Myrosin cells

Figure 4.1 The mustard oil bomb in flower stalks of Arabidopsis thaliana consists of S-cells (with glucosinolates) and adjacent myrosin cells (with myrosinase). This is illustrated by transverse (A,C) and longitudinal (B) sections of a pedicel, analyzed by light microscopy (A,B) and transmission electron microscopy (C). The myrosin cells (m) are in contact with the S-cells (S-c), situated inside the starch sheath ( ) (A,B,C). The myrosin cells are located peripherally in the phloem tissue other cells of the phloem include sieve elements (s) and companion cells (cc, in (C) only).

Staining of consecutive sections with histochemical reagents for protein and antibodies against myrosinase showed that myrosin cells actually contain myrosinase (Fig. 4.2D,E).18,43,44 By electron microscopy immunogold labelling studies, the enzyme was localized to the interior of the vacuoles of the myrosin cells (Fig. 4.2F).18,40,41 It has also been shown by several in situ hybridization experiments that myrosinase transcripts are located in these cells (Fig. 4.2G),6 demonstrating that the cellular localization of myrosinase is due to transcriptional regulation and not to a transport process. No evidence for transport of myrosinase currently exists. These methods for detection and identification of myrosin cells and myrosinase expression are illustrated (Fig. 4.2). For a historical overview of myrosinase localization studies, see Bones and Rossiter.45... 

Transmission electron microscopy analyses of ultrathin sections have indicated that there are several vacuoles in myrosin cells of embryos. These vacuoles contain myrosinase, as revealed by immunogold labelling studies, and have been referred to as myrosin grains.40, 1 Recently, confocal laser scanning immuno-microscopy analysis with the anti-myrosinase monoclonal antibody 3D7 has been... 

We use the term myrosin cell structurally (see above), and not functionally (i.e., if a cell contains myrosinase it should be called a myrosin cell). This structural definition should be used because myrosin cell is a well-established anatomical term for this special idioblast. We do not find it useful to coin a specific term for a cell just because a certain protein is expressed in it, especially now in the post-genomic era, where possibly thousands of different proteins can be found in every cell. Husebye et al. named guard cells in Arabidopsis myrosin guard cells because myrosinase was found in these cells.47 This is problematic since these cells do not... 

Fig. 4.3 Immunohistochemical analysis in Brassica napus (A,C,E) and Arabidopsis thaliana (B,D) of myrosinase by use of the antibody 3D7. Myrosinase is present in the ground tissue of cotyledons (left) and radicle (upper right) of B. napus embryo (A), while in A. thaliana seed no expression is detected (B) some cells in the seed coat retain unoxidized substrate. Arrows in (A) show examples of myrosinase-containing myrosin cells. In A. thaliana leaves, myrosinase is located in phloem myrosin cells (D), whereas in B. napus leaves myrosinase is in myrosin cells in the phloem (C), as well as in the ground tissue (E). For experimental details, see1. The size bars equal 100 pm.

Brassica napus L. embryos indicates a separate transport pathway into myrosin cells., Planta, 2001,213,207-213. 

BORGEN, B.H., Functional Analysis of Plant Idioblasts (Myrosin Cells) and their Role in Defence, Development and Growth., PhD thesis, Norwegian University of Science and Technology, Trondheim, Norway, 2002. 

J0RGENSEN, L.B., Myrosin cells and dilated cistemae of the endoplasmic reticulum in the order Capparales., Nord. J. Bot., 1981,1,433-445. 

WERKER, E., VAUGHAN, J.G., Ontogeny and distribution of myrosin cells in the shoot of Sinapis alba L. a light- and electron-microscope study., Israel J. Bot,. 1976, 25,140-151. 

GESHI, N., ANDREASSON, E., MEUER, J., RASK, L., BRANDT, A., Myrosinase and myrosinase-binding proteins are co-localized in grains of myrosin cells in cotyledon of Brassica napus L. seedlings., Plant Physiol. Biochem., 1998,36, 583-590. 

Glucosinolates such as sinigrin are molecules that consist of a /3-thioglucose moiety, a sulfonated oxime, and a variable side chain derived from various amino acids (Figure 5).43 44 Glucosinolates themselves are not toxic to herbivores and are widely distributed in plant tissues. On the contrary, the enzyme called myrosinase or thioglucosidase is distributed in myrosin cells that do not contain glucosinolates. In the flower stalk of... 

In Brassica, the myrosin cells are scattered throughout most tissues of glucosinolafe-confaining plants (Andreasson et al, 2001 Thangstad et al, 2004). In contrast, in Arabidopsis, these myrosinase -containing idioblasts were found in fhe phloem parenchyma additionally, myrosinase is located in the guard cells (Andreasson et al, 2001 Husebye et al, 2002 Thangstad et al, 2004). 

Borgen, B.H., Thangstad, O.P., Ahuja, I., Rossiter, J.T., and Bones, A.M. 2010. Removing the mustard oil bomb from seeds transgenic ablation of myrosin cells in oilseed rape (Brassica napus) produces MINELESS seeds. Journal of Experimental Botany, 61(6), 1683-97. doi 10.1093/j xb/erq039... 

GLSs are chanically and thermally stable to a certain extent and therefore generally enzymatic hydrolysis occurs (Polat 2010). Myrosinase is a specific class of P-thioglucosidases located in idioblasts (myrosin cells) distributed in most tissues... 

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