Therefore, over production of cytokinins can delay senescence. The ipt gene from agrobacterium tumefacions encoding an isopentenyl transferase (Akiyoshi et al.1984) was fused with sensecence-specific promoter, SAG 12 (Gan and Amasino 1996) and introduced into tobacco plants. The leaf and floral senescence in the transgenic plant was markedly delayed, biomass and seed yield was increased but other aspects of plant growth and development were normal. This approach appears to have great potential in improving the crop yields through slowing the senescence and rubisco degradation and thus improving canopy photosynthesis.