demonstrating pollen-parent effects on fruit quality (i.e. xenia). CONCLUSIONS: This study is the first to demonstrate pollen limitation in a mass-flowering tree. Improved pollination led to increased kernel yield of 0.31-0.59 tons ha-1, which equates currently to higher farm-gate income of approximately $US3720-$US7080 ha-1. The heavy reliance of macadamia flowers on cross-pollination and the strong xenia effects on kernel mass demonstrate the high value that pollination services can provide to food production.

SNP markers reveal relationships between fruit paternity, fruit quality and distance from a cross-pollen source in avocado orchards.

Cross-pollination can improve fruit yield, fruit size and nutritional quality of many food crops. However, we rarely understand what proportions of the crop result from self- or cross-pollination, how cross-pollination affects crop quality, and how far pollen is transported by pollinators. Management strategies to improve pollination services are consequently not optimal for many crops. We utilised a series of SNP markers, unique for each cultivar of avocado, to quantify proportions of self- and cross-paternity in fruit of Hass avocado at increasing distances from cross-pollen sources. We assessed whether distance from a cross-pollen source determined the proportions of self-pollinated and cross-pollinated fruit, and evaluated how self- and cross-paternity affected fruit size and nutritional quality. Avocado fruit production resulted from both self- and cross-pollination in cultivar Hass in Queensland, Australia. Cross-pollination levels decreased with increasing distance from a cross-pollen source, from 63% in the row adjacent to another cultivar to 25% in the middle of a single-cultivar block, suggesting that pollen transport was limited across orchard rows. Limited pollen transport did not affect fruit size or quality in Hass avocados as xenia effects of a Shepard polliniser on size and nutritional quality were minor.

Cross-pollination affects fruit colour, acidity, firmness and shelf life of self-compatible strawberry.

Cross-pollination affects the fruit characteristics of many crops but the effects of cross-pollination on fruit quality of strawberry (Fragaria × ananassa Duch.) are poorly known. This study determined how cross-pollination affects fruit quality of the strawberry cultivar, Redlands Joy, under controlled environment conditions. Plants were allocated to one of four treatments, with all flowers on each plant receiving either: (1) unassisted self-pollination (Autogamy); (2) hand-pollination with Redlands Joy pollen (Self); (3) hand-pollination with cross-pollen from a small-fruited cultivar (Sugarbaby); or (4) hand-pollination with cross-pollen from a large-fruited cultivar (Rubygem). Cross-pollination did not significantly affect plant yield or fruit mass, size, shape, firmness or shelf life. However, cross-pollination affected fruit colour and taste attributes. Cross-pollinated fruit were 3%-5% darker than self-pollinated fruit. They also had 26%-34% lower acidity and 43%-58% higher Brix:acid ratio. Cross-pollination by Sugarbaby increased fruit P, K, Ca, Fe and Mn, but decreased B, Cu and Zn, concentrations. Cross-pollination by Rubygem increased fruit Mn, but decreased K and Na, concentrations and reduced shelf life. Fruit mass, length, diameter and firmness within all treatments increased with increasing numbers of fertilized seeds per fruit. Hand self-pollinated fruit had a higher percentage of fertilized seeds than fruit arising from autogamy and they were also darker, redder, firmer, and had a longer shelf life, higher protein concentration, and lower Al and Na concentrations. The results indicate that strawberry fruit quality can be affected by both the source of pollen and the number of stigmas pollinated.

Lessons from Exploring Chemical Space and Chemical Diversity of Propolis Components.

Propolis is a natural resinous material produced by bees and has been used in folk medicines since ancient times. Due to it possessing a broad spectrum of biological activities, it has gained significant scientific and commercial interest over the last two decades. As a result of searching 122 publications reported up to the end of 2019, we assembled a unique compound database consisting of 578 components isolated from both honey bee propolis and stingless bee propolis, and analyzed the chemical space and chemical diversity of these compounds. The results demonstrated that both honey bee propolis and stingless bee propolis are valuable sources for pharmaceutical and nutraceutical development.

Transcriptome analysis of the medicinally significant plant Fontainea picrosperma (Euphorbiaceae) reveals conserved biosynthetic pathways.

Euphorbiaceae is a large and diverse family of herbs, shrubs and trees that includes a number of species of considerable economic importance as sources of food, medicines and raw materials. One member of this family, Fontainea picrosperma, is the source plant for the diterpene ester tigilanol tiglate, a natural product recently approved as a treatment for canine mast cell tumours. Here we report the development of reference transcriptomes from root and leaf tissues of F. picrosperma, which include core diterpene biosynthesis genes. A total of ~12 Gb of combined clean reads were generated for assembly into 167,566 contigs with a GC (guanine-cytosine) content of ~41%. Gene ontology showed that 2286 and 2504 transcripts were enriched in the cellular process and 2369 and 2529 transcripts were enriched in the metabolic process categories in leaf and root tissue, respectively. The reference transcriptome contains genes coding for core enzymes involved in common secondary metabolite biosynthetic pathways, including the diterpene biosynthesis pathway within the mevalonate (MVA) and 2-C-methyl-D-erythritol 4- phosphate (MEP) pathways. A phylogenetic analysis using these genes found that F. picrosperma clustered most closely to Jatropha curcas. We found a significantly higher concentration of tigilanol tiglate in F. picrosperma root tissue, which correlated with higher levels of gene expression for enzymes associated with the MVA (6 genes) and MEP (7 genes) pathways, and we hypothesise that the initial stages of tigilanol tiglate biosynthesis occur primarily in the roots of F. picrosperma. This study provides a resource for future gene-related biodiscovery investigations in F. picrosperma and diterpene biosynthesis, in particular for tigilanol tiglate and related macrocyclic diterpenes.

