Morphology and Histochemistry of the Glandular Trichomes of Isodon rubescens(Hemsley) H.Hara(Lamiaceae)

The morphology and distribution of leaf trichomes of Isodon rubescens were studied using light microscopy.(1)Three morphologically distinct types of trichomes were observed on I.rubescens leaf surfaces:non-glandular,peltate and capitate glandular.The glandular and non-glandular trichomes were present on both the adaxial and abaxial surfaces.Peltate and capitate glandular trichomes comprised one basal cell,one or two stalk cells and one head.The head of mature peltate glandular trichomes generally consisted of four secretory cells while that of capitate glandular hairs was composed of two cells.(2)Histochemical results indicate existence of flavnoids in both peltate and capitate glandular trichomes.In addition,terpenoids,including monoterpenes,sesquiterpenes etc.,exist in peltate glandular trichomes.Peltate glandular trichomes are probably only site of oridonin accumulation,however,this need direct proof to clarify.High density of peltate trichomes might be considered as an important selection character for the screening of I.rubescens with rich content of oridonin.