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In the seeds of Hevea brasiliensis, the cyanogenic monoglucoside linamarin (2-b3-D-glucopyranosyloxy-2-methylpropionitrile) is accumulated in the endosperm. After onset of germination, the cyanogenic diglucoside linustatin (2-[6-f8-D-glucosyl-,f-D-glucopyranosyloxyJ-2-methylpropio- In addition, a linustatin-splitting diglucosidase in Hevea is described. From its activity in different developmental stages and in different tissues it is suggested that this enzyme is involved in the metabolism of cyanogenic glycosides. It is deduced that linustatin is a metabolite in the pathway by which linamarin is metabolized and utilized. MATERIALS AND METHODSSeed Drainage. The seed drainage technique is described elsewhere (17). Additionally, some of these seed drainage experiments were run in a gastight system in which a stream of moistened air was used to exchange the atmosphere in the experimental system continuously. By bubbling this air through 5 ml of 1 M NaOH any HCN liberated from the seedling during the experiment was trapped for quantitative determinations.HCN Determination. The HCN was estimated with the Merck

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Abstract-Quantitative experimental results on the antiherbivorous effect of cyanogenesis are rare. In our analyses, we distinguished between the total amount of cyanide-containing compounds stored in a given tissue [cyanogenic potential (HCNp)] and the capacity for release of HCN per unit time (HCNc) from these cyanogenic precursors as a reaction to herbivory. We analyzed the impact of these cyanogenic features on herbivorous insects using different accessions of lima beans (Phaseolus lunatus L.) with different cyanogenic characteristics in their leaves and fourth instars of the generalist herbivore Schistocerca gregaria Forskål (Orthoptera, Acrididae). Young leaves exhibit a higher HCNp and HCNc than mature leaves. This ontogenetic variability of cyanogenesis was valid for all accessions studied. In no-choice bioassays, feeding of S. gregaria was reduced on high cyanogenic lima beans compared with low cyanogenic beans. A HCNp of about 15 mmol cyanide/g leaf (fresh weight) with a corresponding HCNc of about 1 mmol HCN released from leaf material within the first 10 min after complete tissue disintegration appears to be a threshold at which the first repellent effects on S. gregaria were observed. The repellent effect of cyanogenesis increased above these thresholds of HCNp and HCNc. No repellent action of cyanogenesis was observed on plants with lower HCNp and HCNc. These low cyanogenic accessions of P. lunatus were consumed extensivelyVwith dramatic consequences for the herbivore. After consumption, locusts showed severe symptoms of intoxication. Choice assays confirmed the feeding preference of locusts for low over high cyanogenic leaf material of P. lunatus. The bioassays revealed total 0098-0331/05/0700-1445/0 # 2005 Springer Science + Business Media, Inc. 1445Journal of Chemical Ecology, Vol. 31, No. 7, July 2005 DOI: 10.1007/s10886-005-5791-2 * To whom correspondence should be addressed. E-mail: dballhorn@iangbot.uni-hamburg.de losses of HCN between 90 and 99% related to the estimated amount of ingested cyanide-containing compounds by the locusts. This general finding was independent of the cyanogenic status (high or low) of the leaf material.