Investigating the role of sucrose in controlling lateral root formation in Arabidopsis thaliana

Abstract

Sucrose is the major transported carbon in plants and its dual role as both a nutrient and a signal, enables it to promote diverse physiological processes in plants, both directly and indirectly. In Arabidopsis thaliana (Arabidopsis), sucrose has been reported to promote lateral root formation, however mechanistic understanding of how sucrose promotes lateral root formation in Arabidopsis is lacking. Efforts aimed at studying the effect of sucrose on lateral root formation in Arabidopsis have been mostly focused on quantifying lateral root numbers, lengths, and densities. These parameters only give insights into the effect of sucrose on the emergence and outgrowth of lateral roots; not the primordia initiation and morphogenesis stages that underpin root system architecture and development in Arabidopsis. Those studies that have quantified lateral root primordia have not categorised them into the various developmental stages, therefore potential checkpoints of regulation by sucrose in the initiation and development of lateral root primordia cannot be determined. This thesis, therefore, aimed at understanding how sucrose might promote lateral root primordia initiation and morphogenesis, focusing on the effect of sucrose on the distribution of lateral root primordia among the various developmental stages. It did this by generating experimental methodologies that allowed the temporal dynamics of lateral root primordia development to be studied to identify potential checkpoints of regulation of lateral root primordia initiation and development by sucrose. Using a combination of tools from physiological and cell biology, this thesis shows that, sucrose promotes lateral root primordia formation by accelerating the rate of the developmental progression of lateral root primordia from the early stages to later stages. Sucrose does this by potentially promoting nuclear migration of lateral root founder cells towards their common cell wall to signal the initiation of lateral root primordia and the initiation of lateral root primordia itself. This thesis also shows a new experimental system that allows the direct supply of exogenous sucrose to the shoot without the contact of the root with sucrose.

This new system can be a valuable tool for studying the relationship between shoot-derived resources and root growth and development under in vitro conditions.