Increased seed cytokinin levels in transgenic tobacco influence embryo and seedling development

Seed-specific expression of a heterologous vicilin-isopentenyl transferase (ipt) gene has been determined in transgenic tobacco lines 7 and 16. Genetic analysis of self-fertilized progeny showed that a single copy of the vicilin-ipt gene had been integrated, and T2 progeny had become homozygous for the transgene. Stable inheritance of the vicilin-ipt gene in T3 progeny was verified by polymerase chain reaction analysis. Seed cytokinin levels were 2-3-fold higher than control levels. Cytological analyses revealed a significant increase in the number of plerome cell layers and enlargement of diameter in transgenic embryos compared with controls. Dry weight of mature seeds and subsequent seedling growth was increased significantly. This correlated with the level of vicilin-ipt overexpression and increased cytokinin levels in transgenic tobacco seeds. The results suggest a crucial role for cytokinins in regulation of tobacco embryo development.