Catálogo de publicaciones - libros

A large number of reactions in hormone biosynthesis and catabolism pathways are located in theendoplasmic reticulum (ER). These reactions are catalysed by cytochrome P450s, a large family of enzymesinvolved in many metabolic pathways in plants. As well as being involved in hormone synthesis and inactivation,many of the P450s involved in hormone biology are likely to be under regulation both to maintain hormonehomeostasis and in response to environmental signals. This chapter describes the roles of the ER-locatedP450 enzymes in plant hormone biology.

Calcium is one of the most versatile messengers in biological systems, translating developmental andenvironmental cues into cellular responses. The endoplasmic reticulum (ER) constitutes one of themost important calcium holding organelles in higher eukaryotes. Upon stimulation, calcium is released fromthe ER into the cytosol where it may trigger downstream effectors. However, the release of calciummay also affect internal ER functions, such as protein folding and secretion. It is therefore importantnot only to view cytosolic calcium signals as isolated events, but also in context to the organellar calciumstatus. In animals, the calcium levels of the ER can be sensed by other calcium resources, such as theplasma membrane, which may allow calcium uptake or release depending on the overall demand in the cell.In this chapter we have tried to convey the diverse aspects of calcium and its potential impact on differentER processes, and organellar communications, in plants.

The endoplasmic reticulum (ER) is an essential component of plasmodesmata, the membrane-lined poresthat interconnect plant cells. The desmotubule which traverses the centre of a plasmodesma is formedfrom, and continuous with, the cortical ER. Whilst the exact role of the ER is only now being characterised,it is recognised that the ER is intimately involved in the transfer of molecules to and through plasmodesmata,providing a number of pathways for movement between cells as well as being implicated in the mechanismsthat control transport. It is believed that molecules may be transported by passive flow within the desmotubulelumen, by diffusion along the inner desmotubule membranes or by specific attachment to the cytoplasmic faceof the desmotubule followed by facilitated transport through the cytoplasmic sleeve. The ER is also involvedin the formation of plasmodesmata either during cell division or when formed de novo across non-divisionwalls. This chapter focusses on the role of the ER in plasmodesmatal formation and function.

All eukaryotic positive-sense single-strand RNA viruses, (+)ssRNA, replicate their genome in associationwith membranes of host cells. The presence of a replicating virus frequently induces proliferationand rearrangement of the host membranes into various cytopathic structures, including invaginations, vesicles,spherules or membranous webs. Such structures are considered to be virus-induced organelles specializedin replication functions. Virtually all membranes are able to be rearranged to support replication. Thus,membranes from peroxisomes, endosomes, lysosomes, vacuoles, mitochondria, and chloroplasts are used for(+)ssRNA virus replication, but the endoplasmic reticulum (ER) is by far the preferred organelle. The specifictype of membrane system utilized in assembling the viral replication complex is strictly dependent on individualviruses and is likely to be genetically determined. The various molecular interactions that govern ER targetingof plant viruses highlight how viruses can exploit the diversity of interactions that occurs between proteinsand membrane or lipid structures.