Identification of a New Glucosinolate-Rich Cell Type in Arabidopsis Flower Stalk

Abstract

Distribution of K, Ca, Cl, S, and P in freeze-dried sections of Arabidopsis flower stalk was analyzed by energy dispersive x-ray imaging. Concentrations of these elements in different cell types were quantified by microanalysis of single-cell samples and phloem exudates. Results showed a differential pattern of distribution for all five elements. K concentration was found to be highest in the parenchymatous tissue around vascular bundles. Ca and Cl were present mainly in the central part of the flower stalk. P was largely located in the bundles and in the parenchyma surrounding them. S signal was extraordinary high in groups of cells (S-cells) situated between the phloem of every vascular bundle and the endodermis. Enzymatic hydrolysis by thioglucosidase of cell sap collected from S-cells using a glass microcapillary resulted in the release of glucose, indicating that these cells contain glucosinolates at high (> 100 mm) concentration, which is consistent with the concentration of S (> 200 mm) estimated by x-ray analysis of cell sap samples. Since their position outside of the phloem is ideally suited for protecting the long-distance transport system from feeding insects, the possible roles of these cells as components of a plant defense system are discussed.

Survey of glucosinolate variation in leaves of Brassica rapa crops

“…The highest gsl concentrations were found in young leaves and reproductive organs such as seeds, siliques, flowers and developing inflorescences (Brown et al 2003). Exceptionally high concentration of gsl was reported in the sulfur-rich S-cells of the flower stalk (Koroleva et al 2000). This was the first report of gsl accumulation localized to a specific cell type found just outside the phloem.…”

BRANCHED-CHAIN AMINOTRANSFERASE4 Is Part of the Chain Elongation Pathway in the Biosynthesis of Methionine-Derived Glucosinolates inArabidopsis

“…arabidopsis.org/info/expression/ATGenExpress.jsp), show identical light-dependent mRNA accumulation (Figure 4), and are both induced by wounding (Figure 3). Fifth, BCAT4 is expressed in the phloem in direct vicinity to the S-cells, which have been suggested to be the major storage sites of glucosinolates in flowering stalks (Figure 2; Koroleva et al, 2000). A strong phloemspecific expression of BCAT4 has recently also been observed in a microarray analysis of root hypocotyls in Arabidopsis.…”

“…This includes the so-called S-cells, which have been identified between the phloem and the endodermis of flowering stalks. These cells have been suggested to be the predominant storage sites for glucosinolates (Koroleva et al, 2000). Thus, biosynthesis of Metderived glucosinolates starts in a tissue adjacent to the major storage cells.…”

Flutuação populacional e distribuição vertical de Brevicoryne brassicae (L.) (Hemiptera: Aphididae) em couve

“…Esse incremento pode estar relacionado tanto com a distribuição quanto com a concentração do cál-cio, que interferem no aumento da hidrólise enzimática pelas enzimas tioglicosidases que catalizam uma das rotas metabólicas de glucosinolatos, provocando em conseqüência aumento significativo nos teores desses compostos (>100 mM) translocados no floema (KOROLEVA et al, 2000). Por outro lado, deve-se considerar também o efeito do magnésio, que provoca aumento significativo da atividade catalizadora das enzimas mirosinases, resultando no incremento de glucosinolatos (LUDIKHUYZE et al, 2000).…”