Kelsey R. Downum

The spectral distribution of biologically active solar radiation at Miami, Florida, USA

The spectral distribution of solar radiation was studied under different sky conditions during a 15-month period in Miami, Florida (USA), and over a latitudinal gradient at solar maximum. Spectroradiometric scans were characterized for total irradiance (300–3000 nm) and the relative energetic and photon contributions of the following wavelength regions: UV-B (300–320 nm); UV-A (320–400 nm); B (400–500 nm); PAR (400–700 nm); R (600–700 nm); and FR (728–732 nm). Notable results include: (i) significantly higher UV-A energy fluxes than currently in use for laboratory experiments involving the biological effects of this band-width (values ranged from 33.6 to 55.4 W/m2 in Miami over the year); (ii) marked diurnal shifts in B:R and R:FR, with elevated R:FR values in early morning: (iii) a strong correlation between R:FR and atmospheric water content; and (iv) unusually high PAR values under direct sunlight with cloudy skies (2484 μmol/2 per s).

Inhibition of Bacterial Quorum Sensing and Biofilm Formation by Extracts of Neotropical Rainforest Plants

Bacterial biofilms are responsible for many persistent infections by many clinically relevant pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. Biofilms are much more resistant to conventional antibiotics than their planktonic counterparts. Quorum sensing, an intercellular communication system, controls pathogenesis and biofilm formation in most bacterial species. Quorum sensing provides an important pharmacological target since its inhibition does not provide a selective pressure for resistance. In this study, we investigated the quorum sensing and biofilm inhibitory activities of 126 plant extracts from 71 species collected from neotropical rainforests in Costa Rica. Quorum sensing and biofilm interference were assessed using a modified disc diffusion bioassay with Chromobacterium violaceum ATCC 12,472 and a spectrophotometric bioassay with Pseudomonas aeruginosa PA14, respectively. Species with significant anti-quorum sensing and/or anti-biofilm activities belonged to the Meliaceae, Melastomataceae, Lepidobotryaceae, Sapindaceae, and Simaroubaceae families. IC50 values ranged from 45 to 266 µg/mL. Extracts of these active species could lead to future development of botanical treatments for biofilm-associated infections.

Structure revision of a furanocoumarin from Dorstenia contrajerva

Abstract Two furanocoumarins have been isolated from Dorstenia contrajerva L.: bergapten and 4-[[3-(4,5-dihydro-5,5-dimethyl-4-oxo-2-furanyl)-butyl]oxy]-7H-furo[3,2-g][1]benzopyran-7-one. The structures were established by UV, NMR and mass spectrometry. The structure of the second compound, an unusual furanocoumarin, was confirmed by X-ray analysis. This substance has already been isolated from D. contrajerva, but the structure was incorrectly elucidated.

Phenylheptatriyne variation in Bidens alba var, radiata leaves

Variation of phenylheptatriyne (PHT) in leaves of Bidens alba (Linn.) var. radiata (Shultz-Bip.) was investigated across its Florida range, throughout the year, and in response to the photoenvironment. A survey of PHT in B. alba leaves was done at 13 sites in Florida and three sites throughout the year. PHT concentrations differed among populations (P < 0.001), but little of the variation was explained by latitude (R2 = 0.024) or longitude (R2 = 0.022). Leaf concentrations of PHT fluctuated throughout the year (P < 0.001); they were highest in October and lowest in January and April. Experimental manipulations of light quality and quantity caused increased PHT accumulation when UV wavelengths were filtered out and decreased accumulation under low R/FR treatments. Low light levels did not significantly influence the concentration of PHT on a dry weight basis, but did decrease leaf biomass and PHT levels on a leaf area basis. The results suggest that PHT in B. alba leaves varies in nature and that light quality affects PHT biosynthesis in situ.

A furanocoumarin from dorstenia contrajerva

Abstract A new furanocoumarin, 5-[3,4-epoxy-2,7-dimethyl-6,7-octenoyl]psoralen was isolated and identified from Dorstenia contrajerva .

Plant secondary compounds in the canopy and understorey of a tropical rain forest in Gabon

Given their difficulty of access, the canopies of tropical rain forests are considered a last frontier of biological/ecological research (Lowman & Nadkarni 1995). Climbing techniques are arduous and do not reach the tips of branches; towers, cranes and walkways limit the spatial exploration of the forest.

Insecticidal and growth-reducing activity of foliar extracts from Meliaceae

SummaryThirty-one species in twenty genera of the plant family Meliaceae were assayed for the production of growth-inhibiting phytochemicals, using the generalist herbivorePeridroma saucia. Most species were inhibitory when methanolic extracts were incorporated into artificial diets at concentrations at or below those occurring naturally. In general members of the subfamily Melioideae were more inhibitory than members of the Swietenioideae. Extracts of deciduous species with short leaf lifetimes were significantly more inhibitory than those of evergreen species with longer leaf lifetimes. In a smaller sample of species, evergreen species showed a trend towards having tougher leaves than deciduous species. These results support the resource availability hypothesis of Coleyet al. (1985), and suggest that life history attributes may be of some value in selecting plants for phytochemical prospecting.