The regulation of leaf senescence

Leaf senescence is an age related process that allows the movement of nutrients from areas where they are no longer required to areas where they are needed such as in reproductive development. The process itself is ordered and allows the cell to keep alive for the longest possible time; this enable the maximum salvage of nutrients. There are many genes thought to be involved in senescence, and over 800 genes have been identified by microarray technology in Arabidopsis. The senescence process is intricate, allowing for the controlled termination of leaf cells, tissues and organs and thus requires to be finely regulated. Although an age dependent process senescence is influenced by many internal and external factors such as plant hormones and shading response.

Factors involved in the regulation of leaf senescence

In addition to a plants developmental age other stimuli are involved in the regulation of the onset of senescence:

1. External Factors
    a. Nutrients
    b. Temperature
    c. Drought
    d. Pathogen interaction
    e. Shade
    f. Ultraviolet light and ozone damage
2. Internal Factors
    a. Hormones (Abscisic acid, Auxin, Cytokinins, Ethylene, Jasmonic          acid, Salicyclic acid).
    b. Reproductive factors

Another process that is involved in the age dependent onset of senescence of leaves is that of metabolic rate.

These stimuli act alongside developmental age to form a complex and finely controlled senescence regulatory network. Ultimately these factors lead to the onset of senescence. The senescence processes include:

1. Macromolecule degradation
2. Detoxification
3. Defence
4. Salvage of Nutrients
5. Translocation of Nutrients
6. Cell death
    a. Nucleotide cleavage
    b. Plasma disintegration
    c. Membrane digestion

Regulation of senescence by sugar

It is thought that one of the processes that is involved in the control and response to senescence regulatory networks is that of sugar status. A high level of sugar in plants has been shown to both decrease the levels of photosynthetic activity and to initiate the senescence process.