Phloem transport of flowering signals

Auxin and other signals on the move in plants

As multicellular organisms, plants, like animals, use endogenous signaling molecules to coordinate their own physiology and development. To compensate for the absence of a cardiovascular system, plants have evolved specialized transport pathways to distribute signals and nutrients. The main transport streams include the xylem flow of the nutrients from the root to the shoot and the phloem flow of materials from the photosynthetic active tissues. These long-distance transport processes are complemented by several intercellular transport mechanisms (apoplastic, symplastic and transcellular transport). A prominent example of transcellular flow is transport of the phytohormone auxin within tissues. The process is mediated by influx and efflux carriers, whose polar localization in the plasma membrane determines the directionality of the flow. This polar auxin transport generates auxin maxima and gradients within tissues that are instrumental in the diverse regulation of various plant developmental processes, including embryogenesis, organogenesis, vascular tissue formation and tropisms.

From Arabidopsis to rice: pathways in pollen development

The control of male fertility is of vital importance for crop breeding, hybrid generation, and the control of pollen release. Recent development in the analysis of Arabidopsis male sterile mutants has meant that there is a greater understanding of the gene regulatory networks controlling maternal development of the anther and the resultant sporophytes. With the advent of the genome sequence and tools to allow the analysis of gene function, this knowledge base is now extending into the monocot crop rice. This has shown high levels of similarity between the networks of pollen development in Arabidopsis and rice, which will serve as valuable tools to understand and manipulate this developmental pathway further in plants.