Antibacterial 5α-Spirostane Saponins from the Fruit of Cordyline manners-suttoniae.

Antibacterial-activity-guided fractionation of a dichloromethane extract from the fruit of Cordyline manners-suttoniae and subsequent structure-activity investigations resulted in the identification of 10 new (1-10) and one known (11) 5α-spirostane saponin. The structures of the new compounds were established by 1D and 2D NMR analyses. The absolute configurations of the isolated compounds were determined by X-ray diffraction analysis or chemical derivatizations. The most active compound, suttonigenin F (6), inhibited the Gram-positive bacteria Staphylococcus aureus with MIC75 values that were comparable to those of the antibiotic chloramphenicol. Structure-activity relationships were also obtained from the assessment of antibacterial and cytotoxic activities of the isolated saponins.

Short distance pollen dispersal and low genetic diversity in a subcanopy tropical rainforest tree, Fontainea picrosperma (Euphorbiaceae).

Gene flow via pollen movement affects genetic variation in plant populations and is an important consideration in plant domestication. Fontainea picrosperma is a subcanopy rainforest tree that is of commercial interest because it is the source of tigilanol tiglate, a natural product used for the treatment of solid tumors. We identify patterns of pollen-mediated gene flow within natural populations of F. picrosperma and estimate genetic parameters and genetic structure between adult and juvenile groups using microsatellite markers. Our results show pollination events occur over much shorter distances than reported for tropical canopy species. At least 63% of seeds are sired by male trees located within 30 m of the mother. On average, 27% of the local male population contributed to successful reproduction of F. picrosperma with most fathers siring a single seed, however, the contributions to reproduction were uneven. Larger male trees with more flowers had greater reproductive success than those with less flowers (P < 0.05). There were comparatively low levels of genetic variation across the species (HE = 0.405 for adult trees and 0.379 for juveniles) and we found no loss of genetic diversity between adult and juvenile trees. Short distance pollen flow and low genetic diversity is theoretically a prelude to genetic impoverishment, however F. picrosperma has persisted through multiple significant climatic oscillations. Nevertheless, the remaining low genetic diversity is of concern for domestication programs which require maximal genetic diversity to facilitate efficient selective breeding and genetic improvement of this commercially significant species.

Natural products isolated from Tetragonula carbonaria cerumen modulate free radical-scavenging and 5-lipoxygenase activities in vitro.

BACKGROUND: Propolis and cerumen are plant-derived products found in honeybees and stingless bees, respectively. Although propolis is an ancient folk medicine, the bioactivities of cerumen obtained from Australian native stingless bees (Tetragonula carbonaria) have not been widely studied. Therefore, we investigated selected anti-oxidant and anti-inflammatory properties of T. carbonaria cerumen. METHODS: A methanolic extract was prepared from the combined cerumen of 40 T. carbonaria hives, and HPLC was used to screen for chemical constituents that scavenged 2,2-azobis(2-methylpropionamidine) dihydrochloride (AAPH). The ability of cerumen extracts to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) and to interfere with leukotriene B4 (LTB4) production in ionomycin-stimulated human neutrophils was also examined. RESULTS: The extract dose-dependently scavenged DPPH (EC50 = 27.0 ± 2.3 µg/mL); and inhibited the 5-lipoxygenase (5-LOX)-mediated oxidation of linoleic acid (IC50 = 67.1 ± 9.6 µg/mL). Pre-treatment of isolated human neutrophils with the methanolic cerumen extract additionally inhibited the ionomycin-stimulated production of LTB4 from these cells (IC50 = 13.3 ± 5.3 µg/mL). Following multi-solvent extraction, the free radical-scavenging and 5-LOX-inhibiting activities of the initial cerumen extract were retained in a polar, methanol-water extract, which contained gallic acid and a range of flavonone and phenolic natural products. CONCLUSIONS: The findings identify free radical scavenging activity, and interference by extracts of T. carbonaria cerumen in 5-LOX-LTB4 signaling. Further investigation is needed to determine whether the extracts will provide therapeutic benefits for medical conditions in which oxidative stress and inflammation are implicated, including cardiovascular disease and impaired wound healing.

The value of nature's natural product library for the discovery of New Chemical Entities: the discovery of ingenol mebutate.

In recent decades, 'Big Pharma' has invested billions of dollars into ingenious and innovative strategies designed to develop drugs using high throughput screening of small molecule libraries generated on the laboratory bench. Within the same time frame, screening of natural products by pharmaceutical companies has suffered an equally significant reduction. This is despite the fact that the complexity, functional diversity and druggability of nature's natural product library are considered by many to be superior to any library any team of scientists can prepare. It is therefore no coincidence that the number of New Chemical Entities reaching the market has also suffered a substantial decrease, leading to a productivity crisis within the pharmaceutical sector. In fact, the current dearth of New Chemical Entities reaching the market in recent decades might be a direct consequence of the strategic decision to move away from screening of natural products. Nearly 700 novel drugs derived from natural product New Chemical Entities were approved between 1981 and 2010; more than 60% of all approved drugs over the same time. In this review, we use the example of ingenol mebutate, a natural product identified from Euphorbia peplus and later approved as a therapy for actinic keratosis, as why nature's natural product library remains the most valuable library for discovery of New Chemical Entities and of novel drug candidates.