Research in my lab focuses on addressing these questions: How is determinacy in shoot meristems achieved? What regulates the timing of determinacy? How is determinacy of the meristem related to differentiation of the shoot? How is determinacy coordinated among cells of the meristem? To address these questions, we have been examining shoot meristems during both vegetative and reproductive growth in two model species, maize and tomato. Some of our projects are outlined below.

We have developed techniques for growing isolated meristems in culture to study vegetative determinacy in maize. Using this technology, we have been able to investigate the interplay between the shoot meristem and the rest of the plant that results in determinacy. We have learned that the leaves signal the shoot meristem of maize plants to trigger terminate vegetative growth by commencing the transition to reproductive growth. We have also found that meristems can be 'rejuvenated' by undergoing culture: an old meristem can form juvenile organs, indicating that developmental phase (juvenile vs. adult) is determined not by age, but by the physiological state of the plant. We are currently using meristem culture to investigate the regulation of phase-specific gene expression.

We have also employed this technology to gain a better understanding of the fates of cells in various locations in the meristem. We have evidence that the apical initials, which form the shoot meristem during embryogenesis, become quiescent after germination. They resume division only when the plant has become reproductive, contributing to the formation of the tassel and the flowers on it. The conclusion that the apical initials of maize, unlike many plants, serve as an ersatz germline, has evolutionary implications.