Benzoylcyclopropane Derivatives from Hypoxis hemerocallidea Corms

Two monobenzoylcyclopropane (hypoxhemerol A (1) and hypoxhemeroloside G (2)) and three dibenzoylcyclopropane (hypoxhemerol B (3), hypoxhemeroloside H (4), and hypoxhemeroloside I (5)) derivatives were isolated from the hydro-alcoholic extract of Hypoxis hemerocallidea corms. This is the first instance where benzoylcyclopropane analogs were isolated from any natural source. Structure elucidation was mainly based on 1D- and 2D-NMR and HRESIMS data. The absolute configuration (2R, 4R) of 1 was determined via NOESY NMR and experimental and calculated ECD data analyses. Compounds 1–5 and 11 recently reported metabolites (hypoxoside, obtuside A, interjectin, acuminoside, curcapicycloside, and hypoxhemerolosides A – F) were screened for in vitro antimicrobial activity against various bacterial and fungal strains. Curcapicycloside and acuminoside exhibited antibacterial activity against Escherichia coli with 78 and 79% inhibition at 20 µg/mL, respectively. Hypoxhemeroloside A showed mild antifungal activity against Cryptococcus neoformans with 63% inhibition at 20 µg/mL.

Synergistic broad-spectrum antibacterial activity of Hypoxis hemerocallidea-derived silver nanoparticles and streptomycin against respiratory pathobionts

Respiratory tract infections arise due to the introduction of microbes into the airway, disrupting the normal, healthy, complex interdependent microbiome. The selective disruption of this community can be either beneficial or dangerous. Nanoparticles are a potential tool for modifying this population. Coated silver nanoparticles (AgNPs) were synthesized using ethanolic extracts of Hypoxis hemerocallidea (EEHH), a Southern African plant used extensively in traditional medicine and the source of many bioactive secondary metabolites. The room temperature reaction between silver nitrate and EEHH forms largely spherical AgNPs with an average diameter of 6–20 nm. These nanoparticles show similar levels of antibacterial activity as the broad-spectrum antibiotic streptomycin against Bacillus cereus, Streptococcus pneumonia, Escherichia coli, Pseudomonas aeuroginosa, and Moraxella catarrhalis. However, the AgNPs synergistically increase the antibacterial activity of streptomycin when they are applied in combination (30–52%). AgNPs are reiterated to be promising dual-function antibiotics, synergistically enhancing activity while also acting as delivery agents for small molecules.

Transcriptome and proteome of the corm, leaf and flower of Hypoxis hemerocallidea (African potato)

The corm of Hypoxis hemerocallidea, commonly known as the African potato, is used in traditional medicine to treat several medical conditions such as urinary infections, benign prostate hyperplasia, inflammatory conditions and testicular tumours. The metabolites contributing to the medicinal properties of H. hemerocallidea have been identified in several studies and, more recently, the active terpenoids of the plant were profiled. However, the biosynthetic pathways and the enzymes involved in the production of the terpene metabolites in H. hemerocallidea have not been characterised at a transcriptomic or proteomic level. In this study, total RNA extracted from the corm, leaf and flower tissues of H. hemerocallidea was sequenced on the Illumina HiSeq 2500 platform. A total of 143,549 transcripts were assembled de novo using Trinity and 107,131 transcripts were functionally annotated using the nr, GO, COG, KEGG and SWISS-PROT databases. Additionally, the proteome of the three tissues were sequenced using LC-MS/MS, revealing aspects of secondary metabolism and serving as data validation for the transcriptome. Functional annotation led to the identification of numerous terpene synthases such as nerolidol synthase, germacrene D synthase, and cycloartenol synthase amongst others. Annotations also revealed a transcript encoding the terpene synthase phytoalexin momilactone A synthase. Differential expression analysis using edgeR identified 946 transcripts differentially expressed between the three tissues and revealed that the leaf upregulates linalool synthase compared to the corm and the flower tissues. The transcriptome as well as the proteome of Hypoxis hemerocallidea presented here provide a foundation for future research.

Buried but unsafe – defoliation depletes the underground storage organ (USO) of the mesic grassland geophyte, Hypoxis hemerocallidea

Mesic grasslands in South Africa (> 650 mm a-1 MAP) are rich in herbaceous forbs, which outnumber grass species by more than 5 to 1. Many of these forbs have underground storage units (USOs), such as thickened rootstocks, rhizomes, bulbs, or corms, that provide resources (non-structural carbohydrates, minerals, and water) enabling them to resprout after dry, frosty winters, and fire. However, despite their extensive biomass and reserves ostensibly protected underground, geophytic mesic grassland forbs can be severely depleted or extirpated by chronic trampling and grazing of their aerial parts by livestock. This study examined a possible explanation for forb demise in overgrazed grassland by investigating, in a pot trial, whether the growth of forbs and the size of their USOs are negatively affected by simulated green leaf loss. In a 2x2 factorial (clipped vs. unclipped x spring regrowth in the dark vs. light), five replicate plants of Hypoxis hemerocallidea, a common mesic grassland forb that resprouts from a corm, were subject to six severe (clipped to 80 mm) defoliations during the growing season and regrown in spring under full or restricted light to measure stored reserve contribution to regrowth. Defoliated plants were resilient to defoliation during the growing season, matching the total biomass production of unclipped plants, though cutting reduced the number of leaves by ~60% and flowers by almost 85%. Spring regrowth on stored reserves equalled that from reserves plus concurrent photosynthesis, indicating the value of USOs for regrowth. However, there was a marked carry-over effect of previous season defoliation, resulting in a one-third reduction in shoot growth and 40% fewer inflorescence in spring. Crucially, corm mass was more than halved by clipping. Above-ground spring growth was linearly related to corm mass. It was concluded that buried stored reserves are not protected by recurrent disturbance to aerial plant parts and that continued diminishment of USOs under chronic disturbance by overgrazing or frequent mowing would weaken and likely eventually kill plants, reducing forb species richness. Lenient management by infrequent summer mowing or grazing at moderate stocking rates combined with periodic rotational full season resting and dormant-season burning is recommended to maintain the USOs and vigour of forbs in mesic grassland.