Effects of cyanogenesis in bracken fern (Pteridium aquilinum) on associated insects

Abstract. 1. The relationship between cyanogenesis in bracken fern and the insect fauna feeding on the plant was investigated over a 3 year period. The most common insects between May and July, while cyanide levels were high, were the sawflies Strongylogaster impressata Provancher, S.multicincta Norton, Aneug-menus fzavipes (Norton), the aphid Macrosiphum euphorbiae (Thomas) and a microlepidopteran species of Monochroa .
2. Collections of insects from cyanogenic and acyanogenic fronds showed significantly fewer sawflies on the cyanogenic fronds. The aphid and the microlepidopteran were randomly distributed with respect to cyanogenicity.
3. Feeding tests for two of the sawfly species ( Simpressata and Smulticincta ) showed that larvae grew more slowly and had a higher mortality when raised on cyanogenic fronds than on acyanogenic ones.
4. Field collected cyanogenic bracken fronds were found to have sustained less damage from chewing herbivores compared with acyanogenic fronds.     

Tissue and cellular localization of individual β‐glycosidases using a substrate‐specific sugar reducing assay

Traditional methods to localize β‐glycosidase activity in tissue sections have been based on incubation with the general substrate 6‐bromo‐2‐naphthyl‐β‐d ‐glucopyranoside. When hydrolysed in the presence of salt zinc compounds, 6‐bromo‐2‐naphthyl‐β‐d ‐glucopyranoside affords the formation of an insoluble coloured product. This technique does not distinguish between different β‐glycosidases present in the tissue. To be able to monitor the occurrence of individual β‐glycosidases in different tissues and cell types, we have developed a versatile histochemical method that can be used for localization of any β‐glycosidase that upon incubation with its specific substrate releases a reducing sugar. Experimentally, the method is based on hydrolysis of the specific substrate followed by oxidation of the sugar released by a tetrazolium salt (2,3,5‐triphenyltetrazolium chloride) that forms a red insoluble product when reduced. The applicability of the method was demonstrated by tissue and cellular localization of two β‐glucosidases, amygdalin hydrolase and prunasin hydrolase, in different tissues and cell types of almond. In those cases where the analysed tissue had a high content of reducing sugars, this resulted in strong staining of the background. This interfering staining of the background was avoided by prior incubation with sodium borohydride. The specificity of the devised method was demonstrated in a parallel localization study using a specific antibody towards prunasin hydrolase.     

Cyanogenic glycosides from the rare Australian endemic rainforest tree Clerodendrum grayi (Lamiaceae)

The cyanogenic diglycoside lucumin ((R)-mandelonitrile-β-d-primeveroside) and monoglucoside prunasin ((R)-mandelonitrile-β-d-glucoside) were isolated from the foliage of the rare Australian rainforest tree species Clerodendrum grayi (Lamiaceae). This is the first reported isolation of the diglycoside lucumin from vegetative tissue (foliage), and the first reported co-occurrence of lucumin and prunasin. Furthermore, unusually, the diglycoside lucumin was the most abundant cyanogen accounting for approximately 60% of total cyanide in a leaf tissue.     

Biosynthesis of flavan-3-ols and other secondary plant products from (2S)phenylalanine

(2S)-Phenyl[2-¹⁴C,3R-³H₁]alanine and (2S)-phenyl[2-¹⁴C,3S-³H₁]alanine have been employed as substrates to study procyanidin and flavan-3-ol biosynthesis. Parallel studies with the cyanogenic glucosides prunasin and sambunigrin, Winterstein's acid [(3R)-3-dimethylaminophenylpropionic acid] and tropic acid show these to be derived by stereospecific processes from (2S)-phenylalanine. New proposals for procyanidin biosynthesis are briefly commented upon.     

Glucose-1-benzoate and prunasin from Prunus serotina

β-d-Glucopyranose 1-benzoate and prunasin have been isolated from the leaves of Prunus serotina. Both can yield benzoic acid, a potential allelopathic inhibitor of Acer rubrum.     

Cyanogenic glycosides in leaves of Perilla frutescens var. acuta

Besides 7-(2-O-β-D-glucuronyl-β-D-glucuronyloxy)-5,3′,4′-trihydroxyflavone, scutellarin, rosmarinic acid and caffeic acid, two cyanogenic glycosides have been isolated from the dried leaves of Perilla frutescens var. acuta. One of them is prunasin and the other is (R)-2-(2-O-β-D-glucopyranosyl-β-D-glucopyranosyloxy)-phenylacetonitrile, a new isomer of amygdalin.     

Detection and identification of cyanogenic glucosides in six species of Acacia

The presence of prunasin in Acacia deanei ssp. paucijuga, sambunigrin in Acacia cunninghamii, and acacipetalin in Acacia giraffae has been established by both chromatographic and NMR spectral evidence. Mandelonitrile glucosides of unknown configuration in Acacia parramattensis and Acacia pulchella and (an) as yet unidentified glycoside(s) in Acacia farnesiana are also reported.     

Prunasin and amygdalin from Sorbus Commixta

A new peptide, L-γ-glutamyl-2-amino-3-hexanone has been isolated from a mushroom Russula ochroleuca. The suggested structure is supported by ¹H and ¹³C NMR spectroscopy. It is the first natural α-aminoketone associated with glutamic acid.