Gametophytic selfincompatability in the Papaveraceae

A second gametophytic SI system has been found in Papaver rhoeas L. (field poppy) and is mechanistically distinct from that found in the families described above. In this species, in contrast to the Solanaceae, inhibition of incompatible pollen occurs on the stigmatic papillae and initial arrest of pollen growth is rapid, occurring within minutes. As in the S-RNase-based system, SI is controlled by a single, multiallelic S-locus (Lawrence et al., 1978). A number of alleles of the stigmatic...

Signalling between organ primordia and the meristem

As organs emerge from the shoot apical meristem, they typically flatten laterally before developing unique cell types along the adaxial (facing the meristem) - abaxial (away from the meristem) axis. A connection between the ad-abaxial patterning of a lateral organ and the shoot apical meristem was first established by surgical experimentation (Sussex, 1955 Snow & Snow, 1959 Hanawa, 1961). When an incision or impermeable barrier was placed between a young organ primordium and the meristem,...

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Deplasmolysis and some pharmcological treatments have been found to increase the SEL. Schulz (1999) hypothesised that the prime mechanism for control of non-selective trafficking is the rapid and transient conformational change in plasmodes-mal proteins brought about by changes in calcium and or ATP levels. Comparatively small and local changes (elevation) in Ca2+ concentration will cause a decrease in plasmodesmal SEL. However, longer term blockage caused by wounding may depend on a massive...

Proteolytic processing of prohormones

Insulin was the first hormone found to be derived from a precursor (Steiner & Oyer, 1966). Later discoveries revealed that multiple peptide hormones can be produced from a common precursor (Mains et al., 1977). Only 15 years ago the first prohormone processing enzyme (Kex2) was identified in yeast (Fuller et al., 1989). It is now known that peptide signals are generally synthesized as larger inactive precursors that undergo limited proteolysis to yield active peptide signals. Such...

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Photos Primary Membrane Plants

Figure 5.2 Schematic representation of a simple plasmodesmata in longitudinal (A) and transverse (B) sections. CW, cell wall D, desmotubule CR, central rod CS, cytoplasmic sleeve PM, plasma membrane SP, spoke-like extensions PMP, plasma-membrane-embedded proteins DP, desmotubule-embedded proteins. Figure adapted from Roberts and Oparka (2003) and based on the model in Ding et al. (2003). sleeve (Overall & Blackmann, 1996). In some cases this constriction is thought to be an artefact owing to...

Celltocell movement of RNA silencing

Cell-to cell movement upon phloem unloading. Upon phloem unloading, silencing usually spreads across the whole leaf lamina, indicating cell-to-cell movement of the silencing signal. The pathway for this cell-to-cell movement was elucidated by observations made in the N. benthamiana inducible GFP silencing system. Hence, there was no GFP silencing in the stomata guard cells of leaves that were already expanding at the time of silencing initiation (Voinnet et al., 1998). Stomata guard cells...

Regulation of SRK

Receptor kinase activity is generally tightly regulated to avoid their spontaneous activation. In the case of SRK, this is an important consideration as non-specific activation could easily lead to sterility (Kemp & Doughty, 2003). Multiple mechanisms have been identified and characterised in animal systems that act often in a concerted manner to down-regulate kinase activity (Cock et al., 2002). In vitro, both the truncated kinase domain and the full-length SRK protein autophosphorylate in...