Roger I. Pennell

Soluble Signals from Cells Identified at the Cell Wall Establish a Developmental Pathway in Carrot.

Cells in a plant differentiate according to their positions and use cell-cell communication to assess these positions. Similarly, single cells in suspension cultures can develop into somatic embryos, and cell-cell communication is thought to control this process. The monoclonal antibody JIM8 labels an epitope on cells in specific positions in plants. JIM8 also labels certain cells in carrot embryogenic suspension cultures. We have used JIM8 and secondary antibodies coupled to paramagnetic beads to label and immunomagnetically sort single cells in a carrot embryogenic suspension culture into pure populations. Cells in the JIM8(+) population develop into somatic embryos, whereas cells in the JIM8(-) population do not form somatic embryos. However, certain cells in JIM8(+) cultures (state B cells) undergo asymmetric divisions, resulting in daughter cells (state C cells) that do not label with JIM8 and that sort to JIM8(-) cultures. State C cells are competent to form somatic embryos, and we show here that a conditioned growth medium from a culture of JIM8(+) cells allows state C cells in a JIM8(-) culture to go on and develop into somatic embryos. JIM8 labels cells in suspension cultures at the cell wall. Therefore, a cell with a role in cell-cell communication and early cell fate selection can be identified by an epitope in its cell wall.

The Development of the Male Gametophyte and Spermatogenesis in Taxus baccata L.

The development of the male gametophyte of Taxus baccata has been studied over a period of 20 weeks, from germination of the microspore in February to spermatogenesis in July. A few days after germination the microspore nucleus divides and a transverse wall forms at the equator cutting off the small generative cell and a large tube cell. The latter immediately begins to expand to form the pollen tube. The first division thus establishes the polarity of the gametophyte and the generative cell is regarded as proximal. The transverse wall is ephemeral, and within six weeks it has disappeared. The nucleus of the generative cell divides while still at the proximal pole. The two daughter nuclei are unequal in size, but they remain associated and together move distally. The larger nucleus eventually becomes the nucleus of the spermatogenous cell, and the smaller the sterile nucleus. The spermatogenous cell acquires a distinctive cytoplasm and becomes surrounded by a wall which arises de novo. The nucleus of the spermatogenous cell enlarges, but always remains towards one side of the cell so that at mitosis the spindle is contained within one hemisphere. After division the wall of the spermatogenous cell is ruptured and the two sperms are released as naked nuclei of equal size. The cytoplasm of the spermatogenous cell degenerates as it enters the tube, but remains recognizable until fertilization.

Chapter 9 Monoclonal Antibodies to Cell-Specific Cell Surface Carbohydrates in Plant Cell Biology and Development

Publisher Summary This chapter illustrates the variety of ways in which monoclonal antibody (MAb) technology can be used for the analysis of cell- and tissue-specific carbohydrate antigens present at the surfaces of plant cells. MAbs to cell-specific cell surface carbohydrate epitopes are versatile molecular probes with multiple applications for plant cell biology and development, for plant molecular biology, and for plant cell and tissue culture. MAbs have been essential probes for identifying and characterizing developmentally regulated cell surface epitopes in plants, and now can be used for the manipulation of the cells in which they are expressed. The chapter focuses on the use of MAbs for the purification and characterization of cell- and tissue-specific carbohydrate antigens and for the manipulation of defined cellular targets. Indirect immunolabeling techniques are used in this chapter. The MAb is first bound to the antigen then, after washing to remove surplus MAb, is tagged with an enzyme, radioisotope, fluorochrome, electron-opaque particle, or paramagnetic bead. The chapter illustrates the variety of ways in which MAb technology can be used for the analysis of cell- and tissue-specific carbohydrate antigens present at the surfaces of plant cells.