No abstract

SummaryWe have isolated and characterized a cDNA encoding a novel diterpene cyclase, OsDTC1, from suspensioncultured rice cells treated with a chitin elicitor. OsDTC1 functions as ent-cassa-12,15-diene synthase, which is considered to play a key role in the biosynthesis of (À)-phytocassanes recently isolated as rice diterpenoid phytoalexins. The expression of OsDTC1 mRNA was also con®rmed in ultraviolet (UV)-irradiated rice leaves. In addition, we identi®ed ent-cassa-12,15-diene, a putative diterpene hydrocarbon precursor of (À)-phytocassanes, as an endogenous compound in the chitin-elicited suspension-cultured rice cells and the UV-irradiated rice leaves. The OsDTC1 cDNA isolated here will be a useful tool to investigate the regulatory mechanisms of the biosyntheis of (À)-phytocassanes in rice.

The binding study on nicotinoids, neonicotinoids and the related compounds using [3H]a-bungarotoxin and [3H]nicotine as probes revealed that binding to the recognition site of nicotinic acetylcholine receptor (nAChR) in insects requires the molecules to have 3-pyridylmethylamino moiety, while high ionization in vertebrates. When [3H]phencyclidine was used as a probe for the ion channel opening of Torpedo nAChR, it was indicated that high ionization of the molecule is important to be agonistic, although the presence of 3-pyridylmethylamino moiety is preferred. 15N NMR of the amino nitrogen atom of nicotinoids and the corresponding one of neonicotinoids indicated that the latter was far deshielded as compared with the former. The result implies that the unshared electron pair on the concerned nitrogen atom is delocalized by the presence of strong electron-withdrawing group and the nitrogen atom becomes partially positive. Such nitrogen is enough to interact with the insect nAChR, but not with the vertebrate one. The overall results explain why nicotine is highly toxic to mammals and rather limited in insecticidal activity, whereas imidacloprid is highly insecticidal and low in mammalian toxicity.

No abstract

An important biological event in phytopathogens of the genus Phytophthora is sexual reproduction, which is conducted by two mating types, A1 and A2. A factor known as hormone alpha1 is secreted by the A1 mating type and induces the formation of sexual spores (oospores) in the A2 mating type. Here we describe the asymmetric synthesis and assignment of the absolute configuration of hormone alpha1 by oospore-inducing assays of the synthesized isomers.