[Macroscopic and microscopic identification of Chinese herb belonging to genus Senecio].

The medicinal herbs derived from genus Senecio have been commonly used in Chinese medicine and triggered attention in recent decades for that they contain the hepatotoxic pyrrolizidine alkaloids. Therefore the botanical pharmacognostic study to authenticate those herbs based on their macroscopic and microscopic characteristics is important for the assurance of safety when they are applied as raw material for extracts or for finished products. In this paper, 13 taxa (11 species and 2 varieties) of Senecio plants were collected and their macroscopic and microscopic characteristics were observed and described by digital microscopic illustration. The results showed that the distribution of collenchyma in the cortex, the level of development for pericycle, the location of the phloem, and the ratio of pith in transverse sections of the stems, and the morphology of the leaf epidermal cells, the stomatal types and the non-glandular hairs in leaf surface view were found to be the main microscopic characteristics for authentication of different Senecio species. The herbs derived from genus Senecio can be distinguished from each other on the basis of their macroscopic and microscopic characteristics, and those observation can be used for the identification of commercial crude drugs from Senecio plants.

The role of stigma peroxidases in flowering plants: insights from further characterization of a stigma-specific peroxidase (SSP) from Senecio squalidus (Asteraceae).

Angiosperm stigmas have long been known to exhibit high levels of peroxidase activity when they are mature and most receptive to pollen but the biological function of stigma peroxidases is not known. A novel stigma-specific class III peroxidase gene, SSP (stigma-specific peroxidase) expressed exclusively in the stigmas of Senecio squalidus L. (Asteraceae) has recently been identified. Expression of SSP is confined to the specialized secretory cells (papillae) that compose the stigma epidermis. The literature on stigma peroxidases and hypotheses on their function(s) is reviewed here before further characterization of SSP and an attempt to determine its function are described. It is shown that SSP is localized to cytoplasmic regions of stigmatic papillae and also to the surface of these cells, possibly as a component of the pellicle, a thin layer of condensed protein typical of "dry" stigmas. Enzyme assays on recombinant SSP showed it to be a peroxidase with a preference for diphenolic substrates (ABTS and TMB) and a pH optimum of approximately 4.5. In such assays the peroxidase activity of SSP was low when compared with horseradish peroxidase. To explore the function of SSP and other stigmatic peroxidases, levels of reactive oxygen species (ROS) in stigmas of S. squalidus were investigated. Relatively large amounts of ROS, principally H(2)O(2), were detected in S. squalidus stigmas where most ROS/H(2)O(2) was localized to the stigmatic papillae, the location of SSP. These observations are discussed in the context of possible functions for SSP, other peroxidases, and ROS in the stigmas of angiosperms.

Cell-specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloid pathway in Senecio vernalis, in comparison with its ancestor, deoxyhypusine synthase.

Pyrrolizidine alkaloids (PAs) are constitutive plant defense compounds with a sporadic taxonomic occurrence. The first committed step in PA biosynthesis is catalyzed by homospermidine synthase (HSS). Recent evidence confirmed that HSS evolved by gene duplication from deoxyhypusine synthase (DHS), an enzyme involved in the posttranslational activation of the eukaryotic translation initiation factor 5A. To better understand the evolutionary relationship between these two enzymes, which are involved in completely different biological processes, we studied their tissue-specific expression. RNA-blot analysis, reverse transcriptase-PCR, and immunolocalization techniques demonstrated that DHS is constitutively expressed in shoots and roots of Senecio vernalis (Asteraceae), whereas HSS expression is root specific and restricted to distinct groups of endodermis and neighboring cortex cells located opposite to the phloem. All efforts to detect DHS by immunolocalization failed, but studies with promoter-beta-glucuronidase fusions confirmed a general expression pattern, at least in young seedlings of tobacco (Nicotiana tabacum). The expression pattern for HSS differs completely from its ancestor DHS due to the adaptation of HSS to the specific requirements of PA biosynthesis.