Current Research Program:

Our research programmes examine many aspects of plant and embryo development and utilize a combination of cytological, biochemical and molecular approaches. One major area of our research focuses upon an examination of mechanisms that underlie seed dormancy. In a dormant seed, there is a block to germination such that the seed does not germinate, even when the appropriate hydrated conditions are provided. The requirements for germination of yellow-cedar seeds (a prolonged period of warm/cold stratification) suggest that a complex coat-imposed dormancy mechanism is involved. Factors contributing to coat-imposed dormancy of yellow-cedar seeds are being studied including mechanical restraint of the seed tissues enclosing the embryo as well as the role of plant hormones such as abscisic acid (ABA) and gibberellin (GA). We have demonstrated that termination of dormancy is accompanied by a decline in embryo sensitivity to ABA as well as an enhanced capacity of the embryo to metabolize this hormone. We are also working toward isolating genes underlying dormancy inception, maintenance and termination in yellow-cedar. This research will serve as an important model for other conifer species exhibiting deep and prolonged dormancy. The seeds of many plant species do not exhibit dormancy and germination commences with the uptake of water by the quiescent dry seed and terminates with the elongation of the embryonic axis. Another research area focuses on the nondormant seed and examines the role of desiccation (maturation drying) as a regulatory cue that triggers the transition from seed development to germination. A central focus here is on the role of desiccation in terminating the expression of genes that are expressed at high levels during seed development (eg., genes encoding storage proteins) while inducing the on-regulation of mRNA synthesis associated with germination and growth. We have recently extended our research programmes to events associated with the post-germinative programme including reserve mobilization and programmed cell death (PCD). PCD can be described as a triggered event in which the cell kills itself from within, in a manner that does not adversely affect the health of neighbouring cells of the organism that have not received signals to die. We are focusing on PCD within the megagametophyte of white spruce (Picea glauca) seeds. Following the completion of reserve mobilization in the megagametophyte during post-germinative seedling growth, the megagametophyte cells are superfluous and die. The process likely involves autophagy and macromolecules remaining in dead and dying megagametophyte cells are degraded, further enhancing the supply of nutrients to the growing axis. We are undertaking studies to examine some of the cellular and biochemical processes that initiate and execute the PCD pathway in megagametophyte cells, and in particular the role of proteases and nucleases. The role of ABA and GA in the death process (as signalling molecules or as part of the signal transduction chain) will be examined.