Towards an integrated view of monocarpic plant senescence

After the flowering of an annual plant, the whole plant will senesce and die. For the process to go to completion, this monocarpic senescence must include three coordinated processes, which have not previously been considered as a total syndrome: (1) the arrest of growth and senescence of the shoot apical meristem; (2) senescence of the leaves; and (3) the suppression of axillary bud growth. Concurrently there is a shift in resource allocation from continued vegetative growth to reproductive growth, combined with a withdrawal of nutrients, especially nitrogen compounds, from the leaves and the transfer of these nutrients to the developing seeds. The start of the senescence process is caused by a shift, almost certainly in gene expression, very early in the reproductive phase. Continuation of the resource transfer and senescence of the vegetative plant involves hormonal regulation and continued changes in gene expression. Each of these processes is examined, especially with reference to the transfer of resources from vegetative to reproductive growth.